Low clouds and snow which are bright in the visible channel but not in the infrared channel result in yellow shades. High cirrus which is bright in the infrared but not in the visible result in blue shades. This multispectral imagery can be very beneficial. Relative cloud heights and depths can be determined at a glance. Non-precipitating clouds can easily be distinguished from more substantial cloudiness.
Visible imagery appears darker in the morning and evening than they do at noon.
By calculating the geographic position of each point in the image and knowing the time the image was captured, they can compute how high in the sky the sun was. This algorithm then brightens the pixel based on that sun angle. DMSP OLS in the visible channel can also detect the aurora , also referred to as the northern lights. This phenomena, believed to be of electrical origin, is best seen in arctic regions. To see an example of this imagery, click here .