Comparison of measured signal coherence time in shallow and deep water

Temporal coherence of acoustic signals determines the processing of a sonar system for various applications. This paper studies the frequency and range dependence of the temporal coherence time of signal propagation in deep water versus that in shallow water. The signal coherence time has been measured in deep water since the 1970s, in terms of a parameter called the phase rate (the rate of phase change of the signal). Signal coherence time in shallow water has received little attention until only recently. We compare measurement data from more than a dozen of experiments covering a wide range of frequencies at different source‐receiver ranges in deep and shallow water. We find that the signal coherence time in both shallow and deep water can be fitted with a universal equation, which exhibits a 3/2 power frequency dependence and 1/2 power range dependence. The signal coherence time in shallow water is two to five times longer than the signal coherence time in deep water at the same frequency and range. The signal coherence times are comparable between shallow and deep water if measured in terms of the range‐to‐depth ratio. [This work is supported by the U.S. Office of Naval Research.]