Absolute Total Electron Content (TEC) estimation from Spire Global CubeSat Coherent GNSS-Reflectometry Measurements

In this work, we investigate coherent global navigation satellite system reflectometry (GNSS-R) measurements obtained from Spire Global commercial CubeSat as a potential new data source for absolute ionospheric total electron content (TEC). Current ground-based GNSS TEC measurements and modeling efforts have limited spatial coverage and temporal resolutions due to spare data coverage over open oceans, polar caps, and unreachable territories which requires more data sources to be introduced. The circular length and kurtosis methods are used to identify the signal coherency for GNSS-R. Our analysis indicates that GNSS-R signals have high enough coherency over sea ice and calm sea that enable the dual-frequency pseudorange and carrier phase TEC retrieval. Simultaneous cycle slip and noise filtering (SCANF) is applied for our TEC retrieval task and Spire’s differential code bias (DCB) is estimated. The retrieved slant TEC from GNSS-R follow a similar trend with respect to the TEC from Madrigal database. Also, a case study of Tonga volcano eruption on January 15th , 2022 is demonstrated. The result shows clear ionospheric TEC disturbances on the event day whereas the reference day remains quiet. Potential error sources and mitigation techniques are also discussed.