SATELLITE LASER AND RADAR ALTIMETERS OBSERVING THE POLAR AND SUBPOLAR SEAS NOW PROVIDE AN EXTENSIVE AND ROUTINE MONITORING OF THE SEA ICE COVER SPANNING TWO DECADES. WE ARE MOTIVATED TO USE THESE NOVEL DATA TO PROVIDE NEW INSIGHT INTO THE DYNAMIC AND THERMODYNAMIC CHANGES OCCURRING IN THE ARCTIC SEA ICE COVER TODAY. WE SEEK TO DETERMINE THE DECADAL TRENDS AND INTER-ANNUAL VARIABILITY IN SEA ICE THICKNESS AND VOLUME SO AS TO IMPROVE KNOWLEDGE OF THE COMPLEX RELATIONSHIP BETWEEN THE ICE COVER AND THE POLAR CLIMATE SYSTEM AND TO ENHANCE MODELING CAPABILITIES FOR THE PREDICTION OF FUTURE CHANGE. THE KEY AIM OF THIS PROPOSAL IS TO CREATE A SYNTHESIZED TIME SERIES OF ARCTIC SEA ICE THICKNESS AND VOLUME CHANGE USING MEASUREMENTS COLLECTED BY ICESAT CRYOSAT-2 AND ICESAT-2. WE WILL AUGMENT THIS TIME SERIES WITH COMPLEMENTARY MEASUREMENTS COLLECTED BY THE RADAR ALTIMETER ON-BOARD THE EUROPEAN SENTINEL-3A MISSION. THE PROPOSED INVESTIGATION IS UNIQUE IN ITS SYSTEMATIC APPROACH TO MAPPING THE POLAR SEA ICE THICKNESS DISTRIBUTION UTILIZING A WIDE RANGE OF MULTI-MISSION ALTIMETER DATA AND LINKING TO OTHER REMOTE SENSING INCLUDING AIRBORNE ALTIMETRY FROM OPERATION ICEBRIDGE (OIB) SCATTEROMETER DATA FROM QUIKSCAT AND ASCAT AND EXPANSIVE IN SITU MEASUREMENTS INCLUDING FROM ICE MASS BALANCE BUOYS (IMBS). WE WILL USE THE INDEPENDENT OIB AIRCRAFT OBSERVATIONS AND IMB FIELD MEASUREMENTS TO VALIDATE THE CAPABILITIES OF THE SATELLITE ALTIMETER SYSTEMS AND UNDERSTAND POTENTIAL INTER-SATELLITE BIASES BETWEEN SATELLITE SENSOR TECHNOLOGIES. THE MAJOR FOCUS OF THIS PROJECT IS THE STATE OF THE NORTHERN HEMISPHERE ICE PACK DUE TO ITS INFLUENCE ON THE CLIMATE ECO-SYSTEM AND HUMAN INFRASTRUCTURE OF THE REGION. WE EXPECT OUR KEY ANALYSES TO INCLUDE: (I) AN INTEGRATED TIME-SERIES OF ARCTIC SEA ICE THICKNESS AND VOLUME CHANGE SPANNING TWO DECADES AND AN IMPROVED TRACKING OF THE TRENDS AND VARIABILITY IN THE FIRST-YEAR AND MULTI-YEAR SEA ICE THICKNESS DISTRIBUTIONS. (II) BASIN-SCALE MAPPING OF ARCTIC SEA ICE FREEBOARD THICKNESS AND VOLUME RELEASED ON MONTHLY SEASONAL AND ANNUAL TIME SCALES. (III) NEAR-REAL-TIME MONITORING OF ICESAT-2 SEA ICE FREEBOARD AND THICKNESS SPECIFICALLY DIRECTED TOWARDS OPERATIONAL ACTIVITIES SITUATIONAL AWARENESS SHORT-TERM FORECASTING AND MODEL ASSIMILATION. (IV) DATA PRODUCTS THAT WILL BE MADE PUBLICLY ACCESSIBLE VIA A DEDICATED PROJECT WEBSITE AND DISSEMINATED THROUGH A NATIONAL DATA CENTER SUCH AS THE NATIONAL SNOW AND ICE DATA CENTER (NSIDC). AS PART OF THE PROPOSED RESEARCH WE WILL ALSO CREATE A MODIFIED SNOW DEPTH CLIMATOLOGY UTILIZING NOVEL MEASUREMENTS OF SNOW DEPTH FROM OIB RADAR SYSTEMS COMBINED WITH DIRECT MEASUREMENTS FROM IMBS. THIS SNOW CLIMATOLOGY WILL BE USED TO DERIVE ICE THICKNESS BUT WILL ALSO PROVIDE A NOVEL PRODUCT OF INTEREST TO THE COMMUNITY IN ITS OWN RIGHT. THE RESEARCH PLAN RESPONDS DIRECTLY TO MANY OF THE KEY PROGRAM GOALS ASSOCIATED WITH THE NASA RESEARCH ANNOUNCEMENT OF OPPORTUNITY: A.16 STUDIES WITH ICESAT AND CRYOSAT-2 IN THAT THE PROPOSED RESEARCH SEEKS TO EXPLOIT ICESAT CRYOSAT-2 ICESAT-2 ALTIMETER DATA TO PRODUCE AN LONG TERM INTEGRATED RECORD OF CHANGE FOCUSING ON THE NORTHERN HEMISPHERE ICE PACK OF THE ARCTIC OCEAN. THIS STUDY WILL PROVIDE NEW METRICS AND DATA PRODUCTS AIMED AT UNDERSTANDING THE FACTORS DRIVING CHANGE IN THE ARCTIC CLIMATE SYSTEM AND IMPROVING PREDICTIVE MODEL CAPABILITIES.