固体潮位移InSAR相位模拟及对广域地表形变监测的影响初探

InSAR phase simulation of solid earth tide and its influence on surface deformation monitoring at wide-area scale

固体地球潮汐(Solid earth tide,SET)在地表产生的径向位移可达40~50 cm,形变梯度可达2 cm/100 km,是各种精密大地测量和地球物理观测必须考虑的因素之一.随着星载合成孔径雷达干涉测量(Interferometric synthetic aperture radar,InSAR)地表形变监测范围的不断增大以及对精度要求不断提高,固体潮位移对InSAR观测的影响不容忽视.本文利用固体潮位移理论模型,根据InSAR测量基本原理和Sentinel-1卫星成像参数,模拟了固体潮位移InSAR相位,定量分析了其时空分布特征,并以我国江汉平原和北美大平原的Sentinel-1数据为例,探讨了固体潮位移InSAR相位对广域地表形变监测的影响.结果表明:(1)固体潮位移对InSAR广域地表形变监测存在较大影响,在250 km×250 km范围中,以C波段为例,其相位变化可达12 rad(对应52 mm视线向形变);(2)固体潮位移相位在中低纬度(60°S—60°N)地区变化较大,两极地区较小,且在时间上具有明显的周期性;(3)在Sentinel-1 InSAR观测中,通过固体潮位移相位改正去除了干涉图中的部分低频相位偏差,相比原始干涉图,改正后的解缠相位标准差减小了约29%.本研究对于认识固体潮位移InSAR相位的时空分布特征以及提高星载InSAR广域地表形变监测的准确度与可靠性均具有重要意义.

The amplitude of vertical displacement caused by solid earth tide(SET)on the Earth′s surface can reach 40~50 cm and its deformation gradient can reach 2 cm/100 km,which is one of the main influence factors that should be corrected in precision geodetic and geophysical measurements.With the increasing observation swath and accuracy requirements of space-borne interferometric Synthetic Aperture Radar(InSAR),the influence of SET on InSAR deformation measurements can not be ignored.In this paper,based on the InSAR observation geometry and the Sentinel-1 satellite imaging parameters,the phase of SET displacement is simulated by using the SET displacement theoretical mode.We quantitatively analyze the temporal and spatial characteristics of InSAR phase of SET.Moreover,two case studies based on Sentinel-1 SAR images are carried out at the Jianghan Plain in the central China and the Great Plain in the Midwestern United States to explore the SET influence on monitoring large-scale deformation with the InSAR technique.The results show that the contribution of SET displacement has a great influence on interferometric phase and should be corrected in interferometric processing.In the range of 250 km×250 km,the variation can reach 52 mm for C-band SAR.And the phase of SET displacement varies greatly in the middle and low latitudes(60°S—60°N)but small in the two poles,and its temporal evaluation is obviously periodic.In the two case studies,the interferometric phase is improved after removing the SET phase.Compared with the original interferogram,the standard deviation of the corrected unwrapped phase is reduced by about 29%,which demonstrates potentials of the SET theoretical mode to migrate the SET influence on InSAR deformation measurements.This study is of great significance for understanding the temporal and spatial characteristics of SET InSAR phase and improving the accuracy and reliability of space-borne InSAR for monitoring wide-area surface deformation.