A multi-frequency method for improved accuracy and precision of in situ target strength measurements

The effectiveness of a split-beam echosounder system to delineate single scatterers and accurately measure in-situ target strengths (TS) is dramatically enhanced (98.2 -99.4%) by combining synchronized signals from two or more adjacent split-beam transducers of different frequencies. The accuracy of the method was determined through controlled test tank experiments using multiple standard spheres and 38 and 120 kHz split-beam transducers. Furthermore, by utilizing the angular position information from one of the split-beam transducers, additional corresponding TS measurements can be collected with juxtaposed single-beam transducers. Both methods were utilized to extract in-situ TS measurements of Antarctic scatterers simultaneously at 38, 120, and 200 kHz. Differences in the resulting TS measurements provided information about the identity of constituents in a mixed species assembly.