Research On Geophysical Prospecting Method And Theory With Laser Doppler Effects

Energy is the basis of the safety of national economy and even of the country itself.The oil being of the important strategic material, affect the economy conditions andthe social development as well. In face of the global energy crisis, every country istaking every measure to scramble for the limited oil energy, improving theprospecting technology is a promising method. Nowadays, the consumption of theenergy is extraordinary so high that we must introduce the advanced prospecting tomaintain the necessary supply. As the easily discoverable energy has been exploited,the prospecting will become more and more difficult, and we need to advance theprospecting technology urgently.The laser Doppler measurement is characteristic of the high precision, rapid dynamicresponse,large measure range,non-contact measure, immunizing to electromagneticdisturb and non-response to transverse vibration. This technique is one of the hotspotof the information acquisition, and especially the remote measurement on the basis ofthe self-mixing effect of the laser diode has been paid much attention on. Thisresearch is under the support of " Research on Geophysical Prospecting Method andTheory with Laser Doppler Effects ". And the major works are:The characteristic of the seismic wave and the common rule of its transmission wereanalyzed, and the key element and the restrict factor of the high precision/highresolution seismological prospecting was fully investigated. Since the performancesof conventional geophone are the bottleneck of the high resolution seismicprospecting, the study of the novel geophone based on laser Doppler effect is one ofthe important works. All the above researches are very important to the usage of thelaser Doppler technique in seismic prospecting.The laser Doppler frequency shift of scatters and diffract grating was discusstheoretically. On the view of the optical beat, the characteristics both the homodynesystem and heterodyne system, and also the configuration of optical systemrespectively, were analyzed. The characteristics of the Doppler signal wereinvestigated, and bring forward the non-sine and non-cosine trait of the Dopplersignal. The conditional subdivision measure of the Doppler signal process is on thebasis of the frequency shift is direct proportion to the motion, and it is not completecorrect, especially not suit for the vibration measurements. The design principle andmethod of the bandwidth of the Doppler vibration measure system were studied, andthe calculating method of the small amplitude less than the equivalence was broughtforward.The self-mixing effect of laser diode including the self-mixing model, the problem offeedback coefficient, measure principle was studied. The characteristic of theVCSELs seismic acquisition system was studied by experiments.By studying the structural characteristic of the Doppler harmonic sensor, a dampingsystem base on the eddy was proposed. As the groundwork of design a sensor, wetheoretically analyzed the magnetic distribute field and the engendered force. Theconfiguration has many advantages, such as adjustable damping ratio, light structure,immunizing to the transmission distance, and suppressing lateral oscillation.The Doppler signal processing, such as picking up, coordinating, extracting anddemodulating were studied. Based on the weak signal detection theory, and thecharacteristics of noises, we brought forward that the lock in amplifier is not suit forthe seismic acquisition system based on laser Doppler effects. To abstract the signalout of the great noise, a novel auto-optimization filter was proposed, the results ofsimulation certified its efficiency. The signal processing circuses, including thelow-noise pre-amplifier, the filter and the phase lock loop (PLL) demodulation weredesigned.