Abstract:

Several algorithms have been proposed for broadband matched-field processing; however, the issue of signal coherence across frequency and its implications for the signal coherence has not been treated consistently. If one uses a wide sense stationary random process model for a passive source, then spectral bands are uncorrelated, and one is led to an incoherent sum of energy of the optimal beamformer across frequency bins. Active sources imply a model where there is signal coherence across frequency which can be characterized using the two-frequency coherence function. Here, it is important to preserve phase in the output of the optimum beamformer since it contains the group speed information of the several rays and/or modes of the propagation. Models for transient signals fall in between the passive and active ones. The limited duration of the transient contains multipath/multimode information; however, the signal waveform is usually not known so matched filtering is not possible. The presentation will relate the issues of signal coherence broadband MFP algorithms and provide examples of the performance under different model assumptions.