Quality Control, Ambiguity Resolution and GPS Network Adjustment

Shaowei Han and Chris Rizos

Abstract:	Modern GPS carrier phase-based survey techniques such as "rapid static" and "stop & go" are fast becoming the standard operational modes for building local geo-detic control networks or for the densification of an ex-isting network. However, such techniques do have an increased chance of deriving a biased baseline vector due to faulty ambiguity resolution compared with tradi-tional GPS surveying techniques based on the analysis of static observation spans of an hour or more in length. Hence the application of reliability assurance proce-dures to verify "rapid static" or "stop & go" surveyed baselines at the subsequent network adjustment step be-comes an important issue. What needs to also be ac-counted for is: (a) that the formal output variance-covariance matrix of a baseline solution is generally over-optimistic, and (b) redundant baselines could be derived by baseline determination software if more than two GPS receivers are used simultaneously in the sur-vey. In this paper a GPS network adjustment procedure is proposed, which can be summarised as follows: (1) All possible combinations of pairs of receivers must be processed as baseline solutions. (2) All variance-covariance matrices of the baselines in a session should be scaled by a factor that is a function of the number of GPS receivers that have been used, the date rate and the length of observation span. The unit weight variances should then be re-computed. (3) For the network adjustment step, all baselines, with their apriori variance-covariance matrices, are treated as new (baseline vector) observations, and the least squares adjustment can be per-formed with minimal constraints. Based on this procedure, the internal and external reli-ability measures that consider the correlation between baseline components have been derived in order to evaluate the quality of the network. The ability to detect any baseline solution biases caused by wrong ambiguity resolution has been analysed. On the basis of this study some practical suggestions for designing GPS survey network are made.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	39 - 48
Cite this article:	Han, Shaowei, Rizos, Chris, "Quality Control, Ambiguity Resolution and GPS Network Adjustment," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 39-48.
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