EXPERIMENTAL-MEASUREMENT OF THE ARRAY BEARING ERROR CAUSED BY BATHYMETRIC REFRACTION

Experimental measurements have been carried out to identify the effect s of a realistic bottom bathymetry on detecting a source with a horizo ntal line array, The measurements have been conducted over a 1:10 000 scale model of the Santa Lucia Escarpment, The experiments measured th e bearing error obtained in locating a CW source with a horizontal lin e array using plane-wave beamforming, The error in the detected bearin g is caused by the bending of sound rays in the horizontal plane, comm only referred to as horizontal or bathymetric refraction, The results of the experiment demonstrate large bearing errors which vary rapidly and do not increase monotonically with range. The rapid variation of t he bearing errors was unexpected and was a result which has not been p reviously identified, The magnitude of the errors was also a function of the across slope look direction and frequency, with bearing errors as large as 26 degrees for low frequencies. At higher frequencies, the bearing error is reduced. An analytical solution for the acoustic fie ld over a shear supporting sloping bottom has been used to approximate the results of the experiment, The simulation confirmed the trends in the experimental results by showing bearing errors of the same order of magnitude with the same dependence on across slope direction and fr equency. Most importantly, the theoretical results also showed a rapid ly varying bearing error as a function of across slope range.