PERFORMANCE OF A NEW PHASE ALGORITHM FOR DISCRIMINATING BETWEEN SINGLE AND OVERLAPPING ECHOES IN A SPLIT-BEAM ECHOSOUNDER

The performance of a new single target detection algorithm (version 5. 0) in the Simrad EK500 split-beam echosounder which uses the standard deviation in the sampled phase of received echoes as a detection crite ria, was tested under controlled conditions using spheres as targets. Although not infallible, the new algorithm enables the user to achieve improved rejection performance without inducing a bias against weaker single targets, when operating at pulse durations of 1.0 ms at 38 kHz . At a pulse duration of 0.3 ms, however, the phase discrimination was unreliable due to the reduced number of samples falling within the -6 dB limits of the echo peak. The implications of this behaviour on in situ estimation of TS are discussed. (C) 1997 International Council fo r the Exploration of the Sea.