A comparison of swept frequency and FFT methods used to calibrate array test modules

A description is given of swept frequency and Fast Fournier Transform (FFT) methods used to calibrate array test modules. The FFT method is shown to give sensitivity versus frequency plots with relative ease and known accuracy. The swept frequency method is capable of giving similar results but only after operator interpretation of the mean of fluctuating signals and calculations on a point to point basis. A digital filtering method is briefly described which can be used to process the signals obtained in swept frequency calibration obviating the need for operator interpretation. The accuracy of the FFT method is discussed and an overall accuracy figure is obtained for the derived sensitivity of the test array. A summary of the FFT method is given as a guide for future hydrophone calibration experiments.