Matched mode localization

Range and depth source localization in shallow water amounts to the estimation of the normalmode structure of the acoustic field. As "seen" by a vertical array, and from a modeling point of view, the normal-mode structure appears as a set of nonplane coherent waves closely spaced at a vertical angle. This paper presents a full-wave-field narrow-band high-resolution technique that uses the spectral decomposition of the sample covariance matrix to resolve the vertical arrival structure of the harmonic acoustic field. The broadband processor is obtained by weighted averaging of the narrow-band range-depth ambiguity estimates within the source signal frequency band. Results obtained on synthetic data show that its performance is always better than or equal to that of the generalized minimum variance processor, which itself largely outperforms the conventional matched-field processor. It is shown, using both simulated and experimental data, that the effect of the broadband processor is to increase the stability of the source location estimate. Results obtained with this processor on short transient pulses collected during the North Elba'89 experiment with a 62-m-aperture vertical array, showed stable and accurate localizations over long time intervals. It is also shown that the sound field, received over a given frequency band, is relatively stable over time and is in agreement with the predictions given by a standard normal-mode propagation model.

mentioning

confidence: 99%

Broadband matched-field processing of transient signals in shallow water

Jesus

1993

“…Mode filters have been applied to VLA data for the analysis of shallow water channel response and source localization. 8,9 FIG. 2.…”

Section: Mode Filtering With a Horizontal Line Arraymentioning

confidence: 96%

Use of mode subspace projections for depth discrimination with a horizontal line array: Theory and experimental results

Premus

Helfrick²

2013

A solution to the problem of acoustic source depth discrimination in a downward refracting, shallow-water ocean waveguide is presented for the case of a horizontal line array at endfire. The approach exploits the phenomenon of mode trapping, wherein a shallow acoustic source cannot excite the lowest order waveguide modes due to its evanescent amplitude dependence near the surface. The important implication of this "trapping" behavior is that, given sufficient spatial aperture, it provides a mechanism for differentiating a shallow acoustic noise source from one at depth. The method does not require array cant, or physical vertical aperture of any kind, but instead relies only on the sensitivity of a line array at endfire to differences in horizontal wave number to resolve low and high order mode subspace excitations. The only inputs to the algorithm are an approximate sound speed profile, water depth, and bottom type. The theoretical basis for the test statistic is first reviewed, followed by discussion of key requirements, and illustration of the concept using results from a RAM PE simulation for a downward refracting environment. Finally, the algorithm is experimentally demonstrated using data from a bottom-mounted HLA deployed in the moderately cluttered continental shelf environment of the Florida Straits.

“…Yang 8 derived range/ depth estimation patterns from simulated data and successfully applied the method to experimental data obtained from a long-range source signal propagation in the Arctic surface duct. In studies by Yang 8 and Wilson et al,9 the sound field was unresolvable by the receiving array; i.e., there were more modes than sensors, but the array still spanned a large porfor an "infinite" number of source range/depth combinations gives rise to an ambiguity surface. The coordinates of the maximum of this surface are the matched-field estimates of the actual range and depth source location.…”

Section: Has Been Used In a Very Similar Fashion By Wilson Et Al 9 Mmentioning

confidence: 98%

Normal-mode matching localization in shallow water: Environmental and system effects

Jesus

1991

Matched-field processing is a passive range and depth source localization technique that has been extensively used in shallow-water environments. A vertical array of sensors is used to spatially sample the acoustic waveguide where the source signal embedded in additive ambient noise propagates. The array output is then matched with the signal replica field generated by a normal-mode model based on the environmental parameters that characterize the waveguide. Recent results obtained from real data show the feasibility of the technique and give evidence of its strong dependence both on the array aperture and on the knowledge of the environmental parameters used in the model. This paper describes a modified matched-field technique, called normal-mode matching, that is applied to real shallow-water data. Its performance is compared to that obtained by conventional matched-field processing using the same data set. Unlike conventional matched-field processing, the results indicate that unambiguous localizations can be obtained even for "short" arrays spanning only half of the water column.