RRS Charles Darwin CD33B
Cruise summary report
|Ship name (ship code)||RRS Charles Darwin (74AB)|
|Cruise period||1988-06-23 — 1988-07-02|
|Port of departure||Tauranga, New Zealand|
|Port of return||Nuku'alofa, Tonga|
|Objectives||To provide Gloria sonograph data over those areas of the Havre Trough designated by the representative of the Defence Scientific Establishment, New Zealand Ministry of Defence.
Personnel were embarked and the vessel sailed for the beginning of the DSE survey at 2230 on 23 June. The survey equipment was redeployed and online by 0940 on 24 June. The survey began very well, with excellent sonograph images over the rumble seamounts until 1945 when the airgun failed. Several problems with the 300cu. inch airgun airgun were encountered, mainly it was believed, due to problems in sealing the guns with their waveshape kits. Boy 0207 on 25 June it was decided to continue the seismic profiles with a 160 cu. inch gun without a waveshape kit. At 0649 we began to record the Gloria data on analogue tape for use in detailed acoustic reflectivity bottom studies.
At 1425 we altered course due east to begin the double-swath survey across the width of the Havre Trough over an area previously mapped using Seabeam. During this eastward leg, the weather deteriorated, producing 3-5m seas and 30kt winds. It was decided to try again with a 300cu. inch airgun with a waveshape kit, and this was running successfully by 0050 on 26 June. At 0344 we altered course to 270 degrees onto the westward leg of the Havre Trough study area. The central Havre Trough survey was completed by 1717, and we recovered the the airgun and hydrophone enabling us to increase Gloria survey speed to 10kts along the western flank of Colville Ridge. At 0311 on 27 June we altered course to 065 degrees to run a final transect across the Havre Trough. The seismic reflection profiling system was redeployed to obtain records across the centre of the Trough. The seismic system was back online at 0500 and surveying continued at 8kts. By 2000, both the sea and the wind had moderated considerably, giving a substantial improvement in record quality. At 2130 we began a small survey on the fore-arc wall, upslope of an anomalously high backscattering target identified on Gloria data obtained by Dr L Parson during RRS Charles Darwin cruise 33. At 0500 on 28 June the airgun developed another fault and was recovered by 0520, however, it was decided to continue steaming at 8kts and to redeploy the airgun after it had been fixed so that we could retain the benefit of the waveshape kit. The repaired gun was redeployed by 0920. Once again the airgun began giving problems, it was seen to be mis-triggering at 1540, and the system was switched off at 1600. The survey at the upper slope continued until 1830, when we slowed to recover Gloria, the hydrophone, and airgun. After the above were recovered, we steamed at full speed (approx 12kts) until 1206 on 29 June, when all the survey equipment was once again streamed to carry out the final part of the survey over part of Louisville Ridge including the eastern flank of the Osbourn Seamount. The equipment was streamed without incident and online by 1320. The survey continued until 1048 on 30 June when the airgun and 3.5kHz systems were closed down.
Between 1048 and 1204 various experiments for DSE were carried out using the Gloria sonar. The standard Gloria coverage resumed at 1204, without the airgun and 3.5kHz profiler systems until 0100 on 1 July, when further DSE experiments were carried out. Gloria was eventually recovered after these experiments at 0145, and speed was increased to 12 kts, heading for Tonga. The magnetometer and the 10kHz fish were recovered and data logging ceased at 0400.
|Chief scientist||Colin L Jacobs (Institute of Oceanographic Sciences Wormley Laboratory)|
|Cruise report||(0.44 MB)|
|General||South West Pacific Ocean (limit 140W)|
|Track charts||(0.02 MB)|
|Bathythermograph||Quantity: number of profiles = 17|