G-TERN  stands for „GNSS Transpolar Earth Reflectometry moNitoring system“. It is an innovative climate research experiment, which was proposed within the recent ESA call for Earth Explorer missions (9). G-TERN was proposed by an international team of 25 scientists from 11 countries and an industry consortium of 7 partners. The proposal was submitted June 15, 2017. The mission is jointly coordinated by Estel Cardellach (IEEC, Spain) and Jens Wickert (GFZ). The industry consortium is led by OHB, Germany.
Within G-TERN it is planned to use navigation satellite signals for remote sensing of ocean, ice and land surfaces and also for atmosphere sounding to derive information on climate change. Main mission goal is the precise determination of the height and roughness information of ice and ocean surfaces with main focus to polar regions to investigate the complex interactions of the cryosphere with the other components of the Earth system with new aspects. Ocean surfaces on a global scale can be very precisely monitored as well. Additional mission goal is the observation of land surfaces and their variation in context of global change.
The technical concept of G-TERN is based on the GEROS-ISS-Mission [2, 3], which finished it’s Phase A in 2016. In total 13 mission proposals were submitted for the revised Earth Explorer Call 9. End November ESA will decide, which two of these missions will go to Phase A. A launch of G-TERN with the European VEGA-C can be expected in 2025, the mission duration is foreseen to be 10 years.
 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.
 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.