MODELING OF GREEN'S FUNCTION WITH BOTTOM REFLECTIVE PARAMETERS (P, Q) INSTEAD OF GA PARAMETERS

Abstract

In shallow-water acoustic waveguide, the bottom of the sea (as the boundary condition that determines the Green's function of the sound propagation) plays an extremely important role in the sound field in water medium, especially at low frequency. Commonly the bottom is characterized by geoacoustic (GA) parameters and nearly all the existing numerical codes for sound field prediction use the GA parameters as the input of the bottom. However, the GA parameters are model based (needs a specified layered bottom model to mount the parameters in) which in practical applications may cause a series of problems such as model mismatching, extra uncertainty for field prediction and time consuming in MFP inverting. When the two bottom reflective parameters (P, Q) are used instead of GA parameters, which are model-free and directly determine the effect of the bottom on the sound field respectively in phase and strength, those problems will be solved naturally. In this paper, for range-independent waveguide using (P, Q) directly as input to construct the Green's function in terms of normal mode field is fully developed. For range-dependent waveguide, we propose an effective-equivalence based mapping between the bottom reflective parameters (P, Q) and the effective half-space (EHS) GA parameters to make (P, Q) as input parameters indirectly. Then all the existed numerical codes can still be used for the calculation of sound field without any modification except using P and Q as the input parameters of the bottom. The accuracy of this mapping is verified for both range-independent and range-dependent waveguide. At last the uncertainty analysis in GA space as well as in PQ space is briefly discussed to reveal the "extra uncertainty" due to the inter-coupling among the GA parameters.