Enhanced Orbit Determination For GNSS By LEOs And Its Contribution To Earth Rotation Parameters

Low earth orbit satellites(LEOs)are playing an increasingly important role in geodesy and other fields owing to their many advantages.The launch of large-scale LEO constellations in the future will also contribute to their broad application prospects.Based on the background,this manuscript focuses on the application of LEO enhancement.The LEO enhanced global navigation satellite system(GNSS)precise orbit determination,the LEO enhanced GNSS satellite antenna phase center variation(PCV)calibration,and the LEO enhanced Earth rotation parameters(ERP)estimation were investigated using onboard data from 8 LEOs(Swarm-A/B/C,GRACE-C/D,Sentinel-3A/3B,Jason-3).Main work and conclusions are given as follows:1.Using the onboard observations from multiple LEO satellites,this manuscript delves into the impact of the LEO altitude,the combination of LEOs from different planes,and the LEO number on the LEO enhancement to the GNSS satellite precise orbit determination.With one LEO satellite included,the LEO satellite with a higher altitude exhibits a more noticeable enhancement to GNSS satellite orbit.With multiple LEO satellites included,a combination of LEO satellites from different orbit planes can enhance GNSS satellite orbit more effectively.The increasement of LEO satellites can further improve the orbit accuracy of navigation satellites as well as LEO satellites.The inclusion of 8 LEO satellites under the condition of 12 regional stations can improve the orbit accuracy of navigation satellites by about 70%,whereas the orbit accuracy improvement brought by a single LEO satellite will gradually decrease as the LEO satellite number increases.As the number of stations increases,the orbit enhancement of LEO satellites to GNSS satellites will be weakened gradually.The GNSS satellite orbit accuracy achieved by joint processing of data from 12 regional stations and 8 LEO satellites is nearly equivalent to that achieved by processing of data from 40 global stations.The orbit accuracy achieved by joint processing of data from 40 global stations and 8 LEO satellites is nearly equivalent to that achieved by processing of data from 95 global stations.2.Based on the ambiguity-fixed resolution,this paper built the model of LEO satellite antenna PCV and investigated the difference between the model derived by the residual method and that by the direct method.The calibration results from residual method will be affected by the ambiguity and clock parameters.By comparison,the direct method can effectively reduce the influence of other parameters on the LEO PCV.When the direct method is applied in calibrating LEO PCV with ambiguity-fixed resolution,the part of the PCV originally absorbed by the ambiguity parameter is correctly estimated,making the estimated result closer to the real PCV information.The LEO orbit determination results with LEO PCV calibration shows that the LEO PCV from direct method with ambiguity-fixed resolution can contribute to higher orbit accuracy.3.The contribution of LEO satellites to the GNSS satellite PCV calibration in two modes,namely the LEO-ground joint calibration mode and the LEO-based calibration mode,was investigated.For these two modes,the stability of GPS PCV results is within0.5 mm and 1 mm respectively.The mean difference between the calibration results and igs14.atx antenna model is within 1 mm and 2 mm for these two modes respectively.As the number of LEO satellites increases,the consistency of the PCV calibration results will gradually get improved.The validation results of LEO kinematic orbit determination show that the application of the estimated PCV can achieve slightly higher accuracy than the application of igs14.atx model.4.The estimation of ERP with the LEO enhanced GNSS precise orbit determination was achieved,which proves to be an effective approach to improve the ERP accuracy under the condition of regional stations.Under the condition of 12 regional stations,the inclusion of LEO satellites can effectively improve the estimation accuracy of ERP.As the number of LEO satellites increases,the accuracy of ERP will further get improved.The inclusion of 8 LEO satellites can improve the accuracy of ERP by about 60%.Under the condition of global stations,LEO satellites can also improve the accuracy of ERP to a certain extent,but the improvement is limited which is much smaller than that under the condition of regional stations.