Combining StereoSAR And InSAR Technology To Rxtract DEM From Difficult Mountainous Areas

It is difficult to obtain and update the terrain information in difficult mountain areas with bad weather and complex terrain by using the conventional mapping technology,whileSAR has the advantages of high efficiency,fast,not limited by weather conditions,and so on.Therefore,usingSAR image to extract DEM can solve this problem well.At present,there are two main methods to extract DEM fromSAR Images:SAR stereo measurement andSAR interferometry.StereoSAR technology based on intensity information is less affected by spatiotemporal decorrelation and atmospheric interference,and the DEM obtained has high reliability,but it is affected by the intersection angle of stereo pairs and the matching accuracy of stereo pairs,and it is seriously affected by radar shadow and layover,resulting in low accuracy of results;while the InSAR technology based on phase can obtain a large range of DEM efficiently and quickly.It has the advantages of strong continuous observation ability and high imaging accuracy,but it is easy to be affected by spatiotemporal decorrelation and atmospheric interference,resulting in low reliability of the results.Based on this,considering the side-looking imaging characteristics ofSAR and the topographic characteristics of difficult mountainous areas,this thesis selects a certain area in Maoxian County,Sichuan Province as the experimental area,and takes a pair of ascending orbit StereoSAR images,a pair of descending orbit StereoSAR images,a pair of ascending orbit InSAR images,field measured image control points and ASTER GDEM of the experimental area as the experimental data,and combines the StereoSAR technology and InSAR technology to extract complete high-quality DEM.The main research work is as follows:(1)Based on the analysis of the influence of terrain characteristics andSAR side view imaging characteristics on the radar echo signal and DEM accuracy,using the high-resolution ascending orbit StereoSAR image pair and descending orbit stereoSAR image pair,taking aster GDEM as reference DEM and image control point as external GCP constraint,the ascending orbit StereoSAR DEM and descending orbit StereoSAR DEM are extracted,and the accuracy of DEM is analysed from slope,aspect and radar echo signal.The results show that the higher the terrain slope is,the lower the DEM accuracy is;the stronger the radar echo signal is,the higher the DEM accuracy is;the DEM accuracy is related to the slope direction;the introduction of the measured image control points can effectively improve the DEM accuracy.(2)The radar echo intensity maps corresponding to the ascending and descending orbit StereoSAR DEM are calculated,and then DEM fusion is carried out based on the radar echo signal strength corresponding to the same point position.The results show that the method of fusing high-resolution StereoSAR DEM with ascending orbit and descending orbit can effectively improve the accuracy and reliability of extracted DEM.(3)On the one hand,the fused StereoSAR DEM is used as reference DEM to assist InSAR Technology in DEM extraction;on the other hand,considering the factors affecting DEM accuracy,the paper proposes to set threshold based on coherence coefficient,and fuse InSAR DEM and StereoSAR DEM to improve DEM reliability and accuracy.The results show that the combination of InSAR DEM and StereoSAR DEM can extract DEM with high quality(high precision and high reliability).