POTENTIAL IMPROVEMENTS TO CURRENT METHODS OF RECOGNIZING SINGLE TARGETS WITH A SPLIT-BEAM ECHO-SOUNDER

The precision of in situ target-strength (TS) estimates generated by T S analysers is directly related to the ability of single-target detect ors to reject multiple echoes in dense aggregations. The rejection per formance of five single-target detection algorithms, utilizing phase, amplitude, and echo duration information from a split-beam echo-sounde r as rejection criteria, were tested by simulation for tar et pairs ra ndomly generated in a three-dimensional resolution volume. Each algori thm was also tested for selection bias. It was found that all five alg orithms accept multiple echoes preferentially when they are in phase. Of the phase methods, that which used the standard deviation in phase rejected the multiples most effectively, while the echo duration metho d performed relatively poorly. A method which relies on the magnitude of amplitude differences between split-beam elements performed well, p articularly for stronger targets. Another advantage of this method is that it also preferentially accepts our-of-phase multiples, thus partl y compensating for its bias towards multiples which are in phase. We c onclude that implementation of algorithms using either the standard ph ase deviation or the amplitude difference will lead to a significant i mprovement in single-target detection. The performance of the amplitud e difference technique is particularly encouraging, considering the po tential improvements possible by using averaging techniques to minimiz e the influence of noise. (C) 1996 International Council for the Explo ration of the Sea