For seamless and highly accurate operational processing of GNSS Radio Occultation data (RO data), precise orbit determination (POD) is required for all LEO satellites equipped with a dedicated RO receiver. Since 2001, the final RO products (vertical profiles of temperature, humidity, or bending angles) have been used to improve global weather forecasting models. To serve this purpose effectively, these products must ideally be delivered to meteorological services 24/7 and within a maximum delay of three hours after the measurement is taken onboard the satellite. To meet these requirements, GFZ operates a satellite ground station in Ny-Ålesund on Svalbard. This allows for near real-time access to data from the GPS POD and RO antennas of the polar-orbiting LEOs on every orbit, with minimal delay.

Section 1.2 of GFZ operates two orbit determination systems as part of the overall processing of RO data:

• Near-Real Time Orbits (NRT): The NRT system provides satellite orbits in near real time, with a latency of only 15-30 minutes. These orbits are crucial for the computation (performed in section 1.1) and subsequent assimilation (by meteorological services) of radio occultation products in weather forecasting.
• Rapid Science Orbits (RSO): This system provides precise satellite orbits with a delay of a few days, which are used for validation of the NRT orbits and for non-real-time applications. 

Orbit determination is carried out using state-of-the-art software, including EPOS-OC, which was developed at GFZ. Both systems support a wide range of satellite missions such as CHAMP, COSMIC, GRACE, and SAC-C, as well as current missions like GRACE-FO, TanDEM-X, and TerraSAR-X. They achieve an accuracy of up to one centimeter, validated through independent Satellite Laser Ranging (SLR) measurements.

Through the joint efforts of Sections 1.2 and 1.1, GFZ makes valuable contributions to the improvement of weather forecasts and the understanding of the ionosphere by providing high quality orbit and RO products (see publication list in Section 1.1). These products are freely available to the scientific community via the ISDC. 

Project partners:

• Section 1.1, GFZ

Project duration:

• Since 2001

Funding:

• GFZ