A Method to Calibrate Phased Hydrophone Array Elements in Near Field

Performance of the underwater acoustic imaging systems relies on the performance of hydrophone array elements used in the phased array sonar system. Calibrating array elements in the restricted tank geometry is practically difficult due to the array size. This paper proposes a method for calibration of amplitude and phase of linear array hydrophone elements within the tank. In this paper an experimental method is presented which measures the gain and phase variations of array elements using near field computation. Omni-directional hydroacoustic projector is used as the transmitting source in near field. Since the distance between the source and receiver is lesser for far field plane wave propagation, near field spherical wave is considered for phase or time delay computation. The signal due to the spherical wave reaching the array elements are acquired simultaneously for computation. Time delay is computed based on the spherical wave reaching the array elements in the near field. Phase measurement or the fractional time delay is measured using weighted least square method. Performance of the hydrophone array is compared after compensating for the time delay and gain.