GNSS Receiver for Atmospheric Sounding (GRAS)

On board the European Metop weather satellites RUAG Space GNSS Receivers for Atmospheric Sounding (GRAS) provide sounding data for numerical weather prediction models.

RUAG Space developed the GRAS instrument which is in operation on the MetOp series of satellites since 2006 and provides 700 daily atmosphere soundings for numerical weather prediction. The instrument is characterised by its accurate measurements and its high availability.

The Radio Occultation (RO) measurements are achieved by the precise tracking of GNSS signals while transecting the atmosphere at very low elevation angles. This is accomplished through high gain antennas pointed in the velocity and anti-velocity direction of the satellite. The signal bending due to atmopheric refraction can then be derived. These measurements contain information that can be used in numerical weather models to retrieve atmospheric parameters such as temperature and humidity.

RUAG Space has also been selected for the development of the next generation of RO instrument for the MetOp Second Generation (MetOp-SG) programme.

The GRAS-2 for MetOp-SG has the capability to track signals from several GNSS constellations: Galileo, GPS, GLONASS, and Compass. It uses advanced signal processing technique to allow continuous measurement coverage to the Earth’s surface. It will also provide ionospheric electron density measurements for space weather applications. The first flight unit will be provided 2019.