Tropospheric Error Budget for GNSS-R Altimetry at Low Grazing Angles

Margaret Scott, Carolyn Roesler, Yang Wang, Y. Jade Morton, and Steve Nerem

Abstract: Global Navigation Satellite System—Reflectometry (GNSS-R) measurements have demonstrated ability in high precision altimetry applications due to their potential for centimeter-level ranging precision, small spatial footprint sizes, and frequent revisit times. However, centimeter-level ranging precision is only achievable when the reflected signal can be coherently tracked, and coherent reflections more commonly occur when the incident ray is at a low elevation angle. A challenging factor is the tropospheric delay, which is significantly larger at low elevation angles, and becomes a dominant source of error in GNSS-R carrier-phase based altimetry. In this paper, we present a tropospheric error budget at low grazing angles specifically for GNSS-R applications using the Global Pressure and Temperature-3 model. The error budget is created by comparing GPT3 to a truth reference over 328 days in 2019 at specific elevation angles of 45, 30, 20, 15, 10, 7, and 5 degrees. The tropospheric error budget was generated at the KUUJ station in Hudson Bay and the CPNM station in the Java Sea to account for performance differences between dry and humid climates, respectively. Overall, we find clear regional, seasonal, and elevation angle dependencies in the tropospheric error budget. At 45 degrees elevation, the monthly mean tropospheric error ranges from -6.8 cm to 5.4 cm at KUUJ, and -18.4 cm to 20 cm at CPNM. When the elevation decreases to 5 degrees, the tropospheric error range significantly increases to a range of -46.7 cm to 38.3 cm at KUUJ, and -143.3 cm to 146.3 cm at CPNM.
Published in: Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021)
September 20 - 24, 2021
Union Station Hotel
St. Louis, Missouri
Pages: 4021 - 4029
Cite this article: Scott, Margaret, Roesler, Carolyn, Wang, Yang, Morton, Y. Jade, Nerem, Steve, "Tropospheric Error Budget for GNSS-R Altimetry at Low Grazing Angles," Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021), St. Louis, Missouri, September 2021, pp. 4021-4029.
https://doi.org/10.33012/2021.18029
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