Precise Orbit Determination For CHAMP With GPS Point Positioning

Methods and theories of precise orbit determination of LEOS with GPS have been developed very quickly in recent years ,Using economy , consecutive, precise data from GPS receiver of LEO satellite , precise orbit determination of LEOS is efficiently achieved .Precise orbit determination with GPS has the good and applied foreground. Compared with differencing model, the method of precise orbit determination of low earth orbiters with GPS point positioning have a few advantages, such as no using of terrain receivers, small amount of work. It has a good foreground in precise orbit determination. So the theory, methods and some key issues of kinematic orbit determination are discussed in this dissertation:1. Observation equations and correction models have been presented in details in thispaper.The observation equations are related to user position, clock, and ambiguity parameters, it is the base of Precise Point Positioning .The correction model is quite important in PPP. This paper has presented the observation equations and correction model in details.2. The preprocessor is build up successfully through several combinations of observation.It was found that the geometric CHAMP orbit solutions are very sensitive to data editing performed in the preprocessor. Data editing consists of applying a signal-to-noise filter and a rate-of-change of widelane-phase minus narrowlane-pseudorange linear combination filter. The former removes low strength signals at the measurement input stage, while the latter eliminates measurements that deviate from the norm before the initial estimation process. This preprocessor strategy therefore cleans the data in the measurement domain, without need for post-estimation residual analysis or need for a reference CHAMP orbit to constrain the definition of typical measurement behaviour.3. The theories, principles, specific methods and selection of suitable design of GPS-based absolute OD are discussed at full length.Firstly, the principles, specific method and precision evaluation of GPS-basedOD using carrier-phase smoothed ionosphere-free combination of dual-frequeny P codes is discussed. Then the method of combination of both codes and carrier phase is discussed .The last results show that the precision of GPS-based absolute OD using carrier-phase smoothed ionosphere-free combination of dual-frequency P codes can attain 1 meter level, and the combination of both codes and carrier phase, can reach to less than 1 meter. 4. Ambiguity of ionosphere-free combination was well studied.For high speed LEOS, the ill-conditioned problem exists in absolute OD using GPS carrier phase data. To get rid of ill-conditioned problem, the P codes are used to constrain ambiguity solution. And the method using Melourne-Wubbena (M_W) linear combination of phase and code observations to first resolve the wide-lane ambiguities and the narrow-lane ambiguities resolved through ionosphere-free linear combination of the L] and L2 phase observations is not ok for POD, because of high speed change of ionosphere.