Expanding Coherent Array Processing to Larger Apertures using Empirical Matched Field Processing

• Main Authors: Ringdal, Frode, Harris, David B., Kvaerna, Tormod, Gibbons, Steven J.
• Other Authors: NORWEGIAN SEISMIC ARRAY (NORSAR) KJELLER
• Format: Text
• Language: English
• Published: 2009
• Subjects: Miscellaneous Detection and Detectors; Explosions; *SURFACE TRUTH; *UNDERWATER EXPLOSIONS; *ARRAYS; DETECTION; BROADBAND; CLASSIFICATION; CALIBRATION; DIFFUSION; AMPLITUDE; UNDERWATER ACOUSTICS; APERTURES; SYMPOSIA; UNDERWATER TARGETS; USSR; SPATIAL DISTRIBUTION; *MATCHED FIELD PROCESSING; SEISMIC SIGNALS; MINE EXPLOSIONS; PE62601F; WUAFRL1010SMA1; Khibiny; Kola Peninsula; Olenegorsk; kola peninsula
• Online Access: http://www.dtic.mil/docs/citations/ADA505264; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA505264

We have adapted matched field processing--a method developed in underwater acoustics to detect and locate targets--to classify transient seismic signals arising from mining explosions. Matched field processing, as we apply it, is an empirical technique, using observations of historic events to calibrate the amplitude and phase structure of wavefields incident upon an array aperture for particular repeating sources. The objective of this project is to determine how broadly applicable the method is and to understand the phenomena that control its performance. We obtained our original results in distinguishing events from ten mines in the Khibiny and Olenegorsk mining districts of the Kola Peninsula, for which we had exceptional ground truth information. In a cross-validation test, some 98.2% of 549 explosions were correctly classified by originating mine using just the Pn observations (2.5-12.5 Hz) on the ARCES array at ranges from 350 - 410 kilometers. These results were achieved despite the fact that the mines are as closely spaced as 3 kilometers. Such classification performance is significantly better than predicted by the Rayleigh limit. Scattering phenomena account for the increased resolution, as we make clear in an analysis of the information carrying capacity of Pn under two alternative propagation scenarios: free-space propagation and propagation with realistic (actually measured) spatial covariance structure. The increase in information capacity over a wide band is captured by the matched field calibrations and used to separate explosions from very closely-spaced sources. In part, the improvement occurs because the calibrations enable coherent processing at frequencies above those normally considered coherent. We are investigating whether similar results can be expected in different regions, with apertures of increasing scale and for diffuse seismicity. The original document contains color images. All DTIC reproductions will be in black and white. Published in the Proceedings of the 2009 Monitoring Research Review, Ground-Based Nuclear Explosion Monitoring Technologies, held in Tucson, AZ, on 21-23 September 2009, vII pp 379-388, 2009.