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One of the most important steps in the processing of VSP data is the separation of
upcoming and down going waves. It can be performed by applying a velocity filter
either in the f-k or 't-p domain. In the f-k domain, upcoming and down going waves
will be separated into two groups having negative and positive wave numbers,
respectively. A simple way of extracting them is to remove energies with the positive
or negative velocities in the f-k plane. Similarly, by transforming VSP data from t-x
domain to 't-p domain, upcoming and down going wave fields become separable and
they are mapped to different quadrants of a 't-p plane. This allows either upcoming or
down going waves to be reconstructed by the application of inverse Radon transform
to the related quadrant of the 't-p plane. Results obtained by the 't-p method are
similar to those obtained by the f-k velocity filtering. However, by implementing an
amplitude ratio-resting filter in the forward slant stack, the quality of the
reconstructed wave field would be improved. The filter was based on the amplitude
of a slant-stacked event. The event with different amplitudes can be identified and
suppressed when amplitudes are incoherent. In this regared, the efficiency of the f-k
filter and the Radon transform over synthetic and real VSP data are considered. For the real data, we compared the results of our written soft wares with those of the
Prom AX software.