Research On GNSS Data Quality Assessment And Preprocessing

Main observations of GNSS include: pseudo-range observations,carrier phase observations,broadcast ephemeris,etc.Accurate evaluation can test the service performance of GNSS system and provide reference for error sources,which is beneficial to the control and optimization of the system.Reasonable preprocessing of GNSS observations is conducive to shortening the time of positioning and improving solution accuracy and data utilization.We carried out the research on "data layer","computing layer" and "presentation layer" around critical processes before positioning such as efficient obtainment of GNSS data,quality assessment of observations,detection and repair of cycle slips,mainly completed following works:(1)Based on the IGS products naming rules,data centers archiving rules and the open source software rtkget,realize the rapid download of GNSS data in large quantities.It has been verified that the fast download program is more than 10 times faster than the original rtkget,and it can download 1070 precise ephemeris in about 10 minutes.(2)Evaluate pseudo-range and carrier phase observations accuracy of multiple stations,apply statistical method to test the random characteristics,explore the factors affecting the observations accuracy.It turns out experimentally,observations accuracy will decrease at lower satellite elevations;and the signal accuracy is not exactly at the same level for different types of receiver and different stations using receivers with the same type,it should be analyzed on a case-by-case basis in practical application.(3)Evaluate the orbit and clock difference accuracy of broadcast ephemeris.Propose an algorithm to solve the phase center correction values and put forward a new method to eliminate systemic clock difference bias.The main conclusions of the three experiments are as follows: The SISRE accuracy of four mainly GNSS from high to bottom is: Galileo,GPS,BDS and GLONASS,the accuracy of all indexes of BDS-3 is the best among the four mainly GNSS.The accuracy of GPS broadcast ephemeris will change significantly with the implementation of various policies and atmospheric phenomena.The Precision of GPS Block IIIA satellite SISRE is about 0.2m,which is about one time higher than Block IIF.(4)Propose a step by step cycle slips detection method for BDS,which combines spatial search assisted with the I-norm minimization principle.Evaluate the approximate level of GPS L1 ionospheric error between 30 s sampling interval epochs with different ionospheric degree of activity,different latitude,different seasons and different receivers.It is verified that this method not only suit for 1s sampling interval BDS satellites observations of different orbits,but also suit for 30 s sampling interval observations during the period of geomagnetic storm.(5)Write large quantities GNSS data download software "data Downloader",multi-system GNSS broadcast ephemeris quality assessment software,GNSS triple-frequency cycle slips detection and repair software.It can be proofed that all the above software can realize the desired function,furthermore,they all have friendly interface,reasonable interface reservations,which are convenient for optimization and further development.