For around 20 months GOCE will be gathering data to map the Earth's gravity field with unprecedented accuracy and spatial resolution. The final gravity map and model of the geoid will provide users worldwide with well-defined data products that will be instrumental in advancing science and applications in a broad range of disciplines. These will range from geodesy, geophysics and surveying to oceanography and sea-level research. All products are available free of charge to scientific and non-commercial users.
However, there are a number of steps that have to be taken in order to turn the raw data gathered by the GOCE satellite into a product suitable for the users worldwide. This part of the mission involves the so-called ground segment, which is essentially made up of three main elements – the satellite control element, the processing element and the archiving element as well as services to provide users with the data.
GOCE is controlled and operated by the Flight Operations Segment (FOS) at ESA's European Space Operations Centre (ESOC), in Darmstadt, Germany. From here, the health and status of GOCE is monitored and commands are generated and up-linked to the satellite.
GOCE data flow
Raw data are down-linked from the GOCE spacecraft to the ground station in Kiruna, northern Sweden, which is suitably located for GOCE's near-polar orbit. On receipt, the data are immediately forwarded to the FOS in ESOC which then links the data through to the Payload Data Ground Segment (PDGS) at ESA's European Space Research Institute (ESRIN), in Frascati, Italy. Here, through a process of calibration and validation the data undergo an important transformation from telemetry to level-1b data products. Level-1b data products are the time series of converted, calibrated and validated measurements taken by GOCE. They consist mainly of the gravity gradients in the local satellite reference system and the orbit data (Satellite-to-Satellite Tracking observations, positions and velocity) in an Earth-fixed coordinate system. In addition, satellite data such as the attitude of the spacecraft and other housekeeping data complete the level-1b data.
These level-1b data are subsequently processed to level-2 through the High-level Processing Facility (HPF). Under ESA's control, 10 European universities and research facilities that have complementary expertise in gravity and geodesy-related science fields, have joined together to operate the HPF throughout the lifetime of the GOCE mission. Within the HPF there are three parallel methods used for gravity field determination – this cross-validation ensures the high quality of the GOCE gravity field product. In addition, two complementary strategies employed to derive the orbit provide the possibility to validate the solutions against each other.
The level-2 data are the fundamental products that will be available to users worldwide. They consist of a spectral representation of the gravity potential on a sphere, gridded values of geoid heights and gravity anomalies, including error information and calibrated gravity-gradients in different reference frames.
For general opportunities to obtain Earth Observation data please visit: ESA's Earth Observation Principal Investigator Portal.
Accessing GOCE data: