GNSS radio occultation technique and space weather monitoring

Since the pioneer GPS/MET mission, low Earth orbit (LEO) based global navigation satellite system (GNSS) Radio Occultation (RO) technique has been a powerful technique in ionosphere monitoring. After that, many LEO satellites were launched with RO payload, include: CHAMP, GRACE, SAC-C/D, COSMIC, C/NOFS, Metop-A/B, TerraSAR-X/TanDEM-X, and etc. COSMIC was the first constellation of satellites dedicated primarily to RO and delivering RO data in near real time. Currently in UCAR CDAAC, we process most of these missions' RO data for the community. As for space weather, we provide the following products: slant total electron content (TEC) along GNSS ray, Abel retrieved electron density profile (EDP) of each occultation, and amplitude scintillation index (S4) along the GNSS ray. In this paper, we will generally describe the data processing in UCAR/CDAAC first. Then the data precision and accuracy will be summarized. The efforts to evaluate and improve EDP retrieval in CDAAC will be mentioned. We will finally highlight some applications of RO data in space weather monitoring.