Measuring fish and zooplankton with a broadband split beam echo sounder

Prototype broadband split-beam echo sounder transceivers from Kongsberg Maritime have been used for about 3 years in a fishery research project. Linear chirp signals of different bandwidths and shapes have been transmitted and received on standard split-beam composite element transducers (nominal frequencies of 70, 120, 200, and 333 kHz), covering a frequency range of 50 to 450 kHz, suitable for investigating the most interesting backscattering spectra of several fish and zooplankton groups. The system was used on vessel-mounted transducers as well as on transducers in a profiling acoustic probe. Examples from calibration exercises and measurements on animals, including euphausiids, mesopelagic fish, blue whiting, herring and saithe is presented.