Remote sensing of the optical and microphysical properties of cirrus clouds using EOS-MODIS channels

Generating global maps that describe the spatial and temporal behavior of the optical and microphysical properties of cirrus clouds can help better characterize the modulation of atmospheric radiation fluxes. In addition, improved knowledge of these properties could provide the basis for the atmospheric correction necessary for the accurate remote sensing of atmospheric and surface constituents.; This dissertation documents the development of a methodology for the remote sensing of cirrus optical depth and mean effective ice crystal size, based on measurements of reflected solar radiation collected by a modern spectroradiometer. The algorithm utilizes lookup tables developed using scattering and radiative transfer methods specifically developed to account for the complex microphysics of cirrus clouds. The retrieved results are validated using concurrent radiometric and microphysical measurements collected during field campaigns targeting cirrus clouds.; The effects of the physical assumptions involving ice crystal microphysics and non-Lambertian surface effects are examined. The microphysical assumptions are found to introduce error bars of approximately 10% and 10–20 μm on the retrieved optical depth and mean effective ice crystal size, respectively. The surface effects are found to have the potential to preclude practical retrievals of thin cirrus properties over complex land surfaces.; Explicit calculations of the emerging cloud base reflectance fields are carried out in order to reduce the uncertainty associated with the variability of the surface reflectance. For ocean surfaces, the anisotropic reflectance is atmospherically corrected using appropriate radiative transfer calculations and the retrieved values of aerosol optical depth based on a simple aerosol microphysical model. For land surfaces, a mosaic of ecosystems is used to compute the anisotropic reflectance associated with the surface terrain variability. We show that using these explicit computations of the emerging cloud base reflectance, thin cirrus optical depth and ice crystal size over ocean surfaces can be retrieved accurately. Moreover, uncertainties in the retrieved optical depth and ice crystal size over complex land surfaces are reduced by 20% and 45%, respectively.