High-Accuracy Atmospheric Correction Generation Method for Compact RTK for Expanded Area (COREA)
Bu-Gyeom Kim and Changdon Kee, Department of Aerospace Engineering and SNU-IAMD, Seoul National University
Date/Time: Wednesday, Sep. 18, 11:03 a.m.
The COREA system aims to provide cm-level positioning accuracy across a nationwide area using only 5-7 widely spaced reference stations within a network spanning up to 1,000 km. The COREA system's correction consists of precise satellite orbit, satellite clock corrections, ionospheric corrections, and tropospheric corrections. Among these, it is crucial to generate atmospheric corrections, which include ionospheric and tropospheric corrections, with high accuracy using only a sparse network of reference stations. Tropospheric corrections are created using precise estimates of zenith delays determined during ambiguity resolution between reference stations, along with delays calculated by using meteorological data collected from weather station. These tropospheric zenith delays at reference station and weather station locations are modeled using spherical harmonics, with the modeling coefficients provided to users as correction. For ionospheric corrections, ionospheric delays based on double-differenced carrier phase measurements and pseudorange measurements are used after resolving ambiguities between reference stations. The modified single-layer model is employed to model the vertical ionospheric delays using spherical harmonics, with the resulting coefficients provided to users as corrections. A simulation analysis was conducted to evaluate the accuracy of these corrections and their impact on user positioning performance. A network of approximately 1,000 km was formed using six NOAA’s CORS in the United States. The residual error analysis showed that while correction accuracy decreased toward the network's boundary, all COREA users within the network maintained residual errors below 20 cm, unlike network RTK users who could not resolve ambiguities beyond 200 km from the master station. Consequently, all COREA users achieved 100% correct ambiguity resolution within 30 seconds, resulting in positioning errors within 1 cm.
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