The GNSS-based Upper Atmospheric Realtime Disaster Information and Alert Network (GUARDIAN) is a near-real-time (NRT) ionospheric monitoring software that supplements existing natural hazards early warning systems. Its main products are NRT total electron content (TEC) time series, allowing users to explore ionospheric TEC perturbations that occur on Earth due to natural and anthropogenic events.

The NRT GUARDIAN time series are validated against well-established post-processing methods. Currently, time series are computed for more than 90 Global Navigation Satellite Systems (GNSS) ground stations distributed around the Pacific Ring of Fire, which monitor the four main GNSS constellations: the Global Positioning System (GPS), Galileo, BeiDou Navigation Satellite System (BDS), and GLObal NAvigation Satellite System (GLONASS).

GUARDIAN was developed at NASA’s Jet Propulsion Laboratory. Near real-time TEC data from GUARDIAN are archived through the NASA's Crustal Dynamics Data Information System (CDDIS).