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Enhanced Satellite Geodesy through the Addition of a Pseudorange Observable

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Master's thesis Apr 1986-May 1989

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GPS satellites transmit suppressed carrier signals which are modulated by pseudorandom ranging codes known as CoarseAcquisition CA and Precise P codes. Range information can be derived by measuring the reconstructed carrier phase or delay of the code modulation of a received signal. Subcentimeter-level relative positioning was achieved by measuring carrier phase. Improvements in relative positioning were achieved by combining P code delay or pseudorange observations with phase observations. Since changes in the GPS will make P code observations impossible for civilian users, this study examines the effect of combining CA code observations with carrier phase observations. Carrier phase observations represent relatively precise, but biased, measurements of the satellite-to-receiver range. If phase observations are differenced between receivers and satellites, the bias is an integer number of cycles. If this integer value can be determined, position-determination accuracy is improved. Range measurements based on code delay may help to determine integer bias. Unfortunately, the CA code provides a relatively noisy range measurement. This study simulates CA code observations using actual phase observations. Mean values of ionospheric contributions to the simulated observations were determined from the international reference ionosphere model, and variations about the means were derived from actual dual-frequency phase observations. These phase and CA code observations were used to estimate biases and baseline vectors, for baseline lengths of 10, 100, and 330 km. Simulation results indicate no significant improvement in positioning accuracy is obtained by adding CA code to carrier phase observations. EDC

Subject Categories:

  • Geodesy
  • Navigation and Guidance

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