Shallow water pulsed source ranging based on Dedispersion Transform

摘要

In this paper two single receivers are used for pulsed source ranging. A pressure field propagation from a point source in shallow water can be expressed as modes summation by Pekeris's theory. It is known that the group delay difference and group speed of each mode can be used to estimate the range of the source, and the group speed of each mode requires environmental information to be known. The ranging method used in this paper uses two hydrophones geometry. Supposing that data from two horizontally separated receivers (1st and 2nd) are available, then the group delay difference between the mth and nth modes of the 1st and 2nd receivers (Δtmn1 and Δtmn2) (where the distance between the two receivers is d and the source bearing is θ) can be used to estimate the range of the source without prior knowledge of environmental information. The main difficulty of this method in shallow water is a severe intramodal dispersion, which makes it hard to measure the group delay difference of each mode. To overcome this problem, the Dedisperison transform (DDT) is performed to remove intramodal dispersion. DDT was proposed by authors of this paper (Journal of Computational Acoustics, Vol. 18, No. 3 (2010) 245-257). The DDT can transform signals from the time domain with intramodal dispersion to the b domain without intramodal dispersion. After DDT, the difference of dispersion parameters, Δbmn, which is proportional to the group delay difference of each mode, Δtmn, can be measured with high precision because the intramodal dispersion of each mode has been removed. The proposed method was benchmarked by numerical simulation and validated through experimental data obtained in August 2011 on the Yellow sea. It is shown that this method can even be used in circumstances where the interval distance between two hydrophones is less than 100 meters.