InSAR DEM error modeling and calibration

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ABSTRACT This paper provides a error modeling and calibration method to the geolocation error problem arising in the generation of digital elevation model (DEM) via interferometr ic synthetic aperture radar (InSAR) technique. DEM error is divided into two parts, systematic error and random error, they are modeled respectively. The baseline error is of crucial importance in the systematic error, it causes a slowly changed height error in the azimuth and a small tilt in the ground range of the DEM, a 2-D polynomial function is used to fit the systematic height error. The corrected DEM is obtained by removing the systematic error from the raw DEM. Computer simulation results prove the availability of the method. Keywords: InSAR; DEM; height error modeling; baseline error; error calibration; GCPs; least-squares method 1. INTRODUCTION The InSAR technique is a very efficient tool for terrain he ight measurement by the interferometry of two or multiple SAR images which are acquired from two or multiple antennas with a slight look angle difference [1]. It can get the DEM of the Earth's surface quickly in all kinds of weather and day or night. DEM is of fundamental importance for a broad range of commercial and scientific applications. For example, many geoscience areas, like hydrology, glaciology, forestry, geology, oceanography, and land environment, require precise and up-to-date information about the Earth's surface and its topography. Nevertheless, in the process of DEM generation, the errors of the instrument, orbit, and processing parameters which have been used in the InSAR processing affect the accuracy of DEM significantly. TanDEM-X mission provides an example [2], The TanDEM-X mission is the first bistatic satellite synthetic aperture radar mission which is formed by flying TanDEM-X and TerraSAR-X in a closely controlled helix formation. The primary mission goal is the derivation of a high-precision global digital DEM according to High-Resolution Terrain Information (HRTI) level 3 accuracy. The finite precision of the baseline knowledge and uncompensated radar instrument drifts along with some other parameter errors introduce errors that may compromise the height accuracy requirements. To fulfill the its demanding requirements, a DEM calibration method which uses absolute height references and the information provided by adjacent interferogram overlaps is pr oposed to minimize th e residual height errors. It can be seen that the correction of systematic height errors in the DEM is necessary to achieve the specified accuracies [3-4]. In the future InSAR system, the required DEM accuracy will be more and more precise, therefore, the DEM calibration will play a more important role in the DEM post-processing. The main purpose of this paper is to describe the influe nces of the systematic error and obtain a more precise DEM by removing it from the overall DEM. Section 2 provides a brie f analysis of the total DEM height error, and classifies it into two groups, the systematic error and the random error. Section 3 sets up the models of systematic error especially the baseline error and presents a DEM calibration method. Sec tion 4 is the computer simulation results which prove the availability of the method. The paper concludes in Section 5.