APPLICATION TO SYNTHETIC DATA

Synthetic data were created for a 240 channel array. The array has twelve lines of 20 receivers each, with an inline spacing of 100 feet and a crossline spacing of 150 feet. This is essentially the array used in the SEP drill-bit experiment (Cole, 1991). The synthetic dataset contains a source at depth of 1000 feet. The figures below show semblance as a function of x and y for this depth. In other words what is shown are horizontal slices through the 3-D grid of possible source locations. All computations were made using a frequency of 50 Hz.

Figure shows the semblance for a dataset containing only one source. Figure is after adding another source of 10 times larger in amplitude at depth of 300 feet. This is the unwanted or interfering source. The first source is totally hidden by this stronger source. Figure was obtained after removing the stronger source using the single-channel algorithm.

The next dataset also contains two sources, but the ratio of amplitudes is 50. Figure shows the result of applying the single-channel algorithm to this dataset. The weaker source can not be seen after the subtraction. The result of applying the multi-channel algorithm is shown at Figure . Obviously, here subtraction did a very good job of suppressing the unwanted source.

 

1
Figure 1 1

Semblance for depth 1000 meters, one source.

 

210
Figure 2 2a

Semblance for depth 1000 meters, two sources, ratio 1:10.

 

210r
Figure 3 2a.rs

Semblance after applying single-channel subtraction, two sources, ratio 1:10.

 

250r
Figure 4 2.rs

Semblance after applying single-channel subtraction, two sources, ratio 1:50.

 

250m
Figure 5 2.mr

Semblance after applying multi-channel subtraction, two sources, ratio 1:50.