The GPS/GLONASS Integrated CORS Network Atmosphere Modeling And RTK Algorithm Implementation

As the recovery of the GLONASS constellation, it's possible for GLONASS system to get Full Operational Capability (FOC) before the end of 2010, and also the first GLONASS-K satellite which can broadcast CDMA signal will be launched on December 2010. All these evidences show that the GLONASS system will come back to compete with GPS system again. For the civilian users, it could be good news as there will be more visible satellites, which mean the improvement of the precision and reliability for the positioning.This paper mainly focused on the implementation of GPS/GLONASS integrated Network RTK system and the contribution of this work can be list as following:1. The Construction of GPS/GLONASS Integrated Double Difference EquationsIn this paper, we use the least square method to construct the function model and stochastic model. The paper firstly has a brief description for the GPS/GLONASS integrated measurements, the linear combination of the dual frequencies and also the datum difference between the two systems. The paper also analysis the physical influences of the GNSS measurements, and use four different method to deal with the different physical influences. For the double difference equation construction, we also discuss the method for the reference satellite selection. Finally, three different models including geometry free model, geometry fixed model and geometry based model are introduced for GNSS resolution models, and all of these three models will be use in the following implementation of the Network-RTK system.2. Data Pre-processing for GPS/GLONASS Pseudo-range MeasurementsFor GNSS data processing, the quality for the pseudo-range is very important for the carrier phase ambiguity resolutions. In this paper, the data pre-processing including the sidereal day filter to reduce the pseudo-range multi-path effect and also the carrier phase smoothing pseudo-range. The test data shows that with the sidereal day filter, the precision for the pseudo-range can be improved to several centimeters level, and this can faster the wide-lane ambiguity resolution.3. GPS/GLONASS Integrated Ambiguity ResolutionFor the GPS/GLONASS integrated ambiguity resolution, we use the method Leick proposed in 1995 (Leick 1995):firstly, the reference satellite's single difference ambiguities are estimate with the pseudo-range and carrier-phase measurements. It can be proved that, the precision of the estimated single different ambiguities will not influence the integer property of the double difference ambiguities. After the GLONASS reference satellite single difference ambiguities are fixed to a approximate value, the traditional "three step" (bootstrap) method are implemented with Kalman filter. And finally, the cycle-slip detection and recovery for CORS baseline are discussed.4. The Comparison of the Network Interpolation Method for Atmosphere DelaysIn this paper, we compared several interpolation method which are commonly used for the Network-RTK, including DIM(Distance-Based Linear Interpolation Model) model, LCM(Linear Combination Model) model, LIM (Linear Interpolation Model) model, LSM (Low-Order Surface Model) model, LSC(Least Squares Collocation) model and Kriging model. The tested data show that, although most interpolation method are quite similar, for the SYDNET data, the Kriging method's perform best for ionospheric delay interpolation and LSM3 model performs best for tropospheric delay interpolation.5. The Generation of the VRS MeasurementsTo guarantee the precision of the VRS observation, the paper proposes to decompose the double difference atmospheric delay to single difference delay between two stations. In the meantime, the difference between precise orbit and broadcast orbit are added to the VRS observation. And also the sidereal day filter is proposed to be added to the VRS observation pseudo-range measurements.6. The Implementation of GPS/GLONASS Integrated RTKThe same as CORS baseline resolution, the GPS/GLONASS integrated RTK need firstly solved the GLONASS reference satellite's single difference ambiguities, and then the double difference ambiguity can be fixed to be integer for the GLONASS satellites. As the relationship between the measurements and the rover station's coordinate is not linearism, the extended Kalman filter is proposed for the implementation work of the GPS/GLONASS integrated RTK algorithm.