HR: 1340h
AN: A43B-0076    [Abstracts]
TI: An Alternative Algorithm for Ice Cloud Property Retrieval Using NPOESS/VIIRS Data
AU: Han, Q
EM: han@nsstc.uah.edu
AF: University of Alabama in Huntsville, 320 Sparkman Dr., Huntsville, AL 35805 United States
AU: * Welch, R M
EM: welch@nsstc.uah.edu
AF: University of Alabama in Huntsville, 320 Sparkman Dr., Huntsville, AL 35805 United States
AB: The current algorithm for ice cloud property retrieval developed for VIIRS is based on six measured size distributions obtained from aircraft measurements at different regions and seasons (Ou et al. 2003), which is similar to the approach used by MODIS and CERES. These measured size distributions are characterized by one parameter: effective size (diameter or radius). However, it is demonstrated (Han et al. 2005) that the adoption of such measured size distributions leads to inconsistent results in retrieved cloud properties because neglecting the effect of effective variances causes non-monotonic relations between crystal size and single scattering properties. An error of 10 mm in retrieved effective diameter could be resulted in typical cirrus clouds by the ad hoc choice of various measured size distributions. Similar to the cases of spheres (Hansen and Travis 1974) and spheroids (Mishchenko et al. 1996), it is found that single scattering properties of most observed size distributions of hexagonal columns can be adequately characterized by effective radius and effective variance. Therefore, in remote sensing of ice cloud properties, theoretical size distributions with explicitly assumed effective variances should be used, similar to the practice adopted for water clouds. Another issue in ice cloud property retrieval is the various non-spherical shapes of ice crystals. One type of such shapes is pristine columns, plates, and their aggregates and another type is rough surfaced crystal characterized by fractals. There are evidences suggesting regional differences of crystal shapes from aircraft measurements although the dominant crystal shape varies among clouds even within a same region. However, it is not possible in current satellite retrievals to distinguish which type of crystal shape is dominant for a specific scene and therefore it is difficult to know which phase function and single scattering albedo should be used in the retrievals. As a result, different shapes are assumed in satellite retrieval algorithms. For example, the current VIIRS algorithm assumes pristine hexagonal columns, which is different from the algorithm of MODIS that includes specific percentage of different shapes. We have developed an alternative algorithm for ice cloud property retrieval using VIIRS data that is based on theoretical size distributions with explicitly assumed effective variances, in which pristine hexagon and rough surfaced crystals are assumed independently. The practice of assuming a fixed value of ve could be further improved when ve can be retrieved using multi-angle polarized reflectances from upcoming missions like NASA/Glory and NPOESS/APS.
DE: 0319 Cloud optics
DE: 0321 Cloud/radiation interaction
DE: 0360 Radiation: transmission and scattering
DE: 1640 Remote sensing (1855)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005