Satellite instruments measure electromagnetic energy that the Earth and the atmosphere reflect, transmit and emit. These passive remote instruments are called radiometers. Two common types of radiometers are used in satellite meteorology. One type measures the amount of visible light from the Sun reflected back to space by the Earth’s surface or by clouds. The second measures the amount of radiation emitted by the surface or clouds.

The radiometers on satellites are not cameras although they do produce images. Radiometers use moving mirrors to view different regions of Earth. The instrument begins at a starting point in one direction and then scans across a scene line-by-line making observations as it proceeds. They scan the Earth much like the way we read lines of text in a book. The data is recorded in a two-dimensional format 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 data about the observed radiation represented by each pixel is presented in terms of a grayscale. Each pixel can be one of 256 possible gray shades, ranging from 0 for pure black to 255 for pure white.

Analysis of a satellite image allows meteorologists to locate thunderstorms, hurricanes, fronts, and fog. Weather events can be tracked using time sequences of satellite images, allowing weather forecasters to predict their movement over short time periods. For example, at one-half hour periods or smaller. Horizontal wind speed and direction can also be determined by tracking cloud features in a time sequence of satellite images.

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