Approximation of the dynamics of a towed sonar antenna using linear FIR filters

Abstract

In low‐frequency sonar systems, long towed arrays are used to estimate target parameters like bearing etc. The standard method for bearing estimation is based on conventional beamforming. This procedure requires the knowledge of the sensor locations. Therefore, a point mechanical model for the dynamics of a towed array is developed, which is described in the Proceedings of the IEEE‐ICASSP, 1984. These results show that the dynamics of a towed array can be approximated by linear systems with transfer functions given by polynomials (FIR filters). The advantage of this method is that the shape of the towed array can be easily estimated in real time by convolution while the tow ship is performing maneuvers. One needs the system functions which are only calculated once and then stored in a computer. For each point of the towed array there exists a different system function. The input of the system “towed array” is the course Φ0(t) of the towing ship at time t and the outputs are the directions Φi (t) of the tangential vectors at different points i = 1,…,N of the towed array. This method is very useful, for example, for adaptive beamforming or for evaluation of the sensitivity of the beam pattern to the two ship's maneuvers. Examples show that the approximation is valid for a wide range of parameters. This is also verified by measurements.