Reverberation mapping for basin‐wide bathymetric surveys

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Abstract
Research conducted by the Naval Research Laboratory in low‐frequency, long‐range underwater reverberation has led to an acoustic operation and processing technique that is applicable to basin‐wide bathymetric surveying. The technique uses 23‐kg explosive sources and a commercial seismic array receiver to obtain topographic reverberation data covering radial distances of more than 500 nautical miles (NM). After filtering and beam forming, the processing provides spatial stabilization of beams and averaging over multiple shots to correct for left‐right ambiguities. The resulting product is a plot of the locations of major topographic reverberators over entire basin areas. The processing technique has been applied to data collected in two tests conducted in a Pacific basin northeast of New Zealand. Processing and averaging of more than 200 explosive shots from each test produced maps covering more than 1 million sq NM. In addition to identifying the locations of all major known topographic features, the reverberation maps showed the existence of new features which were subsequently verified by depth sounding. The paper presents design criteria for future applications to other areas. The reverberation mapping technique could eventually be developed into an on‐board system that would survey entire basin areas in one week's time.