GIFT-BDS: A high-resolution TEC and Gradient Ionospheric Index dataset over China derived from BeiDou GEO fixed-geometry observations

Abstract. High-resolution ionospheric total electron content (TEC) gradient observations are well-suited for characterizing ionospheric spatial structure and for assessing ionospheric effects on Global Navigation Satellite System (GNSS) positioning applications. Existing global ionospheric products provide valuable information on large-scale ionospheric conditions, but their spatial and temporal sampling is generally not sufficient to resolve fine-scale TEC gradient structures over China. We present GIFT-BDS (Gradient Ionospheric index from Fixed-geometry TEC observations using BDS GEO satellites), a high-resolution regional ionospheric dataset derived from a dense ground-based GNSS network and BeiDou geostationary Earth orbit (GEO) fixed-geometry observations. The network consists of more than 200 ground-based GNSS receivers and five BeiDou GEO satellites, providing stable receiver-satellite geometries and repeated sampling of nearly fixed ionospheric pierce points. The released dataset contains two product levels. Level-1 provides 30 s GEO-derived slant TEC (STEC) time series for individual receiver-satellite links. Level-2 provides gridded vertical TEC (VTEC), rate of TEC index (ROTI), Gradient Ionospheric Index (GIX), and directional TEC gradient components. The TEC-gradient products are provided on a 0.25° × 0.25° grid with a temporal resolution of 15 min. The dataset is assessed using STEC stability statistics, internal consistency diagnostics, and comparison with Global Ionospheric Map (GIM) derived gradients. Selected examples illustrate the use of GIFT-BDS for studies of daytime Equatorial Ionization Anomaly (EIA) morphology, nighttime Equatorial Plasma Bubble (EPB) evolution, and ionospheric effects on Precise Point Positioning (PPP) and Real-Time Kinematic (RTK) positioning performance. The dataset is available at https://doi.org/10.5281/zenodo.21090695 (Li et al., 2026a), with daily updates provided at https://data.bdsmart.cn/pub/campaign/iono/. GIFT-BDS extends the currently available ionospheric data resources over China by providing continuous high-resolution observations of TEC and TEC gradients, enabling investigations of ionospheric dynamics, space-weather effects, and GNSS positioning error characterization.