HR: 0800h
AN: NS31B-0385    [Abstracts]
TI: Subsurface Imaging Based on Frequency Dispersion
AU: * Cao, J
EM: caojx@cdut.edu.cn
AF: Chengdu University of Technology, 1 Erxianqiao Dongsanlu, Chengdu, 610059, China
AU: He, X
EM: hexy@cdut.edu.cn
AB: It has been known that different rocks has different responses (absorption, reflection and so forth) on different frequency electromagnetic (EM) waves and, sometimes, seismic waves. Change of the wave field dependent on frequencies is the called frequency dispersion. Seismic wave and EM wave used in geophysical exploration is ordinarily excited by pulse source, and so they are broadband wave. The measured response in the geophysical survey contains the contribution of the frequency dispersion. If we can determine quantificationally the dispersion relation, we can image the subsurface rock by inversion of the dispersion field. We can also obtain dispersion images by calculation the difference between the images obtained from different single frequency data. Imaging based on frequency dispersion let us can ¡°see¡± the subsurface earth medium from a new angle of view. The frequency dispersion of the wave can be divided into two kinds. One is that the dispersion is dependent only on the frequency of the wave, and another is that the dispersion is dependent on both the frequency of the wave and the medium physical parameters. In the first case, the physical parameters of the medium are independent of the frequency of the wave. In the second case, the physical parameters of the medium are dependent on the frequency of the wave, in other words, the physical parameters of the medium are function of the frequency of the wave. In the second case, we can obtain the frequency-dependent information of the rocks. In most cases, it is of logo quality to the rocks. We have developed two subsurface imaging techniques based on frequency dispersion. One is for broadband electromagnetic wave field inversion, and another is for seismic wave field imaging. The application cases show that both can give us new information of the subsurface medium. The dispersion imaging for broadband electromagnetic wave is a tomographic inversion of the frequency dispersion field, which is defined as the difference of the field values measured at two different frequencies. In the deduction of the tomographic inversion equations, a supposition that the electromagnetic parameters are independent of the frequency is introduced. The dispersion imaging for seismic wave field is implemented by calculation the difference of two single frequency images, which are obtained by time-frequency analysis. The work was supported by NSFC under grant No. 40574032.
DE: 0629 Inverse scattering
DE: 0910 Data processing
DE: 3260 Inverse theory
DE: 3299 General or miscellaneous
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting