| The distributed InSAR satellite system is a new kind of the conceptual radarsystem, which combines the technology of the satellite formation and the InterferometrySynthetic Aperture Radar (InSAR). The entire performance of the SAR satellite systemcan be well enhanced, and the distributed InSAR satellite system has a broad prospect.However, there also exist some challenges in basic theory and technique. The highprecision determination of inter-satellite baseline is just one of challenges. As a result,in this paper, the high precision determination of inter-satellite baseline of thedistributed InSAR satellite system is selected as the research background, and thespacrborne dual-frequency GPS is used for measuring. According to the relationsbetween the distributed InSAR mission, especially the inter-satellite baselinedetermination and precise orbit determination of single satellite, high precision relativepositioning of inter-satellite, the high precision determination of inter-satellite baselineof the distributed InSAR satellite system is studied surrounding the main line of singlesatellite, inter-satellite and baseline.The main work includes three parts:Aiming at the single satellite absolute position and velocity determination, theprecise orbit determination approach of single satellite based on dual-frequencyGPS is studied, and a mixed error modeling and revising approach of the GPSreceiver phase center variation synthetically considered the systematic error andrandom error is proposed, which improves the precision of the precise orbitdetermination of single satellite. At first, the preprocessing of dual-frequency GPSobservations is studied, and the reduced dynamic prcise orbit determination approach ofsingle satellite is analyzed. Secondly, according to the GPS carrier phase observationmodel and GPS receiver phase center model, a mixed error modeling and revisingapproach of the GPS receiver phase center variation synthetically considered systematicerror and random error is proposed. In this approach, the phase center variation error ismodeled as a systematic and a random component each depending on the direction ofGPS signal reception, and the systematic part and the standard deviation of the randompart in the phase center variation error model are respectively estimated by the bin-wisemean and standard deviation values of phase post-fit residuals computed by orbitdetermination.. The GPS observation data of Gravity Recovery And ClimateExperiment (GRACE) satellites are processed, and there types of orbit solutions areproduced. These orbit solutions are tested by three validation methods. The validationresults show that the orbit solutions obtained by the mixed error modeling and revisingapproach are all the best of the three types of the orbit solutions. Meanwhile, by theresults of the orbit comparisions between the orbit solutions obtained by mean value revision of phase post-fit residuals and the mixed error modeling and revising approach,it is shown that the impact of random part of the mixed error model on precise orbitdetermination can not be neglected.Aiming at the inter-satellite relative position and velocity determination, thehigh precision inter-satellite relative positioning approach based on the wide andnarrow lane double difference (DD) integer ambiguity resolution strategy isstudied, and a new DD integer ambiguity resolution strategy based on the a-priorirelative orbit and clock solutions is proposed, the success rate of the DD integerambiguity resolution and the precision of relative positioning are both improved.1mm level relative positioning for GRACE formation can be realized. At first, aimingat the problem that the reference GPS satellite is continually replaced, a partitionstrategy of ambiguity resolution is proposed, which keeps the common reference GPSsatellite unchangeable in every partition interval. Based on this strategy, the reduceddynamic relative positioning approach based on the DD integer ambiguity resolutionstrategy of the wide and narrow lane strategy is studied, which is used for the relativepositioning expriment of GRACE satellites. In this experiment, the sucess rate of theDD integer ambiguity resolution is84.73%, and the standard deviation of K-bandRanging (KBR) system for relative position validation is1.26mm. These resultsillustrate the validation and correctness of the programme. Then, aiming at the problemof the forementioned strategy that the resolution of the DD integer wide-lane ambiguityis easily affected by the quality of GPS P-code observation, a new DD integerambiguity resolution strategy based on the a-priori relative orbit and clock solutions isproposed. In this strategy, the a-priori relative orbit and clock solutions are firstlygenerated by the single difference reduced dynamic ionosphere-free combination batchleast-squares relative positioning approach, and then the wide lane ambiguities aresolved by the optimization of the P-code and phase data. The GPS observation data ofGRACE satellites are processed. The sucess rate of the DD integer ambiguity resolutionis89.89%, and is improved by5%, which shows that this stretegy could overcome theproblem of the wide and narrow lane strategy. The standard deviation of KBR systemfor relative position validation is1.01mm, and the accuracy of relative positioning isalso improved.1mm level relative positioning can be realized. The relative positionsolutions obtained by two strategies are compared. The comparison results in radial,transverse and normal directions are0.43mm,1.01mm and0.81mm repectively. The3-dimensional result is1.37mm. These comparison results also indicate that thechanges induced by the newly proposed strategy.Aiming at the inter-satellite baseline measurement scheme based ondual-frequency GPS, the error characters of the spatial baseline determination arestudied in detail, and the impact of each error on the spatial baselinedetermination is theoretically analyzed. An error modeling and simulating approach for the spatial baseline determination is proposed, in which themathematical model of each error is set up, and the impacts of each error, thepartial error source, and entire error sources on inter-satellite baselinedetermination are analyzed by the the simulations. At first, according to the theoryof the spatial baseline determination, the error sources of the spatial baselinedetermination are classified into two parts, the error source related to GPS measurementand the error source related to baseline transformaion. The classifications and charactersof errors are analyzed, and the impacts of the error items on spatial baselinedetermination are theoretically analyzed. Then, according to the characters of erroritems, an error modeling and simulating approach for the spatial baseline determinationis proposed. In this approach, the error items are modeled separately, and the impacts ofa single error item, the partial error source and the entire error sources on spatialbaseline determination are analyzed by simulations. It is shown by the simulations thatthe error source related to GPS measurement is the main errors for the spatial baselinedetermination, and the carrier phase noise of GPS observation and the fixing error ofGPS receiver antenna are the main factors of the error source related to GPSmeasurement, and the impact of the entire error sources on spatial baselinedetermination in International Terrestrial Reference Frame (ITRF) is0.500mm ofx-axis,0.500mm of y-axis,0.452mm of z-axis, and0.845mm of3dimensions.Therefore,1mm (each axis) level InSAR spatial baseline determination can be realized. |
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