HR: 1330h
AN: H32B-0558    [PDF]
TI: Improved Nighttime and Twilight Polar Cloud Detection Algorithms Using Terra and Aqua Observations
AU: * Trepte, Q Z
EM: q.z.trepte@larc.nasa.gov
AF: SAIC, One Enterprise Parkway, Suite 300, Hampton, VA 23666 United States
AU: Minnis, P
EM: p.minnis@nasa.gov
AF: Atmospheric Sciences Competency, MS 420, NASA Langley Research Center, Hampton, VA 23681 United States
AU: Spangenberg, D A
EM: d.a.spangenberg@larc.nasa.gov
AF: AS\&M, One Enterprise Parkway, Suite 300, Hampton, VA 23666 United States
AB: The Arctic and Antarctic regions play important roles in the global climate system. Accurate detection of clouds over snow and ice surfaces using satellite radiance observations is a crucial first step in determining surface and top-of-atmosphere radiative fluxes. Scene identification during polar nighttime and twilight is challenging, in part, due to the lack of brightness temperature contrast between clouds and surface properties and by the sensitivity of algorithms to large reflectance uncertainties in twilight conditions. Measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA's Terra and Aqua satellites provide valuable new spectral information and enhanced spatial and temporal resolution to study clouds and the surface energy balance at high latitudes. The Clouds and Earth's Radiant Energy System (CERES) nighttime and twilight polar cloud masks were developed and further improved using the MODIS observed Brightness Temperature Differences (BTD) of 3.7 and 11 micron, 3.7 and 12 micron, 6.7 and 11 micron, 8.5 and 11 micron, and 11 and 12 micron. The algorithms use these BTDs, which are combined with other ancillary information such as snow and ice maps from the National Snow and Ice Data Center to determine the presence of snow and ice surfaces. Special sets of tests are applied for regions with very cold surface skin temperatures (i.e., Greenland and the Antarctic plateau). MODIS frequently observes the Earth in "twilight" conditions at high latitudes, especially during spring and autumn seasons. The twilight cloud detection scheme utilizes the reflected solar components at 1.6, 2.1 and 3.75 micron in addition to the BTDs. Comparison of the results from the improved nighttime and twilight polar cloud masks with the Micropulse Lidar (MPL) observations at South Pole and Barrow, Alaska shows good agreement.
DE: 1863 Snow and ice (1827)
DE: 3309 Climatology (1620)
DE: 3349 Polar meteorology
DE: 3360 Remote sensing
DE: 4207 Arctic and Antarctic oceanography
SC: Hydrology [H]
MN: 2003 Fall Meeting