Estimation of bottom backscattering strength from measured and modeled AN/SQS-53C reverberation levels

Abstract

Hamilton type geoacoustic models were developed for Area Foxtrot, a NUWC test bed for emerging active sonar systems where the surface sediment type is highly spatially variable. Reverberation levels (RL) were modeled using the FEPE propagation model to augment the GSM propagation model because the bottom loss model in GSM did not estimate transmission loss accurately in shallow water. FEPE estimates reveal there is over a 15 dB difference between TL for sand and silt-clay sediments in Area Foxtrot. The comparison between modeled RL and measured RL (from a 1991 ASW exercise conducted by MUWC) enabled bottom scattering strength kernels to be developed for Area Foxtrot Bottom scattering strength was found to be a function of sediment type. Hard sand sediment has a bottom scattering strength which obeys Lambert's law (sin2 (theta)) while that of silt clay sediment is consistent with volume scattering (sin (theta)). The RLs in Area Foxtrot are azimuth-dependent and are a function of TL and bottom scattering strength (and hence bottom sediment type). Sonar beams steered towards the hard sand show higher.