A.  Cruise Narrative: AR18

A.1.  Highlights
      WHP Cruise Summary Information

WOCE section designation                  AR18
Expedition designation (EXPOCODE)         74AB62A
Chief Scientist(s) and their affiliation  M. A. Srokosz/RSADU/JRC 
Dates                                     1991.08.06 - 1991.09.28
Ship                                      RRS CHARLES DARWIN
Number of stations                        32
                                                    63° 57.77 ' N
Geographic boundaries of the stations     6° 17.92' E           3° 32.15' E
                                                     62° 15.9 ' S
Floats and drifters deployed              See Mooring Operations 
Moorings deployed or recovered  


INSTITUTE OF OCEANOGRAPHIC SCIENCES
DEACON LABORATORY
CRUISE REPORT NO. 229

RRS CHARLES DARWIN CRUISE 62A
06/09/1991 - 28/09/1991

ERS-1 calibration and validation in the region of the Iceland-Faeroes Front

Principal Scientist
M A Srokosz

1992

DOCUMENT DATA SHEET


AUTHOR
  Srokosz, M. A. et al
  
PUBLICATION DATE
  1992


TITLE
  RRS Charles Darwin Cruise 62A, 06 Sep - 28 Sep 1991. ERS-1 calibration and
            validation in the region of the Iceland-Faeroes Front.


REFERENCE
Institute of Oceanographic Sciences Deacon Laboratory, Cruise Report No 229, 
49pp


ABSTRACT

RRS Charles Darwin cruise 62A in September 1991 was a joint venture involving 
RSADU, JRC and IOSDL. The primary aim of the cruise was to gather in situ data 
for the calibration and validation of measurements made by sensors on the 
recently launched European Space Agency satellite ERS-1. To this end a mixture 
of buoy and shipboard meteorological, wave, sea surface temperature, current and 
hydrographic measurements were made. The measurements were made in a triangular 
region to the east and north of the Faeroes, two sides of the triangle being 
coincident with the ground track of the satellite.

KEYWORDS
  "CHARLES DARWIN"/RRS - cruise (1991) (62A)
  ERS-1
  ICELAND-FAEROES FRONT 

ISSUING ORGANISATION
  Institute of Oceanographic Sciences  Director: Colin Summerhayes DSc
  Deacon Laboratory                    Telephone Wormley (0428) 684141
  Wormley, Godalming                   Telex 858833 OCEANS G.
  Surrey GU8 5UB. UK.                  Facsimile (0428) 683066


            CONTENTS
            
            SCIENTIFIC PERSONNEL				
            SHIP'S PERSONNEL					
            SCIENTIFIC OBJECTIVES				
            NARRATIVE						
            WEATHER						
            METEOROLOGICAL, SST AND WAVE MEASUREMENTS	
            Introduction					
            Mean Meteorological Conditions		
            MultiMet						
            Meteorological Observations			
            Radiosondes						
            Meteorological Buoy				
            SST Measurements					
            Thermosalinograph					
            Trailing Thermistor				
            SST Radiometer and Video			
            Wave Measurements					
            Ship-Borne Wave Recorder			
            Directional Waverider Buoy			
            Video System					
            Measurement of Wind Stress			
            Shipborne Dissipation Measurements		
            Sonic Buoy						
            Instrument Developments				
            GPS System						
            WFAX							
            HYDROGRAPHIC AND CURRENT MEASUREMENTS	
            CTD							
            XBT							
            ADCP (Acoustic Doppler Current Profiler)	
            VAESAT Buoy						
            MOORING OPERATIONS				
            Shelf Slope Moorings				
            Directional Waverider				
            VAESAT Buoy						
            Sonic Buoy						
            Deepwater Mooring					
            Meteorological Buoy				
            Oceano Releases					
            SATELLITE DATA					
            ERS-1							
            MacSat						
            MISCELLANEOUS					
            PES							
            Computing						
            Communications					
            ACKNOWLEDGEMENTS					
            REFERENCES						
            TABLES AND FIGURES				


            SCIENTIFIC PERSONNEL  
            --------------------------------
            SROKOSZ, M. A.       RSADU / JRC
            ALDERSON, S. G.      IOSDL
            BIRCH, K. B.         IOSDL
            CLAYSON, C. H.       IOSDL
            CRISP, N. A.         IOSDL
            FORRESTER, T. N.     JRC
            GUYMER, T. H.        JRC
            JONES, A. K.         JRC
            JORDAN, S. M.        RVS
            KENT, E. C.          JRC
            LEWIS, D.            RVS
            MORRISON, A. I.      RSADU / JRC
            PASCAL, R. W.        IOSDL
            PHIPPS, R. A.        RVS
            TAYLOR, P. K.        JRC
            TOKMAKIAN, R. T.     JRC
            WADDINGTON, I.       IOSDL
            YELLAND, M. J.       JRC
            
            Key
              RSADU  Remote Sensing Applications Development Unit
              JRC    James Rennell Centre for Ocean Circulation
              IOSDL  Institute of Oceanographic Sciences Deacon Laboratory
              RVS    Research Vessel Services
            
            SHIP'S PERSONNEL  
            ----------------------------------------
            HARDING, M. A.       Master
            LOUCH, A. R.         Chief Officer
            CLARKE, J. L.        Second Officer
            WARNER, R. A.        Third Officer
            BAKER, J. G.         Radio Officer
            McGILL, I. G.        Chief Engineer
            MOSS, S. A.          Second Engineer
            HOLT, J. M.          Third Engineer
            PERRIAM, R. J.       Electrical Engineer
            MACDONALD, R.        CPO (D)
            BOWEN, A. M.         Seaman
            HARRISON, M. A.      Seaman
            OLDS, A. E.          Seaman
            DEAN, P. H.          Seaman
            PETERS, K.           CPO (C)
            BISHOP, P.           COOK
            OSBORN, J. A.        Second Steward
            ELLIOTT, C. J.       Steward
            LINK, W. J.          Steward
            BRENNENSTHUL, M. J.  Motorman
   
   
SCIENTIFIC OBJECTIVES

The overall objective of the cruise was to calibrate and validate data from the 
sensors on board the European Space Agency ERS-1 satellite against in situ 
measurements, to improve the utility of that data for oceanographic studies. 
Specific objectives included:

* The validation of ERS-1 altimeter significant wave height measurements.
* The calibration and validation of ERS-1 altimeter wind speed measurements.
* The validation of ERS-1 altimeter sea surface topography measurements.
* The calibration and validation of ERS-1 scatterometer wind speed and direction 
  measurements.
* The investigation of the relationship between wind stress at the sea surface 
  and radar backscatter as measured by the scatterometer (including the effect 
  of wave conditions on this relationship).
* The calibration and validation of ERS-1 Along Track Scanning Radiometer (ATSR) 
  sea surface temperature (SST) measurements.

These objectives were to be achieved by a mixture of shipboard and buoy 
measurements. Despite some problems due to bad weather and the loss of the 
directional Waverider Buoy, the objective of obtaining in situ data for 
comparison with ERS-1 measurements was met. In fact, it proved possible to make 
some initial comparisons between in situ and ERS-1 data during the cruise as 
data from altimeter and scatterometer on the satellite were received on board 
the Darwin in near real time (typically, a day after acquisition).


NARRATIVE

The RRS Charles Darwin sailed from Troon on the morning of Friday 6th September 
(day 249, 1020 GMT; all subsequent times will be given by day number and GMT). 
Sailing had been delayed to await the arrival of some CTD spare parts from RVS. 
These failed to arrive on time and the Darwin was forced to sail to catch the 
tide. The ship subsequently waited off Ayr for the spare parts to be brought out 
by small boat and finally departed Ayr at 1200, heading towards the Faeroes 
along the so-called "Garden Route" between the Scottish islands. Logging of GPS 
and MX1107 transit satellite fixes on the shipboard computing system had been 
started in Troon, prior to departure. Additionally, while in Troon harbour, some 
ERS-1 altimeter data were received on the Marinet system from the Rennell Centre 
(via RVS), as a test for receiving ERS-1 data at sea.

The objective of the cruise (being to obtain data to compare with ERS-1 
measurements) had determined the area of operation for which the ship was 
headed. This was a region to the east and north of the Faeroes where the 
satellite ground tracks intersected (see Figure 1). ERS-1 was in a three day 
repeat orbit, re-visiting the same spot on the Earth's surface every third day, 
so making measurements at a 'cross-over' point would maximise the number of 
intercomparisons obtained, as such a point would be visited by the satellite 
twice every three days. (The three day repeat orbit also put a constraint on the 
timing of various ship measurements, which had to coincide with the satellite 
overpasses.)

In the afternoon, on the first day, the Acoustic Doppler Current Profiler (ADCP) 
was tested by dropping the ship speed from 12 knots to 8 knots and increasing 
the speed by one knot, every ten minutes, back to 12 knots. Good data quality 
(100%) at the surface was obtained at 8, 9 and 10 knots, dropping to 
approximately 50% at 11 knots and zero at 12 knots.

On day 250 rostered watches for meteorological observation were started at 0800. 
Later in the morning the Darwin emerged from the shelter of the Scottish islands 
allowing the scientists on board to try out their sea-legs. The non-toxic pumped 
seawater supply was turned on and the PES fish deployed. As a precautionary 
measure, air was bled from the ADCP "top-hat" housing, but this appeared to make 
no difference to the ADCP data quality. The first radiosonde was successfully 
launched from the ship just before noon.

In the afternoon two ADCP calibration runs were made with the ADCP in bottom-
tracked mode. This involved the ship performing 90( turns every 20 minutes, in a 
zigzag pattern, for two hours. A run at 10 knots was made from 1330 to 1530, and 
one at 8 knots from 1630 to 1830; the gap between the two runs occurring while 
the ship passed the island of Rona.

The morning of day 251 found the ship in position (62( 18.6 N, 4( 55.8 W) to 
deploy the first moorings (see Figure 2). The weather was calm, ideal conditions 
for mooring work. A PES survey of the bottom was carried out prior to 
deployment. The directional Waverider buoy was deployed successfully at 1334, 
followed by the VAESAT buoy at 1451, a short distance away. The ship stayed in 
the vicinity of the buoys and data were received on the shipboard ARGOS 
receiver. Both buoys appeared to be working satisfactorily. At 1611 a test CTD 
dip was carried out to check the system. This worked well, except that the first 
bottle did not fire and, consequently, the reversing thermometers failed to 
reverse. As the third buoy (sonic anemometer meteorological buoy) was not ready 
for deployment at this stage the ship departed at 2000 for the deep water 
meteorological buoy mooring position. During the day a number of fishing vessels 
were observed in the vicinity of the buoys, leading to some concern for their 
safety.

The Darwin arrived at the deep water mooring position (63( 57.6 N, 6( 18.6 W; 
see Figure 2) at 0745 on day 252. A PES survey of the bottom showed it to be 
relatively flat and the toroidal meteorological buoy was deployed successfully 
by 1444. The ship remained on position until 2200 to check on the buoy and then 
departed for the southern mooring position. XBT drops were carried out once per 
hour on this leg, in an attempt to delineate the structure of the Iceland-
Faeroes front. During the day the first ERS-1 data for the study area were 
received over the Marinet system, consisting of altimeter wind speed, wave 
height and sea surface topography observations for day 250. At this stage no 
scatterometer data were received.

The ship arrived at the southern mooring position at 0915 on day 253. The 
directional Waverider and VAESAT buoys were located and found to be alright. The 
ship hove to and remained on station making meteorological measurements and 
receiving data via the onboard Argos receiver from the Waverider. Preparations 
for the launch of the sonic anemometer buoy continued. Late in the evening the 
ship's teleprinter terminal failed. Attempts to repair it led to a loss of 
satellite communications from ship to shore (telephone, fax, Marinet), reducing 
communications to the radio telephone.

Day 254 found the ship hove to, making further meteorological measurements, 
while work on the sonic anemometer buoy continued. A problem was discovered with 
the Oceano release for buoy mooring. The spare release was also found to have a 
problem, but by combining components from both, a working release was obtained. 
At 1813, the sonic anemometer buoy still not being ready for deployment, the 
decision was taken to steam to the northern mooring position to start the first 
CTD survey (see Figure 2) on the following morning.

Early on day 255 the Darwin was in position (at 63( 57.6 N, 6( 18.6 W) to being 
a CTD survey round a triangle whose eastern and western sides corresponded to 
the ground tracks of ERS-1, the northern side being surveyed to complete the box 
(see Figures 1 and 2). Before commencing the survey a check on the met. Mooring 
was made. The first CTD station was started at 0629. On completion of the 
station the ship headed east, going clockwise round the triangle. Thereafter CTD 
stations were made approximately every 40km, with XBT drops approximately every 
10km between stations. A combination of T5 (depth limit 1830m) and T7 (depth 
limit 760m) XBTs were used depending on the depth of water (the southern end of 
the triangle being in only 250m of water, while the northern side was in 3000m). 
Further details of the CTD stations and XBT measurements can be found in Tables 
3 and 4. Between stations the ship maintained a speed of 10 knots and underway 
ADCP measurements were made, as well as those taken while on station.

A major event of day 255 was the restoration of satellite communications, after 
valiant (and successful) efforts by the radio officer and Derek Lewis (of RVS) 
to repair the teleprinter terminal.

Day 256 saw the continuation of the CTD survey round the triangle, with the 
Darwin arriving at the southern corner (62( 18.6 N, 4( 55.8 W) at 1841. On 
arrival at this position the directional Waverider buoy was found to be missing. 
Interrogation of Argos showed its last transmission to be at 1031 on day 255. 
Acoustic interrogation of the mooring release showed it to be present. Further 
investigation of the mooring was postponed until after the completion of the CTD 
triangle. At this stage the sonic anemometer buoy was ready for deployment, but 
the weather was considered too bad for the mooring to be deployed. The decision 
was made to delay deployment and to continue the CTD survey. In the evening the 
skies were clear and at 2144 ERS-1 was sighted, passing overhead.

The CTD survey was completed at 1415 on day 257 at the north west corner of the 
triangle (63( 57.6 N, 6( 18.6 W). Again a check was made on the toroid buoy at 
that position before returning to the southern corner of the triangle, ready for 
the deployment of the sonic anemometer buoy the next day.

Day 258 was spent with the ship hove to by the VAESAT buoy waiting for the 
weather to moderate so that the sonic anemometer buoy could be deployed. This 
gave opportunity for further shipboard meteorological measurements to be made.

Early on the morning of day 259 the weather had moderated sufficiently and the 
sonic anemometer buoy deployment was completed successfully by 0723. At 0920 the 
release for the directional Waverider mooring was triggered acoustically and the 
subsurface mooring buoy and release recovered. Inspection of the mooring 
suggested that the Waverider buoy itself had been trawled by a passing fishing 
vessel. At this time the Argos data transmission from the VAESAT buoy was 
checked and found not to be working, but it was thought probable that the 
onboard data logging was unaffected. The ship remained hove to near the sonic 
anemometer buoy overnight, so that a check could be kept on the buoy and 
comparison data obtained from the ship's meteorological measurements.

At 0205 on the morning of day 260 the fire alarm went off in the constant 
temperature  laboratory. This was due to a failure of the thermostat, bringing 
the temperature down below freezing and leading to condensation in the smoke 
detector. In fact, the temperature was so low that three of the bottles of sea 
water stored in the laboratory, awaiting salinity determination, froze and 
cracked. Fortunately, no other bottles were affected.

Later in the morning (0645) the sonic anemometer buoy was observed floating 
upside down, having overturned the previous evening (as was ascertained 
subsequently by examining the data logged by the buoy). The acoustic release on 
the buoy mooring was triggered and the buoy was successfully recovered, with 
recovery complete by 1040. At 1100 the ship started a sea surface temperature 
survey, in an attempt to delineate the Iceland-Faeroes front (see Figure 3). At 
the end of the survey the ship hove to at the southern mooring position, 
intending to stay there overnight, making meteorological measurements, weather 
reports having warned of a force 10 storm approaching the Faeroes region. Just 
before midnight, with the weather deteriorating, the captain decided to head for 
shelter in the Faeroes.

At 0355 on day 261 the Darwin arrived at the Faeroes and sheltered between the 
islands of Vidoy and Fugloy, remaining there for the rest of the day. This break 
in the cruise gave the scientific party an opportunity to play with the fire 
extinguishers, fire hoses and other fire fighting equipment under the 
instruction of the first mate!

On day 262, the weather having abated, the ship sailed from the Faeroes at 0315 
and returned to the southern mooring position by 0830. The VAESAT buoy was 
sighted and a check made on its Argos transmission. The ship remained hove to, 
making meteorological measurements, until 1222, after the mooring overpass of 
ERS-1 (at 1156), and then the second CTD survey round the triangle was started 
(see Figure 4). From 2130 to 2200 the ship was hove to for the second ERS-1 
overpass (at 2144), so that good wave data could be acquired by the SBWR and a 
radiosonde launched. The CTD survey was then resumed.

At 0915 on day 263 the Darwin arrived at the northern mooring position (north 
west corner of CTD survey triangle, 63( 57.6 N, 6( 18.6 W; see Figure 2). The 
toroid buoy was sighted and the mooring release fired acoustically. Recovery of 
the mooring was completed at 1250. After an XBT drop and a CTD dip, the ship set 
off eastward to survey the northern side of the triangle (Figure 4). At this 
point a revision to the CTD survey plans was made to allow two stations to be 
made in the interior of the survey triangle. Unfortunately, the weather 
deteriorated and it was not possible to carry out this plan.

At 0105 on day 264 the ship was in position at 63( 57.6 N, 4( 27.4 W for a CTD 
station. However, the weather had deteriorated and the decision was made to miss 
out this station and cut across the corner of the triangle to 63( 38.4 N, 3( 
50.0 W for the next CTD station (see Figure 4), where a successful CTD dip was 
carried out during a lull in the bad weather. This decision to cut the corner 
was made taking into account the lower speed of the ship in heavy seas and the 
need to be in position for the ERS-1 overpass on the following day. At the next 
CTD station (63( 18.5 N, 4( 06.0 W) the ship hove to, making meteorological 
measurements, waiting for the weather to improve so that a CTD dip could take 
place. After waiting several hours, at 2000 it was again decided to skip this 
CTD station and to move on to the next one.

The weather having improved, it was possible on day 265 to make the remaining 
three CTD stations on the eastern side of the triangle. The final station at the 
southern corner being completed at 1103. The ship then hove to for the ERS-1 
overpass at 1156. After lunch the VAESAT mooring was recovered successfully, 
recovery being completed by 1405. The light on the top of the buoy and the top 
of the buoy were damaged during the recovery by the air gun mountings on the 
hull of the Darwin. (Damage had also been caused by these mountings to the 
toroid meteorological buoy when it was recovered on day 263). After recovery of 
the VAESAT buoy the ship again hove to awaiting the ERS-1 overpass at 2144. At 
2210 the ship left the southern corner of the triangle and headed due north to 
make two CTD stations in the interior of the triangle (see Figure 4).

The weather on day 266 being fine it was possible to complete the remaining 
three CTD stations (including one missed due to bad weather earlier in the 
cruise) and then to return to the southern corner of the triangle at 1835. The 
ship was then hove to and remained on station making meteorological measurements 
until midnight on day 267 when we left the study area on passage back to the RVS 
base at Barry. At this point rostered watches ceased and the non-toxic water 
supply was switched off.

On day 268 an ADCP calibration run was carried out, beginning at 0825 and ending 
at 1025, consisting of a series of six zigzags. Each leg of the zigzag pattern 
was traversed for twenty minutes and a 90( turn made between legs. Due to the 
weather conditions the speed along legs varied between 8 and 10 knots. At the 
end of the calibration run the Darwin hove to and the PES fish and "soap-on-a-
rope" thermistor were recovered. Passage to Barry was then resumed.

Passage home on day 269 was enlivened by passing through the Kyle of Lochalsh, 
the Sound of Mull and the Sound of Islay, together with a life boat drill. 
During the lowering of the lifeboat, one scientist was heard to comment, "This 
is the nearest I have been to the water for a long time". The Irish Sea was 
crossed on day 270, some excitement being caused during the afternoon by an RAF 
rescue helicopter practicing dropping a man onto the aft deck. The Darwin 
finally docked at Barry at 2114 on day 270, at the end of an eventful and 
successful cruise.
                                                                            MAS


WEATHER

Overall, the weather in the cruise area was characterised by a mobile south-
westerly flow with a number of deep depressions passing through from SW to NE. 
The deepest of these (central pressure 962mb) passed directly over the ship on 
day 267. The maximum 1 minute mean wind speed was 27m/s recorded whilst 
sheltering in the lee of the Faeroes on day 261. Air temperatures were mostly 
10-11(C and within 1 or 2 degrees of the sea temperature. However, near the 
beginning a strong northerly brought air temperatures of 6(C for a short period. 
The maximum visually observed waveheight was 20 feet (compared with 5m on the 
SBWR).


DETAILS

When the Darwin arrived on station on day 251 a blocking anticyclone was 
situated to the west of Scotland with small low pressure areas running eastwards 
along a front on its northern flank and light westerlies in the cruise area. By 
day 252 the high had begun to move SE into the continent allowing the front to 
move south, crossing the area at 1700. It was accompanied by a 90( wind veer and 
increasing winds. Drizzle and mist gave way to rain near the frontal passage 
followed by a clearance. The following day (253) was one of squally showers, at 
least one including hail, in the strong northerly winds (16m/s gusting to 25m/s 
in one shower) which developed behind the cold front. During the night the dry 
bulb temperature had dropped to 6(C. Throughout the evening and day 254 the wind 
moderated to 2m/s as an anticyclone moved SE towards Scotland. Stratocumulus 
began to break. By day 255 the high passed over Scotland and into the North Sea, 
allowing weak fronts to affect the area with showers and rain in the morning and 
a freshening WNW wind. A cold front moving slowly south brought a clearance in 
the evening and the following night was calm and fairly clear.

This period was short-lived as the front returned northwards on day 256 as a 
warm front in strengthening south-easterlies ahead of a complex area of low 
pressure to the west of the UK. Several fronts were developing in its 
circulation. Temperatures rose and for a time the wind waves and swell were in 
opposing directions. Altostratus thickened soon after dawn and rain started at 
0900, lasting for several hours. The clearance was erratic but by 2145 cloud had 
almost gone and conditions enabled ERS-1 and several other satellites to be seen 
with the naked eye, as well as the aurora. Within a short time cloud had 
increased again and at 0000/257 it was raining from a warm front. This was 
quickly followed by the cold front which became slow moving in the region. 
However, further cyclogenesis was taking place and another low with its fronts 
headed NE. These fronts passed through the area during the day with some rain 
but again skies had cleared sufficiently behind the last of these for an aurora 
to be visible at 2300.

On day 258 a NNWly of 14m/s was established as the low moved away to the NE. A 
transient ridge followed during the night resulting in very light winds and lack 
of low cloud. The next low pressure, a complex area lying E-W to the west of 
Scotland, affected the area on day 259. Winds increased from dawn to reach 15m/s 
ESEly and cloud thickened to produce rain from mid-afternoon until midnight as 
an occluded front oriented E-W became slow moving over the area. On day 260 a 
new low to the west of Scotland moved NE and its fronts caught up the old 
occlusion. Winds moderated to 10m/s and there was some drizzle but in the 
evening the wind strengthened from SSE and as a force 10 was forecast Darwin 
headed for shelter in the lee of the Faeroes. All of day 261 was spent in 
shelter; despite this protection, in the showery airstream which developed 
behind an occluded front winds were very strong and gusty, reaching 27m/s at 
0600. As winds decreased a little during the early hours of day 262 the vessel 
left shelter. Winds were lighter than expected for a while, due to the effects 
of a small wave depression running east to the south. Convective cloud was 
observed, sometimes with cumulus in lines parallel to the wind.

A warm front, accompanied by rain, crossed the area from the SW at 0900 on  day 
263 associated with a low to the SW of Iceland. The wind, which had dropped 
light during the night, picked up from the SE ahead of the front. As the front 
passed it turned foggy. By day 264 the low pressure area had developed several 
centres to the north and south of Iceland. A strong (18m/s) SSEly prevailed and 
several front passed through. The low continued to move north and on day 265 a 
colder, unstable airstream affected the area, with scattered cumulus and 
cumulonimbus. During the day pressure rose, the wind dropped and the swell died 
away rapidly. A weak ridge followed (day 266) and convection was organised both 
in lines and mesoscale cells. In the late afternoon frontal cloud was observed 
in the SW which spread rapidly across the sky. Winds increased quickly to 18m/s 
by 0000/267 and rain, moderate to heavy at times started at 2110. The winds then 
quickly decreased to 5m/s and changed from easterly to Swly as the centre of the 
low became situated right over the area, with a pressure of 962mb being recorded 
at the ship; in fact with one centre to the NE and the other to the W. For a few 
hours the weather was calm and sunny but as the low continued to move slowly ENE 
winds again picked up quickly to reach 19m/s during the evening, this time from 
the NNW. RRS Charles Darwin left station for Barry while these winds were still 
at their height.
                                                                            THG


METEOROLOGICAL, SST AND WAVE MEASUREMENTS

INTRODUCTION

The main aims of the meteorological and wave research during the cruise were to 
gather data on the meteorological conditions, sea surface temperature, and wave 
height for the calibration and validation of the ERS-1 satellite, and to measure 
the wind stress under different conditions of wind velocity and sea state. 
Instrument development and testing was also undertaken.

For ERS-1 validation, the mean meteorological conditions were measured on the 
ship using a MultiMet meteorological instrumentation system and also by taking 
manual observations. Since it was planned that the ship would spend a 
significant part of the cruise at the southern ERS-1 cross-over point and main 
mooring site, a meteorological buoy was also moored in the colder water further 
north along the ascending (western; see Figure 2) ERS-1 ground track to monitor 
conditions there. For validation of the ERS-1 ATSR, the sea surface temperature 
was recorded throughout the cruise using a thermosalinograph and trailing 
thermistor; also preparations were made for mounting an SST radiometer on the 
ship on later cruises.

Wave measurements were required for validation of the ERS-1 altimeter and for 
interpretation of the wind stress measurements. These were obtained using a 
Shipborne Wave Recorder (SBWR), a directional Waverider buoy, and through a 
video record of the sea state.

The wind stress was measured on the ship using the inertial dissipation method 
and data from two sonic anemometers and a propeller-vane anemometer. The "sonic 
buoy", which carries a sonic anemometer based dissipation system was deployed 
for the first time during the cruise. The plan was to establish a site at the 
ERS-1 cross-over point at which the sonic buoy wind stress estimates were 
supported by wave measurements from a directional wave buoy, and near surface 
current measurements from the VAESAT buoy. Initial problems with the sonic buoy 
hardware, which delayed deployment, and the early of the Waverider buoy, meant 
that this plan was not achieved. However, despite the capsize of the buoy some 
10 hours after launch, the sonic buoy deployment was successful, in that a good 
data set was obtained for evaluation of the buoy mounted wind stress system.

As part of the continued development of the MultiMet instrument systems, A GPS 
and compass system, and a personal computer based weather FAX system were tested 
during the cruise. These systems are needed primarily for use on ships other 
than those operated by NERC where a full range of navigational support may not 
be available.
                                                                            PKT


MEAN METEOROLOGICAL CONDITIONS

MULTIMET

The MultiMet meteorological instrumentation system was operated throughout the 
cruise with data collection and storage on Eprom logger, and, through a level A 
interface, on the ship's SUN computer system. There were 14 sensors with 19 
channels, measuring air and sea temperature, air pressure, wind speed and 
direction, downward long and short wave radiation, and ships heading (Table 1).

TABLE 1: Sensors logged by the MultiMet system

Variable            Instrument            Position
-------------------------------------------------------------------------------
Dry and wet         Vector Instruments    Foremast (x2), port and star-
 bulb temperature    psychrometer (x4)     board sides of wheelhouse top

Wind speed          Vector Instruments    Mainmast, wheelhouse top
                     cup anemometer (x3)   psychrometer positions

Wind direction      Vector Instruments    Mainmast
                     wind vane

Wind speed and      R. M. Young           Foremast
 direction           propeller-vane

Ship's heading      Ship's gyro           (Logged through a level-A interface)

Sea surface         Trailing thermistor   Deployed from port side of foredeck
 temperature 

Air pressure        IOSDL instrument      In plot

Downward shortwave  Kipp and Zonen        Port and starboard sides of foremast
 raidation           radiometer (x2)       platform (gimbal mounted)

Downward longwave   Eppley pyrgeometer    Top of foremast (gimbal mounted)
 radiation 


Difficulties at the start of the cruise in logging the data on the SUN system 
were overcome on day 252 by using a direct RS232 link from the level A to a 
terminal server, rather than the Cambridge ring. Because of these problems, the 
MetMan display program (running on a BBC Master) was modified to enable storage 
of the uncalibrated data to disk. Later in the cruise the MetMan program was 
also modified to optionally create a data file of calibrated data in "Cricket 
graph" or "DaDisp" format. This facility will mainly be of use on non-NERC 
ships.

Incorrect wiring of the Young anemometer on the foremast resulted in the data 
having a floating zero up to day 255 at 2116 when the fault was corrected. An 
attempt to calculate a correction for the data was made after comparison with 
the Vector Instruments anemometer on the main mast. The resulting linear 
calibration of the Young wind speed seemed satisfactory. To ensure data quality, 
the forward mast starboard psychrometer was changed on day 257 after the wet 
bulb measurements had become noisy. Erroneous data values were also noted from 
the starboard wheelhouse top psychrometer, air pressure and sea surface 
temperature sensors during HF radio telephone calls. The sea surface temperature 
sensor was replaced on day 261.

A series of UNIX scripts were revised to improve daily processing and quality 
control of the MultiMet data. Reading and calibrating the data from RVS format 
to Pstar format, merging of navigation and EM log data, calculation of the true 
wind speed and direction, and plotting of the data were all performed 
efficiently on a daily basis using these scripts.

The documentation describing the routine maintenance and data processing for the 
MultiMet system was revised and extended.
                                                                  KGB, ECK, RWP

METEOROLOGICAL OBSERVATIONS

Three-hourly weather observations were conducted from 0900 day 250 to 0000 day 
268 in order to provide a description of cloud and sea state conditions as well 
as a check on MultiMet data. Starting at approximately 25 minutes to the hour 
the following sequence was undertaken: wet and dry bulb temperatures using a 
clockwork Assmann psychrometer, bucket sea surface temperature (ship's steaming 
bucket deployed from the bridge), cloud amount and type, present and past 
weather, eyeball averages of relative wind velocity, ship speed and heading from 
readouts in the bridge, pressure (precision aneroid barometer on bridge, 
uncorrected for height above sea level), wind waves and swell waves (visual 
estimates of height and period and, for swell, the direction). The sequence was 
concluded on the hour. Occurrences of special features, for example, frontal 
passages, aurora, were also recorded. Observations were possible in all weather 
conditions. The highest wind speed recorded by observers was 55 knots. In such 
conditions it was impossible to get the SST bucket into the water.

Cloud and sea state observations are rather subjective and their accuracy 
depends much on observer experience. Despite the uncertainties they are still 
valuable because it is difficult or impossible to obtain all the required 
parameters by instrumental techniques. The quality of the psychrometer data was 
variable and readings were nearly always high compared with the MultiMet values. 
A major reason is the difficulty of holding the instrument in a well-exposed 
location for long enough (5-10 minutes) to get a stable reading. It would have 
helped if the psychrometer could have been fixed to a supporting bracket each 
time the observer started his measurements. Also, at night a low-intensity, 
wide-beam lamp slung round the neck would have allowed observers to have both 
hands free for handling equipment. This would have reduced the number of 
thermometers broken and would generally be safer in rough weather. A stronger 
case in which to carry the SST thermometer on deck would also have reduced the 
likelihood of breakage.
                                         MJY, SGA, AIM, ECK, PKT, TNF, RTT, THG

RADIOSONDES

Radiosonde data were gathered to give a description of the atmospheric 
conditions for the cruise period and area, as well as to derive the water vapour 
content at various levels for validation of ERS-1 altimeter and ATSR atmospheric 
corrections.

Vaisala RS-80-15 sondes, measuring temperature, pressure and relative humidity 
were launched twice per day from days 250 to 267 using 200g TOTEX balloons 
fitted with string unwinders. Ascents were generally timed for 1100 and 2300 but 
were adjusted when ERS-1 altimeter overpasses occurred to be a few minutes 
before the overpass time (1156 and 2144). A total of 35 flights were made most 
of which reached a height of greater than 50mb, well into the stratosphere (see 
Table 5). On one occasion the sonde reached only 690mb before slowly descending 
due, it is suspected, to leakage of gas from the neck of the balloon.

Balloons were inflated in a restrainer, placed on the aft portion of the boat 
deck (port side) with plastic tubing connecting it to helium bottles secured on 
the aft deck. Launching usually required two people, although in light winds 
(less than 10m/s) one would be sufficient. Provided the relative wind was at 
least 20( on the starboard bow balloons could be released clear of obstructions 
for all wind strengths. In light winds a wide range of relative wind directions 
could be tolerated. Successful launches were made in winds up to 20m/s. On two 
or three of the strong wind occasions, however, the balloons were caught in 
eddies shed by the ship which caused the sondes to come very close to hitting 
the sea. The best way of avoiding this was for the person launching the balloon 
to wait for a suitable lull using the pull of the wind on the balloon to judge 
the optimum moment for release.

Signals from the sondes were received by a Vaisala UR-15 unit via an omni-
directional antenna located on the port rail of the wheelhouse top. Strong 
signals were obtained by the receiver which was being used for the first time 
(in place of the ancient and unwieldly LO-CATE W2 set). The receiver performed 
extremely well, the only problem being interference from other sondes launched 
from upper air meteorological stations. This was overcome by retuning our 
sondes' transmitting frequencies to greater than 404MHz. After passing through 
the PTU processor the calibrated data were displayed and written to floppies 
using a BBC Master.

The raw data were transferred onto a SUN computer and edited to the required 
limits. A series of shell scripts were written to process the data using Pstar 
programs. Potential temperature and specific humidity were calculated and 
plotted against pressure, as was relative humidity and temperature. A set of 
contour plots for each parameter set against time and pressure for various 
periods throughout the cruise was produced.
THG, TNF

METEOROLOGICAL BUOY (Mooring 510)

The meteorological buoy consisted of a 2.45m diameter toroidal hull supporting a 
1m deep steel keel to which was bolted a 2.5m high aluminium instrument tower. 
The meteorological logging package was an Aanderaa Sensor Scanning unit type 511 
utilising ten channels scanning analogue and digital sensors with a DSU 2990E 
(Expanded) data storage unit. The package scanned and logged all sensors at five 
minute intervals.

The sensor suite (Table 2) was designed to measure wind speed and direction, sea 
and air temperature, solar radiation, and buoy orientation. Wind speed and 
direction sensors were duplicated due to the past incidence of damage during 
launch and other operational failures, and a ruggedised IOSDL vane was fitted to 
one wind direction sensor. During the deployment the wind direction sensor on 
channel 2, a new manufacturer's supplied unit, failed due to the sealed vane 
locking screw becoming loose.

TABLE 2: Sensors on the Meteorological buoy

Channel  Sensor            Type                                  Number
--------------------------------------------------------------------------
  1      Reference         Fixed reference value                 n/a
  2      Wind direction    Rotary vane                           2053
  3      Wind speed        Three cup rotor (mean wind speed)     2740
  4      Wind speed        Three cup rotor (maximum wind speed)  2740
  5      Solar radiation   Pyranometer                           2770
  6      Buoy orientation  Magnetic compass                      2084
  7      Sea temperature   Platinum resistor in IOSDL            2812
          1 metre depth     underwater housing  
  8      Air temperature   Platinum resistor radiation screen    1289 4011
  9      Wind direction    Rotary vane IOSDL modified            2053
 10      Wind speed        Three cup rotor IOSDL interface       VI1991

On recovery, all the sensors except the VI1991 and 2812 suffered extensive 
damage (see Mooring Operations, section 6). The tower was also damaged, several 
welds having cracked and the top protective ring and supports being severely 
distorted. The buoy hull was relatively intact, the only apparent minor damage 
being to the glass reinforced external lugs.

The data were downloaded from the DSU to a PC using the P3059 software with raw 
and calibrated listings and plots. The data for the ten day deployment period 
indicated no data errors and a clean record has been produced.
IW


SST MEASUREMENTS

THERMOSALINOGRAPH

The thermosalinograph (TSG) was built and provided by RVS, it has two CTD 
Seabird sensors which measure conductivity and temperature from water taken 
through the non-toxic intake at a depth of 5m. Conversion of the sensor outputs 
to actual temperature and salinity was computed using two separate techniques, 
one as used by RVS (programs gencal and protsg) and one developed by IOSDL 
(ptsgcal). The temperatures calculated from bothe methods agreed to the fifth 
decimal place in all cases. Temperature was calibrated against CTD measurements 
coincident in time but averaged between a depth of 4.5m and 5.5m. A constant 
offset of +0.041(C was found for the TSG reading.

The salinity readings from the TSG, as calculated using the IOSDL method, were 
between 0.0205 and 0.0274 above those of the RVS method. This offset was 
inversely related to the magnitude of the total salinity and temperature 
readings, giving a low offset when the reading of each parameter is high and 
vice versa. The salinity of bottle samples, (which were taken at four hour 
intervals from the TSG outflow) were derived from comparisons against standard 
sea water (this work was carried out by N. Crisp, A. Morrison and R. Tokmakian) 
using an Autosal salinometer. These data were compared to the TSG salinity, 
giving a correlation coefficient of 0.0962 and a standard error of 0.058. 
Further calibration of the salinity against calibrated CTD data showed that the 
TSG salinity was under reading by 0.01.

Contour plots of both temperature and salinity from the TSG data were prepared 
to give an indication of the SST distribution over the cruise area. This 
information was used to guide an SST survey, which was carried out on day 260. 
The aim of this survey was to observe the SST distribution within the triangular 
course of the cruise and to attempt to "link up" regions of strong SST gradients 
on opposing sides of the triangle. The range of SST's throughout the cruise was 
between 7.8(C to 11.3(C.
                                                                            TNF

TRAILING THERMISTOR

The MultiMet system measured the sea surface temperature using a trailing 
thermistor ("soap-on-a-rope"). The thermistor, which was set inside a protective 
casing attached to the end of a rope containing the conducting cable, was 
deployed from an outboard extending pole, on the port side of the ship near the 
bow. Weights attached to the rope were adjusted to minimise the horizontal 
undulations of the sensor at varying ship speeds.

Throughout the cruise the thermistor sea surface temperature readings varied 
significantly from those of the thermosalinograph. During the first ten days 
(from day 251) the thermistor reading slowly drifted from 0.2(C below that of 
the thermosalinograph to 0.6(C above. Such a slow and steady drift in accuracy 
was uncharacteristic of the instrument's behaviour as observed on past cruises. 
Attempts to correlate this trend with other physical parameters being measured 
was made but to no avail.

This first sensor failed completely on day 261, and the replacement gave an 
approximately constant offset of +3.5(C (compared to the thermosalinograph) 
throughout the remainder of the cruise, despite a thorough check of the 
instrument electronics and calibrations.
                                                                  TNF, KGB, RWP

SST RADIOMETER AND VIDEO

For ATSR validation it is planned to mount an SST radiometer on the foremast of 
the RRS Charles Darwin looking out to starboard of the bow. Although the 
mounting and wiring were installed for this cruise, the radiometer, which is 
being specially built by a commercial firm, was not available in time. A video 
camera will be operated alongside the SST radiometer to record any contamination 
of the field of view by the ship's bow wave. This camera was operated during the 
cruise. The video signals were connected to a monitor and a recorder in the 
plot. Recordings obtained under different sea state conditions and at varying 
ship's speed confirmed that the foremast site will provide a view of a region of 
the sea surface which, for most of the time, is undisturbed by the bow wave from 
the ship.
                                                                       KGB, PKT


WAVE MEASUREMENTS

SHIP-BORNE WAVE RECORDER

A standard IOS Mk3 SBWR was logged continuously throughout the cruise by a PC-
based system. The instrument was also connected via a level A unit to the ship's 
level B system; one second samples were logged continuously as a back up, but 
were not processed. At 20 minute intervals, the PC-based system initiated the 
collection of 2 x 1024 sample time series at 2Hz sampling rate. The time series 
were spectrally analysed, averaged and filed as two sets of 128 spectral 
estimates. The files were periodically backed up and transferred to the SUN 
computer system, for further processing and archiving. Uncorrected readings of 
significant wave height were also printed out by the PC for diagnostic purposes.

The pairs of ten minute spectra were read into a Pstar format using the program 
"rdvalid", and a frequency response correction was applied (Pitt, 1988). The 
significant wave heights were then recalculated for comparison with the ERS-1 
altimeter data.
                                                                       CHC, MJY

DIRECTIONAL WAVERIDER BUOY

A Datawell Directional Waverider was used to give estimates of the directional 
wave spectrum. This buoy was equipped with on-board processor and transmitter 
for acquisition of the processed data via the Argos system. The buoy was 
deployed at 1334 on day 251, using a mooring design which followed the Datawell 
recommendations. In addition to the asynchronous acquisition of data via Service 
Argos, Toulouse, the buoy transmissions were also received on the ship, when 
within about a 5 mile range. The significant wave height was extracted from the 
condensed message format for comparison with the ERS-1 altimeter values; 
significant wave heights of up to 5 metres were obtained, comparing favourably 
with the SBWR. Directional spectra were also plotted out at intervals and were 
found to agree with visual observations.

At some time after the last transmission was received via Argos at 1031, day 
255, it is believed that the buoy was trawled. No further transmissions were 
received either by Service Argos or the ship. The buoy was not sighted in 
position at 1841, day 256, but the mooring was checked acoustically at 1900, day 
256, and found to be in the correct position. On recovery of the mooring at 
1010, day 259, the upper mooring cord was found to have been broken near the 
buoy end and both cords had been damaged in a number of places. In addition, one 
of the glass float hard hats above the release had been damaged. It must be 
assumed that the transmitter antenna was damaged at the time of this incident.

                                                                       CHC, THG

VIDEO SYSTEM

A time-lapse video system (loaned by the Physics Department of UMIST) was 
mounted with the camera on the bridge viewing the port bow of the ship. This 
will provide a visual record of the sea state, from which the presence and 
direction of any significant wave swell can be detected. It will also provide an 
indication of periods of precipitation. The latter may be important in 
evaluating the performance of the sonic anemometer systems.
                                                                            PKT


MEASUREMENT OF WIND STRESS

SHIPBORNE DISSIPATION MEASUREMENTS

For measurement of the wind stress using the dissipation technique, three fast 
response wind sensors were deployed on the forward mast; two Solent sonic 
anemometers and a Gill propeller vane. The Solent sonic anemometers were 
operated in 56Hz sampling mode, with the twelve minute data cycle of collecting 
data, calculating and storing the spectra commencing on each quarter hour under 
the control of an NEC PC. The Gill anemometer was digitised at 8Hz by a Fast 
MultiMet Logger with 10 minute samples logged and processed by an Archimedes 
computer on a continuous free running sampling scheme.

The Gill was deployed in the same location on the forward mast portside 
throughout the cruise. Initially the two Solent sonic anemometers were mounted 
side by side on the starboard side of the foremast platform. From day 257 the 
inboard sonic anemometer was deployed upside down below the foremast platform to 
allow a comparison of turbulence and mean wind measurements as a function of 
height. In case of calibration differences the two sonic anemometers were 
exchanged one for another on day 265. From day 266 the lower sonic anemometer 
was removed. An Asymmetric Head Solent sonic (as used on the sonic buoy) was 
mounted side by side with the symmetric head instrument to compare the effects 
of the different head configurations.

The two symmetric head anemometers agreed to within 1% for wind speed estimates, 
when deployed at the same height, but differed in PSD (power spectral density) 
estimates by 20% on average. The reason for this is not yet known. When the two 
sonics were deployed at different heights, the lower one produced lower wind 
speed readings and higher PSD values, as expected. For this period the estimates 
of the friction velocity, u*, and drag coefficient, CD, from the two systems 
were in good agreement.
                                                             KGB, CHC, RWP, MJY

SONIC BUOY

Problems with the operation of the sonic buoy on the internal batteries 
prevented deployment on day 254, and although the buoy was ready for deployment 
on day 257, the first deployment opportunity was on day 259 at 0723. During the 
day the ship kept station on the buoy to allow observation of the buoy 
performance in the rising wind and sea conditions. The buoy was seen to 
generally align with the wind, but the cross swell and adverse current 
occasionally caused oscillations to 90( to the wind. The buoy light was not 
sighted during repositioning on day 260 at 0400, and at first light it was 
observed that the buoy had overturned. It was recovered by 1040 without any 
further damage.

All recording systems were still functioning on recovery, however the wind 
sensors were no longer operational due to immersion. Data from the sonic and 
MultiMet loggers were replayed to allow comparison with the ship mounted 
systems. Initial analysis showed the buoy to be working successfully until the 
moment of capsize (day 259, 1705), although the data from the air temperature 
sensors suffered from periodic interference from the Argos transmitter.

Overall, the deployment was a successful instrument trial which highlighted the 
need for further development of the mooring and for the resolution of the radio 
interference problems.

The sonic anemometer produced PSD estimates which showed clearly the expected 
increasing trend with wind speed. The wind speeds measured by the Young 
anemometers were significantly higher than those from the sonic. This may have 
been due to the buoy motion causing over-speeding in the propeller-vane 
instruments.
                                                             KGB, CHC, RWP, MJY


INSTRUMENT DEVELOPMENTS

GPS SYSTEM

This was the first operational trial of a portable GPS and Flux Gate Compass 
data logging system designed to obtain ship's velocity and ship's head 
information for the calculation of true wind and wind stress. The system will 
mainly be used on non-NERC ship's where data from a full navigational system may 
not be available.

The GPS aerial was mounted on the wheelhouse top with the receiver, flux gate 
compass and controlling NEC PC computer located in the plot. System 
initialisation was completed on day 248 prior to sailing. Data recording was 
continued throughout the cruise, however a software problem caused the logging 
program to halt on a number of occasions throughout the cruise. Attempts to 
identify this intermittent error were successful, with a software fix on day 
265.

Although the KVH compass has a self correcting facility, attempts to initiate 
this by steaming the ship in a circle failed. It was therefore the uncorrected 
compass readings which were compared with data on the ship's heading derived 
from gyro readings. The compass deviation varied with heading by about (50(, 
following a characteristic curve which suggested that the ship's magnetic field 
strength was about 0.8 of that of the Earth. For a given site on the ship it 
should be possible to determine this curve and correct for the ship's deviation 
error. After correction, it should be possible to routinely obtain bearing 
accuracies significantly better than the (5( required for true wind calculation.

It was hoped during the cruise to determine setup parameters for the GPS system 
in order to optimise both the quality and period of record of the ship's 
velocity data. GPS coverage in the region was good with satellite fixing 
possible for all but two half-hour periods per day. It was difficult to 
correlate differences between fixes from the portable GPS with the ship's GPS 
with the satellite constellation parameters, so effort was concentrated on 
devising an editing routine for ship's speed to minimise the difference between 
the speeds from the two systems. The apparent acceleration of the ship was 
calculated using successive fixes from the portable GPS system. Following the 
subtraction of a 5 minute running average, representing genuine large 
accelerations by the ship, the time series of residual acceleration data was 
examined for values greater than two knots per minute. The speed data associated 
with these large residual accelerations were then removed from the GPS system 
comparisons. This scheme succeeded in reducing the standard deviation of the 
speed difference between one GPS system and the other by about 30%, and brought 
the 15 minute mean speed measurements to within the required accuracy of 
(0.1m/s. The accuracy of these speed measurements did not appear to change 
significantly with the different setup parameter combinations used.

                                                                  ECK, RWP, PKT

WFAX

A weather facsimile system, using a communication receiver and an "ICS-FAX" 
software on an MS-DOS personal computer, was tested during the cruise. The 
system successfully captured a large number of weather charts in automatic mode. 
However, attempts to computer control the communications receiver, to 
selectively receive charts at set times on chosen frequencies, were not 
successful. The addition of the commercially available computer interface will 
probably be necessary.
                                                                       RWP, PKT


HYDROGRAPHIC AND CURRENT MEASUREMENTS

CTD

Two CTD surveys were conducted on Cruise 62A. The surveys were defined by a 
triangle under the location of a descending and ascending pass of the ERS-1 
satellite (see Figures 1, 2 and 4). It was planned to have both surveys cover 
the same track. The bottom corner of the survey is the point at which the two 
satellite tracks cross. Due to rough weather the second survey was modified 
slightly by missing out the top right corner of the survey triangle (see Figure 
4). Hence, the sampling order, in time, of the stations was different for the 
two surveys. Two additional stations were added to the second survey to sample 
the interior of the CTD triangle. There were a total of 27 stations (see Table 
3; station 1, a test dip, and station 10, a failure, were excluded from the data 
analysed).

The CTD equipment, supplied by RVS, consisted of a Neil Brown MkIIIb CTD, an 
Aquatracka fluorometer, a SeaTech transmissometer with a path length of 25cm and 
an IOS 10kHz pinger. Calibration coefficients for all the instruments were 
supplied by RVS. The initial set of calibration values were not complete and 
part way through the first survey, RVS received a second set of coefficients 
that were then entered into the calibration file. Twelve 1.7 litre Niskin 
sampling bottles were used on the rack to calibrate the conductivities measured 
by the CTD. Also attached to the sampling bottles were two SIS digital reversing 
thermometers.

The first survey began at approximately 0630 on day 255 and finished on day 257 
at noon. This survey included 13 stations; 2 through 15, excluding 10; with 
depths of the casts varying from 3400m at the northwest corner to about 200m at 
the southern corner on the Faeroes shelf. Sampling bottles were triggered at 
various depths depending on the total depth of water at the station. Twelve 
bottles were triggered for the deep stations, two at each of six depths. The 
shallow stations had fewer bottles triggered. The only problem encountered 
during the first survey was the breakdown of the RVS deck unit. Station 11 was a 
repeat of the shallow station 10. It was repeated because the bottle firing pin 
had not been placed in the correct location. No loss of data occurred.

The second survey, from 1200 on day 262 to 1200 on day 266, took longer to 
complete than the first survey due to bad weather, the additional two stations 
in the middle of the survey, and a delay due to a mooring recovery. The two 
right stations on the top leg of the triangle were skipped due to bad weather 
(see Figure 4). There was also the constraint that the ship needed to be at the 
cross-over location at the time of the next satellite overpass. One station, 18, 
was not logged onto the level C at the time of the cast, due to a problem with 
the RVS logging system. It was recovered from tape satisfactorily at the end of 
the survey.

Data collection occurred via the RVS logging system, first through the level A, 
then level B archive, and finally to the level C on the Sun computer system. 
Data were extracted from the level C system into Pstar by Pexec command files. 
The calibration constants were supplied by RVS for their CTD equipment. The 
calibration coefficients were not consistent with the values needed for the 
Pexec programs. Additional values were requested by RVS personnel from Barry for 
the fluorometer and the transmissometer. The fluorometer were not examined in 
the processing because the calibration coefficients could not be applied 
correctly. The oxygen sensor data were not calibrated and, therefore, not used. 
Bottle salinities were analysed using the IOSDL Autosal. The CTD conductivity 
measurements were calibrated to the bottle salinities. The downcast data were 
then recalibrated, despiked and averaged to 2 decibars. Contour plots for sigma-
0 and potential temperature were also created.

The calibrated data show a cold core, eddy-like feature in the middle portion of 
the triangle to approximately 500m. Below this depth, the water mass is uniform. 
The mixed layer, with an approximate potential temperature of 9-10(C extends to 
about 70m across the whole survey triangle. The southern region of the triangle 
has warmer water over the shelf.

Although, no overwhelming problems occurred during the CTD surveys, we think 
that a considerable amount of confusion in the processing of the CTD data could 
be eliminated if calibration coefficients for the instruments being used were 
obtained before the cruise. Additionally, the processing path used for 
processing the data should be standardised. Hooks should be placed in the 
command files to allow a PSO to change the manner of processing the CTD data 
instead of requiring the command files to be modified for each separate cruise. 
A straight forward CTD processing package should be available for cruises that 
do not require extremely high precision.
                                                        AIM, MAS, SGA, NAC, RTT


CTD DATA FOR CRUISE CHARLES DARWIN 62A
(6th September 1991 - 28th September 1991)

1. Introduction

CTD profile and bottle data are presented from the ERS-1 validation cruise 
Charles Darwin 62A, as reported by Srokosz et al. (1992). The data collection 
and calibration procedures have been described by Tokmakian et al. (1992).


2. INSTRUMENTATION

The CTD profiles were taken with a Neil Brown Systems MkIIIb CTD, mounted 
beneath a 12 by 1.75 litre bottle rosette. The CTD was fitted with a pressure 
sensor, conductivity cell, platinum resistance thermometer, a dissolved oxygen 
sensor, an Aquatracka fluorometer, a Sea Tech 25cm path transmissometer and an 
IOS 10kHz pinger. 3 SIS (Sensoren Instrumente Systeme) digital reversing 
thermometers (T219, T220, T260) were attached to the Niskin bottles.

For the bottle rosette system the bases and tops of the bottles were, 
respectively, 0.00m and 0.55m above the CTD pressure sensor. The digital 
reversing thermometers were mounted 0.20m above the CTD temperature sensor.


3. DATA ACQUISITION

Lowering rates for the CTD package were generally in the range 0.5-1.0ms-1 but 
could be up to 1.5ms-1. CTD data were logged at 16 frames per second. The CTD 
deck unit passes raw data to a dedicated Level A microcomputer where 1 second 
averages are assembled. During this process the Level A calculates the rate of 
change of temperature and a median sorting routine detects and removes pressure 
spikes. This data is sent to the Level B for archival. The data are then passed 
to a Level C workstation for conversion to Pstar format and calibration.

Water samples were acquired on the up cast with the winch stopped. The CTD data 
acquisition system sends out a bottle firing code at the time of bottle firing. 
The code is logged as serial data by the Level A which timestamps its arrival.

A total of 27 stations (01 - 29) were occupied. Station 01 was a test dip and 
station 10 a failure. Station 11 was a repeat of station 10. The reversing 
thermometer T260 was only used at station 02.


4. DATA PROCESSING

4.1. CTD DATA

The 1 second data passed to the Level C were converted to Pstar format and 
initially calibrated with coefficients from laboratory calibrations. The up cast 
data were extracted for merging with the bottle firing codes, on time, thus the 
CTD variables were reconciled with the bottle samples. Final calibrations were 
applied using the sample bottle data.

The oxygen, fluorometer and transmissometer data cannot be used because of 
problems with the calibration coefficients supplied by RVS.

PRESSURE

The pressure values were calibrated using the equation:

                    p (dbar) = 0.394 + 0.99986 x praw x 0.1

No further pressure corrections were applied.

TEMPERATURE

The temperature values were calibrated using the equation:

                 T ((C) = 0.999978 x (0.0005 x Traw) + 0.03176

No further temperature corrections were applied.

SALINITY

Raw conductivities were scaled to physical units using the relationship:

                    C (mmho/cm) = CR x (0.001 x Craw) + 0.0

where the conductivity ratio (CR) = 1.000. The conductivity ratio was recomputed 
for each survey by comparing the conductivities computed from the bottle 
salinities and the average conductivity from the up casts at the time the 
bottles were fired. For the first survey, the conductivity ratio was 
recalculated as 1.001, and for the second survey it was 1.0015. The up cast and 
down cast data were recomputed using these values.

For each station the differences between the bottle sample salinities (Sbot) and 
the down cast CTD salinity (Sctd) were calculated. The CTD salinity values were 
taken from those down cast locations which match closest the average pressure 
and potential temperature around the time each bottle fired in the up cast. A 
routine was used to derive coefficients for the relationship:

                  Sbot - Sctd = a + (b x press) + (c x potemp)

The derived a, b, and c coefficients for a station were then used to correct all 
CTD salinities for the down cast of that station.

4.2. SAMPLE DATA

SALINITY

Salinity samples from the Niskin bottles were analysed using a Guildline 8400 
bench salinometer set to run at 24(C in the temperature controlled laboratory 
(22(C). After every 12 analyses standardisation was done using IAPSO Standard 
Seawater batches P114 and P115.

Two bottles were fired at each selected depth, and two samples were taken from 
one of these; the other bottle only being sampled if a problem occurred with the 
first. Only 5% of the paired samples from the same position differed by more 
than 0.002psu.

REVERSING THERMOMETERS

3 SIS digital reversing thermometers were attached to the Niskin bottles.


5. BODC Data Processing

No further calibrations were applied to the data received by BODC. BODC were 
mainly concerned with the screening and banking of the data.

5.1. CTD DATA

The CTD data were received as 2db averaged pressure sorted down cast data. The 
data were converted into the BODC internal format (PXF) to allow the use of in-
house software tools, notably the graphics editor. During this process all the 
oxygen, fluorometer and transmissometer data were set null. Spikes in the data 
were manually flagged 'suspect' by modification of the associated quality 
control flag. In this way none of the original data values were edited or 
deleted during quality control. These data from cruise CD62a required little 
flagging and just a few points were set suspect.

Once screened, the CTD data were loaded into a database under the Oracle 
relational database management system. The start time stored in the database is 
the CTD deployment time, and the end time is the time the CTD reached the 
bottom. The start time is more precisely the start of data logging. Latitude and 
longitude are the mean positions between the start and end times calculated from 
the master navigation in the binary merged file.

5.2. SAMPLE DATA

BODC conducted extensive quality control to eliminate rosette misfiring and any 
incorrectly assigned flag codes. Before loading to the database the data were 
averaged if bottles fired within (4.0db of each other. The reversing thermometer 
data were received with only a 'wire out' value and were therefore manually 
associated with the bottles.


6. REFERENCES

Srokosz, M.A. et al. (1992). RRS Charles Darwin Cruise 62A. Institute of   
    Oceanographic Sciences Deacon Laboratory, Cruise Report No. 229, 49pp.

Tokmakian, R.T. et al. (1992). CTD and XBT collected on ERS-1 validation cruise   
    RRS Charles Darwin Cruise 62A, Iceland-Faeroes region. Institute of 
    Oceanographic Sciences Deacon Laboratory, Report No. 294, 86pp.


XBT

During the cruise a number of XBTs were launched to add to the information 
gained from the CTDs over the survey triangle. 83 probes were launched in total 
with varying degrees of success. Two different types of probe were used, the 
first, T5 had an operating depth of 1830m, the second, T7 was limited to 760m.

XBTs were controlled by a Bathysystems SA810 controller connected to an IBM PS2 
running Bathysystems software, both of which were in the plot. The XBT launcher 
itself was connected via a cable to a socket on the aft end of the main 
laboratory, and from there to the PC. This arrangement required the launcher and 
cable to be stored between launches and connected immediately before a drop. 
This operation raises the chances of breaks and snags in the cable, since there 
was no proper storage for the cable. Also two people were required for each 
launch since the deck unit was so far away from the launch point, that the 
software would time out before a single operator could get in position. A simple 
set of signals from the bridge wing was adopted to tell the launcher when to 
load the XBT and when to begin the drop. At night this was effected using a 
torch. Safety gear in the form of ear protectors and gloves were provided, but 
on the whole not used.

New software was loaded into the system before Cruise 62 by the Hydrographic 
Office. However, no documentation was provided, and the correct sequence of 
steps was only established by trial and error. The format that the software 
writes data to disk was also changed, which forced the introduction of two new 
steps in procedures on Cruise 62.

Since the XBT system is provided by the Hydrographic Office, they require that 
the data should then be transmitted to them by satellite. This is carried out by 
queuing the data, which are then automatically sent out during four transmission 
windows throughout the day. However, the queuing buffer allows only two XBT 
drops to be sent at one time, which led to a backlog of unsent data at the times 
when four or more XBTs were being launched in a six hour period.

Two distinct groups of XBT failures occurred. The first were simply caused by 
operator error, when the software was told that the launcher was loaded when it 
was not, or the controller was not reset before launch. The second was 
associated with bad weather when the ship was underway. Here the drop terminated 
abnormally before either the bottom or the maximum operating depth was reached.
It was soon observed that the near surface temperatures calculated by the XBT 
were often wrong. This was especially true in the top metre, within which the 
data was always a number of degrees different from other observations. To 
provide some degree of understanding of the characteristics of the XBTs, at each 
corner of the survey triangle, before a CTD was lowered, an XBT was launched. 
Early comparisons suggest that XBT temperatures in the whole of the mixed layer 
may be suspect.

Further consistency checks were made by performing a number of drops at the same 
location and changing the input parameters to the program. Most significantly 
varying the injection (or bucket) temperature value required by the program from 
9 to 10(C or using 99.9 which is its default value, produced temperatures in the 
first metre which ranged from -1 to 12(C, when other observations suggested an 
SST of 10(C. It was decided from this point to use an injection temperature of 
99.9 throughout. This was an arbitrary choice, since an error of 2(C is as bad 
as one of 11(C.

The depths are calculated from the time elapsed using a quadratic function of 
time whose parameters vary between types of XBT. A comparison of the depths 
reached by XBTs which hit the bottom with the corrected echo sounder readings in 
the same time interval suggest the XBT depths are too shallow by more than 10 
metres.

It is clear from these problems that the software used to control and interpret 
the XBT data needs to be corrected. Ideally the user should be provided with an 
exact description of the algorithms used to produce the data from the 
measurements, so that they can more easily interpret and correct their data.

The data were copied to floppy disk and then read into the level C Sun where it 
was translated into ASCII and then into RVS data format, at the same time 
calculating depth from elapsed time. Copies were then made in Pstar format. Each 
XBT was despiked before they were gridded into sections along each side of the 
survey triangle. Comparisons of the deeper structure (below about 200m) between 
the CTD and XBT sections show quite good agreement. It is hoped to use the XBTs 
to improve the resolution of the survey.

A summary of the XBT drops is given in Table 4.
                                                                   SGA, AIM, DL

ADCP (Acoustic Doppler Current Profiler)

The shipboard R. D. Instruments 150kHz ADCP was set up to give 64 x 8m bins, and 
an ensemble average every 2 minutes. As only a small portion of the work was to 
take place in waters shallower than 400m, this set-up was used throughout the 
cruise. In addition, bottom tracking mode was enabled for the purpose of 
calibrating the ADCP (Pollard and Read, 1989) and was successful to a depth of 
about 650m. The use of bottom tracking meant that the set-up was the same for 
the calibration as for the rest of the work, but at the price of a lower ping 
rate.

The data quality from shipboard ADCPs seems very dependent on the ship's speed, 
heading relative to the wind, and sea state, so initial calibration runs were 
made at both 8 and 10 knots. Although much better at 8 knots, the data quality 
whilst underway was generally very poor and extremely variable from ensemble to 
ensemble. The results of both calibration runs were very similar and so could be 
applied to the data collected at either speed, however, an effort was made to 
adhere to 8 knots when the timing of satellite overpasses would allow.

Initial data processing, to the derivation of absolute currents, was achieved 
through the use of a set of Pstar command files which have accumulated during 
the last few years use of ADCPs by IOSDL and JRC.

The Data Acquisition Software (DAS) crashed once after a restart, necessitating 
a reset of the PC, but otherwise the ADCP and its associated hardware operated 
without any problems.

After subtracting the ship's velocity from the ADCP currents, underway currents 
appeared to be larger than those on-station by a factor of 2 or 3. Initially 
this difference was thought related to the values obtained for misalignment 
angle and amplitude correction in the initial calibration runs, as they were 
slightly larger than those measured on previous Darwin cruises. Unless, however, 
a mechanical shift of the transducers had occurred since the previous cruise 
(62) which immediately preceded this one, the amount by which they differ cannot 
account for the difference.

The ADCPs four transducers allow quantities like 'vertical velocity' and 'error 
velocity' to be measured, and these play a part in determining the data quality 
measured by the ADCP. The 'error velocity' was found to be negatively biased 
whilst underway as noticed by Saunders (Saunders, 1991) on Cruise 42, resulting 
in an under-estimation of the ship's velocity and, therefore, larger absolute 
currents. This is the most likely explanation, but what effect it has on the 
possible interpretation of the underway data is not yet known.

Bubbles passing under the ship and collecting in the "top-hat" housing in which 
the ADCP is mounted are one of the possible causes of the under-estimation, so 
to minimise this build-up of air, the top-hat was bled on two occasions; 0830 on 
day 250, and 1600 on day 261.
                                                                            NAC

VAESAT BUOY

The VAESAT buoy consists of an Electromagnetic Current Meter (ECM) providing 
measurements at a depth of 1m every minute, and a 1MHz Acoustic Doppler Current 
Profiler set up for sixteen 1.5m bins starting 2.5m below the surface, and a 
data interval of 5 minutes. The data from both instruments are recorded on Sea 
Data cassettes, and a portion of the ECM data is transmitted to the Argos 
satellite. This also allows data (including diagnostics) to be received on the 
ship whilst within a two mile radius of the buoy, and means that backup data 
including positional information are recorded.
Useful communication with the buoy ceased on day 255 when the Argos link showed 
only zeros instead of data. Unfortunately, this was also the case with the data 
that were recorded to tape and suggests failure of one of the analogue-to-
digital converters in the ECM hardware.

Post recovery checks on the ADCP showed normal operation. However, attempting to 
read the data cassette showed a deterioration in recording quality soon after 
the buoy was deployed and means that the amount of recoverable data is as yet 
unknown.

Any data that are recovered from the buoy will provide useful comparison data 
for the shipboard ADCP.
                                                                            NAC


MOORING OPERATIONS

SHELF SLOPE MOORINGS

A bathymetric survey (day 251) of the proposed mooring sites showed a gentle 
gradient from 220m to 256m deepening towards the north east. Depths at the 
mooring locations were determined and mooring line lengths adjusted for correct 
subsurface positioning.

DIRECTIONAL WAVERIDER (Mooring 508, Figure 5)

DEPLOYMENT

The Waverider buoy was deployed on day 251 (at position 62( 18.329 N, 04( 55.795 
W) from the after deck using the starboard Effer crane and no load release hook. 
Mooring rubber cord and line was deployed by hand as the vessel moved ahead at 
one knot. The subsurface sphere was lifted over and released using the crane and 
no load hook technique. The remaining line and acoustic release being 
preconnected were deployed to the anchor hung overside on a cut-off rope. A 
short tow commenced onto position where the anchor was cut away to freefall to 
the sea bed.

The mooring was observed to settle correctly on position and the acoustic 
release transponder was interrogated to establish correct depth and operation.

RECOVERY

The Waverider was known to be either missing or sunk when retrieval operations 
commenced (day 259). The acoustic release was located and triggered to release 
the anchor. The subsurface buoy was sighted at the surface within one minute of 
triggering and the vessel moved alongside to grapple. During this phase a glass 
Benthos sphere was seen floating close by. Once grappled, the subsurface was 
hauled aboard by winch with the remaining mooring parts being rapidly hand 
hauled aboard.
The Waverider was not recovered as the rubber cord had parted due to severe 
laceration of the upper five metres. This was caused by a fishing wire, traces 
of broken strands being embedded in the cord and blue paint streaks evident near 
the parted end. One of the two line support buoys above the subsurface had been 
punctured by impact and was flooded. The mooring line to the anchor was abraded 
along its length with frequent traces of grease. The upper release support buoy 
was missing and the casing shattered, the sphere seen earlier was likely to have 
come from this casing, presumable shaken out of the remnants when the anchor was 
released. This evidence indicates that the mooring had been trawled from seabed 
to surface with the Waverider bungee parting as the mooring load was exceeded.

VAESAT BUOY (Mooring 509, Figure 6)

DEPLOYMENT

The VAESAT buoy was deployed on day 251 (position 62( 18.641 N, 04( 55.238 W) 
using the same technique as the Waverider. A short tow was necessary to position 
the mooring with the anchor cut away on reaching the position. The buoy was 
observed to settle on position and the acoustic release transponder 
interrogated.

Argos transmissions were monitored onboard with a useful range of two miles.

RECOVERY

The buoy was relocated on position day 266. The poor weather conditions 
precluded use of the Searider work boat and necessitated the ship manoeuvering 
to the buoy. The acoustic release was triggered with the ship two cables 
downwind and the subsurface buoy seen to surface approximately 100m clear of the 
VAESAT. The ship came alongside the surface buoy where with some difficulty a 
line was attached to the lifting strops. The buoy was easily passed astern on a 
handling line for winching aboard. Unfortunately the buoy was hit by the 
protruding airgun boom mounting and the light and top cone were destroyed. The 
buoy was winched aboard with the remaining mooring well astern. The subsurface 
buoy and acoustic release then being recovered by winch.

The damage to the light and top cone was caused by the airgun boom mounting 
which is a steel fabricated structure faired fore and aft but not vertically. 
Thus when the ship is pitching a flat steel surface is presented directly over 
any buoy alongside. It would be desirable to have this faired in such a way that 
a buoy would be deflected out and clear of this hazard.


SONIC BUOY (Mooring 511, Figure 7)

DEPLOYMENT

The sonic buoy was deployed on day 259 (position 62( 18.52 N, 04( 56.37 W) using 
the technique employed for the Waverider. As the buoy has extremely vulnerable 
sensors mounted on the top ring two control lines were used to position the 
sensors as far outboard as possible. The no load release control string was 
broken twice on lifting the buoy outboard as the correct pull angle was 
difficult to achieve. On the third attempt the release operated and the buoy 
moved slowly clear of the ship. On anchor release the buoy was seen to move 
rapidly towards the drop position and apparently almost capsize due to the speed 
of pull and wave motion.

RECOVERY

The buoy was relocated capsized on day 260 and a recovery operation was mounted. 
The acoustic release was triggered and the subsurface buoy located shortly 
afterwards. The ship then made a close pass of the rig to establish the 
condition of the lines.

By maneouvering the ship alongside the subsurface buoy, the lines could be 
grappled and brought aboard. The buoy and acoustic release were then recovered 
by winch. With the sonic buoy line connected to the winch, the buoy was hauled 
aboard inverted. Although the buoy was capsized the mooring had not been 
damaged.

DEEPWATER MOORING

The deepwater mooring was designed to locate a meteorological buoy in 3000m 
water depth for the duration of the cruise. The technique chosen was a long line 
mooring of scope (line length/water depth) 1.5. The line to be compliant nylon 
near the surface and near seabed with the remainder of polyester. All previous 
IOSDL moorings have utilised polypropylene as the main line with steel wire near 
the surface. Deployment was to be buoy first with freefall anchor.

A bathymetric survey of the mooring site was carried out on day 252 and the on-
site depth determined at 3180m situated on a gentle slope.

METEOROLOGICAL BUOY (Mooring 510, Figure 8)

DEPLOYMENT

The buoy was deployed first using the release hook on the starboard. Effer crane 
through the stern A frame. The ship made way at 1 knot to draw clear of the buoy 
as it was released. The buoy chain was deployed by hand to the ballast which was 
freefall off the stern taking away the carefully coiled nylon line off the deck. 
Mooring line was then deployed off wooden storage drums through the double 
barrel capstan as the vessel made headway of 1 to 1.5 knots. The depth having 
been determined of the site the mooring lines were adjusted during deployment.

With the line fully deployed a short tow commenced onto position to stretch out 
the mooring.

On anchor release (63( 57.58 N, 06( 18.826 W) the ship was turned towards the 
buoy and visual contact established. Some buoy motion was observed towards the 
anchor release position. The buoy was monitored into the dark hours to check the 
light and radar signature.

RELOCATION

The toroid was relocated on day 255 by Argos reception onboard and acoustic 
range, 3210m, on the release. No visual contact could be established due to poor 
visibility.

A further relocation was made on day 257. Radar at 3 miles, Argos at 2.5 miles, 
visual at 1.5 miles. A close pass was made observing the buoy sensors. The red 
wind direction vane appeared distorted.

RECOVERY

On arrival at the anchor lay position on day 263 the buoy could not be seen or 
detected on Argos. The ship then steamed to the location of last visual sighting 
on day 257. With the ship hove to an acoustics range of approximately 3500m was 
obtained. Argos contact was then established, intermittent probably due to 
swell. Visual and radar detection were severely restricted due to sea state and 
rain clutter. The buoy was detected visually at 3 cables. The ship then steamed 
to a position 1 cable downwind of the buoy and the release was triggered at the 
first transmission.

The ship maneouvred alongside the buoy and grappling attempts commenced. The 
buoy deployment strop was hooked with a heavy duty hook on a pole and hauled 
astern with the winch. The tower took several hard knocks without sustaining any 
sensor damage. However, as the buoy passed around the quarter, the tower came up 
beneath the steel airgun boom mounting and most of the sensors were effectively 
destroyed. Once astern the buoy was recovered using DBC and Rexroth winches to 
alternately haul and stop off the buoy chain. The line was hauled on the DBC and 
fed into a large wooden crate for stowage. The top 500m of line had several 
turns taken into itself which were cleared by stopping off using a rope stopper. 
No significant damage was apparent at these turns.

The tower had suffered damage due to being under the airgun fender, several 
welds having cracked and severe distortion of the top protective ring and 
supports having occurred. The buoy hull was relatively intact, all impact with 
the ship being on the tower. The only apparent minor damage being to the glass 
reinforced external lugs. As with the VAESAT buoy (mooring 509) the damage 
sustained by the buoy was entirely due to the airgun boom mounting. If this is 
not modified further damage will occur when attempting this type of operation.

Overall the mooring appears to have worked as expected. Future deployments will 
perhaps incorporate a longer nylon section near to the surface to reduce the 
tangling seen in the upper polyester line. Further studies of this should take 
place at IOSDL.
                                                                             IW

OCEANO RELEASES

The Oceano releases used with the moorings again proved to be very reliable and 
capable of working equally well in shallow and deep water. The only problem that 
occurred was prior to the launch of the sonic buoy, the release and the spare 
were found to have faults but a working release was obtained by combining parts 
from both.
                                                                            AKJ


SATELLITE DATA

ERS-1

The ERS-1 satellite, launched on the 16th July of 1991, provided Cruise 62A with 
the satellite data to be validated against the in situ data measured. The 
satellite, two months after launch, was still in the commissioning phase. Data 
from two instruments, the altimeter and the scatterometer, were examined during 
the cruise. The altimeter data, at 7km resolution along track, has a temporal 
sampling of 1 second. Wind speed, significant wave height and range values were 
extracted from the ESA altimeter URA fast delivery product. The scatterometer 
gathered data, stored as a 19 x 19 array with spatial separation of 25km, to the 
side of the satellite track at a temporal rate of one array approximately every 
minute. Wind speeds and directions were examined from the scatterometer fast 
delivery, UWI product.

The satellite data are received, initially, by the ERS-1 receiving station at 
Kiruna, Sweden. It is then passed to the data processing facility at ESRIN in 
Frascati, Italy. Once the fast delivery products have been created, they are 
sent to the individual ESA member countries' meteorological offices. The Met 
Office in Bracknell receives the satellite data for the UK. Due to contractual 
problems, the Met Office does not pass the data along to any institute that may 
require it. Mullard Space Science Laboratory has paid for a link between itself 
and the Met Office to receive ERS-1 altimeter and scatterometer data. The 
Rennell Centre, with a contract with the Earth Observation Data Centre, was 
allowed to extract the data for the altimeter and the scatterometer for the 
region between 55( and 70(N for the time period of Cruise 62A. The altimeter 
data were extracted for only the two passes, one ascending and one descending, 
which were located within the cruise region. With the much appreciated help of 
Peter Challenor and David Cotton at the Rennell Centre, the data were formatted 
and sent via RVS in Barry, on the Marinet system, to the RRS Charles Darwin.
On board the ship, the satellite data were formatted into Pstar files and 
plotted. Wave heights were compared with the directional Waverider and the 
shipborne wave recorder for the coincident location and times. Wind speeds from 
the altimeter and the scatterometer were compared with coincident Young wind 
vane anemometer data on the foremast and the cup anemometer data on the main 
mast. In addition, the scatterometer plots were compared qualitatively with the 
synoptic weather charts received by the ship. The altimeter range measurements 
were averaged to produce a mean range value along track. This mean was then 
subtracted from the range values and the residual range values plotted. The 
range data were used only qualitatively to note the possible change in sea 
surface height along each track. Without a long time series and a known 
satellite orbit, the range data contain too many errors to be used onboard the 
ship in a quantitative manner.

The algorithm for the altimeter wind speeds was not known to be in a stable 
configuration. Before the cruise, Richard Francis, the ERS-1 altimeter engineer, 
indicated that the algorithm for computing wind speeds might be changed. (In 
fact, the altimeter algorithms for significant wave height and wind speed were 
altered on the 17th of September, day 260.) The scatterometer data received were 
of low quality when the product confidence was examined. In the earlier portion 
of the cruise, the product confidence word on the scatterometer data received 
indicated that one of the three beams, the forebeam, was not being used to 
produce the estimate of the wind speeds and directions. This would introduce 
ambiguity in the wind direction indicated. There was also a contradiction in how 
the data were scaled between the documents supplied by ESA and the Met Office. 
We were not able to resolve the contradiction while onboard the ship. 
(Subsequently, it was found that there was a calibration problem with the ERS-1 
scatterometer.)

Since the objective of the cruise was to calibrate and validate instruments 
onboard the ERS-1 satellite, the ability to receive the data onboard the ship 
was worthwhile. It was a little frustrating, however, that the specifications 
for the satellite algorithms and data were unclear or contradictory. It would 
have been helpful to have more pre-cruise time to sort the problems out, which 
was not possible. The problems encountered were not surprising because the 
satellite was still in its commissioning phase.

[During the cruise, ERS-1 went over the area in which measurements were being 
made on days 253, 256, 259, 262 and 265. Its times at the cross-over point (see 
Figures 1 and 2) were 1156 on the descending track (eastern side of the 
triangle, travelling south), and 2144 on the ascending track (western side of 
the triangle, travelling north).]
                                                                  RTT, MAS, THG

MACSAT

MacSat is a satellite data acquisition and data display package built around the 
Apple Macintosh II computer, enabling Automatic Picture Transmission data to be 
received from a number of meteorological satellites at a spatial sampling of 
5km. At sea its use is restricted to polar orbiting satellites. The object on 
the cruise was to monitor weather systems in real-time and, when cloud 
conditions allowed, to identify sea surface temperature features. However, it 
was first necessary to investigate several problems which had arisen on its last 
use at sea (Charles Darwin 58; Pollard, Leach & Griffiths, 1991) and which had 
rendered the system virtually useless at the time.

After some experimentation the omni-directional antenna and its preamp were 
fixed to the port rail of the wheelhouse top. This position was a compromise 
between minimisation of interference from the HF and INMARSAT antennas and 
avoidance of obstruction by the main mast and funnel. In neither of these 
respects was the location ideal. Cabling from the preamp ran via a conduit into 
the plot where the receiver and Mac II were situated. This avoided use of the 
ship'' cabling which can be a potential source of signal loss, through impedance 
mismatching. Good quality images were obtained soon after the ship sailed from 
Russian satellites using a transmitting frequency of 137.30MHz. No data of 
usable quality could be obtained from the NOAA satellites which use 137.50 and 
137.62MHz. This behaviour was similar to that found on Cruise 58 and appeared to 
be caused by interference confined to these two channels. Investigations 
suggested that this was probably not from the ship but from feedback within the 
synthesized receiver. By tuning the receiver manually in 10kHz steps instead of 
relying on the preset channels it was found that much higher signal to noise 
ratios could be obtained on 137.53 and 137.64MHz. These were used on the rest of 
the cruise for acquiring data from NOAA 10, 11 and 12, giving adequate picture 
quality on the majority of occasions.

The MacSat software enables predictions to be made of when each satellite should 
be visible for a given geographical position. These were found to be accurate to 
within a minute but the signal strength was usually insufficient for the first 
and last two minutes of each transmission to be usable. Several passes per day 
were acquired and, after discarding the poorer quality data, over 60 images were 
stored on hard disk. A subset of these (the best pass for each day) were saved 
to floppy disks. A choice has to be made between visible or infra-red channels 
when displaying and saving images and the latter was normally selected. However, 
from day 255 onwards the analogue signal was also stored on cassette by 
connecting a domestic tape recorder to the output socket of the MacSat receiver. 
Replay of these tapes will allow VIS and IR to be replayed and optimum A/D 
conversion to be chosen via the MacSat software (not always possible in real-
time). Because the signals were not all that strong the option of using the 
computer's internal clock to synchronise signals rather than the spacecraft 
clock was selected. This is important if the images are not to get out of sync 
every time the signal fades and was undoubtedly a problem on Cruise 58. It is 
then straightforward to position the start of each scan line at the left hand 
edge of the window on the monitor.

All of the images which have been archived show cloud patterns associated with 
the weather systems observed at the time. It was, however, difficult to 
geographically register the images. A reasonably successful solution was to 
construct an overlay based on gridded images obtained from the NERC Satellite 
Station at Dundee. By identifying coastlines and knowing the predicted orbits of 
each pass it was often possible to position the overlay on the monitor screen 
and thereby reference features to latitude and longitude. (The latest version of 
MacSat overlays grids on NOAA images as part of the processing and this would be 
of great benefit for our applications.)

In cloud free areas an attempt was made to identify sea surface temperature 
features for real-time cruise planning. Although some gradients could be seen in 
UK coastal waters none were discernible in the cruise area, possibly because 
they were relatively small in magnitude (typically, a few tenths of a degree in 
10km). One problem is a 'herring-bone' interference pattern on most images which 
dominates in any attempt to enhance the IR images. Another is that complete 
dropouts in signal occurred, probably when the line-of-sight to the satellite 
was obstructed by structures on the ship. It is recommended that in future the 
MacSat antenna should be placed in a more elevated position to improve the view 
of the horizon in all directions.

Although there are still problems to be sorted out, the performance of MacSat on 
the cruise showed the viability of this cheap system for acquiring satellite 
images in real-time. The images will be used as a quick-look to identify 
priority occasions for detailed processing of the 1km resolution NOAA data 
obtained by Dundee and for ERS-1 ATSR data.
                                                                       THG, TNF

MISCELLANEOUS

PES

The PES fish and Simrad echosounder deck unit worked well throughout the cruise.

                                                                            AKJ

COMPUTING

The RVS computer system was used to log data from ten instruments, these being 
EM Log, Gyro, GPS and MX1107 satellite navigators, echo sounder, CTD, 
thermosalinograph, MultiMet, Shipborne Wave Recorder and ADCP. In addition, XBT 
temperature data were transferred from the XBT PC on floppy disks and processed 
on the level C to produce a depth versus temperature file.

Most of the data processing on board was done using the IOSDL Pstar suite of 
programs, but the RVS system was used for producing navigation plots and 
provided corrected navigation for the Pstar processing.

The system worked well after initial problems getting the logging started for 
the MultiMet and Shipborne Wave Recorder.

For some reason not determined, the MultiMet level A data could not be 
transferred over the Cambridge Ring network that links the level A's in the plot 
to the level B in the computer room. The problem was overcome by transferring 
the data on a hard-wire link.

The Wave Recorder logging failed shortly after it had been started due to the 
level A interface becoming faulty. This was due to failure of the level A, 
analogue input PCB. Of the spare analogue PCB's on board the first two that were 
tried were also faulty, but eventually a good one was found and the interface 
made operational again.
                                                                             DL

Communications

A contributor to the success of the cruise was the ability to receive ERS-1 data 
a day after it was acquired, via the Marinet system, from the Rennell Centre. 
The failure of the teleprinter terminal (on day 253) and the consequent loss of 
the satellite communications could have impaired the work on the cruise. All 
credit must go to the radio operator and Derek Lewis (RVS) for managing to fix 
it. However, the incident raises serious concerns about the lack of adequate 
spares or alternative means for maintaining the satellite link.
                                                                            MAS

ACKNOWLEDGEMENTS

Being a principal scientist for the first time on this cruise, I am grateful for 
all the help, advice and encouragement that I received from the Master and 
Officers of the Darwin, and also from the more experienced sea-goers amongst the 
scientific staff. The success of the cruise is more a reflection of the skills 
and dedication of the Master, Officers, crew and scientists taking part in the 
cruise, than of any ability on the part of the principal scientist.

In addition, I wish to express thanks to the Mullard Space Science Laboratory 
and also particularly to Peter Challenor and David Cotton of the Rennell Centre 
for their work in gettin the ERS-1 altimeter and scattermometer data transmitted 
out to the RRS Charles Darwin during the cruise.
                                                                            MAS


REFERENCES

Pitt E. G., 1988. The application of empirically determined frequency response 
    functions to SBWR data. Institute of Oceanographic Sciences Deacon 
    Laboratory. Report No.259, 82pp.

Pollard R. T., Leach H. & Griffiths G., 1991. Vivaldi '91. Institute of 
    Oceanographic Sciences Deacon Laboratory. Report No.228, 49pp.

Pollard R. T. & Read J. R., 1989. A method for calibrating shipmounted acoustic 
    doppler profilers and the limitations of the gyro compass. J. Atmos. and 
    Oceanic Tech., 6, 859-865.

Saunders P. M., 1991. Combining hydrographic and shipborne ADCP measurements. 
    Deep-Sea Research, (in press).


TABLES AND FIGURES

Table 1:  Sensors logged by the MultiMet system.
Table 2:  Sensors on the Meteorological buoy.
Table 3:  CTD casts on Cruise 62A.
Table 4:  XBT drops on Cruise 62A.
Table 5:  Radiosonde ascents on Cruise 62A.

Figure 1:  ERS-1 ground tracks and CTD survey triangle.
Figure 2:  Ship's track during first CTD survey and mooring positions.
Figure 3:  Ship's track during SST survey.
Figure 4:  Ship's track during second CTD survey.
Figure 5:  Directional Waverider mooring (No. 508).
Figure 6:  VAESAT buoy mooring (No. 509).
Figure 7:  Sonic buoy mooring (No. 511).
Figure 8:  Meteorological buoy mooring (No. 510).



TABLE 3: CTD CASTS ON CRUISE 62A

Cast  Date    Time  Latitude  Longitude  Depth  Closest     Comment
No.   yymmdd  hhmm  deg. min. deg. min.    m    approach m
---------------------------------------------------------------------
01    910908  1623  62 19.20  04 55.26     260    20        trial dip
02    910912  0730  63 56.50  06 12.07    3400    50  
03    910912  1228  63 57.60  05 22.80    3372    80  
04    910912  1750  63 57.00  04 27.00    3206    40  
05    910912  2247  63 57.89  03 32.14    3055    40  
06    910913  0321  63 38.21  03 51.19    2738    60  
07    910913  0739  63 18.66  04 05.34    2661   130  
08    910913  1209  62 59.13  04 21.25    2190    50  
09    910913  1605  62 38.78  04 37.93     707    45  
10                                                          failed
11    910913  2007  62 17.40  04 57.00     224    25  
12    910913  2323  62 38.40  05 12.60     578    25  
13    910914  0253  62 58.80  05 27.60    1812    50  
14    910914  0703  63 19.01  05 45.79    2211    25  
15    910914  1102  63 37.91  05 59.86    2141    45  
16    910919  1214  62 15.60  05 01.20     192    15  
17    910919  1603  62 39.00  05 12.60     585    25  
18    910919  1951  62 58.80  05 28.20    1754    45  
19    910920  0042  63 18.60  05 45.00    2175    30  
20    910920  0511  63 38.40  05 59.40    2162    55  
21    910920  1433  63 56.40  06 18.00    3194    25  
22    910920  1953  63 57.60  05 23.40    3371    25  
23    910921  0657  63 38.40  03 50.40    2737    20  
24    910922  0004  62 58.80  04 22.20    2176    50  
25    910922  0612  62 39.00  04 37.80     715    20  
26    910922  1055  62 17.40  04 55.80     225    20  
27    910923  0313  62 58.20  04 57.00    2010    45  
28    910923  0703  63 18.60  04 56.40    2368    30  
29    910923  1115  63 18.60  04 06.00    2695    35  



TABLE 5: RADIOSONDE ASCENTS ON CRUISE 62A

Flight
Number  Day/Time  Tcor  Ucor  Height mb  Comments
------------------------------------------------------------------------------
 1      250/1144   0     0       221     Cap off. Disk filled.
 2      250/2337  -0.2   2       148     Cap off. Unwinder not working?
 3      251/1115  -0.1   1       120     Cap off. Little low cloud.
 4      251/2308  -0.2   2       350     Cap off.
 5      252/1110  -0.2   2        29     Cap on.  First data cycles not logged.
 6      252/2159  -0.4   1        39     Cap off. Hit sea then recovered.
 7      253/1140  -0.2   1        53     Cap off. Unwinder not working?
 8      253/2142  -0.2   1        25     Cap off.
 9      254/1120  -0.3   2        61     Cap off. Into cloud at 915mb.
10      254/2325  -0.2   1        23     
11      255/1126   0.1   1        45     Cap on.  Raining.
12      255/2144  -0.4   1        44     Cap off.
13      256/1120  -0.4   0        30     Cap on.
14      256/2135  -0.4   1        29     Cap off.
15      257/1010  -0.3   2        43     Cap off. Into cloud 10:14:06.
16      257/2301  -0.4   0        45     Cap off.
17      258/1140  -0.1   0        43     Cap off.
18      258/2325  -0.1   1        31     Cap off.
19      259/1135   0     1        41     Cap off. Into cloud 11:42:41.
20      259/2140   0     1        50     Cap on.  Raining.
21      260/1138  -0.2   0        60     
22      260/2309  -0.3   0        50     Cap on.
23      262/1130  -0.2   0        42     Cap off.
24      262/2130  -0.1   1        52     Cap off.
25      263/1122  -0.3   1        41     Cap on.
26      263/2300  -0.8   0        78     Cap on.
27      264/1128  -0.3   0        34     Cap off.
28      264/2334  -0.2   0        81     Cap off.
29      265/1129   0.0   3        34     Cap off.
30      265/2133  -0.2   0        80     Cap off.
31      266/1059  -0.1   0        35     Cap off.
32      266/2300   0.1   0       690     Cap on.  Balloon leaking?
33      267/0014  -0.1   0        48     Cap on.  Replacement flight.
34      267/1138  -0.1  -1        30     Cap on.
35      267/2135   0.1   0        39     Cap off.
   
