Extracting bottom information from towed-array reverberation data. Part II: Extraction procedure and modelling methodology

Reverberation data were gathered on the NATO Research Vessel Alliance, using the SACLANTCEN/NURC towed arrays, during the Rapid Response Exercises (1996-1998) and the Boundary Characterization experiments (2000-2004). Most of the sites were in the Mediterranean, but there were shallow-water sites on the east and west Atlantic continental shelves. A companion paper discusses the data gathering, polar-plot displays, and at-sea rapid environmental assessment of the reverberation and scattering features. This paper describes our efforts to use reverberation data from beam time series without prominent scattering features to extract estimates of bottom loss and scattering strength. The emphasis of this paper is on the procedure for extraction of the geoacoustic properties of the seafloor and on the modelling methodology used for the model-data comparisons. Towed-array beam patterns are included in the modelling, so polar plots of model-data differences can be used to provide a crude scattering map of the area. A manual inversion procedure was used at sea during the experiments for extracting bottom properties; the results compared reasonably well with post-trial measurements and estimates using an automated version of the extraction procedure. [Work supported in part by the US Office of Naval Research, DRDC Atlantic, and NATO SACLANTCEN/NURC].