Calibration of the direction of a linear horizontal hydrophone array on the sea bottom

The direction of an underwater target can be estimated by one seabed linear horizontal hydrophone array via analysis of the received target acoustic data. Because the estimated direction is referenced to the linear array coordinate, the direction of the linear array should first be determined in order to derive the absolute direction of the underwater target as referenced to the north. Generally, the direction of the linear array can be obtained by an instrument such as compass installed on the array. Unfortunately, when there is no compass some other underwater acoustic method must be designed to estimate the direction of the linear array. A calibration method of the direction of linear array is proposed in this paper when there is no compass installed. Firstly, the location of the array is measured by GPS when the array is deployed. Then an acoustic signal is transmitted at several different locations while the location is measured by GPS The relative direction of the acoustic signal can be estimated by the horizontal hydrophone array. By combining the relative directions estimated by acoustic data and the absolute direction as measured by GPS, the direction of the array can finally be estimated. Because of the effect of the varying source position to the direction of the linear array, the selection of the measured position has to be considered carefully. Furthermore, the effect of the ambiguous direction of the linear array is considered in the paper and its performance is analyzed. The proposed method is validated by simulation and lake trial data processing. The effect of the signal-to-noise ratio on the direction estimation is considered, and the results show that the direction estimation accuracy is relatively close, with the signalto noise ratio and the number of the array elements.