Space-based measurements of the Earth System, including its atmosphere, oceans, land surface, cryosphere, biosphere, and interior, require extensive prelaunch and post launch calibration and validation activities to ensure scientific accuracy and fitness for purpose throughout the 
lifetime of satellite missions. This requirement stems from the need to demonstrate unambiguously that the space-based measurements, typically based on engineering measurements by the detectors (e.g. photons), are sensitive to and match up with the geophysical and/or biogeochemical quantity of interest at a broad range of measurement locations on Earth. Most geophysical parameters vary in time and space, and the retrieval algorithms used must be accurate under the full range of conditions. Calibration and validation need to be carried out over the lifetime of missions in order to assure that any long-term variation in observation can be definitely be tied to the evolution of the Earth system. Such activities are also critical in ensuring that measurements can be inter-compared and used seamlessly to create long-term multi-instrument//multi-platform data sets, , which enable large-scale international science investigations into topics with high societal or environmental importance such as determining the ice mass balance of Greenland, monitoring the evolution of sea ice and snow cover in the Arctic and improving our knowledge of the terrestrial carbon cycle through multi-sensor forest biomass mapping. . This session seeks presentations on the use of surface-based, airborne, and/or space-based observations to prepare and calibrate/validate space-based satellite missions measuring our Earth system. A particular but not exclusive focus will be on activities carried out jointly by NASA and ESA as part of their Joint Program Planning Group Subgroup on calibration and validation and field activities.