Reciprocity Calibration by FM Signal-Correlation Methods

In a previous paper [1], it is demonstrated that the FM-signal modulated by a binary Poisson process is of use in compensating the narrow-band gain characteristic of the underwater acoustic transducers, under suitable adjustment of the FM-parameters to extend the effective crossspectrum bandwidth for the measurement. On the basis of this property, we have performed the reciprocity calibration of the underwater acoustic transducer by applying the cross-spectrum technique. The features of this technique are as follows: (1) The S/N-ratio can be improved by taking the cross-correlation. (2) The resolution in range for multipath situations is higher in comparison with the pulse technique where the rectangular pulse waveform is deformed by the transient effect of the transducer. (3) The calibration can be performed over a wide frequency range by using this FM-signal.