Calibration of the DSCOVR EPIC visible and NIR channels using multiple satellite data

WE PROPOSE TO IMPROVE DSCOVR EPIC CALIBRATION USING MEASUREMENTS OF THE EARTH AND THE MOON FOR COMPARISON WITH DATA FROM SEVERAL EARTH- AND MOON-OBSERVING SATELLITES. THE RESULT WILL PROVIDE A VALIDATED ABSOLUTE AND RELATIVE RADIOMETRIC CALIBRATION OF EACH CHANNEL REQUIRED FOR THE L2 EPIC PRODUCTS. FOR CERTAIN REMOTE SENSING APPLICATIONS SEVERAL CHARACTERISTICS OF THE EPIC INSTRUMENT MAY BE DESIRABLE. THESE INCLUDE FREQUENT SAMPLING OF THE ENTIRE SUNLIT HEMISPHERE ALMOST BACK SCATTERING EARTH-OBSERVING GEOMETRY IMPROVED COVERAGE AT HIGH LATITUDES AND THE LACK OF SHADOWS. EPIC L2 PRODUCTS SUCH AS AEROSOL AND CLOUD PROPERTIES OZONE AND SULFUR DIOXIDE AMOUNTS AS WELL AS VEGETATION PROPERTIES DEPEND ON THE ACCURATE RADIOMETRIC CALIBRATION OF THE INSTRUMENT CHANNELS. THE EPIC INSTRUMENT DOES NOT HAVE IN-FLIGHT CALIBRATION CAPABILITIES MAKING IT NECESSARY TO DETERMINE THE CALIBRATION COEFFICIENTS AND MONITOR THEIR STABILITY BY MEANS OF VICARIOUS CALIBRATION TECHNIQUES. ONE APPROACH IS TO COMPARE EPIC OBSERVATIONS WITH THE MEASUREMENTS FROM POLAR ORBITING RADIOMETERS. ANOTHER ONE IS TO USE THE IMAGES OF THE MOON REGULARLY CAPTURED BY THE INSTRUMENT. MODIS L1B 1KM REFLECTANCES WERE SUCCESSFULLY USED BY THE PI TO DERIVE THE CALIBRATION COEFFICIENTS FOR FOUR EPIC VISIBLE AND NIR CHANNELS (443 551 680 AND 780 NM). FULL-MOON EPIC OBSERVATIONS WERE THEN USED TO CALIBRATE THE EPIC RADIANCES IN O2 ABSORBING BANDS AT 688 AND 764 NM. THE FORTHCOMING THIRD RELEASE OF EPIC DATA WILL CONTAIN A NUMBER OF OPTICAL CORRECTIONS AND IMPROVED GEOLOCATION. IN ORDER FOR THESE ADVANCES TO YIELD MORE ACCURATE L2 PRODUCTS CONCURRENT IMPROVEMENTS IN RADIOMETRIC CALIBRATION ARE REQUIRED. WE SUBMIT THAT SUCH IMPROVEMENTS MAY BE ACHIEVED USING DATA FROM MULTIPLE LOW EARTH ORBIT (LEO) INSTRUMENTS. EPIC S SUNRISE-TO-SUNSET COVERAGE MAKES IT UNIQUELY SUITABLE FOR COMPARISON WITH MEASUREMENTS MADE BY LEO INSTRUMENTS. DATA FROM A NUMBER OF CURRENTLY OPERATIONAL INSTRUMENTS CAN BE EMPLOYED FOR THIS PURPOSE. THUS WE PROPOSE TO EXTEND THE EPIC CALIBRATION PROCEDURE TO EXPLOIT OTHER CURRENTLY OPERATING EARTH-VIEWING INSTRUMENTS SUCH AS SUOMI NPP VIIRS MISR OCO2 GOME-2 AND GOSAT. THIS WILL ENABLE US TO VALIDATE THE CURRENT CALIBRATION IMPROVE ITS ACCURACY BY EMPLOYING A LARGER VOLUME OF MEASUREMENTS FOR ANALYSIS AND MONITOR STABILITY. WE WILL BEGIN BY IDENTIFYING FAVORABLE MATCHING MEASUREMENTS THAT MEET THE CRITERIA OF BEING SPATIALLY AND TEMPORALLY COLLOCATED AND HAVING THE SAME SCATTERING GEOMETRY. TO MATCH EPIC SPECTRAL CHANNELS SPECTRAL CORRECTIONS WILL THEN BE APPLIED BASED ON THE SCENE TYPE. THE SELECTED MATCHING OBSERVATIONS WILL BE STATISTICALLY ANALYZED TO OBTAIN IMPROVED CALIBRATION COEFFICIENTS. WE WILL EXPLORE THE POSSIBILITIES OF USING UNIQUE FEATURES OF THE ABOVE INSTRUMENTS TO IMPROVE EPIC CALIBRATION. THESE INCLUDE A WIDER SWATH FOR VIIRS AND A GREATER NUMBER OF OBSERVATION GEOMETRIES FOR MISR MATCHING O2-ABSORPTION BANDS AND SPECTRALLY RESOLVED INFORMATION FOR OCO-2 GOME-2 AND GOSAT. THE USE OF MULTIPLE INSTRUMENTS WILL ENABLE US TO PERFORM A CROSS-CHANNEL VALIDATION OF THE CALIBRATION COEFFICIENTS. IN ADDITION THE SYNERGISTIC EFFECT OF USING MULTIPLE INSTRUMENTS FOR ANALYSIS WILL IMPROVE THE ROBUSTNESS OF THE DEVELOPED CALIBRATION. FURTHERMORE WE PROPOSE TO EXPLORE THE POSSIBILITY OF USING REGULAR EPIC LUNAR VIEWS IN COMBINATION WITH LRO LUNAR IMAGES TO DERIVE AN INDEPENDENT SET OF CALIBRATION COEFFICIENTS FOR MATCHING CHANNELS IN PARTICULAR FOR THE 688NM O2-ABSORPTION BAND. THIS WORK WILL RESULT IN NEW AND IMPROVED CALIBRATION VALUES FOR THE EPIC SPECTRAL CHANNELS WHICH IS EXPECTED TO BENEFIT MULTIPLE EPIC L2 PRODUCTS.