Adaptive beamforming of a towed array during a turn

Abstract

During maneuvering, towed array beamforming degrades if a straight array is assumed. This is especially true for high-resolution adaptive beamforming. It is experimentally demonstrated that adaptive beamforming is feasible on a turning array, provided that array shape is estimated. The array shape can be inferred solely from the coordinates of the tow vessel's Global Positioning System (GPS) without any instrumentation in the array. Based on estimated array shape from the GPS, both the conventional beamformer and the white noise constrained (WNC) adaptive beamformer are shown to track the source well during a turn. When calculating the weight vector in the WNC approach, a matrix inversion of the cross-spectral density matrix is involved. This matrix inversion can be stabilized by averaging the cross-spectral density matrix over neighboring frequencies. The proposed algorithms have been tested on real data with the tow-vessel making 45 turns with a 500-m curvature radius. While turning, the improvement in performance over the assumption of a straight array geometry was up to 5 dB for the conventional beamformer and considerably larger for the WNC adaptive beamformer.

Range aliasing in frequency coherent geoacoustic inversion

“…The data was collected during the MAPEX2000 experiment conducted by the NURC on November 28, 2000 in a shallow water area north of Elba Island, off the Italian west coast. 10 This area is characterized by a flat bottom covered with a thin clay and sand-clay sedimentary layer. The water depth is 115-120 m. The experimental setup involves a fixed source broadcasting a linear frequency modulated pulse and a 254 m long towed HLA 55-65 m deep.…”

A Time-Frequency Joint Time-Delay Difference Estimation Method for Signal Enhancement in the Distorted towed Hydrophone Array

“…The large aperture is typically formed by trailing a hydrophone array behind a towing platform in a nominally straight line [10,11]. However, the array is often deformed or distorted due to inevitable oceanic currents, hydrodynamics, and tactical maneuvers of the towing platform, resulting in time-delay mismatch in beamforming-based signal enhancement, which seriously degrades the signal enhancement performance [12][13][14][15].…”

Eigenvalues of the sample covariance matrix for a towed array

“…Often, the number of snapshots available for forming the SCM is less than this, especially for large arrays. [4][5][6][7][8][9][10] Using random matrix theory (RMT) 11,12 to model the statistical properties of the SCM, [13][14][15][16][17][18][19] the eigenvalue distributions are more informative than using the expectation alone. A random matrix is a matrix-valued random variable, i.e., the elements are stochastic variables.…”