SEA LEVEL CHANGE IS AN IMPORTANT INDICATOR OF HOW THE EARTH IS RESPONDING TO CLIMATE CHANGE BUT IT IS ALSO IMPORTANT TO UNDERSTAND ITS SOCIOECONOMIC IMPACTS. THEREFORE UNDERSTANDING HOW MUCH SEA LEVEL WILL RISE IN THE FUTURE AND HOW IT WILL IMPACT COASTAL POPULATIONS CENTERS AND INFRASTRUCTURE IS A PROBLEM OF PARAMOUNT IMPORTANCE FOR SCIENTISTS TO ADDRESS. WE RELY ON COUPLED CLIMATE MODELS AND SEMI-EMPIRICAL MODELS TO PROJECT FUTURE SEA LEVEL CHANGES BUT THE PROJECTIONS VARY WIDELY AND THE ERRORS ARE POORLY UNDERSTOOD. HERE WE PROPOSE TO USE NASA OBSERVATIONAL DATASETS TO EVALUATE PRESENT-DAY SEA LEVEL CHANGE IN THE CMIP6 ENSEMBLE AND ICE SHEET MASS BALANCE IN THE ISMIP6 MODEL ENSEMBLE AND OTHER MODELS AND PROJECTIONS AS THEY BECOME AVAILABLE OVER THE PERIOD FOR WHICH WE HAVE OBSERVATIONS (THE LAST 2-3 DECADES). THERE ARE A VARIETY OF SATELLITE AND AIRBORNE MEASUREMENTS THAT CAN HELP US EVALUATE DIFFERENT PROJECTIONS OF SEA LEVEL CHANGE AND ICE MASS LOSS INCLUDING RADAR ALTIMETRY (TOPEX/POSEIDON JASON-1 2 3) SATELLITE GRAVITY (GRACE GRACE FOLLOW-ON) LASER ALTIMETRY (ICESAT ICESAT-2) AND OPERATION ICEBRIDGE (OIB). THE MULTI-MODEL EVALUATION WILL PROVIDE AN ASSESSMENT OF THE MODEL QUALITY IN REPRESENTING SEA LEVEL CHANGE AND ICE SHEET MASS LOSS. THE BEST MODEL(S) WILL BE CHOSEN TO BE USED FOR SEA LEVEL IMPACT STUDIES USING DIFFERENT CLIMATE CHANGE SCENARIOS. TO REPRESENT PROJECTION UNCERTAINTY WE PROPOSE TO EXTRAPOLATE MODEL UNCERTAINTY AS WELL AS THE DIFFERENCE BETWEEN MODEL AND OBSERVATIONS OF THE PRESENT-DAY INTO THE FUTURE. WE PROPOSE TO USE THESE PROJECTION ASSESSMENTS TO STUDY THE IMPACTS OF SEA LEVEL RISE ON COASTAL POPULATIONS AND INFRASTRUCTURE. SUCH STUDIES CAN ONLY BE CONDUCTED AT LOCATIONS WHERE PRESENT-DAY SEA LEVEL IS ACCURATELY KNOWN RELATIVE TO THE LAND USUALLY AT TIDE GAUGES. HOWEVER THERE ARE MANY LOCATIONS IN THE WORLD WHERE WE HAVE NEITHER TIDE GAUGES OR A PRECISE DIGITAL ELEVATION MODEL (DEM). WE PROPOSE TO USE SATELLITE MEASUREMENTS TO DETERMINE A PRECISE DEM AND PRESENT-DAY RELATIVE MEAN SEA LEVEL FOR THE PURPOSES OF EVALUATING THE IMPACTS OF FUTURE SEA LEVEL RISE. THE PRECISE DEM WILL BE DETERMINED USING STEREO IMAGERY FROM THE WORLDVIEW SATELLITE VIA THE STRUCTURE FROM MOTION (SFM) TECHNIQUE. THIS DEM CAN BE TIED INTO A PRECISE TERRESTRIAL REFERENCE FRAME USING ICESAT (AND SOON ICESAT-2) LASER ALTIMETER MEASUREMENTS. PULSE-LIMITED RADAR ALTIMETRY DOESN T REACH CLOSER TO THE COAST THAT 7-10 KM SO WE WILL ALSO USE ICESAT AND ICESAT-2 MEASUREMENTS TO EXTEND TRADITIONAL MEAN SEA SURFACES UP TO THE COAST. IN THIS WAY WE WILL BE ABLE ESTIMATE PRESENT-DAY MEAN SEA LEVEL RELATIVE TO THE LAND USING ONLY SATELLITE MEASUREMENTS. WE WILL TEST OUR METHODS AT APPROXIMATELY A HALF DOZEN SITES AROUND THE WORLD THAT ARE PARTICULARLY VULNERABLE TO SEA LEVEL CHANGE. IN ORDER TO FULLY UNDERSTAND THE IMPACTS OF FUTURE SEA LEVEL RISE WE ALSO NEED TO UNDERSTAND LOCAL VERTICAL LAND MOTION (VLM). WHILE WE NOW HAVE MAPS OF VLM IN MANY LOCATIONS DETERMINED FROM GLOBAL GNSS NETWORKS AND INSAR IMAGING THESE HAVE BEEN DETERMINED FROM VERY SHORT MEASUREMENT TIME SPANS AND THUS REFLECT MANY DIFFERENT GEOPHYSICAL PROCESSES. FOR LONG-TERM SEA LEVEL PROJECTIONS WE NEED LONG-TERM ESTIMATES OF VERTICAL LAND MOTION (E.G. DUE TO GIA TECTONIC PROCESSES LONG-TERM SUBSIDENCE ETC.) SO THAT WE CAN ESTIMATE HOW MUCH ACCUMULATED LAND MOTION WE MIGHT SEE IN THE FUTURE (2050 2100 ETC.). THEREFORE WE ALSO PROPOSE TO DEVELOP A MODEL (GIA+TECTONICS) OF LONG-TERM VLM FROM THE OBSERVED GNSS AND INSAR VLM RATES. WE ALSO CONTINUE TO PRODUCE REGIONAL VLM ESTIMATES FROM THE AVAILABLE GEODETIC DATA. WE PLAN TO CONDUCT THIS INVESTIGATION IN CONCERT WITH THE NASA SEA LEVEL CHANGE TEAM (N-SLCT) AND MAKE OUR RESULTS AVAILABLE THROUGH THE NASA SEA LEVEL WEB PORTAL.