Near-Infrared Light Scattering by Terrestrial Clouds

Abstract

Calculations of the reflectivity of water clouds (liquid and ice particles) are compared to observations of terrestrial clouds in the near infrared. The presentation is divided into four parts which may be consulted individually. Section 3 presents new Mic scattering calculations of general interest, Sections 4–7 compare multiple-scattering results to cloud observations, Section 8 suggests a revision in the optical constants of ice for λ ≈ 3 μ, and the Appendix details several methods which substantially reduce the work load in multiple-scattering computations. Our results indicate that it is possible to use the spectral variation of the reflectivity to derive the size of the cloud particles and their phase (liquid or solid) as well as the total optical depth of the clouds. Typical results show dense cirrus clouds to have an optical depth ≥10 and to be composed of ice particles of mean radius 15–20 μ the cumulus clouds which were analyzed showed a more variable, but usually smaller, particle size. In spectral regions where the single-scattering albedo is high it is found that most of the gas absorption takes place within the clouds rather than above them.