Calculation And Analysis Of Zenith Tropospheric Delay By Bei Dou Navigation Satellite System

Drawing on the successful experience of IGS, China is actively constructing iGMAS and the Zenith Tropospheric Delay(ZTD) products are required by iGMAS analysis center.The ZTD with a mature method calculated by GPS observations(the following is called GPS-ZTD) has now been widely used in the meteorology field. BeiDou Navigation Satellite System(BDS) started to run formally on December, 2012, research on the ZTD calculated by BDS observations(the following is called BDS-ZTD) has just begun in the past two years. Therefore this paper is mainly studying on the BDS-ZTD calculating methods based on the existing research of our country. A kind of BDS-ZTD calculating strategies was developed with double difference model based on the independent improved Bernese 5.2 software. Experiment of this strategy was carried out based on the BDS/GPS data of the MGEX Ground-based Tracking Network. And the GPS-ZTD results obtained by the same strategy were used to access the BDS-ZTD results.Furthermore, with the additional observations of BDS, research of ZTD calculating strategies based on the multisystem needs to be carried out in order to make full use of the satellite data resources. Therefore, the BDS and GPS combined data were used to calculate ZTD(BDS/GPS-ZTD) based on the BDS-ZTD strategy. And the results were compared with GPS-ZTD. In order to access the external accord accuracy of the BDS/GPS-ZTD and the GPS-ZTD, the calculating results were compared with the IGS products.The main contents and results of the research include:1. Data of 68 global distributed stations from October 1st to 30 th, 2014 of the MGEX Ground-based Tracking Network were used to calculate the BDS-ZTD and GPS-ZTD. And the GPS-ZTD results were used to access the accuracy of the BDS-ZTD. The results were divided into 4 groups based on the number of the visible satellites of the BDS system in order to be analyzed. The results show that:(1)For the results of the BDS stations with number of visible satellites greater than 8, the average value of the absolute bias is 0.86 cm, the average STD value is 1.07 cm, and the average RMS value is 1.40 cm.(2)For the results of the BDS stations with number of visible satellites between 7 and 8, the average value of the absolute bias is 1.62 cm, the average STD value is 1.40 cm, and the average RMS value is 2.24 cm.(3)For the results of the BDS stations with number of visible satellites between 3 and 7, the average value of the absolute bias is 0.79 cm, the average STD value is 2.08 cm, and the average RMS value is 2.28 cm.(4)For the results of the BDS stations with number of visible satellites less than 3, the absolute differences between the BDS-ZTD and the GPS-ZTD results are no more than 20 centimeters.2. Datas of the 68 stations of the MGEX Ground-based Tracking Network were also used to calculate BDS/GPS-ZTD. And the GPS-ZTD results were compared with it.(1)For the results of the BDS stations with number of visible satellites greater than 8, the average value of the absolute bias is 0.18 cm, the average STD value is 0.53 cm, and the average RMS value is 0.57 cm.(2)For the results of the BDS stations with number of visible satellites between 7 and 8, the average value of the absolute bias is 0.16 cm, the average STD value is 0.48 cm, and the average RMS value is 0.51 cm.(3)For the results of the BDS stations with number of visible satellites between 3 and 7, the average value of the absolute bias is 0.24 cm, the average STD value is 0.45 cm, and the average RMS value is 0.52 cm.(4)For the results of the BDS stations with number of visible satellites less than 3, the average value of the absolute bias is 0.14 cm, the average STD value is 0.63 cm, and the average RMS value is 0.65 cm. As we can see, the average STDs decrease gradually as the number of visible satellites of BDS system changing from 8 to 7 and to 3. Because that the usage of the BDS data is decreasing. For the results of the BDS stations with number of visible satellites less than 3, the BDS data are useless and the average STD doesn’t decrease.3. In order to verify the correctness of the BDS/GPS-ZTD and the GPS-ZTD results of October 29, they were compared with the IGS-ZTD products. Analysis results show that the BDS/GPS-ZTD coincides well with the IGS-ZTD, but the GPS-ZTD doesn’t well coincide with the IGS-ZTD. And it shows that the BDS/GPS combined calculating strategy is beneficial to the stability of the ZTD calculating.