Cloud Optical Thickness Retrievals From Multiangle Measurements

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Cloud Optical Thickness Retrievals From
Multiangle Measurements

• Ákos Horváth
• Roger Davies
• University of Arizona
• 8th Scientific Assembly of IAMAS
• 10-18 July 2001
• Innsbruck, Austria

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Motivation

• Retrieval of global cloud optical depth
  distributions.
• ISCCP tglobal 3.7, Pruppacher Klett tglobal
  58
• solar zenith angle dependence
• plane-parallel albedo bias
• retrieval of large optical depths
• Multiangle data measure of confidence of 1D
  retrievals.

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MISR-DISORT Comparison

• High confidence clouds over ocean.
• Lambertian surface with an albedo of 5.
• Mie phase function (gamma distribution with re8
  mm).
• No Rayleigh scattering, no aerosols.

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Homogeneous example
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Heterogeneous example
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Coregistering images to reflecting level
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Coregistering images to reflecting level
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Coregistering images to reflecting level
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Coregistering images to reflecting level
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Coregistering images to reflecting level
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Separating homogeneous and heterogeneous
pixels (path 114, orbit 6156, block 118)
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Orbital statistics (path 114, orbit 6156)
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Optical thickness distributions (path 114, orbit
6156, block 43-145)
t3
t13
?3 of pixels tgt100
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Summary

• Only a small portion of cloudy pixels is
  consistent with the plane-parallel model (9 at
  275 m resolution).
• At coarser resolutions clouds appear more and
  more homogeneous.
• Homogeneous clouds tend to be thicker.

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Effect of coregistration and error of fit (path
114, orbit 6156, block 126)
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MISR imaging concept