RELIABLE AND ROBUST MONITORING OF SNOW WATER EQUIVALENT AND SNOW DEPTH REMAIN AS IMPORTANT CHALLENGES IN EARTH REMOTE SENSING. EXISTING METHODS USING MICROWAVE RADIOMETRY OR RADAR FACE LIMITATIONS WITH REGARD TO THE SPATIAL RESOLUTION ACHIEVED AND/OR IN TERMS OF THE RANGE OF SNOW DEPTHS THAT CAN BE OBSERVED. THE INFLUENCE OF SCATTERING FROM SNOW GRAINS AND OTHER DENSITY VARIATIONS WITHIN THE SNOWPACK ALSO COMPLICATES THE GEOPHYSICAL RETRIEVAL PROCESS FROM BACKSCATTER OR BRIGHTNESS TEMPERATURE OBSERVATIONS ESPECIALLY THOSE AT X-BAND OR HIGHER FREQUENCIES. THE RECENT DEVELOPMENT OF ULTRA-WIDEBAND MICROWAVE RADIOMETRY AT LOWER FREQUENCIES FROM ~ 500 MHZ TO ~ 2 GHZ MAY OFFER NEW OPPORTUNITIES TO ADDRESS SOME OF THE LIMITATIONS ENCOUNTERED BY CURRENT METHODS. THE USE OF LOWER FREQUENCIES ELIMINATES THE INFLUENCE OF SCATTERING FROM SNOW GRAINS AND THE USE OF MULTIPLE FREQUENCIES ENABLES THE SEARCH FOR OSCILLATORY FEATURES IN THE BRIGHTNESS TEMPERATURE VERSUS FREQUENCY THAT STRONGLY CORRELATE TO SNOW DEPTH AND SNOW WATER EQUIVALENT. SYSTEMS CAPABLE OF PERFORMING SUCH MEASUREMENTS HAVE BEEN DEVELOPED UNDER PAST NASA INSTRUMENT INCUBATOR PROGRAM SUPPORT FOR OTHER APPLICATIONS BUT THEIR USE FOR SNOW REMOTE SENSING HAS YET TO BE DEMONSTRATED EXTENSIVELY. THE PROPOSED PROJECT WILL PERFORM A DETAILED STUDY OF THE USE OF ULTRA-WIDEBAND MICROWAVE RADIOMETRY FROM 0.5-2 GHZ FOR SNOW PARAMETER SENSING THROUGH BOTH MODELING AND MEASUREMENT ACTIVITIES. MODELING ACTIVITIES WILL EXTEND AVAILABLE DESCRIPTIONS OF MICROWAVE THERMAL EMISSION AT 0.5-2 GHZ FROM SNOW MEDIA TO INCLUDE INTERFACE ROUGHNESS AND VEGETATION CONTRIBUTIONS AND WILL INVESTIGATE THE SENSITIVITIES TO SNOW PROPERTIES THAT ARE ACHIEVED THROUGH THE COMBINATION OF MULTIPLE FREQUENCY OBSERVATIONS. THE PROJECT WILL THEN DEMONSTRATE SNOW PROPERTY SENSING EXPERIMENTALLY USING THE EXISTING ULTRA-WIDEBAND SOFTWARE-DEFINED MICROWAVE RADIOMETER (UWBRAD) AND WIDEBAND AUTOCORRELATING RADIOMETER (WIBAR) 0.5-2 GHZ SYSTEMS IN BOTH GROUND AND POTENTIALLY AIRBORNE CAMPAIGNS. THE LATTER WILL BE ACCOMPLISHED THROUGH COLLABORATION WITH FUTURE SNOWEX CAMPAIGN PHASES IN THE 2019-2020 SEASON AND WILL LEVERAGE THE EXTENSIVE GROUND TRUTHING ACTIVITIES OF THE CAMPAIGN. THE PROJECT'S OUTCOME WILL PROVIDE AN ALTERNATIVE SENSOR FOR SNOW PROPERTY SENSING THAT POTENTIALLY WILL EXPAND SNOW REMOTE SENSING CAPABILITIES AND WILL PROVIDE COMPLEMENTARY INFORMATION THAT CAN AUGMENT THE MEASUREMENTS ACHIEVED FROM OTHER METHODS.