Publications
Adaptive estimation of acoustic normal mode amplitudes
Abstract
The normal mode amplitudes and their second order statistics are useful in understanding sound propagation in the medium and for matched mode processing (MMP) and matched field tomography (MFT). Standard modal beamforming techniques introduce a least squares error criterion to compute the modal amplitude estimates. This work uses a method of adaptive estimation which is capable of processing both coherent and incoherent modes. The new approach is fundamentally different from other modal estimators (e.g., MMP) because it is data-adaptive and maximizes SNR against an ambient noise background instead of minimizing squared error in the estimate without regard to the noise. The new methods are studied using simulations which include coherent and incoherent modes and a realistic ocean noise model. The performance of the estimators is evaluated with respect to the following criteria: (i) orthogonality of the sampled mode shapes, (ii) power level and spatial structure of the noise, (iii) mode coherence, (iv) modeling assumptions (number of modes to estimate), and (v) the presence of multiple modal sources. The new methods perform significantly better than least squares in high noise environments and in situations where the sampled modes are not orthogonal.
© 1994 Acoustical Society of America. This abstract may be downloaded for personal use only. Any other use requires the permission of the author and the Acoustical Society of America. The abstract appeared in the Journal of the Acoustical Society of America, vol. 95(5), p. 2981, May 1994 and may also be found on the JASA website.