Ionospheric Sensing Using High-Rate GNSS Reflectometry and Occultation Measurements from Low Earth Orbit

Currently, the major ionospheric sensing systems—such as ground-based GNSS receivers, ionosondes, and incoherent scatter radars—are unevenly distributed, with relatively denser coverage in North America, Europe, and parts of Asia. In contrast, large regions—particularly the oceans, polar areas, and much of Africa and South America—remain under-instrumented, limiting the global coverage and accuracy of ionosphere monitoring. GNSS receivers onboard low Earth orbit (LEO) satellites provide a relatively new source of ionospheric data. While the navigation receivers primarily observe the top-side ionosphere, some remote sensing satellites, such as those using GNSS reflectometry (GNSS-R) and radio occultation (RO), receive GNSS signals that probe into or through the “central” ionosphere. 

This presentation primarily focuses on the high rate (e.g., 50 Hz or 100 Hz) ionospheric total electron content (TEC) measurement in LEO using reflected signals off ocean and ice surfaces, as well as RO signals when the tangent height is below the ionosphere. The Spire GNSS-RO/R constellation, consisting of up to 25 nanosatellites, provides a unique type of grazing-angle GNSS-R data in addition to the “standard” RO products. This presentation will introduce the spatial and temporal sampling characteristics of these data, the processing techniques used to recover ionospheric TEC measurements, and their associated capabilities and limitations. It will also discuss the use of these measurements to help fill data gaps in 2-D TEC mapping and 3-D electron density data assimilation, to improve the monitoring of ionospheric disturbances (e.g., scintillation and steep gradients) and the characterization of their impacts on navigation services, and to support the study of ionospheric plasma structures, such as polar patches, tongue of ionization, and equatorial bubbles.