Improved fish detection in data from split-beam sonar

Hydroacoustic split-beam techniques have been applied to enumerate salmon m igrating in the river Tana (northern Norway) during the summers 1998 and 19 99. Analysing data by single echo detection and tracking was difficult. Mis sing echoes in tracks from fish, combined with noise in the output from the single echo detector was seen as reasons for this. An improved counting me thod is presented. Contours from moving targets are detected by image analy sis. Then, detected single echoes within these contours are combined into t racks. This procedure reduces problems related to noise, and to tracking fi sh with few accepted single echoes. (C) 2000 Ifremer/CNRS/INRA/IRD/Cemagref /Editions scientifiques medicales Elsevier SAS.