THE NATIONAL ACADEMIES 2018 DECADAL SURVEY FOR EARTH SCIENCE THRIVING ON OUR CHANGING PLANET IDENTIFIES IMAGING SPECTROSCOPY AS A NECESSARY MEASUREMENT TO ADDRESS A MOST IMPORTANT OBJECTIVE FOR THE HYDROLOGIC CYCLE: "QUANTIFY RATES OF SNOW ACCUMULATION SNOWMELT ICE MELT AND SUBLIMATION FROM SNOW AND ICE WORLDWIDE AT SCALES DRIVEN BY TOPOGRAPHIC VARIABILITY." MEETING THIS OBJECTIVE REQUIRES THE ABILITY TO MEASURE SNOW ALBEDO AND UNDERSTAND HOW AND WHY IT VARIES ESPECIALLY IN THE WORLD'S MOUNTAINS WHICH COMPRISE A QUARTER OF THE WORLD'S LAND AREA BUT PRODUCE AT LEAST HALF OF THE RUNOFF. THE EUROPEAN SPACE AGENCY HAS SELECTED A CANDIDATE SENSOR TO ADDRESS THESE NEEDS. THE COPERNICUS HYPERSPECTRAL IMAGING MISSION FOR THE ENVIRONMENT (CHIME) IS IN PHASE B1 WITH SPATIAL RESOLUTION OF 20 TO 30 M SPECTRAL COVERAGE FROM 400 TO 2500 NM AT RESOLUTION OF 10 NM OR LESS REVISIT INTERVAL OF 10 TO 12 DAYS 10:30 EQUATOR CROSSING TIME LAUNCH 2026. THE PROPOSED INVESTIGATION WILL ADDRESS THE CAPABILITY OF CHIME TO TACKLE THE FOLLOWING QUESTIONS AND HELP DEVELOP APPROPRIATE LEVEL 2 PRODUCTS. EXPERIENCE AND CROSS-VALIDATION WOULD BENEFIT THE DEVELOPMENT OF NASA S SURFACE BIOLOGY AND GEOLOGY DESIGNATED OBSERVABLE AND SHORTEN THE REVISIT INTERVAL. Q1. HOW DOES SENSITIVITY OF IMAGING SPECTROSCOPY RETRIEVALS OF SNOW AND GLACIER PROPERTIES IN THE MOUNTAINS VARY DEPENDING ON THE SOLUTION METHOD FOR THE INVERSION AND THE ATMOSPHERIC CORRECTION? Q2. HOW DO SNOW SPECIFIC SURFACE AREA RADIATIVE FORCING BY LIGHT-ABSORBING PARTICLES AND SNOW ALBEDO VARY SPATIALLY SEASONALLY AND INTERANNUALLY IN THE WORLD'S MOUNTAINS? Q3. HOW CAN A FUSION OF SPECTROSCOPY DATA WITH MORE FREQUENT AND BROADER COVERAGE FROM MULTISPECTRAL SENSORS ENABLE CHARACTERIZATION OF THE SNOW AND ICE PROPERTIES AND RADIATIVE FORCING OVER LARGER AREAS AND ACROSS SEASONS AND YEARS? THE CORRESPONDING OBJECTIVES ARE: O1. USE CHIME S SURFACE REFLECTANCE PRODUCTS CORRECTED FOR TOPOGRAPHY TO INVERT THE SIGNAL FOR RETRIEVAL OF SNOW PROPERTIES AND THEREBY INFORM ESA OF FEASIBLE LEVEL 2 PRODUCTS FOR SNOW AND GLACIER PROPERTIES. O2. PRE-LAUNCH ANALYZE SPATIAL VARIABILITY OF SNOW SPECIFIC SURFACE AREA RADIATIVE FORCING BY DUST CARBON AND ORGANIC MATERIAL AND RESULTING SNOW AND ICE ALBEDO USING AVAILABLE DATA FROM AIRBORNE SPECTROMETERS. POST-LAUNCH PLAN SIMILAR ANALYSES GLOBALLY IN REPRESENTATIVE MOUNTAIN RANGES. O3. EXAMINE FUSION OF QUANTITATIVE IMAGING SPECTROSCOPY RETRIEVALS TO ENHANCE SEMI-QUANTITATIVE RETRIEVALS FROM MULTISPECTRAL LANDSAT 8/9 OLI AND SENTINEL-2A/B MSI DATA FOR GREATER SPATIAL AND TEMPORAL COVERAGE. THE FORWARD PROBLEM ESTIMATING SNOW SPECTRAL REFLECTANCE BASED ON PROPERTIES OF THE SNOWPACK BENEFITS FROM INSIGHTFUL RESEARCH AND OBSERVATION STRETCHING BACK SIX DECADES. THE INVERSE PROBLEM USING SPACEBORNE REMOTE SENSING TO RETRIEVE THE SNOW PROPERTIES THAT GOVERN ALBEDO HAS SEEN FEWER CONVINCING RESULTS IN MOUNTAINOUS REGIONS WITH OFTEN DISCONTINUOUS SNOW LOCAL AND LONG-DISTANCE TRANSPORT AND DEPOSITION OF LIGHT ABSORBING PARTICLES AND FORESTS AND TOPOGRAPHY THAT SHELTER AND OBSCURE THE SNOW. THE PROPOSED ALGORITHMIC APPROACH TREATS THE SNOW PROPERTIES AS A CONTINUUM AND THE RADIATIVE TRANSFER MODELS ARE INVERTED TO SOLVE FOR A SET OF UNKNOWNS THAT INCLUDE FRACTIONAL SNOW COVER SPECIFIC SURFACE AREA OF THE SNOW AND THE CONCENTRATION SIZE AND OPTICAL PROPERTIES OF LIGHT ABSORBING PARTICLES ACCOUNTING FOR TOPOGRAPHIC VARIABILITY. IN MOST SNOW-DOMINATED ENVIRONMENTS NET SOLAR RADIATION DRIVES MELT AND METAMORPHISM OF SNOW. IN MODELING THESE PROCESSES INACCURACY IN THE ESTIMATION OF SNOW ALBEDO CONSTITUTES THE MAJOR SOURCE OF UNCERTAINTY IN CALCULATING THE SNOWPACK S ENERGY BALANCE. THAT LACK OF KNOWLEDGE PROPAGATES TO UNCERTAINTY IN FORECASTING RUNOFF ANALYZING ECOHYDROLOGICAL PROCESSES ESTIMATING MELT RATE AND DETERMINING WHEN THE SEASONAL SNOW COVER MELTS TO EXPOSE DARKER GLACIER ICE IN THE ABLATION ZONES OF GLACIERS.