| Conventional global navigation satellite system(GNSS)real-time precise point positioning(PPP)usually uses predicted ephemeris or real-time service products.The accuracy of predicted ephemeris products is difficult to meet the requirements of high-precision positioning,while real-time service products are prone to data Interruption phenomenon leads to unstable PPP solution accuracy.At present,The basic data of the current GNSS ground reference station network is complete,and the PPP algorithm with reference station correction can be used to obtain results with higher accuracy than conventional PPP within a certain range in real time.At present,PPP technology has a wide range of applications in GNSS seismic monitoring,water vapor detection,etc.Therefore,the precise point positioning assisted by the reference station has good research value and application potential.The main research contents and conclusions of this paper are as follows:(1)In this paper,the precise point positioning algorithm with reference station correction is studied.Based on the IGU predicted ephemeris and clock offsets products,the correction is calculated by using the known coordinates of the reference station.Then,on the rover,the correction is used to correct the observation,which can reduce the common error between the observation and the reference station,so as to improve the positioning accuracy of the PPP rover station.On the basis of the researched algorithm,the application research of regional realtime PPP assisted by reference station is carried out.Based on Shandong Continuous Operation Reference System(SDCORS),the effects of station spacing,different reference stations,and single/dual reference stations on regional real-time GPS PPP assisted by reference stations was discussed.The test results show that,based on IGU predicted ephemeris and clock offsets products,and using the post-processed GPS PPP single-day solution as reference,the real-time GPS PPP of the rover station assisted by reference stations can reach centimeter level in N,E,U components and point position accuracy.Since the common errors between the rover and the reference station are mainly the satellite orbit and clock errors,the tropospheric delay,ambiguity,etc.are still estimated as parameters,so the real-time PPP accuracy of the rover station has no obvious correlation with the distance between stations.The choice of reference station has a slight impact on the regional real-time PPP,and the accuracy of real-time PPP assisted by dual reference stations is better than that of PPP with single reference station corrections,which has an average improvement in point position accuracy of about 8.6%.Based on the Beidou Navigation Satellite System(BDS)and WHU predicted ephemeris and clock offsets products,a real-time dynamic BDS PPP test assisted by reference station was carried out.The results showed that,taking the post-event BDS PPP single-day solution coordinates as a reference,the real-time BDS PPP of the rover station assisted by reference stations can reach centimeter level in N,E components and decimeter level in U component accuracy,which is better than the conventional real-time BDS PPP,but the accuracy of the BDS PPP assisted by the reference station is slightly lower than that of the GPS PPP.(2)In response to the massive earthquake in Japan on March 11 th,in this paper,using GPS observation data with a sampling interval of 1s during the earthquake,a PPP real-time seismic monitoring study assisted by reference stations was carried out.Taking SHAO as the reference station,selecting MIZU and USUD as the rover stations,and using IGU predicted ephemeris and clock offsets products for testing.The results show that,using the post-processed PPP seismic monitoring results as reference,the ground displacement monitoring accuracy of the two rover stations is basically the same,the mean of root mean square error of the conventional PPP real-time seismic monitoring results in the N,E,U components are 128.4 cm,20.5 cm,and152.2 cm respectively,while the mean of root mean square error of the PPP real-time seismic monitoring results assisted by the reference station are respectively 4.8 cm,6.5 cm,and 16.7cm.The monitoring accuracy and stability of the latter is much better than that of the former,which is consistent with the post-processed PPP.It accurately records the displacement of the station during the earthquake,which can provide a more reliable basis for earthquake monitoring.(3)A PPP water vapor inversion method assisted by reference stations is proposed,the correction of reference station is calculated by using the known coordinates and tropospheric delay of reference station.The accuracy of tropospheric delay parameter calculation can be improved by adding reference station correction to the observation data of the rover station,so as to improve the accuracy of water vapor inversion.The PPP water vapor inversion method assisted by the reference station is tested and verified.Taking HKSC site in Hong Kong as the rover station,TWTF site in Taiwan and HKWS site in Hong Kong as the reference stations,using IGU predicted ephemeris and clock offsets products,the PPP solution assisted by the reference stations is carried out for the water vapor inversion test.The results show that,using radiosonde data and ECMWF data as references,the mean standard deviation of precipitable water vapor(PWV)with the PPP solution assisted by the reference station is 1.9mm and 2.9mm respectively.Compared with the solution of conventional PPP using IGU predicted product,the accuracy is Increases by 60% and 51% respectively.The accuracy of the new method is basically the same as water vapor inversion with the post-processed PPP solution,and the choice of the reference station is basically not limited by the distance,which is more flexible and convenient than the GNSS relative positioning method. |
