TODAY THE SPACEBORNE L BAND RADIOMETERS SMOS AND SMAP PROVIDE PARTIAL ICE SHEET INTERNAL TEMPERATURE INFORMATION THROUGH THEIR SINGLE FREQUENCY MEASUREMENTS. UNDER THE RECENT NASA INSTRUMENT INCUBATOR PROGRAM (2014-2017) THE ULTRA-WIDEBAND SOFTWARE- DEFINED MICROWAVE RADIOMETER (UWBRAD) HAS BEEN DEVELOPED TO ALLOW ICE SHEET INTERNAL TEMPERATURES MEASUREMENTS AT DEPTHS OF HUNDREDS OF METERS OR MORE. IN CONTRAST TO SMOS AND SMAP UWBRAD IS A WIDEBAND RADIOMETER OPERATING FROM 0.5 TO 2GHZ USING 12 FREQUENCY CHANNELS. THE USE OF MULTIPLE FREQUENCIES IN UWBRAD IS INTENDED TO RESOLVE AMBIGUITIES IN TEMPERATURE RETRIEVALS ASSOCIATED WITH SINGLE FREQUENCY MEASUREMENTS. THE WIDEBAND DATA WILL ENHANCE THE RESEARCH COMMUNITY S ABILITY TO DETERMINE THE EASE AT WHICH ICE DEFORMS INTERNALLY THE RATE AT WHICH AN ICE SHEET FLOWS ACROSS ITS BASE THE MONITORING OF AQUIFERS TO COMPILE MEAN ANNUAL TEMPERATURES AND TO MONITOR CLIMATE CHANGE. THE UWBRAD INSTRUMENT WAS INSTALLED ON A TOWER AT DOME C ANTARCTICA IN 2015 AND WAS DEPLOYED DURING A 2016 AIRBORNE CAMPAIGN OVER GREENLAND WITH A SECOND FLIGHT PLANNED IN 2017. THE RESULTS FROM THE 2016 FLIGHT REVEAL STRONG SPATIAL AND SPECTRAL VARIATIONS THAT CORRELATE WITH THE SUBSURFACE PHYSICAL PROPERTIES OF THE GREENLAND ICE SHEET. BASED ON THESE FINDINGS THIS PROPOSAL WILL ADVANCE CURRENT UNDERSTANDING OF WIDEBAND MEASUREMENTS BY (I) INVESTIGATING NOVEL COMBINATIONS OF UWBRAD DATA WITH COMPLEMENTARY ACTIVE AND PASSIVE DATA FOR DEVELOPING A SUBSURFACE TEMPERATURE PRODUCT OF ICE SHEETS AND (II) STUDYING THE USE OF UWBRAD DATA WITH OTHER ACTIVE AND PASSIVE DATA FOR THE DETERMINATION OF SEA ICE THICKNESS. THE PROPOSED PROJECT TEAM HAS PREVIOUSLY PERFORMED PHYSICAL MODELLING STUDIES OF UWBRAD MEASUREMENTS. THESE STUDIES HAVE SHOWN SIGNIFICANT INFLUENCE FROM DENSITY FLUCTUATIONS NEAR THE SURFACE OF THE ICE SHEET ON ICE SHEET EMISSION AS WELL AS THE INFLUENCE OF ICE-LENS STRUCTURES IN THE UPPER FIRN ON THE MEASURED BRIGHTNESS SPECTRUM. BASED ON THESE DEVELOPMENTS AND FINDINGS WE PROPOSE TO: 1.DEVELOP PHYSICAL MODELS OF LAYERING AND VOLUME SCATTERING FOR COMBINED ACTIVE AND PASSIVE MICROWAVE OBSERVATIONS OF THE GREENLAND ICE SHEETS FROM 0.5 GHZ TO C BAND. THE ACTIVE DATA INCLUDE PALSAR SENTINEL AND ARCHIVED AQUARIUS. WE WILL ALSO USE AVAILABLE AIRBORNE RADAR DATA FROM OPERATION ICEBRIDGE (COLLECTED BY THE UNIVERSITY OF KANSAS) WHICH OPERATES OVER A FREQUENCY RANGE SIMILAR TO UWBRAD. THE PASSIVE DATA INCLUDE UWBRAD SMOS SMAP AND ARCHIVED AQUARIUS. 2. DEVELOP THE PHYSICAL MODELS TO INCORPORATE SURFACE AND INTERNAL INTERFACE ROUGHNESS EFFECTS.3.APPLY THE MODELS DEVELOPED TO ANALYZE UWBRAD AIRBORNE DATA COLLECTED OVER GREENLAND AS WELL AS SPACEBORNE ACTIVE AND PASSIVE OBSERVATIONS OF THE GREENLAND ICE SHEET. 4.APPLY THE MODELS DEVELOPED TO ANALYZE UWBRAD AND DOMEX TOWER-BASED BRIGHTNESS TEMPERATURES AT DOME C ANTARCTICA AS WELL AS SPACEBORNE ACTIVE AND PASSIVE OBSERVATIONS OF ANTARCTICA.5.APPLY THE DEVELOPED MODELS TO THE RETRIEVAL OF SUBSURFACE PROPERTIES INCLUDING ICE SHEET TEMPERATURES AND PERFORM SCIENCE ANALYSES TO EXPLORE THE SIGNIFICANCE OF THE RESULTING TEMPERATURE INFORMATION.6.APPLY THE DEVELOPED MODELS TO THE PREDICTION OF ACTIVE AND PASSIVE MULTI-FREQUENCY SIGNATURES OF SEA ICE AND INVESTIGATE THE RETRIEVAL OF SEA ICE THICKNESS INFORMATION. ACHIEVING THESE SCIENCE GOALS WILL IMPROVE OUR ABILITY TO RETRIEVE USEFUL GEOPHYSICAL INFORMATION ABOUT POLAR ICE SHEETS FROM PRESENT SMOS AND SMAP BRIGHTNESS TEMPERATURES THE EXISTING AND FORTHCOMING UWBRAD BRIGHTNESS SPECTRUM MEASUREMENTS AND FROM ACTIVE RADAR SIGNATURES. IT WILL FURTHER EXPLOIT THE WIDE BAND RADIOMETRY OF UWBRAD AND OTHER ACTIVE AND PASSIVE SENSOR MEASUREMENTS TO RETRIEVE SEA ICE THICKNESS. IT WILL ENHANCE THE TECHNOLOGY READINESS OF WIDEBAND PASSIVE MEASUREMENTS FOR SPACEBORNE MISSIONS. IT WILL FURTHER PROMOTE UNDERSTANDING AND CHARACTERIZATION OF THE EFFECTS OF GLOBAL CLIMATE CHANGE THROUGH THE SCIENCE PRODUCTS PRODUCED.