Extreme Ultraviolet and X-ray Irradiance Sensors (EXIS)

The Extreme Ultraviolet and X-ray Irradiance Sensors on the GOES-R series satellites are critical to understanding and monitoring solar irradiance in the upper atmosphere, that is, the power and effect of the sun’s electromagnetic radiation per unit of area.

EXIS will be able to detect solar flares that could interrupt communications and reduce navigational accuracy, affecting satellites, high altitude airlines and power grids on Earth.

On board EXIS are two main sensors, the Extreme Ultraviolet Sensor (EUVS) and the X-Ray Sensor (XRS), which will help scientists monitor activity on the sun. EXIS will reside on the Sun-Pointing Platform (SPP) of the satellite, mounted in the yoke of the solar array. The instrument also includes the EUVS/XRS Electrical Box (EXEB) and the Sun Positioning Sensor (SPS) subsystems.

NOAA requires the real-time monitoring of the solar irradiance variability that controls the variability of the terrestrial upper atmosphere (ionosphere and thermosphere). This requirement supports NOAA’s space weather operations and is implemented with XRS and EUVS.

XRS monitors solar flares and helps predict solar proton events that can penetrate Earth’s magnetic field. The XRS is important in monitoring X-ray input into the Earth's upper atmosphere and alerts scientists to X-ray flares that are strong enough to cause radio blackouts and aide in space weather predictions (this is different from the SUVI instrument which monitors solar flares via images on the X-ray spectrum). EXIS will provide more information on solar flares and include a more complete and detailed report of solar variability than is currently available.

The EUVS will measure changes in the solar extreme ultraviolet irradiance which drive upper atmospheric variability on all time scales. EUV radiation has major impacts on the ionosphere. An excess can result in radio blackouts of terrestrial high frequency communications at low latitudes. EUV flares also deposit large amounts of energy in Earth’s upper atmosphere (thermosphere) causing it to expand into Low Earth Orbiting satellites, causing increased atmospheric drag and reduce the lifetime of satellites by degrading items such as solar panels.

The NOAA Space Weather Prediction Center will rely on the products from the EXIS to issue warnings of radio blackouts. This will aid preserving ground-based radio communications and navigation systems.