干涉基线对地震形变场的影响——以玛尼地震同震-震后形变场为例
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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ERS2SAR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。
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.
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.
引文
何平,许才军.2009.卫星轨道误差对SAR干涉处理的影响研究[J].大地测量与地球动力学,29(5):54—57.HE Ping,XU Cai-jun.2009.Research on effect of satellite orbit error on SAR Interferometry[J].Journal of Geodesyand Geodynamic,29(5):54—57(in Chinese).
孟祥东,王彤,保铮.2008.干涉合成孔径雷达的垂直基线对图像相干性的影响[J].电子学报,36(6):1222—1226.MENG Xiang-dong,WANG Tong,BAO Zheng.2008.The effect of the perpendicular baseline on coherence for SAR im-ages in InSAR[J].Acta Electronica Sinica,36(6):1222—1226(in Chinese).
单新建,马瑾,王长林,等.2004.利用D-InSAR技术获取的地表形变场提取玛尼地震震源断层参数[J].中国科学,32(11):837—844.SHAN Xin-jian,MA Jin,WANG Chang-lin,et al.2004.Co-seismic ground deformation and source parameters of ManiM7.9earthquake inferred from spaceborne D-InSAR observation data[J].Science in China(Ser D),47(6):481—488.
唐晓青,向茂生,吴一戎.2008.一种改进的基于干涉相位的基线估计方法[J].电子与信息学报,30(12):2795—2799.TANG Xiao-qing,XIANG Mao-sheng,WU Yi-rong.2008.An improved baseline estimation approach based on the inter-ferometric phases[J].Journal of Electronics&Information Technology,30(12):2795—2799(in Chinese).
许才军,温扬茂.2008.基于InSAR数据的西藏玛尼MS7.9地震的地壳不均匀性研究[J].武汉大学学报,33(8):847—849.XU Cai-jun,WEN Yang-mao.2008.Nonhomogeneity of the crust from MS7.9Manyi(Tibet)earthquake with InSAR ob-servation[J].Geomatics and Infomation Science of Wuhan University,33(8):847—849(in Chinese).
许力生,陈运泰.1999.1997年中国西藏玛尼MS7.9地震的时空破裂过程[J].地震学报,21(5):449—459.XU Li-sheng,CHEN Yun-tai.1999.Temporal-spatial rupture process of1997Mani,Tibet earthquake[J].Acta Seismo-logical Sinica,21(5):449—459(in Chinese).
徐锡伟.2000.中国地震年鉴:藏北玛尼地震科学考察[M].北京:地震出版社.XU Xi-wei.2000.Yearbook of China Earthquake Research:Scientific Investigation of Mani Earthquake in North Tibet[M].Seismological Press,Beijing(in Chinese).
郑芳,马德宝,裴怀宁.2005.干涉合成孔径雷达基线估计要素分析[J].遥感信息,(3):7—10.ZHENG Fang,MA De-bao,PEI Huai-ning.2005.Analysis of the elements of baseline estimation of interferometric SAR[J].Remote Sensing Information,(3):7—10(in Chinese).
Massonnet D,Feigl K L,Rossi M,et al.1994.Radar interferometric mapping of deformation in the year after the Landersearthquake[J].Nature,369:227—230.
Michael Taylor,Gilles Peltzer.2006.Current slip rates on conjugate strike-slip faults in central Tibet using synthetic ap-erture radar interferometry[J].Journal of Geophysical Research,111,B12402.doi:10.1029/2005JB00401.
Shan X J,Zhang G H.2007.A characteristic analysis of dynamic evolution of preseismic-coseismic-postseismic inerfero-metric deformation fields associated with the M7.9earthquake of Mani,Tibet in1997[J].Acta Geological Sinica(English Edition),81(4):587—592.
Wang H,Xu C J,Ge L L.2007.Coseismic deformation and slip distribution of the1997MW7.5Manyi,Tibet,earth-quake from InSAR measurements[J].Journal of Geodynamics,44(2007):200—212.
Zebker H A,Rosen P A,Goldstein R M,et al.1994.On the Derivation of Coseismic Displacement Fields Using Dif-ferential Radar Interferometry:The Larders Earthquake[J].J Geophys Res,99(B10):19617—19634.
孟祥东,王彤,保铮.2008.干涉合成孔径雷达的垂直基线对图像相干性的影响[J].电子学报,36(6):1222—1226.MENG Xiang-dong,WANG Tong,BAO Zheng.2008.The effect of the perpendicular baseline on coherence for SAR im-ages in InSAR[J].Acta Electronica Sinica,36(6):1222—1226(in Chinese).
单新建,马瑾,王长林,等.2004.利用D-InSAR技术获取的地表形变场提取玛尼地震震源断层参数[J].中国科学,32(11):837—844.SHAN Xin-jian,MA Jin,WANG Chang-lin,et al.2004.Co-seismic ground deformation and source parameters of ManiM7.9earthquake inferred from spaceborne D-InSAR observation data[J].Science in China(Ser D),47(6):481—488.
唐晓青,向茂生,吴一戎.2008.一种改进的基于干涉相位的基线估计方法[J].电子与信息学报,30(12):2795—2799.TANG Xiao-qing,XIANG Mao-sheng,WU Yi-rong.2008.An improved baseline estimation approach based on the inter-ferometric phases[J].Journal of Electronics&Information Technology,30(12):2795—2799(in Chinese).
许才军,温扬茂.2008.基于InSAR数据的西藏玛尼MS7.9地震的地壳不均匀性研究[J].武汉大学学报,33(8):847—849.XU Cai-jun,WEN Yang-mao.2008.Nonhomogeneity of the crust from MS7.9Manyi(Tibet)earthquake with InSAR ob-servation[J].Geomatics and Infomation Science of Wuhan University,33(8):847—849(in Chinese).
许力生,陈运泰.1999.1997年中国西藏玛尼MS7.9地震的时空破裂过程[J].地震学报,21(5):449—459.XU Li-sheng,CHEN Yun-tai.1999.Temporal-spatial rupture process of1997Mani,Tibet earthquake[J].Acta Seismo-logical Sinica,21(5):449—459(in Chinese).
徐锡伟.2000.中国地震年鉴:藏北玛尼地震科学考察[M].北京:地震出版社.XU Xi-wei.2000.Yearbook of China Earthquake Research:Scientific Investigation of Mani Earthquake in North Tibet[M].Seismological Press,Beijing(in Chinese).
郑芳,马德宝,裴怀宁.2005.干涉合成孔径雷达基线估计要素分析[J].遥感信息,(3):7—10.ZHENG Fang,MA De-bao,PEI Huai-ning.2005.Analysis of the elements of baseline estimation of interferometric SAR[J].Remote Sensing Information,(3):7—10(in Chinese).
Massonnet D,Feigl K L,Rossi M,et al.1994.Radar interferometric mapping of deformation in the year after the Landersearthquake[J].Nature,369:227—230.
Michael Taylor,Gilles Peltzer.2006.Current slip rates on conjugate strike-slip faults in central Tibet using synthetic ap-erture radar interferometry[J].Journal of Geophysical Research,111,B12402.doi:10.1029/2005JB00401.
Shan X J,Zhang G H.2007.A characteristic analysis of dynamic evolution of preseismic-coseismic-postseismic inerfero-metric deformation fields associated with the M7.9earthquake of Mani,Tibet in1997[J].Acta Geological Sinica(English Edition),81(4):587—592.
Wang H,Xu C J,Ge L L.2007.Coseismic deformation and slip distribution of the1997MW7.5Manyi,Tibet,earth-quake from InSAR measurements[J].Journal of Geodynamics,44(2007):200—212.
Zebker H A,Rosen P A,Goldstein R M,et al.1994.On the Derivation of Coseismic Displacement Fields Using Dif-ferential Radar Interferometry:The Larders Earthquake[J].J Geophys Res,99(B10):19617—19634.
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