ESA’s Earth Explorer missions are developed in response to Earth observation priorities identified by the scientific community. These reports form the basis for selection of the eighth Earth Explorer mission. Two candidates, FLEX and CarbonSat, have undergone extensive feasibility studies. CarbonSat aims to quantify sources and sinks of carbon dioxide (CO2) and methane (CH4) by measuring their distribution in the atmosphere. FLEX aims to quantify photosynthetic activity and plant stress by mapping vegetation fluorescence. A User Consultation Meeting was held in September 2015. The final selection will be made at the end of November 2015.
these are the full docs (not just the intro normally on Spacebooks)