UNCERTAINTIES OF DIFFERENTIAL PHASE ESTIMATION ASSOCIATED WITH INTERFEROMETRIC SONARS

The differential phase technique has been widely used in various sonar systems; however, uncertainties associated with the estimation of sca tterer depths are not completely understood, Numerical simulations for multiple bottom scatterers are performed, and they show that the unce rtainties of depth measurements, in the absence of noise interferences , are much greater than the amount explainable by the uncertainty asso ciated with the signal-arrival-angle within an instantaneous insonifie d area, The cause of the excess deviation is analyzed, particularly fo r the two-scatterer case, This kind of error is referred to as ''basel ine decorrelation'' which is related to the speckle phenomena and can be considered as an equivalent noise source, Experimental data obtaine d by a particular high-frequency (40 kHz) interferometric system, the Benthic Acoustic Measurement System (BAMS) developed by the Applied Ph ysics Laboratory, University of Washington, at a hat sandy bottom off the coast of Panama City, FL, were analyzed, Both analytical formulas and a numerical model are given to estimate the measurement uncertaint y caused by the baseline decorrelation, as well as noise interferences based on the parameters of the BAMS, in order to understand uncertain ties of the differential phase estimation, It is found that baseline d ecorrelation is the main source of error for the BAMS for grazing angl es greater than 12 degrees, The measurement uncertainties at this graz ing angle interval are in agreement with the theoretical predictions.