LARGE-ARRAY SIGNAL AND NOISE ANALYSIS. SHORT-PERIOD NOISE COHERENCE AMONG SUBARRAYS
Special scientific rept. no. 13
TEXAS INSTRUMENTS INC DALLAS SCIENCE SERVICE DIV
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Much of the analysis of the mantle P-wave noise proposed for this contract depended on the ability to perform coherent processing by treating seismic noise as a compilation of plane waves using the large aperture available at LASA. The subarray outputs should be P-wave-limited, and the large array could be used to dissect the P-wave noise therefore, it is extremely important to understand the coherence of the subarray outputs. This report presents the results of coherence studies among subarrays. Principal results of the study include the development of a program to compute multiple coherences and thus estimate multichannel coherence. A new processing technique to design filters that maximize the coherence between the output of two groups of sensors group coherence was developed and programmed. Presented are results of measured 2- channel and multiple coherence, indicating that the subarray outputs generally are moderately coherent below about 1 cps only within the B ring of the subarrays. Also presented are 2-channel and multiple coherences for several possible noise models. A study of these coherences suggest that the most reasonable models would give little coherence between A0 and the E and F rings. Comparison of model-study results with measured coherences suggests that a considerable portion 25 percent or more of the subarray output power is not interpretable as seismic energy.
- Seismic Detection and Detectors