Cloud Detection and Typing in the NPOESS Era: Addressing the Numerous Operational Requirements with the Single VIIRS Cloud Mask Algorithm

The Visible/Infrared Imager Radiometer Suite (VIIRS) is one of a suite of instruments to be flown on the National Polar-orbiting Operational Environmental Satellite System (NPOESS). The United States is developing NPOESS through the Integrated Program Office (IPO) comprised of the National Oceanic and Atmospheric Administration (NOAA), Department of Defense (DoD), and National Aeronautics and Space Administration (NASA). The first launch of the VIIRS is on the NPOESS Preparatory Project (NPP) mission. VIIRS data will be used to produce 22 Environmental Data Records (EDRs) in an operational environment at weather centrals located at NOAA NESDIS (the National Environmental Satellite, Data, and Information Service), the U.S. Air Force Weather Agency (AFWA), the Naval Oceanographic Office (NAVOCEANO), and the Fleet Numerical Meteorology and Oceanography Center (FNMOC). All VIIRS EDRs will be derived from results created by the single VIIRS Cloud Mask (VCM) algorithm, which has its heritage in the MODIS Cloud Mask Algorithm. The VCM algorithm, however, differs significantly from its heritage algorithm in order to take advantage of the unique spectral data collected by the VIIRS sensor and to exploit advances in cloud detection and typing algorithms developed under the NPOESS program. For example, the dual-gain 412-nm band, originally present for the ocean color algorithm, is used to differentiate between clouds and heavy aerosols and to detect clouds over desert surfaces. In addition, imagery resolution (400-m) bands are nested with radiometry resolution (800-m) bands to allow sub-pixel clouds to be detected and eliminated from ocean surface products during daytime and nighttime conditions. The VCM employs dynamic cloud detection thresholds that vary with satellite-Earth-sun viewing geometry, atmospheric attenuation, and surface background conditions. The VCM also contains a new cloud phase algorithm that not only differentiates between ice and water clouds but also segregates ice clouds into thin, opaque, and overlap cirrus, i.e. lower-level water clouds and higher level thin cirrus clouds existing in the same field of view. In addition, a new approach has been developed to differentiate between clouds and heavy aerosols that typically have been classified as clouds. Finally, geometric cloud shadows are projected onto the Earth's surface to more accurately support the creation of land surface and atmospheric aerosol products. Comparisons between VCM cloud analyses and manually-generated cloud masks suggest that the VCM will satisfy the full range of operational requirements established for the NPOESS program. Pre-launch results obtained with the VCM algorithm have been published extensively in the refereed literature and are highlighted in this presentation.