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 criteria, 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.