The same-mode coherent characteristic quantity in distinguishing the surface and underwater target

摘要

In the technique of matched field processing, target depth can be acquired in ambiguity graphs, which can be employed in the classification between the surface and underwater target. However, performance of depth estimating degenerates with environmental parameter mismatches. In this paper, the conception about the same-mode coherent characteristic quantity is put forward in order to distinguish between the surface and underwater target. In typical ocean waveguides, such as the isothermal layer, negative gradient and the thermocline, the same-mode coherent characteristic quantity can be attained by two hydrophones with certain vertical aperture by using mode filter processing, and by taking on clear orderliness, which means that the mode amplitude is summed with the same order normal mode. When choosing appropriate vertical aperture, the same-mode coherent characteristic quantity can make a distinction between the surface and underwater target in the ambiguity graph as between range and depth - which do not need to match the acoustic field precisely. Moreover, separable depth is put forward, which can be a favourable criterion in distinguishing between the surface and underwater target. Simulation experimentation shows that the characteristic quantity is more robust [is “robust” the right wod here/] with environmental parameters, such as sound speed profile, bottom parameter, and the frequency. The sea trials were undertaken in October 2014, using a vertical array of nearly forty meters. The sound profile of the sea area is the isothermal layer. When choosing the vertical array using two hydrophones , separable depth can be obtained between 10 meters and 15 meters in the ambiguity graph between range and depth. The depth of the source contains 5 meters and 20 meters. Processing the results of experimental data has proved to be effective in distinguishing the sound source, which has good prospects for distinguishing between surface and underwater targets. This conclusion confirms that the same-mode coherent characteristic quantity is correct.