Bistatic reverberation calculations using a three-dimensional scattering function

Abstract

The ocean bottom scattering function depends, in general, on the grazing angles and the azimuthal angles of the incident and scattered energy. However, most measurements are for backscatter only. The few general measurements that are available indicate strong forward scattering near the angle of the specularly reflected ray and weaker, azimuthally isotropic, diffuse scattering away from the specular angle. By combining Lambert’s law scattering with a surface scattering function based on the Kirchhoff approximation, Ellis and Haller [J. Acoust. Soc. Am. Suppl. 1 82, S124 (1987)] proposed a function that incorporated these features. The function is quite simple, and depends on three parameters that can be fitted to backscatter measurements. The functional form thus allows a reasonable extension from backscatter to the general three-dimensional scattering function, which can then be used in bistatic reverberation calculations. It is an improvement over two commonly used methods (which do not include azimuthal dependence) for extrapolating backscattering to general scattering: the separable approximation, and the half-angle approximation. This paper discusses the three-dimensional function in more detail, and presents some comparisons between model predictions and measured bistatic reverberation.

Broadband Models for Predicting Bistatic Bottom, Surface, and Volume Scattering Strengths

“…While a comprehensive parameter study is beyond the scope of this paper, examples are provided to illustrate both how bottom-interface scattering strength depends on these quantities and how complex the scattering response can be. This, in turn, argues for the use of physics-based models (in lieu of an empirical model, such as that of Ellis and Crowe [33]) as bottom scattering strength submodels to active performance models, such as that of Fromm et al [34], for predicting bistatic reverberation. Figure 2 illustrates some key points regarding the use of both SSA and standard first-order perturbation theory (PT) models.…”

“…(33) suggests that when k 0 z sin q is small, such as when the scatterer is within a few wavelengths of the surface, or the grazing angle is very low, then the Lloyd's mirror pattern can modify the freefield acoustic response by a factor between 0 and 16. Figure 9(c) shows a monostatic example of this modification at q = 10∞ for the single salmon of Fig.…”

Recent Advances in Underwater Acoustic Modelling and Simulation

“…Sea -oor. Ellis and Crowe [92] combined Lambert's law scattering with a surface-scattering function based on the Kirchho! approximation to obtain a new functional form that allowed a reasonable extension from backscattering to a general, three-dimensional scattering function useful in bistatic}reverberation calculations.…”

Method of coupled mode for long-range bottom reverberation

“…Then, Ellis extended the model by using group velocities to obtain the travel time of each mode pair [15,16]. For bi-static cases, Ellis and Crowe in 1991 [17] discussed a kind of three dimensional function and on the basis of this function, Liu [18] proposed the bi-static reverberation theory However, all the mentioned work mainly focuses on the incoherent part of the reverberation intensity. In recent years, LePage shows the temporal characteristics of mono-static reverberation [19], and the coherent ray-mode reverberation theory is used to explain the observed oscillation phenomenon of reverberation intensity by Li et al [20].…”