Geophone frequency calibration and laser verification

Abstract

A geophone frequency calibration procedure has been developed that provides both amplitude and phase information over a selectable frequency range with a single measurement. It is easy to perform in either a field or laboratory environment using a two‐channel analog input spectrum analyzer, and an inexpensive, easily constructed, shaker table. A second calibration procedure that uses laser interferometry was also developed and implemented to verify the first, more practical method. Agreement between the two procedures is within the uncertainty limits of the test equipment at all frequencies including those near and at physical resonance. Some concepts of digital signal processing were reviewed that affect the interpretation of both calibration and seismic test data.