Bathymetric Hazard Survey Test

NRL is developing a long range active acoustics technique for estimating seamount heights and mapping undersea topography over an entire ocean basin region. A concept demonstration, the BHST, was conducted in the eastern Atlantic in 1980. The technique uses explosive shot acoustic sources and a large aperture, towed acoustic receiver array. Reverberation data are output to an imaging system to study the spatial distribution of acoustic backscatter. These images are in the form of two-dimensional maps of reverberation, each typically 2000 km on a side. After correction of maps from individual shot detonations for range-dependent propagation loss, and scattering area, we average maps together on a pixel by pixel basis for a clear picture of major bathymetry. We use measured backscattering strengths to estimate seamount heights for all major seamounts in a deep 5 km basin to within or - 1.3 km. This result is comparable to, or better than, that available from other wide area bathymetry surveying methods. We can detect and locate all major within about 2 km of the surface seamounts in a deep basin to within or - 20 km and can identify smaller ones as well. This report describes in detail our analysis of BHST data during the period FY 1982-84, with emphasis on seamount height estimation, topography mapping, and confidence estimates for our results. Keywords Image processing Scattering strength Long range sonar Transmission loss Ray tracing Beamforming Wide field sonar Ocean basin survey techniques Ambient noise Sidelobe suppression Propagation loss Acoustic mapping.