A system for sensing subterranean acoustic waves emitted from an acoustic source includes a plurality of laser sources, a plurality of subterranean optical sensors, at least one optical detector, and electronics. The laser sources each emit light at a different frequency. The subterranean optical sensors receive the light and alter the light in response to the acoustic waves. The optical detector receives the altered light and outputs an electrical signal. The electronics receives the electrical signal and converts it into seismic data format. Preferably, the light emitted from the optical sources is modulated at a plurality of modulation frequencies. The electronics can be used to demodulate the signal.
The electronics may demodulate the electrical signal by mixing the signal with periodic waveforms having frequencies corresponding to the modulation frequencies and twice the modulation frequencies. The modulation frequencies are selected such that at least one of the second harmonic frequencies associated with the modulation frequencies is interleaved in a non-interfering manner within the corresponding set of first harmonic frequencies.
Preferably, the modulation frequencies are selected such that at least one of the first harmonic frequencies is interleaved in a non-interfering manner within the corresponding set of modulation frequencies. The electronic instrument of Claim 10, wherein said demodulator further comprises at least one additional mixer that is electrically connected to a source of periodic waveforms having a frequency that is substantially the same as twice the frequency at which said modulated electrical signal is modulated and that mixes said modulated electrical signals with said periodic waveforms having at the frequency that is substantially the same as twice the frequency at which said modulated electrical signal is modulated, said mixing thereby causing a second mixed signal to be generated.
Neptune Rtp (7 Downloads) - Zedload. Sample Results From Member Downloads. Com provides 2. We currently have 3. Our members download database is updated on a daily basis. These fine-grained rocks were deposited during a tectonically-quiescent stage after the Albian. Laser spot sizes and repetition rates were 30–20 μm and 10 Hz, respectively. Rare earth element (REE) abundances are characterized by a weak enrichment in Light Rare Earth Elements (LREE), with (La/Sm).
The method of Claim 1, 27, or 28, further comprising time stamping said seismic events.