The IMI-30: a 30 kHz imaging and mapping instrument

The Imaging and Mapping Instrument (IMI-30) is a new 30 kHz phase-bathymetric sidescan sonar developed and operated by the Hawaii Mapping Research Group at the University of Hawaii at Manoa. Capable of operation at depths of up to 6000 meters and altitudes above the seafloor of approximately 500 meters, it maps a swath up to 5 kilometers in width. This new system performs all signal processing in the digital domain, using Motorola 56309 digital signal processors to acquire signals from the vehicle´s transducer arrays. All 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. The programmable nature of the system electronics design allows use at a range of frequencies up to 140 kHz, and is also used as part of the DSL-120A sonar operated by the Deep Submergence Laboratory at the Woods Hole Oceanographic Institute. Processed acoustic data, along with environmental parameters and electronics monitors are telemetered to the surface via optical fiber. 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.