Experimental results for matched-field processing with a small-aperture mid-frequency array

Matched-field processing (MFP) is a model based localization technique which is typically applied to low frequency signals (e.g., <300 Hz) received on long vertical arrays. It is well known that MFP performance is sensitive to environmental parameter mismatch and this sensitivity becomes more severe with increasing frequency. Thus, applying MFP to signals of interest in the mid-frequency range (e.g., 1-4 kHz) is a very challenging problem and robust MFP techniques must be utilized. Using a small aperture vertical array which undersamples the water column can also degrade the performance of MFP. However, small aperture arrays are much more practical for real-world systems and must be considered. In this paper, using sea-test data we demonstrate the ability to apply robust MFP to this non-conventional paradigm of mid-frequency signals received on an extremely small-aperture vertical array. Results are presented using the environmentally robust, broadband L_∞-norm estimator on experimental data collected in a shallow water (150 m) environment. This data consisted of broadband signals in the 3-4 kHz band collected on an 8 element, 2.13 m vertical array. These results demonstrate that good localization performance can be attained for this difficult problem. We also generate recommendations on the appropriate use of ray and normal mode propagation models