Bottom Bounce Sonar Signal Characteristics and Target Classification

Abstract : A study of the space-time properties of active sonar echoes is made with a view toward target classification on the basis of shape and aspect at long range in the bottom bounce mode. Spectral and time cross-correlations of the echoes at two space points are examined for feasibility of signal processing with respect to requirements on the transmitted signal and transmitter-target- receiver geometries. STARLITE processing (spectral correlation) is the most promising of the two, but a detailed examination of the echo properties leads to more severe restrictions on the transmitted signal and receiver separations than previously indicated. Ideally, a wide, flat spectral window (created by the transmitted signal), within which a band-limited spectral correlation is performed, is desired. Filtering and spreading of the signal spectrum upon reflection off an irregular, stratified, impedance bottom distorts the spectral window. This places additional constraints upon the operational parameters for which the space-time properties of the echo yield target information beyond that which is available at a single receiver.