Linking deterministic and stochastic aspects of the seafloor's acoustic response in the context of seabed mapping with echosounders.

In the different contexts where the monostatic acoustic seafloor response (ASR) is employed (i.e., measurements with multibeam or singlebeam echosounders, applications in seabed mapping, theoretical models with physical or heuristic parameters), its intrinsic nature can be ambiguous. In this article, an analysis of the discrepancies in semantics is proposed, and then the ASR theoretical and physical definitions are recalled. In theoretical models, and while it is acquired at sea, the ASR is shown to be considered as a deterministic parameter. However, a large variability in its measurements with echosounders is observed, suggesting ASR to be physically a stochastic variable. These two seemingly contradictory observations are linked analytically based on a point scattering model. The theoretical and deterministic ASR is related to its stochastic measurements as the expected value. Based on this connection and under the hypotheses of seafloor homogeneity and large insonified areas, the monostatic ASR measured by echosounders (i.e., the backscattering strength) is derived as twice the parameter of the Rayleigh distribution. Relationships between this result and seabed characteristics are discussed, along with their implications for echosounder operations.