SUBBOTTOM SCATTERING - A MODELING APPROACH

Bottom scatter strength data exhibit artifacts when the sub-bottom pla ys a role in the scattering process. The artifacts arise from the clas sical assumption in the data processing that the scattering process oc curs at the water-sediment interface. Many of the current bottom scatt ering models, even those that explicitly treat sub-bottom scattering, do not address these artifacts. A new bottom scatter modeling approach is proposed. The essence of the approach is to (1) employ a geoacoust ic model capable of predicting the sub-bottom insonified field, (2) av oid the usual plane-wave assumption, and (3) compute the received leve l in the time domain. The first condition suggests the analysis of bot tom loss data concurrent with bottom scatter data and leads naturally to the idea of a self-consistent geoacoustic basis. The model is emplo yed to analyze a data set that showed surprising discrepancies between low angle (<20 degrees) and intermediate angle (28 degrees-50 degrees ) bottom scattering strength. The proposed acoustic model predicts thi s discrepancy, which arises from the fact that the two angular regimes are controlled by entirely different scattering mechanisms. The diffe rence in mechanisms suggests caution in the current and common practic e of extrapolation from survey (intermediate angle) measurements to th e low angles of interest for system performance prediction. (C) 1998 A coustical Society of America. [S0001-4966(98)05208-4].