Target-depth Estimation for Active Towed Array Sonar in Shallow Sea base on Matched Field Processing

Target depth estimation can facilitate classification of surface ships or water-column targets thus reducing the false rates in active surveillance systems. Active sonar mainly determines the distance of the target by measuring the roundtrip time of the transmitted signal to the received echo, but it can't determine the depth of the target. For the long distance sound field, the echo is regarded as a point source sound field emitted from the reflector, the distance-depth space is divided into grids, and the sound field at each grid point is calculated according to the parameters of the ocean environment, and then matched with the received echoes, the best match point is the distance and depth of the target. In the active matched field depth-estimation algorithm, the pulse signal generated by the active sonar is sent to the transmitter to generate sound wave, at the same time, it is sent to the emission model to calculate the copy field of the hypothetical target point, and then the reflected sound field of the hypothetical target is calculated through the reflection model, finally, calculate the total copy vector at the receiving hydrophone array. The active matched field processor matches the received echo signal with the calculated total copy vector and outputs an ambiguity surface, it can be seen that the active matched field processing makes full use of the ocean environment. Since the active sonar has estimated the distance of the target according to the arrival time of the echo, the matched field depth estimation is to search for the target depth in a small range so as to determine the depth of the target. Sea trial data show that under good hydrological conditions, when the SNR of target echo is relatively high, the low-frequency active towed array sonar has good depth estimation capability.