Matched-field replica model optimization and bottom property inversion in shallow water

Abstract

Matched-field replica models based on an inaccurate knowledge of geoacoustic parameters such as bottom attenuation, shear, and interfacial sound-speed discontinuities, can predict an incorrect number of propagating modes for a shallow-water channel. The resulting degradation in the matched-field ambiguity surface can be substantially reduced by obtaining optimal replica models via modal-sum-limit optimization or bottom-property inversion. The use of these techniques for multi-tone (70, 95, 145, and 195 Hz) source-tow data recorded near San Diego during the first Shallow-Water Evaluation Cell Experiment (SWellEX-1) significantly increased matched-field correlation levels and improved source localization relative to results obtained with a previous nonoptimized model. The predicted number of propagating modes was also reduced substantially. The inversion for bottom properties (attenuation, interfacial sound-speed discontinuities, no shear) provided sediment attenuation estimates which agree well with Hamilton's models and were an order-of-magnitude greater than that used in the nonoptimized model, which accounts for the reduction in the number of modes. A simulated modal decomposition using the inverted optimal replica model verifies the number of modes predicted by the modal-sum-limit optimization.

Direction of arrival tracking of an underwater acoustic source using particle filtering: Real data experiments

“…DOA estimation of an acoustic source in the underwater environment is an important topic and lies at the heart of many underwater signal processing applications such as sonar detection and localization [1]- [4], geoacoustic inversion [5], [6], underwater vehicle navigation [7], and ocean biological signal analysis [8]. It is a challenging problem since various uncertainties can arise from following aspects: 1) Source dynamics.…”

Modal-MUSIC: A passive mode estimation algorithm for partially spanning arrays

“…( 9). The single modal-MUSIC spectrum from ship noise at 50.54 Hz during both noise 1 and noise 2 is compared to wavenumbers computed using an established geoacoustic model 17 in Fig. 3(a).…”

“…Polynomials of increasing degree are fit through each mode curve until the change in the residuals with increasing degree falls below a threshold value (we selected 0.1), or the maximum degree of 14 is reached. These polynomial curves provide the final product of normal modes as a function of frequency, and are compared to modes computed with an established geoacoustic model for the SWellEx environment 17 in Fig. 3(c) for both noise 1 and noise 2.…”

Shallow-water sparsity-cognizant source-location mapping

“…This model, which has provided a type of "ground truth" for geoacoustic-inversion studies for this environment, [36][37][38] was determined using matched-field geoacoustic inversion for data collected by a similar VLA along a similar track executed during SWellEX-1 in August 1993. 39 The bottom-depth was assumed to be 198 m and range independent, which approximately holds over most of the northerly portion of the source track. The sound-speed profile is based on conductivity-temperature-depth measurements made in the vicinity of the array at the time of test.…”