A comparison of acoustic imagery data from a 12-kHz sidescan sonar and a 12-kHz hull-mounted bathymetric and imaging system

Seafloor imaging for the purpose of seafloor characterizations and fine-scale feature identification has traditionally been performed using towed sidescan systems. In the past 5 years, advancements have been made in using existing hull-mounted multibeam bathymetric systems as imaging systems. These hull-mounted systems are optimized for bathymetry, whereas the towed systems have been optimized for imagery. Two separate surveys were performed using both the University of Hawaii, Hawaii Institute of Geophysics (HIG) Acoustic Wide-Angle Imaging Instrument, Mapping Researcher 1 (HAWAII MR1 or MR1) system and the Navy's hull-mounted multibeam Sonar Array Survey System (SASS) over the same area. The MR1 operates at 11 kHz (port) and 12 kHz (starboard), transmitting and receiving on two rows of elements mounted on each side of the tow body. It has a variable pulse length ranging from 0.5-10 msec, and a sample rate of 1 kHz. In contrast, the SASS system has a hull-mounted transmit array with a multiple element receive array, pulse lengths from 3-7 msec, and a sample rate of 333 Hz. The study area covers depths ranging from 100-2000 m. Examples of three different morphological areas will be shown: canyons on a continental shelf and slope, it large debris flow at the base of the slope and, pockmarks possibly associated with underlying biogenically produced gas. System characteristics, signal and image processing for each of the systems, and a quantitative comparison of the two data sets, including the spatial scales of detectable features, are presented.