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For inferring cirrus optical and microphysical properties from satellite imagery, a common assumption is that
the radiative properties of a cirrus cloud may be represented by those associated with a specific ice crystal habit, a single
particle size distribution and Ice Water Content (IWC). Various algorithms have been developed to retrieve cirrus optical
and microphysical properties in the past 20 years. They can be categorized into the techniques based on either thermal
infrared or solar reflection measurements. However, in-situ measurements have shown that shapes, sizes and IWC of ice
crystals may vary substantially with height within the clouds. Given the different sensitivity of thermal infrared and solar
wavelength to cloud microphysics, it is unlikely that a single cloud layer with homogeneous cloud properties can be used
to reproduce both type of measurements. Thus, it is necessary to assess the effect of vertical inhomogeneity within cirrus
on the radiative transfer calculations and on the retrieval techniques.
The purpose of this study is to investigate a microphysical cirrus model composed of different layers in terms of
ice crystal habit, size and IWC. The vertical structure will be given by simple analytic formula derived from various
prescribed physical constraints. The primary goal of this study is to determine a simple cloud model that can be used to
retrieve consistent information from both solar and thermal measurements. For this purpose, we examine the sensitivity
of cirrus reflectances and brightness temperature to its vertical description for a suite of MODIS (MODerate-resolution
Imaging Spectroradiometer) bands spanning visible, near infrared and thermal infrared wavelengths. Results of this study
are presented and potential application to remote sensing of cirrus clouds with MODIS are discussed.
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