A Reliable GPS Single Epoch Processing Algorithm with Known Deformation Interval Constraints

With the constructing of large buildings such as tall buildings, large bridges, TV towers, etc, the deformation monitoring for these buildings is becoming more and more important. Traditional surveying methods are difficult in the safety monitoring of buildings continuously and automatically. GPS is an efficient tool for deformation monitoring. The mode of surveying for deformation may be static, fast static, kinematic or real-time kinematic(RTK). The processing methods for these modes of operation can be categorized as ambiguity resolution approach. They have one common, important constraint:they are multi-epoch algorithms. For many engineering sites, w here the signal may be interrupted and cycle slips occur quite frequently, the above methods have difficulty in resolution of ambiguity. Then the research attention has been focused on single epoch processing techniques, which are independent on cycle slips. This algorithm is based on the AFM(ambiguity function method). AFM has the advantage of insensitivity to integers, therefore no ambiguity resolution is required. Traditional single epoch processing algorithm has such problems as less chances for success, bad reliability and separibility, etc. The less success chances results from low accuracy of trial positions, less redundancy of observable, low signal to noisy ratio(SN R)and multi-path effects. After analyzing the problems of current GPS single epoch processing algorithms, the paper presents a reliable GPS single algorithm with height difference constraints or horizontal position constraints for deformation monitoring. When the main deformation is in horizontal direction(such as tall building s, TV towers, and tall chimneys), the height difference constraints can be used for the search of the optimal position. With the addition of the height difference constrains, the search box become a much more flat one. When the main deformation is in vertical direction(such as long-span suspense bridges, cable-stayed bridges), the horizontal position constraints can be used for the search of optimal position. With the addition of horizontal constrains, the research box become very slender. Therefore with the involvement of the proposed constraints, the number of candidates is reduced sharply and the optimal position, which can not be found by traditional algorithm, now can be correctly solved. When the GDOP is not good, the paper uses 5 satellites to compute the trial positions to advance the accuracy of candidates. The proposed algorithm is effective in building sites, where satellite signals are often interrupted and the number of satellites is not ideal as well as the signals are often contaminated by multi-path. Three examples have showen that the proposed algorithm has high successful rate, good reliability and good separibility. Test results also show the proposed algorithm is suitable for both double and single frequency receivers. Three tests show that one epoch of data with 6 to 7 satellites at the m ask angle of 15° is sufficient to achieve the accuracy less than 1 cm in horizontal position and less than 2 cm in height with 100%success rate.