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ABSTRACT
| SCIENTIFIC
PERSONNEL | SHIP’S PERSONNEL
| TABLES | FIGURES |
ACKNOWLEDGEMENTS | OVERVIEW
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CTD | LADCP | NAVIGATION
| VM-ADCP | SAMPLE SALINITY
| UNDERWAY | ECHO-SOUNDER
| COMPUTING | TECHNICAL
SUPPORT | REFERENCES
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7.
ECHO-SOUNDER |
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The RRS James Clark Ross is equipped with two SIMRAD echo sounders, the EM120 and the EA500. During the section the EM120 was periodically switched off as it was interfering with the signal of the EA500. The EA500 has one transducer mounted on the hull just to Starboard. A visual display of the data was displayed on the SIMRAD VDU located on the bridge. An assumed sound velocity of 1500 m/s was used. Raw data were logged by the SCS into the simulated level C data stream SIM500 and retrieved into a twice daily PSTAR file using the script jr67_sim. The script takes raw data from the SCS every 30 seconds and runs a 5 point filter. The filter removes values greater than 100 metres from the median and assigns an absent data value to zero depths. The zero depths occur when no good data is available. This processing effectively removes many of the spikes in the data. pintrp was then used to interpolate between the data gaps and then navigation data was merged in from the BESTNAV data stream using pmerge. Finally the script uses pcarter to correct the depths. The twice daily files were then appended together using papend and then plotted using plotxy for visual inspection. Manual despiking was performed to remove any obviously spurious values using plxyed, followed by pintrp to linearly interpolate onto the missing data points. After the data looked reasonable, they were reduced to a 1km distance resolution on variable distrun using pavrge. This resolution corresponds to approximately a three minute time interval. Two files exist of the outward journey, 67bathsim.cor and 67bathav.cor. 67bathsim.cor shows a peak at around 56.75 S, which is not present in the bathymetry from JR55. It is thought that this peak arises from the ship drifting whilst on station up and down the slope. It has been left in this file but taken out of 67bathav.cor. The latter version of the data is used for the bathymetry in figure 1.3. Unfortunately only the outward journey of the transect was completed as another route was taken from the peninsula heading back to Stanley in order for the swath bathymetry to be completed which was abandoned due to bad weather on the outward journey. |
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