THE GOAL OF THE PROPOSED WORK IS TO MAP THE ANTARCTIC ICE SHEET (AIS) SURFACE MASS BALANCE (SMB) AT AN UNPRECEDENTEDLY HIGH RESOLUTION (1 KM) USING A UNIQUE COMBINATION OF ELEVATION DATA DERIVED FROM RADAR AND LASER ALTIMETRY (CRYOSAT-2 AND ICESAT-2) ATMOSPHERIC REANALYSES AND ICEBRIDGE RADAR DATA. THE UPCOMING NASA ICESAT-2 MISSION WILL PROVIDE HIGH-PRECISION INSIGHT INTO ELEVATION CHANGE OVER THE ICE SHEETS AT HIGH SPATIAL DETAIL AND IS CURRENTLY SCHEDULED FOR LAUNCH IN LATE 2017. A REMAINING CHALLENGE FOR SCIENTISTS HOWEVER IS IN PARTITIONING THESE ELEVATION CHANGES INTO ICE-DYNAMICAL AND SURFACE-INDUCED PROCESSES COMPLICATING THE INVERSION FROM ELEVATION (VOLUME) TO MASS CHANGES THE LATTER OF WHICH ULTIMATELY DETERMINE THE ICE SHEET S CONTRIBUTION TO SEA LEVEL CHANGE. THE SURFACE MASS BALANCE ONE OF THE MAJOR COMPONENTS OF SURFACE-INDUCED ELEVATION CHANGE CAN BE MAPPED IN SPACE AND TIME USING ATMOSPHERIC REANALYSES WHICH ARE MODELS THAT ASSIMILATE OBSERVATIONAL DATA. STATE-OF-THE-ART ATMOSPHERIC REANALYSES CURRENTLY WORKING AT GRID RESOLUTIONS OF APPROXIMATELY 50 TO 100 KM PROVIDE A REALISTIC PICTURE OF LARGE-SCALE ANTARCTIC SMB. AT THIS SCALE SMB IS PREDOMINANTLY DRIVEN BY PRECIPITATION THE SPATIAL PATTERNS OF WHICH ARE MOSTLY DETERMINED BY LARGE-SCALE OROGRAPHY THAT IS WELL RESOLVED BY CLIMATE MODELS. IN CONTRAST UNRESOLVED FINE-SCALE TOPOGRAPHY CAUSES WIND-DRIVEN REDISTRIBUTION AND SUBLIMATION OF SNOW THAT SIGNIFICANTLY AFFECTS SMB AT LENGTH SCALES SMALLER THAN THE MODEL GRID SIZE (SO-CALLED SUB-GRID DRIFTING SNOW PROCESSES) BUT LARGER THAN THE SMALL-SCALE AND HIGHLY MOBILE DRIFTS AND SASTRUGI THAT ARE NOT CONSIDERED IN THIS STUDY. THESE SUBTLE TOPOGRAPHIC VARIATIONS OF A FEW METERS CAN SPAN HUNDREDS OF METERS TO A FEW KILOMETERS AND CAN LEAD TO SMB VARIATIONS OF A FACTOR OF SIX. HERE WE PROPOSE TO MAP ANTARCTIC ICE SHEET SURFACE TOPOGRAPHY AT SUB-GRID RESOLUTION (~1 KM) BY COMBINING ICESAT-2 LASER AND CRYOSAT-2 RADAR ALTIMETRY DATA. IN CONJUNCTION WITH THIS NEW ELEVATION MODEL SURFACE WINDS AND CLIMATE SIMULATED BY NASA S MERRA-2 REANALYSIS WILL PROVIDE THE INPUT FOR A SNOW REDISTRIBUTION MODEL (SNOWMODEL) THAT SIMULATES SMB AT THE ELEVATION MODEL SCALE. THE RESULTS WILL BE EVALUATED AND REFINED USING OPERATION ICE BRIDGE SNOW RADAR DERIVED SMB AND ICESAT-2 DRIFTING SNOW FREQUENCY. OUR NEW SMB MAP WILL AID IN BETTER CONSTRAINING MASS BALANCE OF ANTARCTIC ICE SHEET AND ICE SHELVES AND THE CONTRIBUTION OF THE AIS TO CONTEMPORARY SEA LEVEL RISE (SLR). OUR NEW ESTIMATE OF AIS SMB CAN BE USED DIRECTLY TO DERIVE REGIONAL SCALE MASS BALANCE IMPROVE VOLUME-TO-MASS CONVERSION FOR ICESAT-2 AND CRYOSAT-2 REPEAT ALTIMETRY AND PROVIDE THE ICE CORING COMMUNITY WITH A TOOL TO PICK REPRESENTATIVE DRILLING LOCATIONS FOR SMB RECONSTRUCTIONS. MOREOVER OUR RESULTS WILL PROVIDE UNCERTAINTY BOUNDS ON CLIMATE MODEL SMB BY QUANTIFYING THE IMPACT OF NEGLECTING SUB-GRID DRIFTING SNOW PROCESSES AND HIGHLIGHTING REGIONS ON THE AIS FOR WHICH THESE MODELS ARE MORE OR LESS RELIABLE. THIS PROPOSAL IS HIGHLY RELEVANT TO AT LEAST TWO SPECIFIC GOALS OF THE CALL NAMELY TO GAIN INSIGHT INTO THE SURFACE MASS BALANCE ESPECIALLY TO IMPROVE MODELS OF POLAR PRECIPITATION AND TO USE SATELLITE ALTIMETRY TO DETERMINE ANY OTHER PROPERTIES OF THE ICE SHEETS CRITICAL TO IMPROVED MODELS OF THEIR CONTRIBUTIONS TO CURRENT AND FUTURE SEA LEVEL RISE. THE WORK INVOLVES A UNIQUE COMBINATION OF NASA INVESTMENTS INCLUDING ICEBRIDGE ICESAT-2 AND MERRA-2 AND IT WILL BE AN EARLY RESULT OF ICESAT-2 SINCE IT DOES NOT REQUIRE MULTIPLE CROSSOVERS FOR CHANGE ANALYSIS.