Institute of Acoustics, Academia Sinica, Beijing, 100080, People's Republic of China
Sea-bottom scattering coefficients for extremely low grazing angles have been estimated from sound propagation data in shallow water with a summer thermocline. Explosive charges were detonated under the thermocline and two hydrophones were located, respectively, above and below the thermocline. At moderate and long ranges the signals received by the upper hydrophone are composed of two parts: signals propagating from the source to the receiver and the signals scattered from the sea bottom induced by the sound propagating under the thermocline. The former arrived earlier and was much weaker than the latter. This offers one an opportunity of estimating the characteristics of sea-bottom scattering. The bottom scattering coefficients and their directivities for frequencies 0.8, 1, 2, and 4 kHz are estimated by adjusting the scattering coefficients so as to fit the calculated waveforms of scattered signals to the received ones. The incident field was estimated from the signals received by the lower hydrophone. The effective incident grazing angles are less than 2.5 deg. The bottom reflection losses due to bottom scattering are also estimated.