Research On The Calibration Technology Of Spaceborne SAR Interferometry For DEM

The digital elevation models(DEMs)are the basic data of geospatial information science and have significant application value in the fields of military reconnaissance,national economic construction and scientific research.Traditional leveling and optical photogrammetry methods for DEM acquisition are inefficient,costly and easy to be affected by climate and environment factors,so they cannot be applied to high-precision DEM products in large global regions.Interferometric synthetic aperture radar(InSAR)technology can obtain a wide range of high-precision DEM products in all weather and all day,and it has great advantages and broad application prospects in the field of topographic mapping.With the development of DEM application field,the requirements of DEM acquisition accuracy for InSAR system are increasing,but the existence of system errors restrict the further improvement of DEM products accuracy.The interferometric calibration is to obtain high-precision global DEMs by calculating the interferometric parameters using ground control points(GCPs).However,there are both geometric parameter errors related to positioning accuracy and interferometric parameter errors related to interferometric SAR elevation accuracy in the spaceborne InSAR,which are the direct error sources of DEM.Additional elevation errors are introduced due to geometric position errors,there is a certain coupling between interferometric parameter errors.If the interferometric parameters with different magnitudes of influence are combined to calculate,the corrections of each interferometric parameter can not be obtained accurately.Based on the problem of parameter coupling,the following research is carried out in this paper.1.The geometric calibration of SAR image is established based on precise positioning model.First,The R-D positioning model is established based on the range equation,Doppler equation and ellipsoid equation;Then,the geometric parameters related to positioning accuracy are determined according to the R-D model,including initial slant-range and initial time;Finally,the correction of geometric parameter errors are calculated based on the nonlinear least square method,and the precise geometric calibration model is established.2.Spaceborne SAR interferometry model is established based on three-dimensional reconstruction algorithms.Firstly,spaceborne SAR interferometric model is established based on the range equation,interferometric phase equation and Doppler equation;Then,the interferometric parameters related to elevation accuracy of interferometric SAR are determined according to the interferometric model,including interferometric phase error and the baseline vector error;Finally,the characteristics of these two interferometric error sources are analyzed.3.Interferometric calibration model is proposed of spaceborne SAR based on independent parameter decomposition(IPD).Firstly,the sensitivity of the interferometric parameter errors are quantitatively analyzed according to the spaceborne SAR interferometric model.Then the interferometric phase error is precisely estimated,which can complete the correction of the interferometric phase error,and absolute interferometric phase is compensated by the error.Finally,on this basis,the baseline vector error is precisely estimated,which can complete the correction of the baseline vector error,and the baseline vector is compensated by the error.Four pairs of TanDEM-X data of Weinan area in Shanxi province were uesd.One pair of TanDEM-X data of Zhangjiakou area in Hebei province based on bistatic mode and three scenes GF-3 data of Nanyang area in Henan province based on monostatic mode were chose for interferometric calibration experiment and result analysis in this paper.The results show that the interferometric calibration method proposed can improve the elevation accuracy of DEM products for the experimental data of different modes,which can prove the the reliability and effectiveness and feasibility of the proposed method in this paper.It is hoped that this method can provide certain technical reference for the global topographic mapping mission by InSAR technology in China.