Near Real-Time TEC Maps, Global (beta version)
DLR’s global TEC maps provide information about vertical TEC (VTEC) derived from groundbased GNSS measurements with a latency of not more than 5 minutes and an update rate of 15 minutes. The maps have a global coverage with 2.5° in latitudes and 5° in longitude spatial resolution. This version of the global TEC maps is a beta version, which benefits from a new GNSS pre-processing resulting in a much better data coverage than the recent version. Please consider, the validation of this product has not been completed so far.
This TEC map is generated from ground based GNSS measurements assimilated into an empirical TEC model. The input GPS data is acquired from different providers in real-time via the German Federal Agency for Cartography and Geodesy in Frankfurt. This data is preprocessed in order to derive calibrated slant TEC (STEC) and to update the coefficients of the Neustrelitz Total Electron Content Model (NTCM) serving as ionospheric background. Subsequently the calibrated STEC measurements are assimilated into NTCM, cf. (Jakowski et al., 2011). The TEC is provided in TEC units (10^16 electrons per square meter) for a shell-height of 400 km.
Every 5 minutes a VTEC matrix with an ionospheric grid point spacing of 2.5° latitude x 5° longitude is generated and stored in JSON format. Data is provided here with 15 minutes updated rate. Higher temporal resolution can be provided on request.
The quality of the TEC map depends on the errors of the GNSS measurements. These errors are monitored through the production pipeline and displayed in a TEC error map. This TEC error map is provided as quality information along with the product.
This product can be applied to support the improvement of the accuracy during GNSS positioning. Please consider, this product is provided for test purposes without validation.
Product Specification
| Specification | Description |
|---|---|
| External parties | German Federal Agency for Cartography and Geodesy, data providers below |
| Data providers | IGS, Greenland network of the Technical University of Denmark |
| Input data | GPS dual-frequency measurements |
| Input sampling rates | 1 s |
| Reliability of data source | Data is preprocessed by DLR including e.g. cycle slip detection |
| Region of sensors | Global |
| Sensors | cf. meta data of individual product files |
| Single layer shell height | 400 km |
| Spatial Resolution | 2.5° Latitude x 5° Longitude |
| Boundaries of grid | -90°N – 90°N, 180°W – 180°E |
| Temporal Resolution | 15 min |
| Time Information | UTC Time |
| Reference coordinate System | ECEF coordinate system with WGS84 reference ellipsoid |
| Algorithms | 24 hours weighted least-squares estimate of DCBs, background model coefficients; 5 min updates of DCBs and background model coefficients in linear recursive filter; previous estimates serve as background for the assimilation of estimated calibrated STEC into the update background model by means of a successive correction method (cf. Jakowski et al., 2011). |
| File format | JSON |
Error of the NRT TEC map, global, derived from errors of the GNSS measurements. The given errors are related to the uncertainty of the in real-time derived TEC values from GNSS measurements and the error propagation based on the modelling and assimilation processes. The error/uncertainty is low in regions where a high density of real time measurements is available and higher in regions without measurements, where the TEC values are calculated via the TEC-model only (e.g. over oceans and in mountain regions).
