Development of underwater acoustic backscatter and Doppler instruments from a small and versatile multi-frequency sonar board with software defined processing

The Oceanographic Systems Laboratory at Woods Hole Oceanographic Institution has developed a low-power multi-frequency sonar board capable of operating at a wide range of frequencies from 200 KHz to 2 MHz and suitable for a wide range of applications. Its features include a transmitter, a receiver with gain control, a 24 MHz analog-to-digital converter, a programmable down converter capable of demodulating by four separate frequencies simultaneously, a low power DSP processor, and 64 GB of SD card memory storage. This sonar board is compact (40 mm wide, 100 m long, and 15 mm high), has low power consumption (1 Watt), and is relatively low cost. Thus, it can operate autonomously on a variety of platforms: buoys, moorings, seafloor frames and pipes, gliders, profilers, towed bodies, and autonomous underwater vehicles. The modular design of the circuit board is advantageous because several sonars can be bused together and synchronized to form coherent arrays and multi-static configurations. These design characteristics broaden the field of application of sonar systems. The easily programmable DSP allows a variety of rapidly reconfigurable software-based processing schemes. The board has been incorporated as the core electronics module in a multitude of instruments. To highlight the potential range of applications for the sonar board, five of these instruments are presented here.