| 31 Aug 2026
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.
This manuscript introduces GIFT‑BDS, a new regional high‑resolution ionospheric dataset over China built upon more than 200 ground GNSS stations and five BeiDou GEO satellites. Taking advantage of the nearly‑fixed observation geometry of BDS‑GEO, the dataset provides Level‑1 slant TEC time series and Level‑2 gridded products including VTEC, ROTI, and multi‑component Gradient Ionospheric Index (GIX) with 0.25° × 0.25° spatial resolution and 15‑min temporal cadence. The authors comprehensively document network configuration, full processing workflow, quality‑control schemes, internal consistency diagnostics, and benchmark comparison against CAS GIM. Representative science cases further demonstrate its capability for investigating Equatorial Ionization Anomaly (EIA), Equatorial Plasma Bubble (EPB), as well as quantifying ionospheric impacts on PPP and network RTK positioning performance. The paper is well‑structured; methods are clearly described, validation metrics are properly defined, and example applications are illustrative. Overall, this work is suitable for publication in Earth System Science Data after addressing the following minor points.
1. It lacks external independent validation. This might be difficult.
2. The link, Index of /pub/campaign/iono/GIFT-BDS, has no up to date products. It has the same time period as zenodo link. If there is no operational data product available to the users, the significance of the paper is limited.
3. The authors used the CAS-GIM to estimate the receiver bias. I am not sure i understand correctly or not, this might introduce extra errors in the sTEC and TEC gradient estimation since the GIM is relatively smooth. The authors should emphasize this point.
4. In the inter‑IPP pair‑selection, different distance means smooth the gradient in different scale. When the threshold has a wide range, this is also an error source.