| The Multi-GNSS precise orbit products of high quality are essential to high precision applications.In this study,several aspects to improve BDS-3,Galileo and QZSS precise orbit determination(POD)are presented,including antenna phase center corrections,satellite attitude modes,solar radiation pressure(SRP)modelling,Earth albedo and thermal forces.The basic works and conclusions are:(1)The POD results based on PCO/PCVs from the new metadata have a generally comparable performance those based on DLR/GFZ values,since the two sets of PCOs mainly differ in the z-component,which is highly correlated with satellite clock bias.For the receiving antenna phase center corrections,using robot correction of GPS L1 and L2 in Galileo POD can lead to systematics biases in satellite orbits and sations coordinates.The Up components of station coordinate estimates have a maximum bias exceeding 2 cm.When using the chamer calibrated Galileo E1 and E5a phase center corrections,the disagreement in sations coordinates can be eliminated.Furthermore,the mean biases of Galileo SLR residuals can be reduced,and standart deviation(STD)of SLR residual can be reduced by a maximum of 0.5 cm.(2)Continuous yaw-steering attitude modes are followed by BDS-3 MEO satellites,Galileo satellites and QZSS IGSO J002 and J004.Using the correct yaw angles instead of the nominal ones leads to the reducing of post-fit LC residuals of BDS-3 and Galileo.Take E01 as an example,the RMS of LC residuals can be reduced from 1.80 cm to 1.61 cm when using the modeled yaw attitude.The correct attitude modes can improve the POD performance in deep eclipse seasons.The 24-h orbit overlapping RMS can be decreased by 8.3%,7.4%,4.9%,5.7%,8.7%,7.7%and 12.7%for CAST BDS-3,SECM BDS-3,Galileo IOV,Galileo FOCe,Galileo FOC,QZS-2 and QZS-4 satellites.Also the performance of satellite clock estimates could be improved by using the correct attitude modes in deep eclipse seasons.(3)The a priori box-wing model based on satellite geometry and optical properities can improvce the POD performance of Galileo and BDS-3.When the a priori box-wing model is used,the radial 24-h overlapping RMS can be smaller than 1.5 cm for all Galileo satellites,and the STD of SLR residuals is smaller than 4 cm.The a priori box-wing model can also help to eliminate the SLR dependency with?u and ?.The BDS-3 a priori box-wing model can reduce the 24-h orbit ovaerlapping to(22.1,14.9,5.6)cm and(24.7,13.1,6.7)cm for CAST satellites and SECM satellites in along-track,cross-track and radial components,respectively,with improvements of 13-40%when compared to the empirical ECOM2 model.(4)According to the QZSS metadata,QZS-1,QZS-2 and QZS-4 are equipped with a large L-band antenna,which can be assumed as a circular truncated cone("box-wing-hat").The priori box-wing-hat model can stabilize the estimates of SRP parameters when compared with ECOM,ECOM2 and the priori box-wing model.when the priori box-wing-hat model is used,The radial orbit overlapping RMS of QZSS-1 in YS seasons,QZSS-2 and QZSS-4 can be decreased to 1.6 cm,2.3 cm and 2.7 cm,and the STD values of SLR residuals are 5.6 cm,5.5cm and 5.3 cm,respectively.(5)For Galileo satellites,when ECOM SRP model is used,the modelling of Earth albedo can reducd the mean biases and STD values of SLR residuals by 1.9 cm and 0.1-0.2 cm.When the priori box-wing SRP model is used,the modelling of Earth albedo can lead to larger SLR mean biases.The numerical and the analytical Earth albedo model present similar performances.For QZSS IGSO satellites,the SLR mean bias can be decreased from-5.1 cm to-2.8 cm when modelling of Earth albedo together with ECOM2 SRP models.(6)The consideration of the thermal forces can reduce the radial orbit ovarelpping RMS by 1.0 cm and 1.1 cm for Galileo and QZSS IGSO satellites,respectively. |
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