Localizing a quiet moving source with range-coherent matched field processing

Abstract

We introduce range-coherent matched field processing (MFP) to lower the signal-to-noise ratio (SNR) threshold required to successfully localize a narrowband source in a well-characterized shallow water environment. To accomplish this, range-coherent MFP coherently processes snapshots formed from a moving source. This approach differs from existing MFP approaches that treat each snapshot as having a random phase. Range-coherent MFP requires determination of the source phase acquired between snapshots. With that information, MFP can be applied to the cross-spectrum of the ''supervector'' of concatenated snapshots acquired at different times. Viewed another way, range-coherent MFP is simply MFP applied to a passive synthetic aperture formed from a moving source. The synthetic aperture geometry depends on source velocity, which is included in the MFP search space. Range-coherent MFP produces robust velocity estimates at low SNR, which permits the use of a longer FFT in pre-processing. The synthetic aperture array gain plus the increased input SNR afforded by the enhanced pre-processing significantly lower the signal level required for successful localization. We present the application of range-coherent MFP to data from the SWellEx-96 experiment to localize a source that is too quiet for conventional methods to localize.