SATELLITE OBSERVATIONS ARE AN ESSENTIAL COMPONENT TO THE NASA EARTH SCIENCE PROGRAM WHICH MONITORS AND MODELS THE COMPLEX INTERACTIONS OF THE ATMOSPHERE LAND AND OCEANS. THE LONGTERM ACCURATE MEASUREMENT OF ENVIRONMENTAL PROPERTIES FROM MULTI-PLATFORM AND MULTI-YEAR DATA REQUIRES THAT THE INSTRUMENTS BE CALIBRATED AND THE DATA PRODUCTS BE VALIDATED. THE CALIBRATION OF THESE SENSORS SHOULD BE MONITORED USING INDEPENDENT APPROACHES SO THAT ANY CHANGES CAN BE DISTINGUISHED FROM THOSE THAT MAY OCCUR IN THE ONBOARD CALIBRATION SYSTEM. THE VALIDATION OF DATA PRODUCTS BY INDEPENDENT MEANS IS ALSO CRITICAL TO ENSURE THAT THE ALGORITHMS USED TO CREATE HIGHER-LEVEL DATA PRODUCTS ARE OF THE HIGHEST ACCURACY. THE OBJECTIVE OF THE PROPOSED WORK IS TO CONTINUE MONITORING THE SENSOR CALIBRATION AND SURFACE REFLECTANCE PRODUCTS OF TERRA AND AQUA IMAGING SENSORS USING THE UNIVERSITY OF ARIZONA S RADIOMETRIC CALIBRATION TEST SITE (RADCATS) AT RAILROAD VALLEY NEVADA. A SECOND OBJECTIVE IS TO PERFORM THE CROSS CALIBRATION OF TERRA AND AQUA IMAGING SENSORS WITH SIMILAR EARTH-OBSERVING SYSTEMS. RADCATS IS CURRENTLY BEING USED TO PROVIDE NIST-TRACEABLE RADIOMETRIC CALIBRATION DATA TO A WIDE VARIETY OF EARTH-OBSERVATION SENSORS SUCH AS LANDSAT 7 ETM+ LANDSAT 8 OLI TERRA MODIS MISR AND ASTER AQUA MODIS SNPP VIIRS AND SENTINEL-2A MSI. THE SPATIAL SPECTRAL AND TEMPORAL CHARACTERISTICS OF RAILROAD VALLEY COUPLED WITH THE CURRENT SUITE OF GROUND INSTRUMENTATION MAKES RADCATS WELL-SUITED FOR THE CALIBRATION AND VALIDATION OF SENSORS RANGING FROM MULTISPECTRAL TO HYPERSPECTRAL WITH SPATIAL RESOLUTIONS RANGING FROM 5 1500 M. PREVIOUS NASA FUNDING WAS USED TO PERFORM UPGRADES TO RADCATS WHICH INCLUDED A WIRELESS SATELLITE UPLINK SYSTEM THAT CONNECTS RAILROAD VALLEY DIRECTLY TO THE UNIVERSITY OF ARIZONA. THE AUTOMATED PROCESSING OF RADCATS DATA AND SATELLITE IMAGERY MEANS THAT THE CALIBRATION AND VALIDATION RESULTS ARE AVAILABLE ~2 DAYS AFTER OVERPASS. THE SATELLITE DATA USED FOR CALIBRATION PURPOSES ARE THE LEVEL 1 TOP-OF-ATMOSPHERE RADIANCE PRODUCTS SUCH AS MOD02 IN THE CASE OF MODIS. THE SURFACE REFLECTANCE VALIDATION IS PERFORMED BY COMPARING THE RADCATS MEASUREMENTS WITH THE MOD09 SURFACE REFLECTANCE PRODUCT IN THE CASE OF MODIS. THE INTRINSIC VALUE OF RADCATS IS THE ABILITY TO PROVIDE AN INDEPENDENT ASSESSMENT OF BOTH THE RADIOMETRIC CALIBRATION AND SURFACE REFLECTANCE PRODUCTS OF TERRA AND AQUA IMAGERS USING A MATURE AND WELL-UNDERSTOOD NIST-TRACEABLE METHODOLOGY. THE MEASUREMENTS MADE AT RADCATS THROUGHOUT THE DAY WILL PROVIDE THE MODIS CALIBRATION SCIENCE TEAM AND THE LAND VALIDATION TEAM WITH DATA TO HELP IMPROVE THE CALIBRATION AND ALSO THE ALGORITHMS USED TO CREATE HIGHER-LEVEL PRODUCTS.