Bottom classification in very shallow water by high-speed data acquisition

Bottom classification based on echo features and multivariate statistics is now a well established procedure for habitat studies and other purposes, over a depth range from about 5 m to over 1 km. Shallower depths are challenging for several reasons. To classify in depths of less than a metre, a system has been built that acquires echoes at up to 5 MHz and decimates according to the acoustic situation. The digital signal processing accurately maintains the echo spectrum, preventing aliasing of noise onto the signal and preserving its convolution spectral characteristics. Sonar characteristics determine the minimum depth from which quality echoes can be recorded. Trials have been done over sediments characterized visually and by grab samples, in water as shallow as 0.7 m.