Jon Berger, Duncan Carr Agnew, Robert L. Parker, William E. Farrell; Seismic system calibration: 2. Cross-spectral calibration using random binary signals. Bulletin of the Seismological Society of America ; 69 (1): 271–288. doi:
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We present a rapid and accurate method of calibrating seismic systems using a random binary calibration signal and cross-spectral techniques. The complex transfer function obtained from the cross spectrum is least-squares fit to the ratio of two polynomials in s(s = iω) whose degrees are determined by a linear systems analysis. This provides a compact representation of the system frequency response. We demonstrate its application to two seismic systems, the IDA and SRO seismomenters. This method yields calibrations to an accuracy of better than 1 per cent in amplitude and 1° in phase.