GNSS-Reflectometry Assessment of Requirements and Consolidation of Retrieval Algorithms
- Schematic overview of the GEROS experiment to be installed aboard the International Space Station. Red lines indicate the reflectometry measurements for water, ice and land surface monitoring. Blue lines indicate GNSS RO and coherent reflectometry observations and the green lines symbolize the GNSS signals, received from zenith for Precise Orbit Determination (POD) of the GEROS payload and 3D upside ionosphere monitoring.
- © J. Wickert (TUB/GFZ)
GARCA was a scientific study, funded by the European
Space Agency ESA. It was contributing to the preparation of the
GEROS-ISS  Mission for the application of the innovative
GNSS-Reflectometry (GNSS-R) aboard the International Space Station.
Within GEROS-ISS signals from the Global Navigation Satellite Systems
(GNSS) are foreseen to be exploited for Remote sensing of Ocean, Ice
and Land surfaces but also for atmosphere/ionosphere sounding on a
near-global scale to derive information on Climate Change.
The GARCA study was conducted by an international consortium under lead of GFZ and finished November 8, 2016 after a two-year project period . Seven institutions from six different countries belong to the GARCA consortium:
• Deutsches GeoForschungsZentrum, GFZ, Germany• Collecte Localisation Satellites, CLS, France• DEIMOS Engenharia, Portugal• Institute for Space Studies of Catalonia, IEEC, Spain• Institute français de recherche pour l'exploitation de la mer, Ifremer, France• Nansen Environmental and Remote Sensing Centre, NERSC, Norway• National Oceanography Centre, NERC (NOC), U.K..
The objective of GARCA was to support the assessment and consolidation of scientific requirements and the consolidation of retrieval algorithms for a spaceborne GNSS-R experiment, focusing on the GEROS-ISS concept and its primary and secondary data products (sea surface height and ocean surface roughness). The main work was the development of an end2end-Simulator for the GEROS-ISS measurements (GEROS-SIM), and the evaluation of the expected Level2-data products (L2 performance). A GEROS-SIM version was made available through a web-server, freely accessible to registered scientists. Validation and performance tests benefit from the large amount of GNSS-R data acquired by the consortium members in the last decade, and new dat, which was acquired during a flight campaign in 2015. Three Observing-System Simulation Experiments (OSSE) by JPL, GFZ and NERSC assessed the oceanographic significance of the expected GEROS-ISS measurements and demonstrated the usefulness of the GEROS-ISS concept. Twelve additional external scientific experts supported the GARCA project and were involved in the work as beta-testers of the developments and also to initiate the sustainable formation of an interdisciplinary GEROS-ISS user community, which also initiated new GNSS-R mission proposal, as, e.g., G-TERN, within the Earth Explorer 9 call from ESA .
 Wickert, J., et al., GEROS-ISS: GNSS REflectometry, Radio Occultation, and Scatterometry Onboard the International Space Station, IEEE Journal of selected topics in applied Earth observations and Remote Sensing, Vol. 9, Issue: 10, p. 1_30, 10.1109/JSTARS.2016.2614428, 2016.
 GARCA team, GNSS-R assessment of requirements and consolidation of retrieval algorithms, Final Project Report, ESA-AO1-7850/14-GARCA-FR, pp 463, 2016.
 Wickert, J./Cardellach, E. et al., G-TERN: GNSS Transpolar Earth Reflectometry moNitoring system, Proposal for an Earth Explorer 9 Mission, European Space Agency, 2017.