One very popular method used for calibrating pressure detectors (hydrophones) in the seismic band is the comparison method. The comparison calibration method, which is widely used (Safar and Newman, 1981) in calibrating marine seismic streamers, can be briefly described as follows. A seismic source is placed at some distance from a standard hydrophone with known transfer function Fs(ω) and sensitivity factor Ms. The pressure detector under test is placed as near as possible to the standard hydrophone so that the Fourier transform of the incident pressure, Pi(ω), generated by the seismic source at the pressure detector and the standard hydrophone, can be assumed to be the same. Thus the Fourier transform of the output voltages Vs(ω) and Vp(ω) of the standard hydrophone and the pressure detector are given as
where Fp(ω) and Mp are the transfer function and sensitivity factor of the pressure detector. Elimination of Pi(ω) between equations (1) and (2) gives
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