Some Orbit Determination (OD) of Low Earth Orbiters (LEOs) based on undifferenced spaceborne GPS data were
discussed firstly in this paper. Then the principle and mathematical models of two different types of reduced-dynamic
were present. After that, dual-frequency spaceborne GPS data of doy 89, 2004 from CHAMP and GRACE satellite were
computed using two types of reduced-dynamic POD and the OD results were analyzed. Our CHAMP orbiting results of
one day using two different reduced dynamic POD methods are within 7 centimeters compared with GFZ Post processed
Science Orbits (PSO) and the GRACE orbiting results are with 3 centimeters compared with JPL OD results.
Some orbit determination methods using onboard GPS Observations were discussed firstly in this paper, especially the
principle and mathematical model of reduced-dynamic Precise Orbit Determination (POD) of Low Earth Satellite (LEO)
based on undifferenced spaceborne dual-frequency GPS data. Then a weeklong (from July 28, 2003 to August 3,2003)
dual-frequency onboard GPS observation from CHAMP satellite was computed using reduced-dynamic POD. Compared
with TUM solutions, our CHAMP orbiting results of one week using reduced dynamic POD method are within 8
centimeters, which can meet the requirements of some higher precision orbit satellite orbits. In order to obtain high
precision orbiting results, the impact of different gravity models and proper interval of pseudo-stochastic-pulses on the
orbit determination accuracy were analyzed as well.
Precise Orbit Determination (POD) of Low Earth Orbiter satellites (LEOs) based on Point Positioning (PPP) technique utilizing dual-frequency spaceborne GPS observations has become one of the best POD methods at present. Quality control of raw spaceborne GPS observations is very complex but critical for achieving high orbiting accuracy. Among the various existing methods for detecting outliers, the majority-voting algorithm used in Bernese 5.0 is a very efficient one. However, the performance of this algorithm may be affected by choice of the input parameters such as standard deviation for arranging the observations into groups, standard deviation for setting the rejection threshold and factors <i>α</i> and <i>β</i> whose values are often manually selected by experience. If the threshold is set too high, the relatively small outliers might not be found; on the contrary, more observations might be excluded and no solution could be computed for a particular epoch if the number of satellites per epoch is set to be smaller than 4. To overcome these limitations, this paper presents an improved majority-voting algorithm, which determines the some options by iteration instead of manual selection, and utilizes QUasi-Accurate Detection of outliers (QUAD) to correct the marked observations by this algorithm. The determined orbit of LEO using this new algorithm is continuous and smooth. Therefore, the improved majority voting is feasible and efficient.
The orbit determination (OD) accuracy of kinematic and reduced-dynamic method based on the spaceborne GPS data is strongly dependent on the quality and continuity of GPS observations, and the screening of the Low-Earth-Orbiter (LEO) GPS observations is substantially important. In this paper, an elaborate pre-screening procedure of zero-differenced spaceborne GPS observations was developed. This new efficient data-screening algorithm consists of two steps: in the first step, the "majority voting" method is used to locate the gross errors in zero-differenced GPS data; in the second step, the observation marked as gross error is corrected using the "Quasi-Accurate Detection of gross errors (QUAD)" method. In this step, an iterative least-square adjustment procedure is used to obtain residuals which are screened to detect bad observations thoroughly. For illustration of the feasibility and efficiency of the new algorithm, the processing of a numerical example of CHAMP satellite is presented in this paper.