ESTIMATION OF BOTTOM SCATTERING STRENGTH FROM MEASURED AND MODELED MID-FREQUENCY SONAR REVERBERATION LEVELS

Hamilton-type geoacoustic models were developed for Area Foxtrot, a sh allow water test bed south of Long Island, for emerging active sonar s ystems where the surface sediment type is highly spatially variable, R everberation levels (RL) were modeled using the finite-element parabol ic equation (FEPE) propagation model to augment the generic sonar mode l (GSM) propagation model because the bottom loss model in GSM did not estimate transmission loss (TL) accurately in shallow water, FEPE est imates reveal that there is a greater than 15 dB difference between TL for sand and that for silt-clay sediments in Area Foxtrot. The compar ison between modeled RL and measured RL (from a 1991 active sonar exer cise) enabled bottom scattering strength kernels to be developed for A rea Foxtrot, Bottom scattering strength was found to be a function of sediment type, Hard sand sediment has a bottom scattering strength whi ch obeys Lambert's law (sin(2) theta) while that of silt-clay sediment is consistent with sub-bottom volume scattering (sin theta), The RL's in Area Foxtrot are azimuth-dependent and are a function of TL and bo ttom scattering strength (and hence bottom sediment type), Sonar beams steered towards the hard sand show higher RL's than for silt-clay, an d knowledge of the sediment type and its spatial variation must be kno wn to model RL accurately, A method to determine sediment type using m easured RL's and RL slopes is given.