Bathymetry and seafloor acoustic backscatter imagery with a volume search sonar

Volume search sonars designed for mine hunting applications could be used for environmental sensing, particularly seafloor relief and texture. This capability is explored with a system that transmits a stepped FM pulse over a 243 deg vertical fan beam centered on nadir. It receives with 27 pairs of beams, symmetrically steered about nadir in the fore‐aft direction and spaced at 7.16‐deg intervals across track. The receive beam pair geometry allows simultaneous views of the seafloor in forward, vertical, and aft profiles. Pulse compression, monopulse processing techniques, and temporal and spatial filtering are used to estimate bathymetry and seafloor acoustic backscatter imagery of a sandy bottom and a muddy bottom. Three monopulse techniques have been investigated: conjugate product, difference over sum, and reduced beamwidth which is the most promising for this application. Results are presented for data collected while surveying at roughly 25 knots, showing the combined effects of acoustic geometry and survey speed on the resolution of the bathymetry and acoustic backscatter imagery and on bottom coverage. [Work supported by NRL Grant No. N00173‐00‐1‐G912.]