Abstract
Presently, the global positioning system (GPS) satellite constellation consists of 40% older Block IIA and IIR space vehicles and 60% newer IIR-M and IIF satellites. Only newer GPS satellites are capable of transmitting the L2C signal which is in quadrature to the legacy L2P(Y) signal being broadcast by all satellites. The data format RINEX-2 is not prepared to contain carrier phase observations of both L2 signals, but should contain either one or the other. If a mix of unaligned L2P(Y) and L2C carrier phase observations are stored in a RINEX-2 file, the quarter cycle bias causes the file to be defective and not usable for precise positioning purposes. Algorithms that detect such files are presented in this study. They are mainly based on the analysis of widelane fractional ambiguities and were applied to RINEX-2 files of 2624 reference stations. Seventy-two station files (2.7%) were found to be defective since they contained mixed and unaligned L2P(Y) and L2C carrier phase observations. If such files are used for precise positioning with ambiguities being fixed to integer values, resulting coordinate errors in long baselines can reach centimeter levels. Unaligned L2 observations often prevent ambiguity fixing, especially in short baselines.
Highlights
In 2005, the first global positioning system (GPS) Block IIR-M satellite was launched
WL, Melbourne-Wübbena linear combination, precise point positioning (PPP); each panel consists of sub-panels: upper sub-panels long baseline, (b3) Melbourne-Wübbena linear combination, PPP; each panel consists of 2 sub-panels: refer to L2C, lower sub-panels refer to L2P(Y); the bin width is 0.05 the cycles
Receiver indicate that the Manufacturer applied FCBMW,C1P2 corrections are valid for this observation data set, and Melbourne-Wübbena linear combination (MW)
Summary
In 2005, the first global positioning system (GPS) Block IIR-M satellite was launched. It became the first satellite in the GPS constellation to broadcast an additional signal on L2 frequency (1227.60 MHz), the so-called L2C signal [1,2] With this new signal, receivers had the choice to observe L2 code and carrier phases either on the legacy L2P(Y) signal, the new L2C, or both. L2P(Y) and L2C phase measurements are mixed without being aligned, severe problems in precise positioning applications occur This mix of unaligned observations is referred to as the “L2 quarter cycle problem”. Even if the two L2 carrier components are aligned on the level of quarter cycles, there are still satellite and receiver induced delay differences between L2P(Y) and L2C [4]. The last section demonstrates the effect of the L2 quarter cycle problem on coordinate estimation
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