Estimating the spatial coherence of narrowband underwater acoustic signals

When estimating the spatial coherence of underwater acoustic signals, the estimator characteristics depend heavily on the estimation method (e.g., based on spectral coherence or on cross correlation) and its parameter settings. We address this issue when the source signal is a continuous narrow-band signal. We demonstrate, using numerical simulations for simple, well-defined cases which are representative of real-world effects, how parameter settings for the coherence estimator should be chosen depending on the acoustic channel properties. The measurement bandwidth of the estimator should be large enough to capture channel effects and small enough to avoid poor SNR, and for the spectral coherence based estimator there should be at least about 10 FFT lengths within the integration time.