Reflection

Satellite detectors that are sensitive to radiation in the visible to the 3.9um wavelengths are in a region where reflected solar radiation dominates or at least is significant. In this region, the reflective properties of the Earth and atmosphere are important to understand. The amount of reflection from an object depends on what percentage of the incident radiation is absorbed or transmitted versus how much is returned or reflected off the object. A ratio of reflected to incoming radiation is often used to describe the reflectance or albedo of an object. The albedo of objects or surfaces can also change depending on the angle of the viewer with respect to the sun. A mirror-like surface like calm water reflects incident visible radiation in almost one direction. This type of surface is termed a specular reflector. Fresh snow reflects light in nearly every direction and is thus called an ideal diffuse reflector. Typically, the size of the roughness compared to the wavelength of incident radiation determines what kind of reflector the surface is. A paved parking lot is a diffuse reflector in visible light, but in the radio part of the spectrum, it is a specular reflector.

Here are some subjective comparisons of reflected energy in shortwave (3 to 4 µ m) and visible (0.4 to 0.7 µ m) channels.

energy		reflected
			vis  	shortwave	longwave

snow			hi	low		none
ice			med	low		none
lake			low	low		none
land			low	med		none
water cloud		high	high		none
ice cloud  		low	med		none
dust			med	med		none


Go back one step

Go to front page