Results

Figure 3 shows the impulses reponses derived by autocorrelation and spectral factorization. The ground-roll cone is clearly visible with a velocity of about 150 m/s. Events that may possibly be reflections are visible, however results are definitely not conclusive.

 

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Figure 3 Impulse response calculated by (a) 3-D autocorrelation, and (b) spectral factorization. Compare with Rickett and Claerbout (2000), Figure 3.

Remaining processing problems include how to adaptively remove monochromatic frequency spikes from the raw data, as noise sources drift in and out over time. Ground-roll removal is also a problem since with the 5 m geophone spacing, the 150 m/s velocities are spatially aliased at all frequencies above 15 Hz. The other option of imaging reflectors outside the ground-roll window is restricted by the maximum-offsets of the experiment to events less than 200 ms two-way traveltime.