Technologies And Software Toward Precision Real-time Orbit Determination With Spaceborne GPS/BDS Measurements

In recent years,low orbit satellites have developed rapidly and have been widely used in scientific research,military,and civilian applications.Real-time orbit determination of the low orbit satellites is the basic condition for the implementation of remote sensing and observation of low-orbit satellites.Because GPS is all weather,precision,cheap and continuous,more and more low-orbit satellites are equipped with on-board GPS receivers.And space-borne GPS real-time orbit determination has been one of the main means for observing and controlling of the low-orbit satellites.With the development of Bei Dou navigation system,the coexistence,compatibility and interoperability of multiple systems have become a hot issue in the field of satellite navigation,and low-orbit satellites have begun to be equipped with receivers supporting both GPS and BDS systems.Therefore,the research on the realtime orbit determination theory,model and method of integrating GPS and BDS spaceborne observation data not only conforms to the frontier development trend,but also meets the actual needs.Based on the traditional space-borne GPS real-time orbit determination using pseudorange observations,this paper deeply studies the theory and method of spaceborne GPS/BDS real-time precision orbit determination.The main research contents and achievements are as follows:(1)The basic theory of space-borne GPS/BDS real-time orbit determination are summarized,including time system,space system,satellite dynamics model,satellite kinematics equation and its numerical solution,GPS and BDS observation model.(2)The model and algorithm of space-borne GPS/BDS real-time precision orbit determination are derived in detail,including the state parameters of the spaceborne GPS/BDS real-time orbit determination using carrier-phase measurements,the time update process,the observation equation and the measurement update process.(3)The visibility,carrier-to-noise ratio,pseudorange observation accuracy and carrier phase observation accuracy of the FY3 C satellite on-board GPS and BDS observation data are analyzed.The visibility analysis shows that the number of satellites on the satellite is significantly more than the number of BDS satellites.The carrier-to-noise ratio analysis shows that GPS carrier-to-noise ratio of the two frequencies is quite different.The carrier-to-noise ratio of the two frequencies of the BDS is not that different.The carrier-to-noise ratio of the B1 data on the spaceborne BDS data is slightly lower than the carrier-to-noise ratio of the GPS data L1 frequency,and the signal on the B2 frequency the noise ratio is higher than the L2 frequency.The GPS satellite C1 P code pseudorange observation accuracy is higher than the C2 P code pseudorange observation accuracy,the BDS satellite C1 I code pseudorange observation accuracy is slightly worse than the C7 I code pseudorange observation accuracy.The observation accuracy of the GPS and BDS carrier phase is in the order of mm.(4)The preprocessing methods of the observations are summarized.The characteristics of the GPS and BDS cycle slip detection measurements are studied.The results show that there exist some differences between GPS and BDS detection measurements.This is due to the differences of observation noise and it provides a basis for the threshold setting of the cycle slip detection.(5)The accuracy of GPS and BDS broadcast ephemeris is analyzed in detail.The results show that the accuracy of GPS broadcast ephemeris is 0.1~0.4m,the clock error of GPS broadcast is 0.5~1.2m,the accuracy of BDS broadcast ephemeris is 0.1~1.1m,and the clock error of BDS broadcast is 0.3~3.7m.According to the influence of broadcast ephemeris error,the broadcast ephemeris error is modeled,and the pseudo-ambiguity parameter is constructed.According to the variation characteristics of the pseudo ambiguity parameter,the pseudo ambiguity parameter is designed according to the difference of GPS and BDS.The stochastic model absorbs part of the broadcast ephemeris error and improves the accuracy of realtime orbit determination.(6)Based on the above models and methods and the low-orbit satellite space-borne GPS real-time orbit determination software SATODS,real-time precision orbit determination of space-borne GPS/BDS is realized.Using FY3 C satellite spaceborne GPS and BDS observation data to simulate on-orbit real-time orbit determination processing,the results show that using GPS and BDS pseudorange observation,the position accuracy can reach 0.8~1.2m,and the velocity accuracy can reach 0.8~1.2mm/s.Using the carrier phase observation,the position accuracy is 0.2~0.4m,and the velocity precision is 0.2~0.4mm/s.