Interpreting Satellite Images.
The radiometers flown on satellites are not cameras. Moving mirrors make the radiometer view different regions of the earth. The instrument begins by looking off in one direction and then scans across a scene making observations as it proceeds. In this manner the radiometer scans a scene line-by-line. Data is recorded in a two-dimensional format (line and element) which, when displayed on a computer monitor or television screen, makes up an image. The smallest part of this image is the pixel -- which stands for "picture element." The radiation coming from each pixel is presented in an image format in terms of a gray scale. An image consists of 256 gray shades, ranging from 0 for pure black to 255 for pure white.