Reflection

Much of the light that a satellite can sense is similar to the light we see with out eyes - reflected off of a surface or other boundary. For satellites looking down at Earth, for example, light comes from a source first, usually the Sun. This light hits Earth and is reflected by both the atmosphere, the surface, and about everything between. A lot of this reflected light is scattered which can interfere with getting a clean image from the satellite's sensors. This is where having a selective sensitivity to specific wavelength can come in handy. Different materials and shapes scatter or reflect light in different ways, but they also interact with different wavelengths differently as well. Most reflections tend to be at least somewhat diffuse, that is, they tend to have the appearance of scatter off of a surface but still adhering to the Law of Reflection, that is, an incoming ray of light reflects off a surface at the same angle it approached the surface(Knight). So when selecting a sensor, we can use one that is sensitive to wavelengths that scatter less, or are reflected more often by a specific structure or material so that it is detected more prominently by the satellite. Trying to separate clouds from a snowy ground in a satellite image relies on this! Earth's clouds are highly reflective in the visible spectrum, as is snow. However, clouds are mostly water vapor and water vapor tends to absorb light in the infrared wavelengths, whereas snow reflects much of it. So when a region is being shined on by the Sun, we can pick out the two by looking at infrared wavelengths instead of visual ones.