A POSSIBLE REASON FOR IMPROVING VISIBILITY OF A GROUND-BASED OBJECT OBSERVED FROM SPACE

摘要

This paper considers the image contrast of a non-Lambertian object observed through a layer of a scattering medium against a Lambertian background. The contrast magnitude is shown can behave non-monotonically with increasing optical thickness of a medium between the object and observer to enhance with the thickness increasing. In other words, the object would be here viewed better from higher altitudes than from lower ones. This evidence could be posed as a guess of the fact repeatedly told to us by astronauts that they saw ground-based objects very clearly. Note the paper just advances a preliminary hypothesis, but should in no case be regarded as one giving the full interpretation. A simple physically vivid mechanism of the improving visibility is given at a qualitative level, but the features in the contrast behavior is described quantitatively.