Nearfield high‐resolution source localization

Abstract

An example of passive acoustic array processing consists of localizing the emanating machinery noise sources along a ship shell. When possible, an efficient way to increase the poor accuracy of this localization is to move the array Fresnel zone up to the sources. A linear beamforming with a spherical wave model then provides source bearing, range, and amplitude estimation. However, even for large antennas, the spatial resolution of this nearfield beamforming is limited to a wavelength fraction. To increase the localization accuracy, especially for low frequencies, “high‐resolution” methods should be used. This paper presents, in this case, Capon's method, also called adaptive beamforming. It's performances and resolving power are computed and validated through numerical simulations. They extend to the nearfield case the results usually found in a farfield situation. However, much more drastically than with plane waves, experimental results show that this method breaks down if the source model mismatches the wave fronts actually received. To avoid this strong model sensitivity, a robust approach, extending the spectral density matrix source subspace, is proposed. This method yields correct estimation of the amplitude and position of sources too close to be resolved by linear processing. This enhancement of Capon's method does not require an accurate source model. In addition, it has a low computational cost and is not nearfield dependent. [Work supported by DCN.]