ESA Earth Explorer 7 candidate, CoReH2O (Cold Regions Hydrology High-resolution Observatory) would use twin-frequency 9.6 and 17.2 GHz synthetic-aperture radars to provide all-weather, year-round observations of snow, glaciers, surface water and snow-water equivalent, improving water-balance and high-latitude climate modelling. ESA selected Biomass for Earth Explorer 7 in 2013 while recognizing CoReH2O’s scientific value and advising on ways to realize its potential; CoReH2O remains a documented research concept rather than an implemented mission.