Abstract
The Committee on Earth Observation Satellites (CEOS) recommended Pseudo-Invariant Calibration Sites (PICS) are stable ground-based calibration targets suitable for post-launch radiometric calibration of satellite sensors. The Sonoran Desert is one of the most utilized PICS in the Western Hemisphere that exhibits minimal spatial and temporal variations with a high degree of reflectivity. The site is located within the field-of-view of both the GOES-East and West Imagers. As such, the site is utilized by NASA’s Clouds and the Earth’s Radiant Energy System (CERES) project to monitor the temporal stability of GOES sensors as well as to uniformly scale them to a common radiometric scale using a daily exo-atmospheric radiance model (DERM). The Sonoran Desert DERM is constructed using multi-year clear-sky measurements acquired by a reference GOES instrument that is radiometrically scaled to a well-calibrated sensor, such as MODIS, via direct ray-matching inter-calibration method. The DERM coefficients are then utilized to transfer the MODIS calibration to target GOES sensors located at the same equatorial longitude domain. The flux data provided by the stable GOES imager record combined with CERES measurements can be used to better understand how clouds and regional fluxes vary over time and help in computing the daily average over the CERES record. The current DERM methodology relies on the assumption that the atmospheric column over the PICS is mostly invariant from year to year. The inter-annual variability of the seasonal cycle of aerosols, water vapor burden, and ozone are caused by ENSO events and other factors. This study aims to improve the accuracy of the Sonoran Desert DERM by correlating the observed inter-annual and intra-annual reflectance variability of PICS with atmospheric parameters, such as precipitable water, ozone concentration, surface pressure, etc. The study will also explore improved clear-sky filtering over the PICS utilizing multi-channel radiance information. The study focuses on the characterization of the Sonoran Desert with MODIS using similar angle conditions as GOES and validates the MODIS Sonoran reflectance variability with GOES reflectance variability. The enhanced characterization of the Sonoran Desert will ultimately improve the calibration consistency of the GOES imagers, and thereby, produce more reliable CERES SYN1deg product geostationary derived clouds and fluxes for climate research and modeling.
Enhanced Radiometric Characterization of Sonoran PICS for Vicarious Calibration of GOES Imagers
The Committee on Earth Observation Satellites (CEOS) recommended Pseudo-Invariant Calibration Sites (PICS) are stable ground-based calibration targets suitable for post-launch radiometric calibration of satellite sensors. The Sonoran Desert is one of the most utilized PICS in the Western Hemisphere that exhibits minimal spatial and temporal variations with a high degree of reflectivity. The site is located within the field-of-view of both the GOES-East and West Imagers. As such, the site is utilized by NASA’s Clouds and the Earth’s Radiant Energy System (CERES) project to monitor the temporal stability of GOES sensors as well as to uniformly scale them to a common radiometric scale using a daily exo-atmospheric radiance model (DERM). The Sonoran Desert DERM is constructed using multi-year clear-sky measurements acquired by a reference GOES instrument that is radiometrically scaled to a well-calibrated sensor, such as MODIS, via direct ray-matching inter-calibration method. The DERM coefficients are then utilized to transfer the MODIS calibration to target GOES sensors located at the same equatorial longitude domain. The flux data provided by the stable GOES imager record combined with CERES measurements can be used to better understand how clouds and regional fluxes vary over time and help in computing the daily average over the CERES record. The current DERM methodology relies on the assumption that the atmospheric column over the PICS is mostly invariant from year to year. The inter-annual variability of the seasonal cycle of aerosols, water vapor burden, and ozone are caused by ENSO events and other factors. This study aims to improve the accuracy of the Sonoran Desert DERM by correlating the observed inter-annual and intra-annual reflectance variability of PICS with atmospheric parameters, such as precipitable water, ozone concentration, surface pressure, etc. The study will also explore improved clear-sky filtering over the PICS utilizing multi-channel radiance information. The study focuses on the characterization of the Sonoran Desert with MODIS using similar angle conditions as GOES and validates the MODIS Sonoran reflectance variability with GOES reflectance variability. The enhanced characterization of the Sonoran Desert will ultimately improve the calibration consistency of the GOES imagers, and thereby, produce more reliable CERES SYN1deg product geostationary derived clouds and fluxes for climate research and modeling.