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. Original contains color plates: All DTIC and NTIS reproductions will be in white.