Modeling And Methodology For Airborne And Spaceborne InSAR Calibration

Digital Elevation Model(DEM)has played an important role in many fileds,such as national economy,national defense,environmental planning and disaster monitoring.Compared to the other traditional DEM production methods,such as leveling,GPS,aerial photography and optical images,interferometric synthetic aperture radar(InSAR)has became one of the most important means to obtain high precision DEM data with some prominent merits,such as high-speed,high accuracy,all-day and all-weather,and large area of observation.Airborne InSAR and Spaceborne InSAR are the two main InSAR system,its outstanding representatives are Shuttle Radar Topography Mission(SRTM)and TanDEM-X which are both have accessed to global DEM data in 2000 and 2016 respectively that achievements mark advantages of obtaining global DEM for InSAR.Of course,the acquisition of high-precision DEM data on the one hand depends on the design of the InSAR platform accuracy,on the other hand depends on the security of various calibration techniques.The phase shift error,the SAR device local oscillation error and other system parameter error will corrected in the SAR inner calibration,but some parameter error,such as measurement error,time delay error related to the baseline,slant range error,platform position and velocity error,will influence the DEM accuracy in data processing all the time.It's accutually essential to correct these errors for extracting high precision DEM.Meanwhile the goal of interferometric calibration is to use calibration points to correcte interference parameters error,thus improving the accuracy of DEM.The main steps of InSAR obtaining DEM include interferemetric phase calculation.interferogram sub-phase,phase unwrapping and DEM reconstruction.The 3D reconstruction model is an important method to reconstruct DEM,which directly maps the phase to geodetic coordinates.This method not only helps to reduce the error transmission,but also can effectively control the accuracy of 3D coordinates.In this paper,the new Airborne and Spaceborne calibration model are proposed respectively based on the 3D reconstruction model.The main works involves the following aspects:1.Airborne/Spaceborne Interferometric calibration model based on InSAR 3D reconstruction equation have been established respectively.Concerning the diversificated development trend of the airborne antenna's layout,calibration parameters contains baseline components on Y and Z direction in carrier coordinate system,Doppler frequency,slant range and interference phase in airborne platform.On the spaceborne platform,influence of each intereferometric parametes on 3D position accuracy have been analyzed,and then confirmed 9 calibration parameters including baseline components under C and N direction,initial slant range,interferometric phase and Doppler frequency coefficient f0,f1,f2.2.Both the two interferometric calibration model have the common problems that the sensitivity matrix condition number is too large.In this paper,the regularization method based on ridge estimation is introduced to improve the calibration model to obtain the correct interference parameters.3.Experiment and analysis of interferometric calibration are implemented based on Shanxi Ka-band image.Selecting 4 different types of calibration data layouts to do calibration test and using the calibrated parameters to extract DEM and doing accuracy assessment.Results show calibration data should allow certain rules of clothing at intervals along the distance distribution,and as far as possible in the same azimuth direction.Also it verifies the correctness and usefulness of the interferometric calibration model proposed in this paper,the error of DEM elevation in 0.37 m and 0.54 m in plane positioning error.4.Experiment and analysis of interferometric calibration are implemented based on Beijing TanDEM-X image.Firstly,using the TanDEM-X image in Beijing downtown and the related GCPs,the calibration experiments are carried out,and the comparison between the calibration DEM and the noncalibration DEM is made.The experimental results show that the interferometric calibration can improve the accuracy of the DEM,and the error of the DEM elevation after calibration is 2.08m,and the error in the plane is 8.69 m;Then,using TanDEM-X image in Mentougou region,GPSs and Ice,Cloud and land Elevation Satellite/Geoscience Laser Altimeter System(ICESat/GLAS)data to do interferometric calibration.The experiment selected 3 calibration schemes including calibration by GCPs,calibration by ICESat/GLAS data and united calibration by GCPs and ICESat/GLAS data.The experimental results show that the united calibration by GCPs and ICESat/GLAS data not only can guarantee the uniform distribution of control points in the survey area,but also can improve the accuracy of DEM plane positioning punctuation.The DEM accuracy of last acquisition was 9.54 m,the elevation accuracy is 4.09 m.