COMPARING DISTRIBUTED ACOUSTIC SENSING TO THREECOMPONENT GEOHPONES IN AN UNDERGROUND MINE
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geoscience: Geophysical Engineering
Abstract
Geophones have become the industry standard for seismic data collection. However, a relatively new method is gaining popularity called Distributed Acoustic Sensing (DAS). DAS uses changes in backscattered light of a fiber-optic cable to detect strain from acoustic energy. The purpose of this project was to make a direct comparison between DAS and three component geophones, specifically in a mining setting. Experiments were done in the Underground Education Mining Center on the campus of Montana Tech. The sources used for this project were vertical sledgehammer shots, oriented shear sledgehammer shots, and blasting caps set off in both unstemmed and stemmed drillholes. Although the explosives performed the best for the geophones, the large amount of energy and its close distance from the fiber seemed to compromise the entire fiber loop. In a one to one comparison, the underground hammer shots seemed to produce data that was a rough match between the DAS traces and the geophone traces. However, the shots on the surface of the mine, specifically the shots oriented inline with the cable, seemed be close to an exact match between trace of the fiber and traces of the geophones. The data suggest that DAS is most useful when the fiber can be oriented in the same direction as particle motion from whatever source is used, whereas the three component geophones can accurately capture data from all sources. Keywords: