关键词: 全球GPS/GNSS网, 模糊度解算, 独立双差模糊度选取, SPODS软件

Abstract: Ambiguity resolution plays an essential role in global GPS/GNSS network solution. In order to fix as many double-difference(DD) ambiguities to the nearest integers as possible, a set of "most-easy-to-fix" independent DD-ambiguities has to be defined. The most usable state-of-art method (the "traditional" method)at present is to make the independency checking on two levels firstly on the baseline level and then the network level, in which the DD-ambiguity candidates are sorted by their fixing probabilities on both levels. Considering the fact that, in general global network solution, the number of stations involved is usual times larger than that of satellites, a new approach for independent DD-ambiguities selection was presented, which makes the independency checking in an analogous two-level way firstly on the constellation level and then the network level. Together with a new procedure for sequential ambiguity fixing base on updating the upper triangular square root of covariance matrix, the new approach is implemented in the satellite positioning and orbit determination system (SPODS) software which is designed and developed at Xi'an Research Institute of Surveying & Mapping. Validation experiment with GPS observation data collected from about 64 IGS stations was carried out, which demonstrate that 1D RMSs for daily orbit solution, compared with IGS final combined solution, are about 0.012 m, and about 92% of DD-ambiguities were fixed, with only neglectable tiny difference for both the new and traditional method. Another experiment with varied number of stations indicates that the ratio of the number of DD-ambiguities candidates to be checked for independency on the network level between the new and the traditional approach is nearly equal to the ratio of satellites to stations involved. For the cases that more stations are involved than satellites, which are common in actual GPS/GNSS network solution, the computation time for independent DD-ambiguities selection is reduced with the new approach, the more stations involved, the greater advantage is exhibited.

Key words: global GPS/GNSS network solution, ambiguity resolution, independent double-difference ambiguity selection, SPODS