Coherent Optical Time Domain Reflectometry aka Optical Fiber Distributed Acoustic Sensing PDF
Preview Coherent Optical Time Domain Reflectometry aka Optical Fiber Distributed Acoustic Sensing
Coherent Optical Time Domain Reflectometry a.k.a. Optical Fiber Distributed Acoustic Sensing Mark Zumberge Scripps Institution of Oceanography Phase mode: Two Pulse Rayleigh “Virtual Interferometer” à true strain measurement 10 m between pulse centers defines spatial resolution = Gauge length, L Two Pulses f1 f2 “Mirror 1” “Mirror 2” 10 µs delay for 1km phase I (amp) Rect cos Δf amplitude sin Q Polar phase strain, εL Range gate f1 -f2 = Δf optical carrier Demodulated Phase • Linear, • Quantitative • High dynamic range Courtesy of OptaSense, a Qinetiq company Summary Logistically inexpensive means to deploy a permanent seismic array: just an armored cable on seafloor Electronics: a box w/ laser, photo-‐‑detector aPached to OOI cable for power and data and to a passive optical fiber cable Creates permanent seismic array w/ hundreds of stations Low cost, long lifetime, useful for 4D seismic studies Gravity Observations to Investigate Volcano Structure and Its Evolution Mark Zumberge Glenn Sasagawa Jeff Ridgway Gerald D’Spain Scripps Institution of Oceanography Time lapse gravity ROV deployable gravity meters Observations of CO sequestration 2 Precision of a few µμGal Potential for detection of magma body inflation Scintrex CG5s in gimbal frames • Shock mounted frame • Underway tilt control Shock mounts • On-deck cold bath
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