Abstract: A method is provided to measure a modulus of complex sensitivity of hydrophone data channels using a quasi-diffuse sound field. In the method, a radiation pattern representing shallow water sources directs to a location as a direct acoustic path and sound reflects to the location from the water bottom as a reflected acoustic path. At least one hydrophone receives the sounds at the location as acoustic signals with an acoustic intensity being the sound intensities along the acoustic paths. The sound intensity at the hydrophones also relates to a zenith angle and a bottom intensity reflection coefficient. The modulus of the frequency dependent sensitivity of the hydrophone is computed from measurements of the voltage output and voltages of reference hydrophones with the sound intensity as factor and with uncertainty reduced by averaging hydrophone sensitivities.

Abstract: A method is disclosed for calibration of a towed line array. In a low frequency band, calibration is performed using an acoustic field observed by reference standard hydrophones. The observations form a model of a complex acoustic field throughout a space occupied by a measurement apparatus. The array sensitivities are computed by comparing output voltages of the array with the acoustic field estimated at the locations occupied by hydrophones of the array. Variations in the acoustic field that cannot be accounted for by free field propagation theory are included in the calculation of array channel sensitivities. The method extends the low frequency limit for the calibration to less than the minimum frequency at which free field propagation conditions can be approximated. Boundary reflections and spatial variations in the acoustic field are recognized. The spatial distribution of acoustic energy is used to provide low frequency calibration with improved precision.

Abstract: A method is disclosed for calibration of a towed line array. In a low frequency band, calibration is performed using an acoustic field observed by reference standard hydrophones. The observations form a model of a complex acoustic field throughout a space occupied by a measurement apparatus. The array sensitivities are computed by comparing output voltages of the array with the acoustic field estimated at the locations occupied by hydrophones of the array. Variations in the acoustic field that cannot be accounted for by free field propagation theory are included in the calculation of array channel sensitivities. The method extends the low frequency limit for the calibration to less than the minimum frequency at which free field propagation conditions can be approximated. Boundary reflections and spatial variations in the acoustic field are recognized. The spatial distribution of acoustic energy is used to provide low frequency calibration with improved precision.