Cruise Report – 16 Post-cruise Processing

Cruise Report: R/V Surf Surveyor Cruise S1-00-CL, Mapping the Bathymetry of Crater Lake, Oregon, 2000

 Post-cruise Processing

 

Limited post-cruise processing was necessary on the data set. However, during the post-cruise phase, it was discovered that a mistake appeared in the Simrad software that records the datagrams. Two values of acoustic backscatter are determined by the multibeam system; BSn is the backscatter at nadir and BSo is the backscatter at 25° from nadir. The backscatter is calculated as linear between BSn and BSo and then as a function of the cosine2 of the angle from BSo to the far beams. The gains applied to the received signals are derived from these relationships. The datagram was supposed to record BSn and the difference (BSn-BSo) in two separate fields. Unfortunately, both fields have the value of BSo. The result is a reduced backscatter intensity of from –6 to as much as –13 dB. Because the values are dynamically generated, and because they were not properly recorded, it is impossible to recover the values of BSn.

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