A Method for Processing Intermittent Coherent and Non-Coherent Grazing GNSS-R Measurements

Brian Breitsch and Jade Morton

Abstract:	GNSS receivers aboard low Earth-orbiting (LEO) spacecraft are now routinely being used for remote sensing applications, and in particular for measuring ionosphere total electron content (TEC). Measurements from overhead and occultation geometries are operationally established for ionosphere observation, e.g. with the COSMIC-2 constellation. More recently, grazing GNSS reflectometry (GNSS-R) has offered a compelling new measurement geometry for both altimetry and ionosphere observation. Receiving reflected signals at low satellite elevations, which translates to low reflection grazing angles, allows for recovering the coherent signal carrier phase over calm ocean water or smooth ice surfaces. These measurements can in turn be used for surface altimetry over inland water surfaces and wetlands [1] [2] and over sea ice [3]. Alternatively, when dual-frequency reflection measurement or precise models of signal delay parameters are available, these reflected signals can be used to estimate TEC. The work in [4] establishes and validates carrier-phase based estimation of relative TEC and scintillation indicators, including rate-of-TEC index and sigma-phi, using grazing GNSS-R measurements, and work in [5] uses the established techniques to show examples of TEC enhancements occurring over the polar caps. Recent work in [6] uses grazing GNSS-R to observe traveling ionosphere disturbances (TIDs) associated with the 2022 Tonga volcano eruption. In these examples, GNSS-R offers new measurements of the ionosphere that are particularly valuable because of the lack of observations over oceans and polar caps.
Published in:	Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025) September 8 - 12, 2025 Hilton Baltimore Inner Harbor Baltimore, Maryland
Pages:	3238 - 3250
Cite this article:	Breitsch, Brian, Morton, Jade, "A Method for Processing Intermittent Coherent and Non-Coherent Grazing GNSS-R Measurements," Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025), Baltimore, Maryland, September 2025, pp. 3238-3250. https://doi.org/10.33012/2025.20346
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