Application of echo-sounding principles to submarine detection during World War II resulted in the development of equipment to sound all ocean depths.
In the 1970’s, the dual-beam technique was invented, permitting direct estimation of fish size in-situ via its target strength. The first portable split-beam hydroacoustic system was developed by HTI (Hydroacoustic Technology, Incorporated) in 1991, and provided more accurate and less variable estimates of fish target strength than the dual-beam method. It also permitted tracking of fish in 3D, giving each fish’s swimming path and absolute direction of movement. This feature proved important for evaluations of entrained fish in water diversions as well as for studies of migratory fish in rivers. In the last 35 years, tens of thousands of mobile and fixed-location hydro acoustic evaluations have been conducted worldwide.
