Matched-field minimum variance beamforming in a random ocean channel

Abstract

Matched-field source localization methods that employ deterministic full-wave acoustic propagation models can be seriously degraded due to the presence of random inhomogeneities in the ocean channel. In this paper, a minimum variance (MV) matched-field beamformer is presented that achieves greater robustness to random inhomogeneities in the sound-speed profile between the source and receiver. The proposed modification of the MV beamformer consists of employing multiple linear constraints derived from predicted pressure fields obtained using a set of perturbed sound-speed profiles. In order to investigate the nature of wave-front variations due to random sound-speed perturbations, a normal mode model based on adiabatic and first-order perturbation approximations is examined. The signal wave-front spatial correlation implied by this model suggests that the coherence among modes can remain high even in a fluctuating ocean environment. This in turn implies that the dimension of the signal perturbation constraint space for the MV beamformer can be small for typical soundspeed variations at moderate source ranges. Given the signal constraint space, design of the MV beamformer with sound-speed perturbation constraints is achieved by selecting its quiescent response to maximize the average signal-to-noise ratio gain against spatially uncorrelated noise. This leads to a computationally efficient realization of the beamformer that avoids the need to repeatedly compute perturbed pressure fields. Simulation experiments using a realistic deep-water Pacific Ocean environment are presented, which suggest that robust unambiguous low-frequency source location estimates can be achieved in the presence of mesoscale inhomogeneities given only knowledge of the second-order statistics of the random i'ange-dependent sound-speed profile plus a single environmental measurement at the receiving array.

Electromagnetic Time-Reversal Source Localization in Changing Media: Experiment and Analysis

“…A question arises as to focusing quality when there is a mismatch between the environments considered in steps (i) and (ii). This issue has been examined experimentally in acoustics [8,16,17] and ultrasonics [10], as well as in theoretical studies [6]. Theory predicts that the strength of the refocused signal is a function of the correlation of the two underlying media between the forward and backward stages of the time reversal experiment.…”

Workshop on Imaging of Complex Media with Acoustic and Elastic Waves

“…As with the case of plane wave beamforming, there are an assortment of processors that can be used for MFP/MFT [5] There have been two approaches to deal with environmental mismatch in MFP. The first has been to constructing processors which are tolerant to environmental uncertainty [6,7,8]. These processors trade resolution for lack of precise knowledge of the environment.…”

Near Bottom Data Collection and Data Analysis

“…Incorporating knowledge of this uncertainty can improve substantially adaptive beamformer performance. One approach to the design of such a robust processor in a matched-field framework is documented in [2].…”