Calibration against a reference sensor

Using ground noise or other seismic signals, an unknown sensor can be calibrated against a known one by operating the two sensors side by side [Pavlis & Vernon 1994]. As a method of relative (frequency-response) calibration, this is limited to a frequency band where suitable seismic signals are present well above the instrumental noise level, and are spatially coherent between the instruments. However, when the frequency response of the sensor has been measured electrically, then its absolute gain may be determined quite accurately with this method. The two responses should be digitally equalized before the amplitudes are compared.

In a similar way, the orientation of a three-component borehole sensor may be determined by comparison with a reference instrument at the surface.