Cirrus Cloud Optical Thickness from Reflectance Measurements in the MODIS 1.38-mu m Channel
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Cirrus cloud radiative properties are derived using reflectance measurements in the "cirrus detection" channel, centered at 1.38-um, of the Moderate-resolution Imaging Spectroradiometer (MODIS). The 1.38-um channel is located within a spectral region of strong water vapor absorption; thus, under many circumstances, measured reflectance within this channel is solely attributable to ice clouds (e.g., cirrus). Following a look-up table approach, a new method has been developed to derive cirrus cloud optical thickness on a global scale from reflectance measurements in the 1.38-um channel. The pre-calculated look-up tables are constructed from forward radiative transfer calculations using the discrete-ordinates radiative transfer (DISORT) method coupled with the new bulk-scattering properties of ice clouds developed for the Collection 005 MODIS cloud product (MOD06). An analysis of the various 1.38-um based cirrus retrievals follows. Rigorous forward modeling of realistic cloud scenarios facilitates the establishment of uncertainty estimates for each retrieval technique. It has been found that relatively large uncertainties can result from inadequate knowledge of the cloud microphysics (i.e., ice particle effective size). 2009 American Institute of Physics.
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CURRENT PROBLEMS IN ATMOSPHERIC RADIATION (IRS 2008): Proceedings of the International Radiation Symposium (IRC/IAMAS)
