Abstract:
Experimental measurements over a laboratory scale model with a real three-dimensional bathymetry have identified the effects of bathymetric refraction on detecting a cw (continuous wave) source with a horizontal line array. The results of these experiments showed large bearing errors which vary rapidly and do not increase monotonically with range. The rapid variation of the bearing errors was unexpected, and a result which has not been previously identified. In order to verify the oscillation in bearing error seen in the experimental results, a simulation of bearing detection using a horizontal line array in a wedge shaped environment was evaluated. This approach uses the method of images to approximate the three-dimensional acoustic field. This theory uses a series of image sources which are centered around the apex of the wedge. The rapid variation in bearing error is shown to be caused by the interference of these image sources which represent eigenrays with different propagation paths. Numerical simulations also investigate the bearing ambiguity caused by bathymetric refraction at full ocean scale. These results identify the magnitude of the bearing error as a function of the acoustic similarity parameter kh (wave number multiplied by water depth). [Work supported by ONR.]