InSAR Data Processing Technology Based On Formation Satellites

Interferometric Synthetic Aperture Radar is the extense function of general SAR. It can make interference with the echo data by many receiving antennas, estimate the ground height, make the measurement of the height and the velocity of ocean current, and make the detection and orientation of the ground moving object. The line between the phase center of the receiving antennas is called baseline. According to the angle between the baseline and the direction of flight , InSAR is divided into Across-Track Interferometry with the baseline vertical to the direction of flight and Along-Track Interferometry with the baseline along the direction of flight. Across-Track Interferometry can gain the 3-dimension information of ground quickly. Along-Track Interferometry can be used in GMTI and the measurement of ocean current and wave.InSAR is a kind of technology that uses the phase information derived from the pair of SAR SLC images as data source to acquire the 3-demension information and the deformation on the surface of the earth. It is widely concerned and deeply researched all over the world. In the late 1990s, a new kind technology of satellite constellation called formation satellites is widely concerned. Formation satellite is a new concept, with the breakthrough and the rapid development in spatial technology field. Because of the good agility of satellites formation, and easily satisfying the availability baseline characters needed from the InSAR interference , InSAR technology based on satellites formation is concerned in many countries, and it has become direction in recent years. At present the system which is representative and will come true is Cartwheel by CNES and Japan and the mission of TanDEM-X by DLR. In the mode of Across-Track Interferometry, thesis researches the InSAR data processing technology based on satellites formation, especially studies the key technologies of InSAR data processing based on satellites formation and the requirements of data processing to systematic correlation, and it generalizes concretely as follow:(1) Technology of InSAR data processing. Thesis introduces the basic course of InSAR data processing in detail such as SLC image registration, flattening (flat effect removal) , phase filtering, phase unwrapping and DEM generation etc, and makes the experiments on airborne InSAR data. At the same time, according with the characters of radar imaging of satellite formation, it introduces the InSAR observation decorrelation and pre-filtering technology, in order to improve the correlation of the main image and the slave image in this thesis.(2) Technology of dynamic baseline confirmation. In the InSAR system based on satellites formation, the baseline changes, because the relative position of each satellite participated in formation moves continuously. In the dynamic change, the baseline coming from the baseline measurement is the line of phase center of two satellite radar antennas sometime, but the demanded baseline of InSAR height measurement is the line between the centers of Doppler waveband on imaging, so the measuring baseline can not be directly used in the height measurement, and the baseline must be determined once again. Thesis introduces the viewpoint that the required baseline in InSAR data processing is the useful baseline, and is not the direct metrical baseline gained from the baseline measurement, and combining SAR imaging and the content of InSAR data processing, propounds the methods of dynamic baseline confirmation , and resolves the application problem of the baseline measurement data.(3) Technology of removal the influence of azimuth baseline. On the foundation of the characteristic of InSAR system based on formation satellites, thesis describes the reasons of producing the baseline in satellite flying direction (azimuth direction), gives the viewpoint needed to eliminate the interferential phase in general InSAR data processing, then produces the method of removing the influence of azimuth baseline, analyzes the influence of azimuth baseline to phase precision .The DEM accuracy is effectively improved.(4) Technology of error source analysis. In this thesis, on the foundation of the basic principle of InSAR height measurement, from the five elements of influence on height measure precision such as baseline length, baseline inclination, phase difference, the distance from radar antenna to ground objective and the height of radar antenna, according as the process of causing the five elements, combining the characters of InSAR system based on formation satellites, systematic error sources are researched, error sources of the influence to InSAR system based on formation satellites are more systematically analyzed.(5) Analytic technology of the requirement of data processing to systematic correlation. The coherence of InSAR system echo wave based on formation satellites is an important index to infer whether the system is good or not. If the main image and the slave image are not coherent, it is no significance to data processing. At the same time, according with the coherence requirement of InSAR data processing, in bi-static mode of the radars cooperated with each other, the influence of coherence to the requirement of time synchronization, phase synchronization and space synchronization and InSAR systematic capability are analyzed. In addition, the requirement to the baseline from the different points of view that frequency deviation, the capability of distinguishing the two neighbor units, the spatial decorrelation of baseline, and the footprint of the roof are analyzed. In this paper, the research content does not only includes the requirement to InSAR system based on formation satellites from the point view of InSAR data processing, but also provides the bases for the systematic design and the data processing.