Abstract:

The interferometric baseline is a vital parameter in the InSAR technique,which determines the correlation between two repeat-pass images and imposes direct effect on the accuracy and reliability of the mapping result. If the baseline is not accurately estimated,the residual phases from the orbit and topography will be left in the expected phase of deformation leading to errors of the final result. In this work,we analyze the influences of the baseline on the reference phase and simulated topography phase,and present several methods of interferometric baseline estimation. Then we study the mapping process of the coseismic and post-seismic deformation of the 1997 Mani,Tibet M7.7 earthquake based on the 8-sence ERS2-SAR data and InSAR.Our attention is focused on comparison of interferograms under varied conditions for baseline estimations,such as rough orbit data,precise orbit data,frequency of interferometric fringes and control points on the ground. The result shows that when the baseline is estimated by rough orbit data,the yielded differential interferograms contain considerable phases of orbit residuals which make fringes dense and deformation enlarged. Thus we must use the precise orbit data for baseline estimation. Sometimes,however,the influence of the orbit cannot be removed completely even if we employ precise orbit data. In this case we should make further corrections,including removing superfluous fringes based on interferometric fringes frequency and baseline correction using the control points on the ground. With these improvements,the resultant coseismic displacement along the fault of the Mani earthquake is 4.5m. The post-seismic deformation by this event is concentrated in a narrow 10～20km-long zone around the fault. The accumulated fault slip 508 days after the main shock reaches at least 5.6m,which continues to grow with time. These analysis results are consistent with the field observations,meaning the improvement method presented in this paper is effective.

Key words: InSAR, baseline, deformation, interferometric measurement, Mani earthquake

摘要：

干涉基线是InSAR形变观测中一个非常重要且关键的参数,它不仅对像对的相干性起决定性作用,还对形变观测的精度和可靠性有直接影响。若基线不能被准确估计,就会使轨道残余相位和地形残余相位混入形变相位而导致观测误差。文中首先分析了干涉基线对参考相位和模拟地形相位的影响及几种不同的干涉基线估计方法,然后以6景ERS2 SAR图像为数据源,以1997年西藏玛尼地震的同震-震后形变场为例,对比分析了基于粗略轨道数据、精密轨道数据、干涉条纹频率及地面控制点等不同基线估计条件下的干涉形变场图像。结果表明,粗/精轨道数据差别很大,利用粗略轨道数据估计基线得到的差分干涉图含有明显的轨道残余相位,致使干涉条纹密集,观测形变量偏大。因此,必须利用精密轨道数据进行基线校正。有时精轨数据也不能完全消除轨道的影响,这时还要做基于干涉条纹频率的多余条纹去除校正及基于地面控制点的基线精校正。处理得到的玛尼地震同震形变沿断层走向南、北两盘的最大相对位移约4.5m,与野外观测结果一致。得出的震后形变场主要集中在断层附近10～20km的狭长条形区域内,震后508d的累积形变量至少达5.6cm,随着时间延续,震后累积形变量增加。

关键词: InSAR, 基线, 形变, 干涉测量, 玛尼地震