Improved signal processing and data acquisition electronics for the DSL-120

The 120 kHz phase-bathymetric sidescan sonar operated by the Deep Submergence Laboratory at Woods Hole Oceanographic Institution, the DSL-120, has been extensively upgraded to improve performance and enhance reliability. The Hawaii Mapping Research Group at the University of Hawaii was selected to supply a new data acquisition system consisting of both subsurface electronics and surface control/data logging computer. This new system performs all signal processing in the digital domain, using four Motorola 56309 digital signal processors to acquire signals from three port, three starboard and one subbottom transducer array. All seven transducer channels can be driven with arbitrary waveforms during transmit, allowing both conventional CW transmissions and coded pulses with FM, AM, and/or phase modulation. Center frequencies for quadrature detection are programmable, as is decimation filtering to match the transmitted waveforms. This will greatly improve the cross talk rejection over the previous system, which operated at the same frequency port and starboard. By acquiring data from the previously unused third sidescan transducer rows, bathymetric precision can be improved; the additional row also allows greater flexibility is transmit beam steering and shaping. The processors share a high-speed fiber optic telemetry link, manufactured by Prizm Inc., with other instruments carried in the DSL-120 tow vehicle. At the surface, the sonar telemetry link is converted to a standard AES/EBU digital audio stream for compatibility with commercial off-the-shelf components making up a Linux workstation.