Study And Software Implementation Of GPS Data Pre-processing And Onboard GPS Kinematic Orbit Determination

The quality of GPS data pre-processing is the key to improving GPS positioning precision in either GPS static positioning or dynamic POD. With the development of spatial science, the precision of GPS navigation, positioning and orbit determination is required higher and higher, and the parameters are required to be solved dynamically and rapidly. Therefore, it is a focused topic to study GPS rapid dynamic positioning and determining orbit, currently. For the higher positioning precision requirement, the precision of pseudo-range cannot meet the need of positioning. but for the phase one, cycle-slip and ambiguity are the obstacles of its application. So, we put forward the study on GPS pre-processing based on the optimized Blewitt method and construct a new wavelet function to detect cycle-slip. We brought forward pre-processing scheme based on all kinds of pre-processing methods. Besides measurement type and receiver precision, GDOP is another important factor for improving positioning precision, so it is necessary to study the selection of GPS satellites for the optimum geometry. Precise GPS phase measurement is the basis of on-board GPS/LEO satellite POD, whereas, precise orbit is the foundation to scientific research of LEO satellite, so the onboard GPS kinematic POD is one of the main contents in this dissertation. Therefore, we firstly study GPS data pre-processing and its software implementation: COMPRE, then study the onboard GPS kinematic orbit determination and its program SHKINE software, lastly, determine orbit with SHKINE software after GPS data pre-processing with COMPRE software. All these contents construct the frame of this dissertation. General speaking, the main contents of the dissertation are as follows: Part I: Study on GPS data pre-processing and COMPRE software system 1. We analyzed the error of various combinations of GPS observations and determined the optimal combination with the minimum error; we put forward the differential method and the Vondrak method to delete bad data. 2. We added/reduced one cycle-slip on the data of one GPS satellite, artificially, it is showed that one cycle-slip would cause the positioning error of decimeter. We discussed Blewitt method, mainly, and put forward some advices according to some limits of the Blewitt method, meanwhile, we optimized Blewitt method and presented COMPRE scheme on GPS data pre-processing. 3. An idea is put forth to adjust the number of forward-to-back differential point by using a scale factor. From the character of Shannon function and Gauss window function, Shannon function with good filtering has a slow attenuation speed and bad local character, while Gauss function with the character of controlling wavelet attenuation well controls locality, but it is a bad low-pass filtering. Combining their advantages, we construct a new wavelet function by them. By test it is valid to apply this wavelet function constructed to detect cycle-slip. 4. We anatomized COMPRE program and summarized the innovative points, including deleting bad data, detecting and correcting cycle-slip, and solving float ambiguity. 5. To test the validity of COMPRE, we analyzed some GPS satellites data from Shanghai GPS synthetical network and IGS one, compared the residual of LC-PC of COMPRE and GIPSY software, it is showed that the detection of cycle-slip is valid; compared the RMS of adjustment after pre-processing data with our program to that of GAMIT software, the difference is neglectable and it is showed that the precision of our program is equal to that of GAMIT, and could offer clean data. In addition, when we analyzed the residual of ionospheric model parameter estimation after GPS data pre-processing, it is also tested that our arithmetic and scheme is valid and viable. Part II: Study on onboard GPS kinematic POD and SHKINE software system 6. We discussed the select of GPS satellites for the optimal geometrical configuration because of the signifigance of optimal GPS satellite sky geometry distribution in improving precision of data processing, rapid solution, IGS data processing of reduced dynamic POD, and kinematic POD and so on. We discussed the property of the tetrahedron and derived formulae for computing its volume, and demonstrated that our formulae are more reasonable and accurate. We also discussed the formulae for computing configuration volume and GDOP for multi-satellites, multi-systems, briefly. 7. We presented the GPS measurement models and differential models for a LEO satellite and their properties. We discussed POD with differential method between adjacent epochs, it needed not take into account cycle-slip and ambiguity, and only needed a few epochs for simultaneous observations of more than 5 GPS satellites so that we could solve the coordinate correction for every epoch. But it would discard some non-common satellites data, and the observations cannot be used fully. Some examples showed that the data utility for this method is very low and the solution equations are often singular. 8. To overcome mentioned above questions, we put forward the united POD method of pseudo-range and phase differential in adjacent epochs with appropriate weight. The key to this method is how to determine weight; we derived parameter solution and the computation formulae of the weight in detail. The orbit precision of the method is about 1 decimeter 9. We discussed phase measurement zero-differential kinematic POD to solve parameters, mainly. The parameters to be estimated included coordinates and clock variable of CHAMP and GPS satellite ambiguity. We should divide the coefficient matrix into some sub-matrices and transfer it into upper-triangular matrix with block structure because it is too hugeness to solve directly, then, parameters can be solved with Gaussian elimination method. Finally, we discussed the error resources and processing scheme of CHAMP satellite GPS data. 10. We programmed GPS geometry POD and kinematic POD-SHKINE software. Taking CHAMP satellite data for example, we analyzed its data pre-processing, geometry POD with pseudo-range and pseudo-range smoothed phase, and zero-differential phase measurement kinematic POD. We also analyzed the effect to POD of clock offset, phase center offset, and relativity and so on, and presented a more precise CHAMP orbit and compared it with GFZ one. It is showed that the CHAMP orbit determined by our program of phase measurement zero-different kinematic POD is of inner RMS of about 10cm, outer RMS of about 20~30cm for every coordinate, and RMS of point position is about 30~40cm.