Experimental Analysis of Statistical Property of Low Frequency Reverberation Envelope in Shallow Water

Reverberation is the main background interference of active detection and identification, which is produced with active signal emission. It is traditionally assumed as a combination signal of a large amount of random scatters at the receiving hydrophone which leads to a Gaussian-distributed time-domain signal and a Rayleigh-distributed envelope following the central limit theorem. However, with the advent of high-resolution active sonar systems, the target-like scatter signals namely clutter arising from fluctuation or variety in seafloor or hydrographic would produce the non-Rayleigh reverberation with longer tail and it is a main factor restricting the active sonar long-range detection. Aiming at this phenomenon, the Rayleigh distribution model and two typical non-Rayleigh statistical models-the Weibull distribution and the K distribution model are studied using the low-frequency reverberation test data (signal center frequency at 420Hz) obtained from a typical shallow-water environment in the northern South China Sea. Based on the measured multi-sample reverberation data, the probability density distributions of different signal forms reverberation are calculated respectively. The parameters of different models are estimated by the method of moments (MOM) to perform the theory simulation and curve fitting, and then the correlation between data processing and model simulation results are calculated. Comparative analysis based on the experiments shows that the pulse length of transmitting signal has an important effect on the statistical characteristics of the reverberation in shallow water, which is reflected in the fact that the envelope distribution of short pulse-width reverberation presents stronger non-Rayleigh properties compared with long pulse-width reverberation. In addition, the long-range reverberation present stronger non-Rayleigh properties fitting with the non-Rayleigh models well relative to the short-range reverberation. The effect of frequency form on the reverberation envelope statistical characteristic is relatively insignificant.