Sea-bed echo amplitude fluctuations arising from ship motion

Sea-bed echo amplitude fluctuations result from a displacement of the transducers of a ship-borne echo-sounder relative to the sea bottom. The origins of these fluctuations are discussed and analysis is given which enables an estimate to be made of the magnitude of the various components of a vessel´s motion necessary to ensure that successive echoes are uncorrelated. It is shown that: (1) horizontal motion is of more importance than vertical motion; (2) randomizing displacements are small compared with the dimensions of the insonified area of the sea-bed; (3) some large discrete scatters must be present if small motion fluctuations are to be experienced. Experimental evidence, obtained using a scale model of an echo-sounding environment, is presented in support of the theoretical conclusions.