COMBINING ALTIMETRY WITH ELECTROMAGNETIC AND REGIONAL-CLIMATE MODELS FOR IMPROVED ESTIMATION OF GREENLAND ICE SHEET MASS BALANCEWE PROPOSE TO GENERATE IMPROVED LONG-TERM ESTIMATES OF GREENLAND MASS BALANCE BETWEEN 2003 AND 2019 (AND BEYOND) BASED ON A COMBINATION OF ALTIMETRY GRAVIMETRY AND IN-SITU DATASETS USED IN CONJUNCTION WITH ELECTROMAGNETIC AND REGIONAL CLIMATE MODELING. AMONG THE PRODUCTS OF THIS WORK THERE WILL BE MAPS OF SPECIFIC MASS BALANCE (I.E. THE MASS BALANCE PER UNIT AREA OF THE ICE SHEET EXPRESSED IN WATER-EQUIVALENT ELEVATION CHANGE) AS PARTITIONED BETWEEN CHANGES DRIVEN BY SURFACE MASS BALANCE AND BY ICE DYNAMICS OF FIRN-THICKNESS CHANGE AND OF THE BIAS EXPECTED FOR CRYOSAT-2 BASED ON THE FIRN MODEL AND ALSO IMPROVED GRACE ESTIMATES OF TOTAL MASS CHANGES. WE PROPOSE TO ACCOMPLISH THESE TASKS BY USING THE DIFFERENT DATASETS TO IMPROVE A REGIONAL CLIMATE MODEL TO BETTER CAPTURE THE TIMING AND MAGNITUDE OF SNOW AND ICE ACCUMULATION AND ABLATION SIGNALS. WE WILL THEN USE THE IMPROVED CLIMATE-MODEL OUTPUT COMBINED WITH A FIRN MODEL TO PREDICT ELEVATION CHANGES FOR THE ICE SHEET AND WILL FURTHER ADJUST THE FIRN MODEL TO MATCH MEASURED DENSITY PROFILES AND TO MATCH ELEVATION CHANGES IN DYNAMICALLY STABLE PARTS OF THE ICE SHEET. LAST WE WILL TRANSLATE THE ADJUSTED FIRN-MODEL OUTPUT INTO AN ELECTROMAGNETIC MODEL OF THE SURFACE TO CALCULATE HOW KU-BAND RADAR ENERGY PENETRATES THE SURFACE OF THE ICE SHEET AND TO PREDICTED BIASES AND BIAS CHANGES FOR CRYOSAT-2 DATA UNDER DIFFERENT RETRACKING STRATEGIES. THE OUTPUTS OF THE IMPROVED SMB MODEL WILL ALSO BE USED TO GENERATE IMPROVED GRACE SOLUTIONS OVER GREENLAND AT REGIONAL SCALES (E.G. MASCON SOLUTIONS). THE SYNERGIC APPROACH PROPOSED IN THIS PROJECT OFFERS A UNIQUE AND TO OUR KNOWLEDGE UNPRECEDENTED WAY TO ADDRESS CRUCIAL KNOWN ISSUES CONCERNING THE ESTIMATES OF MASS CHANGES FROM ALTIMETRY DATA AS WELL AS THEIR INTER-MISSION CALIBRATION. THE COMBINATION OF THE DIFFERENT TOOLS (E.G. REGIONAL AND ELECTROMAGNETIC MODELS) OVERCOMES THE LIMITATIONS OF THE SINGLE APPROACHES ADDRESSING ONE OF THE LARGEST PROBLEMS IN ALTIMETRY (AND ICE SHEET REMOTE SENSING IN GENERAL) ON HOW TO RELATE THE KNOWLEDGE OF SNOW/FIRN PARAMETERS TO THE ELECTROMAGNETIC QUANTITIES THAT ARE DRIVING THE SIGNAL RECORDED BY THE REMOTE SENSING INSTRUMENTS. THE FINAL PRODUCT WILL CONSIST OF COHERENT IMPROVED SPATIALLY DISTRIBUTED AND LONG-TERM ESTIMATES OF MASS AND ELEVATION CHANGES WHICH WILL BENEFIT FROM THE PROCESSORIENTED VISION AND TOOLS OF THE PROJECT S TEAM HENCE SUPPORTING NOT ONLY THIS SPECIFIC PROJECT BUT ALSO THE GROWTH OF THE ALTIMETRY COMMUNITY IN ANTICIPATION OF THE ICESAT-2 LAUNCH.