InSAR Deformation Measurement And It's Application In Seismology

InSAR (Interferometric Synthetic Aperture Radar) is a novel space observation technique from satellite which enjoys the merits of high spatial resolution, high precision and area matrix surveying, therefore absorbs many geo-scientists' attention. However, the deformation interferograms only contain the surface deformation information in the radar's line of sight because of the side-looking work mode of SAR. Many problems including the explanation and application of the InSAR interferograms need further research.This paper firstly proposed a simulation method for the interference pattern of surface deformation field using the satellite orbit data and deformation models, based on the image principle of InSAR. Then we constituted three ideal displacement models and obtained the SAR deformation interferograms of three different orientations. Comparing the derived displacements from interferograms with deformation models, we can draw a conclusion that the sensitive of interference pattern to deformation in different orientation is obviously different and the sensitivity value from large to small is vertical, range and azimuth. Considering the interference pattern can not be directly compared with the results derived from GPS, spirit leveling measurement and other general geodetic method, and can not be directly applied to relative researches, a new method of directly acquiring three displacement components from surface deformation interferograms with three different look angles has been proposed. In order to test the efficiency of the method, we modeled SAR interferograms of the same deformation with three different look angles, unwrapped them with phase unwrapping algorithm, thus obtaining the displacements of three different look angles, and finally acquired 3D displacements through the decomposing method of displacement vectors. The results show that the inversed three components of the surface deformation displacements are basically consistent with the models and the errors are less than 15%. Theory and model calculations demonstrated that it is feasible to directly obtain three components of the surface deformation displacement from interferograms.Based on the above-mentioned calculation method, we acquired the 3D coseismic deformation displacement field of the 2003 Bam earthquake, Iran. Using 7 scene ASAR SAR images of Envisat satellite from European Space Agency, we got two descending interferograms and one ascending interferogram through processing by interferometric method. In two descending interferograms, the similarity of the size and shape of interferometric fringes show that they reflect the nearly same deformation fields. Because the main images in interferometric pairs are identical and the slave images are different in look angle, the interferograms derived from those pairs can be considered as the same deformation field's observation with different look angle. Based on the above analysis, we obtained the 3D displacements through the following three steps. Firstly, we retrieved the azimuthal displacements by registered the intensity images in interferometric image pairs. Then by decomposing the azimuthal displacements, we attained the horizontal displacement field. Finally we obtained the vertical displacements from the horizontal and the displacements in the line of radar sight derived from unwrapped phase. The horizontal displacement field suggests that Bam fault is of a right-lateral and strike-slip-type blind fault, which is consistent with the geotectonic background of the whole area. According to the difference of the horizontal displacement vector direction, we described the strike and pattern of the surface rupture. The rupture is "Y" shaped, which is basically consistent with the results given by Nakamura 2005. The research results proved that 3D displacements could be obtained from two interferometric pairs with different look angle and deformation interferograms.The real interferograms are affected by noise, introducing by too long baseline or temporal interval of the interferometric pair and the interfering of atmosphere. Many prevalent noise removal algorithms directly process the interferograms, which can not efficiently suppress noise and may make the useful information loss or distorted. The wavelet multi-solution analysis can effectively represent the no-stationary signal such as noise and make the noise whiten. This paper proposed a new noise reduction scheme, adopting wavelet packet transform as base algorithm and denoising the real and imaginary part of complex interferogram respectively by Wiener filter in wavelet domain. By choosing the different wavelet base function, the filtering results of the simulation interferograms show that the noise reduction effects of interferogram are similar by Daubechies wavelet and Biorthogonal wavelet. In addition, multi-level wavelet packet decomposition precedes one-level wavelet packet decomposition, but the former can make the more useful information loss. To further test the validity of the scheme proposed in the paper, we processed two real interferograms with different noise level using our scheme, Wiener filter and wavelet packet soft thresholding method. The results show that our scheme, which can not only effectively remove noise in interferogram but also preserve the fringe of phase image to the greatest possible extent, clearly outperforms Wiener filtering method and wavelet packet soft thresholding method.To locate the epicenter in underpopulated area with earthquake observation deficiency, we attempt to investigate the precise epicenter location method using InSAR. Presently, it is not mature and under developing to locate the epicenter of earthquake based on InSAR technique. For large earthquakes, the surface ruptures in epicenter are considerably strong and destroy heavily. Therefore the surface deformation pattern may be complex and make the fringes in epicenter area illegible and make it difficult to accurately determinate the epicenter location. For small earthquake, the deformation is too small or the interval of the interferometric pairs is too long, so the surface deformation may not be detected by interferometric method. Fortunately, the deformation of the moderate-sized shallow earthquake is moderate in the epicenter area and adapt to the observation of InSAR. Moreover, the forming fringes are always very clear and less noise. Generally, the farther to the epicenter, the smaller the deformation, the lower the fringe rates of the interferogram, so the precision epicenter location can be determined according to the distribution of interferometric fringe of deformation field. In this paper, we studied the earthquake epicenter locating method based on InSAR technique using three scene SAR images of the 15^th March 1999 Mw=5.4 Kuche earthquake, Xinjiang province, China. We firstly generated the coseismic deformation field interferogram of the Kuche earthquake from SAR data. Then we coded the interferogram using the accurate geo-coding method and acquired the coordinates of deformation field interferogram. However, the intervals between three SAR images of Kuche earthquake are too big, so it is seriously decorrelation in most regions. According to the distribution of the very limited interferogram fringe, we preliminarily determinated the epicenter location of Kucheearthquake at (41°55'N,82°35 E). Comparing the epicenter locations given by us, Harvard,USGS, Xinjiang earthquake bureau, we found that the locations of us, USGS, and Xinjiang earthquake bureau are very approximate and the three locations are less than 1.5km apart. The Harvard's location result deviates badly and seems wrong, whose site apart the others is about 20km. In addition, the epicenter determinated by us locates the most inner isoseismal curves of this earthquake. Those show that the InSAR epicenter location method is credible. Because the available SAR data is of low-level quality and limited, we could not obtain ideal coseismic deformation interferogram, thus the advantages of InSAR epicenter location method are still not adequately revealed. We believe that with high-level quality SAR data available, the InSAR technique will play an important role in precision epicenter location in the near future.