HAWAII MR1: A New Underwater Mapping Tool

Abstract

The HIG Acoustic Wide Angle Imaging Instrument, Mapping Researcher 1 (HAWAII MR1) is an ocean floor mapping sonar designed and built at the Hawaii Institute of Geophysics, of the University of Hawaii. Towed behind a ship at a depth of 100 meters, it is capable of measuring both acoustic back scatter reflectivity and bathymetry over a swath up to 25 km wide, in all ocean depths. This system is unique in that it incorporates a network of digital signal processors, in the tow vehicle and in the shipboard data acquisition electronics, which control tow vehicle operation and process the acquired data. The tow vehicle carries two arrays of transducer elements; to reduce crosstalk, the port array operates a t 11 kHz, while starboard uses 12 kHz. Each array consists of two rows of elements, spaced one-half wavelength apart. Both rows are driven by 10 kW amplifiers, transmitting sound pulses in the water 1- 10 msec long. The transducer arrays are then used to receive reflected sound; the arrays ' output passes through programmable gain amplifiers and then is digitized by dual channel 18 bit A/D converters. The direction from which reflected sound arrives at the array is determined by measuring the phase difference between the two rows. The subsurface processors perform quadrature detection, followed by filtering matched to the transmitted pulse length; these data are then converted to block floating-point for