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Introduction to the Ionosphere 

US TEC Product Archive

Vertical Soundings (Ionograms) 

Definition of Ionospheric Regions

Ionospheric Related Models

Ionospheric Indices (defined)

HF Radio Interest



US Total Electron Content (Vertical and Slant)
Product Archive


US Total Electron Content (Vertical and Slant)
Product Archive

The US Total Electron Content (US-TEC) product, which evolved through a collaboration between the Space Weather Prediction Center * (SWPC), the National Geodetic Survey (NGS), the National Geophysical Data Center (NGDC), and the Global Systems Division (GSD), is designed to specify Vertical and Slant TEC over the Continental US (CONUS) in near real-time. The product uses a Kalman Filter data assimilation model, described in the SWPC Technical Documentation.

This technique is driven by data from ground-based Global Positioning System (GPS) dual frequency receivers. The primary data stream comes from the Maritime and Nationwide Differential GPS (M/NDGPS) real time network of stations operated by the US Coast Guard (USCG), and is provided to SWPC by the NGS continuously operating reference stations (CORS) network. Secondary data streams are provided by the GPS/Met network (meteorological application of GPS data) and the Real Time IGS (International GNSS Service) network. Currently, there are about 80 CORS, 30 GPS/Met, and 15 IGS stations ingested into the model. This number has been gradually increasing and will be augmented by Federal Aviation Administration/Wide Area Augmentation System (FAA/WAAS) data in the future.

The Real-Time US-TEC Product is provided by SWPC as part of its mandate to provide real-time monitoring and forecasting of solar and geophysical events. NGDC is the National Archive for the US-TEC product output and the CORS data.

The US-TEC product includes maps over the Continental US (CONUS) of

  1. the vertical total electron content (TEC)
  2. an estimate of the uncertainty in the map
  3. the recent trend based on the departure of the TEC from the previous 10-day average
  4. ACSII Data files of the vertical and slant path TEC

The slant path data files specify the line-of-sight electron content to the GPS satellites in view at the time. This ionospheric product is designed for estimating the signal delay for single and dual frequency GPS applications. Note that TEC values in regions outside of the CONUS have no data and should be treated with caution.

  • USTEC Product Format (Readme)
  • Products for 2012 and 2013 are available online
  • Products for years before 2012 can be requested from Rob Redmon (ionosphere@noaa.gov)
    • The full list of available day files can be viewed here.
  • Access to historic US-TEC notable events prior to the established archive.

US Total Electron Content Real-time Specification is now fully operational as of June 19, 2007. For more information on US-TEC or to comment on the US-TEC product, please visit the real-time US-TEC Web.

*The Space Weather Prediction Center (SWPC) was formerly known as the Space Environment Center (SEC).