OFF-LINE SIGNAL PROCESSING RESULTS FOR THE LARGE APERTURE SEISMIC ARRAY
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
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The results of a series of off-line signal processing experiments are presented for the experimental Large Aperture Seismic Array LASA located in eastern Montana. In particular, the signal-to-noise ratio gains achievable by maximum-likelihood processing, as well as other simpler forms of processing, are given as a function of frequency, aperture, and number of sensors. A partial discussion of the physical characteristics of the noise field which led to these results is also presented. The spurious precursor introduced by one for of signal processing, and shown to be caused primarily by the signal amplitude scatter within a subarray, can be effectively reduced by using amplitude equalization. The signal amplitude scatter within a subarray, and between subarrays, is thus found not to degrade seriously the performance of the signal processing. In fact, the scatter of amplitudes between subarrays, which is significantly larger than that within a subarray, is a definite asset. It was found that the effectiveness of the processing depends not only on the array spatial filtering ability, but on differences in absolute level of the noises in the various sensors. Long-period array data from the extended TFO array were processed and showed roughly square root of N improvement. Our experience in processing a number of events is illustrated by a discussion of the results obtained on two particularly weak events with the maximum-likelihood filter. The apparent magnitude of one event as averaged over the LASA was 3.5, and that of the other was 4.0.
- Seismic Detection and Detectors