Measurement of complex sensitivity of data channels in hydrophone line array at very low frequency

摘要

A method is disclosed for acoustic calibration of a towed hydrophone line array. In a very low frequency band, calibration is performed using a surrounding ambient acoustic noise environment observed by one or more calibrated reference standard hydrophones and hydrophone channels of the array being calibrated. The array hydrophone sensitivities are computed by comparing output voltages of the array hydrophones with the output voltages of one or more calibrated reference hydrophones. The method extends the low frequency limit for the calibration of a towed hydrophone line array to substantially less than the minimum frequency at which the acoustic projectors commonly used for acoustic calibrations can transmit a useful acoustic signal.

主权项

1. A method for calibration of free field voltage sensitivity of a test article hydrophone data channel in a towed line array, said method comprising the steps of:
providing a measurement apparatus with a cylindrical surface and a plurality of calibrated reference standard hydrophones distributed over an interior of the cylindrical surface; occupying an exterior of the cylindrical surface with the towed line array; measuring two acoustic pressure time series by at least one calibrated reference standard hydrophone and by the test article hydrophone data channel of the towed line array with said measuring step using ambient noise in a natural environment surrounding the towed line array; producing a first signal with the reference standard hydrophone, the first signal representing an acoustic pressure acting on the reference standard hydrophone; producing a second signal with the test article hydrophone data channel of the towed line array, the second signal representing the acoustic pressure acting on the test article hydrophone; transmitting a first voltage ν1 with the calibrated reference standard hydrophone; observing the first voltage ν1; transmitting a second voltage ν2 with the test article hydrophone; observing the second voltage ν2; and calculating a complex sensitivity M2 of the test article hydrophone data channel based on an ensemble average of acoustic transfer functions observed between the calibrated reference standard hydrophone and the test article hydrophone data channel of the towed line array asM2⁡(f)=1N⁢∑n=1N⁢V12⁡(f)⁢M1⁡(f)V11⁡(f)⁢ⅇ-j2⁢⁢π⁢⁢f⁢⁢τ where V12 is a voltage cross-spectrum observed between the calibrated reference standard hydrophone and the test article hydrophone, V11 is an auto-spectrum observed by the calibrated reference standard hydrophone, M1 is a complex free field voltage sensitivity of the calibrated reference standard hydrophone, N is a number of observations, f is a frequency and τ is an interval of time representing the relative delay between data collection systems used for the test article hydrophone and the calibrated reference standard hydrophone.