GNSSROsystemen

GNSSROsystemen, also known as GNSS-RO systems, refer to the use of Global Navigation Satellite System signals to profile the Earth's atmosphere as they are occulted by a satellite in low Earth orbit. When a GNSS signal passes through the atmosphere, it is refracted and its phase and Doppler characteristics change. Tracking these signals as they disappear behind the limb allows the measurement of bending angles and refractivity with high vertical resolution.

From bending-angle measurements, retrieval algorithms derive atmospheric refractivity profiles, which are then converted into temperature, pressure and humidity information for the troposphere and lower stratosphere. Because GNSS signals can be observed at multiple frequencies, ionospheric effects can be separated or corrected, improving the neutrality of the retrieved profiles. The method is largely model-independent and provides altitude-resolved information without reliance on active sounding in all weather conditions.

GNSS-RO data are produced by networks of GNSS satellites and LEO platforms carrying receivers. The most prominent program is COSMIC (Formosat-3), launched in 2006, followed by COSMIC-2 and other missions. Data are distributed to meteorological agencies and research institutions and are frequently assimilated into numerical weather prediction models to improve forecasts and climate analyses. The technique is valued for its high vertical resolution, global coverage (including oceans), and resilience to clouds and precipitation, though it faces limitations in sampling density and the need for precise orbit and clock information.

Applications include weather forecasting, atmospheric and climate research, and ionospheric studies. Open data policies and standardized formats (such as NetCDF or HDF) facilitate widespread use.