| Spaceborne Interferometric synthetic Aperture Radar(InSAR)is an important remote sensing technology to obtain three-dimensional information of the earth.At present,the SAR satellite industry is developing vigorously with various imaging mode,polarization mode and multiple working frequencies.Based on the demand of surveying and mapping satellites,dual-frequency InSAR satellite is the key research object of the new generation SAR satellite in the future,and the corresponding data processing research work is urgently needed.Compared with the traditional singlefrequency InSAR system,dual-frequency InSAR technology can synthesize the advantages of two kinds of frequency band data by using interferograms of different bands,and the jointly obtained elevation has higher accuracy,which makes a breakthrough in the terrain extraction of difficult surveying and mapping areas.Focusing on the theme of spaceborne dual-frequency InSAR,this paper expounds the geometric principle and observation mode of dual-frequency InSAR system,discusses some key technologies in the joint processing of dual-frequency InSAR data,analyzes the factors affecting the accuracy of dual-frequency InSAR system,and compares the effects of combined processing of different working frequencies.The main research content of this paper can be divided into four aspects:(1)Research on joint processing of spaceborne dual-frequency InSAR data.Dual-frequency InSAR data joint processing technology is developed on the basis of InSAR technology,using the complementary advantages of different bands of data to get high-precision DEM in rugged terrain.A method of processing high-and lowfrequency InSAR data jointly is presented in this paper.It includes the following steps:low-frequency data processing,dual-frequency data registration,dual-frequency phase conversion,dual-frequency differential interference,dual-frequency phase unwrapping,elevation value calculation,etc.(2)Research on multi-scale frequency reduction unwrapping method based on phase pyramid.First of all,it is necessary to ensure that the phase of low-frequency data is correctly unfolded,especially in steep observation areas.In order to improve the accuracy of phase unwrapping,a new method — multi-scale frequency reduction unwrapping method based on phase pyramid is proposed in this paper.It takes the number of looks as the scale to build the phase pyramid.Phase unwrapping is carried out after reducing the resolution of the image,so as to ensure the correctness of the results.Taking the phase of the low-resolution image as the input value of the highresolution image,the phase unwrapping is iterated step by step,and the high-precision phase unwrapping result is finally obtained.(3)Research on height Measurement accuracy of Spaceborne dualFrequency InSAR.The accuracy of height measurement is affected by many errors.For the spaceborne dual-frequency InSAR system,the main error sources affecting the height measurement accuracy are comprehensively analyzed,including satellite orbit error,oblique distance measurement error,baseline measurement error,phase noise error and data processing error.These errors are qualitatively described and quantitatively analyzed,and the magnitude and accuracy of the total height measurement error under the dual-frequency InSAR system are summarized.Finally,the accuracy of spaceborne dual-frequency InSAR elevation survey under different topographic conditions is studied and verified by taking the dual-frequency combination of X/C as an example,through the dual-frequency simulation data.(4)Research on the optimal band combination of spaceborne dual-frequency for height Measurement.In spaceborne dual-frequency InSAR height survey,the selection of interference data frequency band is very important.The data with higher frequency have lower height ambiguity,corresponding to higher height measurement accuracy,but at the same time,with higher noise level and dense fringes,phase unwrapping and other follow-up processing becomes more difficult.On this basis,the optimal frequency band combination of spaceborne dual-frequency height measurement is studied,and the optimal dual-frequency combination under different conditions is analyzed.Based on the error analysis of dual-frequency InSAR,the elevation accuracy tests and analysis of pairwise combinations of Ku,X,C and L bands under different terrain conditions are carried out in this paper.It is concluded that Ku/C is the best combination for height measurement,which provides a reference for the development of spaceborne dualfrequency InSAR system. |
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