Detection of Cloud-Top Height from Backscattered Radiances within the Oxygen A Band. Part 1: Theoretical Study

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  • a GKSS-Forschungszentrum, Geesthacht, Germany
  • | b Max-Planck-institut für Meteorologie, Hamburg, Germany
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Abstract

A series of radiative transfer calculations were performed to study the possibility of determining cloud-top pressure (height) from backscattered solar radiances within the oxygen A-band absorption. For the development of a cloud-top pressure algorithm, we also looked into the impact of perturbing effects, such as varying cloud properties, sun elevation, and surface albedo. The most important quantities are total cloud optical thickness δC and the vertical profile of liquid-water content.

The effects of cloud optical thickness-if δC>1-are already taken into account by a cloud-top algorithm, which only considers two radiances inside and outside the oxygen absorption band. For one-layer clouds, the cloud-top heights may be derived to within an accuracy of 200 m. Multilayer clouds or varying liquid-water content profiles can only be matched with an inverse technique using radiances at up to 16 wavelengths, which, however, give cloud-top height estimates to within an error of only 50 m for all 900 cloud cases considered.

Abstract

A series of radiative transfer calculations were performed to study the possibility of determining cloud-top pressure (height) from backscattered solar radiances within the oxygen A-band absorption. For the development of a cloud-top pressure algorithm, we also looked into the impact of perturbing effects, such as varying cloud properties, sun elevation, and surface albedo. The most important quantities are total cloud optical thickness δC and the vertical profile of liquid-water content.

The effects of cloud optical thickness-if δC>1-are already taken into account by a cloud-top algorithm, which only considers two radiances inside and outside the oxygen absorption band. For one-layer clouds, the cloud-top heights may be derived to within an accuracy of 200 m. Multilayer clouds or varying liquid-water content profiles can only be matched with an inverse technique using radiances at up to 16 wavelengths, which, however, give cloud-top height estimates to within an error of only 50 m for all 900 cloud cases considered.

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