Forward scatter target strength extraction in a littoral environment.

Abstract

A rail‐based system was used to collect forward and near‐forward scattered echoes from a spherical shell in 14‐m waters near Shell Island, Panama City, FL. The source was positioned 25 m from the scattering target and the 48‐m horizontal rail on the opposite side, also 25 m from the target. The major obstacle to obtaining high‐quality forward scatter target strength versus frequency and angle is the extraction of the much stronger time and position overlapping incident source signal. In previous laboratory measurements, this is accomplished with high precision by direct measurement of the incident field before the scattering target is positioned, a method not possible in a target search scenario or in a less stable environment. Here an attempt is made to obtain the forward scattered target strength by post‐processing the received signals obtained in the littoral environment which contain both the echo and the overlapping source signal. The methodology involves using a wavenumber domain filter to remove the incident wave followed by standard synthetic aperture procedures to extract the desired target scattered signal. The resulting forward scattered target strength will be compared to what we expect analytically and experimentally from this simple target. [Work supported by ONR].