Spectral variations of cloud reflectance deduced from Apollo 9 SO-65 photography

Abstract Two scenes from the Apollo 9 SO-65 IR photography have been analyzedby a wavelength difference method which greatly enhances the images of subjects that reflect sunlight anomalously (compared with surroundings) in one or more of three wavebands. The general characteristics of wavelength difference patterns are given for the more common subjects, land, ocean, and clouds, allowing background, contrast, and shadings to be selected for best viewing. A cloud halo phenomenon, possibly due to a sparse particle population residual from dissipating clouds, was discovered in one of the six possible wavelength difference patterns. Photodensitometer analysis shows that the halo information was present in the original photography, but at such a level as not to be visible without considerable enhancement. A mathematical analysis of the method shows that tenfold enhancements of such images are quite possible by this technique. Possible applications to earth observations at present include cloud physics research, weather prediction, aerosol distribution, and water pollution. Other applications may be found from further analyses using some improved methods that are indicated by the results of the research reported here.