| Autor: |
Meyer K; Goddard Earth Sciences Technology and Research (GESTAR) Universities Space Research Association, Columbia, Maryland, USA.; NASA Goddard Space Flight Center, Greenbelt, Maryland, USA., Platnick S; NASA Goddard Space Flight Center, Greenbelt, Maryland, USA., Arnold GT; Science Systems and Applications, Inc., Lanham, Maryland, USA.; NASA Goddard Space Flight Center, Greenbelt, Maryland, USA., Holz RE; Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin - Madison, Madison, Wisconsin, USA., Veglio P; Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin - Madison, Madison, Wisconsin, USA., Yorks J; NASA Goddard Space Flight Center, Greenbelt, Maryland, USA., Wang C; Earth System Science Interdisciplinary Center, University of Maryland - College Park, College Park, Maryland, USA. |
| Abstrakt: |
Previous bi-spectral imager retrievals of cloud optical thickness (COT) and effective particle radius (CER) based on the Nakajima and King (1990) approach, such as those of the operational MODIS cloud optical property retrieval product (MOD06), have typically paired a non-absorbing visible or near-infrared wavelength, sensitive to COT, with an absorbing shortwave or midwave infrared wavelength sensitive to CER. However, in practice it is only necessary to select two spectral channels that exhibit a strong contrast in cloud particle absorption. Here it is shown, using eMAS observations obtained during NASA's SEAC 4 RS field campaign, that selecting two absorbing wavelength channels within the broader 1.88 μm water vapor absorption band, namely the 1.83 and 1.93 μm channels that have sufficient differences in ice crystal single scattering albedo, can yield COT and CER retrievals for thin to moderately thick single-layer cirrus that are reasonably consistent with other solar and IR imager-based and lidar-based retrievals. A distinct advantage of this channel selection for cirrus cloud retrievals is that the below-cloud water vapor absorption minimizes the surface contribution to measured cloudy TOA reflectance, in particular compared to the solar window channels used in heritage retrievals such as MOD06. This reduces retrieval uncertainty resulting from errors in the surface reflectance assumption, as well as reduces the frequency of retrieval failures for thin cirrus clouds. |
