Satellite-based remote sensing of cirrus clouds: hyperspectral radiative transfer modeling, analysis of uncertainties in in-situ cloud extinction measurements and intercomparison of cirrus retrievals from a-train instruments

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Title: Satellite-based remote sensing of cirrus clouds: hyperspectral radiative transfer modeling, analysis of uncertainties in in-situ cloud extinction measurements and intercomparison of cirrus retrievals from a-train instruments
Author: Zhang, Zhibo
Abstract: This dissertation consists of three parts , each devoted to a particular issue of significant importance for satellite -based remote sensing of cirrus clouds . In the first part , we develop and present a fast infrared radiative transfer model on the basis of the adding -doubling principle . The model aims to facilitate the radiative transfer computations involved in hyperspectral remote sensing applications . The model is applicable to a variety of cloud conditions , including vertically inhomogeneous or multilayered clouds . It is shown that for hyperspectral applications the model is two order -of -magnitude faster than the well -known discrete ordinate transfer (DISORT ) model , while maintains a similar accuracy . The second part is devoted to the investigation of uncertainties in the FSSP (Forward Scattering Spectrometer Probe ) measurement of cloud extinction by small ice particles . First , the single -scattering properties of small ice particles in cirrus clouds are derived and compared to those of equivalent spheres according to various definitions . It is found that , although small ice particles in cirrus clouds are often ?quasi -spherical ? , their scattering phase functions and asymmetry factors are significant different from those of ice spheres . Such differences may lead to substantial underestimation of cloud extinction in FSSP measurement , if small ice particles are assumed to be spheres . In the third part , we present a comparison of cirrus cloud optical thickness retrievals from two important instruments , MODIS (Moderate Resolution Imaging Spectrometer ) and POLDER (Polarization and Directionality of Earth ?s Reflection ) , on board NASA ?s A -train satellite constellation . The comparison reveals a large difference . Several possible reasons are discussed . It is found that much of the difference is attributable to the difference between the MODIS and POLDER retrieval algorithm in the assumption of cirrus cloud bulk scattering properties . Potential implications of the difference for climate studies are investigated . An important finding is that the use of an unrealistic cirrus bulk scattering model might introduce artificial seasonal variation of cirrus optical thickness and shortwave radiative forcing into the retrieval .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2876
Date: 2009-05-15

Citation

Satellite-based remote sensing of cirrus clouds: hyperspectral radiative transfer modeling, analysis of uncertainties in in-situ cloud extinction measurements and intercomparison of cirrus retrievals from a-train instruments. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2876 .

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