Absolute preserved amplitude processing of seismic data

Absolute amplitude ratios between upgoing and downgoing seismic waves are determined by a process including deconvolving the total wave field by the downgoing waves, normalising the direct arrivals at seismic receivers in the form of a zero phase unit amplitude pulse in a limited frequency band determined by the signal to noise ratio separating the upgoing and downgoing waves by means of multitrace velocity filters and compensating for the differences between the amplitudes received by each receiver due to the spherical divergence between the paths of the upgoing and downgoing waves. The invention is designed to provide an improved method of processing VSP seismic data from borehole surveys to remove the differences in detected amplitudes caused by the spherical divergence of the upgoing and downgoing wave paths to yield an absolute amplitude ratio between the upgoing and downgoing wavefields.