THE IDEA OF THE PROPOSED PROJECT IS TO CREATE AN INTEGRATED TIME SERIES OF ALTIMETRY-BASED ELEVATION MODELS STARTING WITH DERIVATION OF HIGH-QUALITY AND HIGH-RESOLUTION ELEVATION FIELDS FROM EXPECTED ICESAT-2 DATA AND LOOKING BACKWARDS FROM EXPERIENCE GAINED WITH ICESAT-2 ALGORITHM DEVELOPMENT AND LIDAR DATA ANALYSIS AT THE PROBLEM OF INTEGRATING THE EXISTING DATA AND FUTURE DATA FROM ICESAT GLAS ICEBRIDGE ATM AND CRYOSAT-2 SIRAL. THE MOTIVATION FOR CENTERING THE PROPOSED WORK AROUND ICESAT-2 IS TWOFOLD: (1) WITH MORE THAN 100 TIMES BETTER SPATIAL RESOLUTION THAN GLAS DATA DATA FROM THE ICESAT-2 ADVANCE TOPOGRAPHIC LASER ALTIMETER SYSTEM (ATLAS) WILL SET THE NEW STANDARD IN SATELLITE ALTIMETRY AND ALLOW TO APPROACH MANY OF THE PROBLEMS IN GLACIOLOGY AND ENERGY BALANCE THAT COULD NOT BE FULLY ADDRESSED USING LOWER-RESOLUTION DATA FROM ICESAT AND CRYOSAT-2 AND (2) THROUGH DEVELOPMENT OF ALGORITHMS FOR ICESAT-2 DATA AND ANALYSIS OF DATA FROM AIRBORNE ATLAS SIMULATOR INSTRUMENTS THE PROPOSAL TEAM HAS GAINED NEW PERSPECTIVES IN LASER ALTIMETRY LEADING TO NEW APPROACHES TO ANALYSIS OF EXISTING GLAS DATA AND ALTIMETER DATA IN GENERAL WHICH ARE AIMED AT FACILITATING INTEGRATION IN TIME SERIES OF ELEVATION AND ELEVATION CHANGE. THE DENSITY-DIMENSION ALGORITHM FOR ICE-SURFACE ANALYSIS (DDA-ICE) DEVELOPED IN OUR GROUP ALLOWS TO ACCURATELY RETRIEVE ICESAT-2 SURFACE HEIGHTS EVEN IN REGIONS OF HEAVY CREVASSING OR FIRN COVER AND UNDER INTERMITTENT CLOUDS AND WILL BE APPLIED TO DERIVE ALONG-TRACK AND GRIDDED ICE-SURFACE HEIGHT FIELDS. ELEVATION ELEVATION CHANGE AND VOLUME CHANGE PRODUCTS WILL BE DERIVED FOR THE GREENLAND AND ANTARCTIC ICE SHEETS THE BERING-BAGLEY GLACIER SYSTEM AND ICELANDIC ICE CAPS. AS ONE OF THE IMBIE SCIENCE TEAMS OUR GROUP WILL PARTICIPATE IN ASSESSMENT OF MASS CHANGE OF THE GREENLAND AND ANTARCTIC ICE SHEETS AND THEIR CONTRIBUTION TO SEA-LEVEL RISE. TO CONTRIBUTE TO OUR COMMUNAL IMPROVED UNDERSTANDING OF MASS BALANCE SURFACE MELTING AND ENERGY FLUXES IN THE CLIMATE SYSTEM SURFACE ROUGHNESS DATA SETS FROM ICESAT-2 DATA FOR THE GREENLAND AND ANTARCTIC ICE SHEETS WILL BE DERIVED AND APPLIED AS NEW CONTROLS FOR THE REGIONAL ATMOSPHERIC CLIMATE MODEL (RACMO). ESTIMATIONS OF MELT ENERGY IN MODELS HAVE BEEN LIMITED TO DATE BECAUSE ENERGY BALANCE CALCULATIONS ARE INFLUENCED BY SURFACE ROUGHNESS WHICH SO FAR HAS BEEN ESTIMATED RATHER THAN MEASURED. IT IS EXPECTED THAT THE ICE-SHEET WIDE SURFACE ROUGHNESS DATA SETS WILL YIELD A SO-FAR MISSING INGREDIENT IN IMPROVED MORE REALISTIC ESTIMATIONS OF SURFACE MASS BALANCE AND ULTIMATELY MASS LOSS FROM THE ICE SHEETS AND CONTRIBUTIONS TO SEA-LEVEL RISE. A SENSITIVITY STUDY OF RESULTS FROM A DYNAMIC ICE SHEET MODEL (ISSM) TO CHANGES IN PRESENT-DAY SURFACE ELEVATION (USING SEVERAL DIFFERENT YEARS OF THE TIME SERIES DERIVED HERE) WILL BE CARRIED OUT TO INVESTIGATE HOW MUCH THE RESULTS OF DYNAMIC ICE SHEET MODELING CHANGE WHEN CONTROLLED BY THE ACTUAL OBSERVED CHANGES IN ICE-SURFACE HEIGHTS DURING THE LAST YEARS (SINCE 2003 AND THROUGH 2019). THE PROPOSED RESEARCH IS DIRECTLY RELEVANT TO ROSES CALL A.16 IN ALL ITS COMPONENTS. RESEARCH GOALS ARE ALSO SHARED WITH THE PROGRAM FOR ASSESSMENT OF REGIONAL CLIMATE CHANGE IN THE ARCTIC (PARCA) THE SURFACE MASS BALANCE AND SNOW ON SEA ICE WORKING GROUP (SUMUP) TO WHOM RESULTANT DATA SETS WILL ALSO BE CONTRIBUTED THE INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (IPCC) THE WORLD CLIMATE RESEARCH PROGRAMME (WCRP) ESPECIALLY CLIMATE AND CRYOSPHERE (CLIC) WITH THE INTERAGENCY ARCTIC POLICY COMMITTEE (IARPC) AND US CLIVAR.