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Satellite Images

The GOES satellite senses electromagnetic energy at five different wavelengths. Examples of imagery from the two wavelengths most commonly shown on weather broadcasts are displayed below.

The visible (VIS) wavelength is shown on the left, and the infrared (IR) wavelength is represented by the image on the right. These images were taken at the same time. The differences between the two types of images are explained below.

Visible Imagery

Visible satellite images, which look like black and white photographs, are derived from the satellite signals. Clouds usually appear white, while land and water surfaces appear in shades of gray or black.

The visible channel senses reflected solar radiation. Clouds, the earth's atmosphere, and the earth's surface all absorb and reflect incoming solar radiation. Since visible imagery is produced by reflected sunlight (radiation), it is only available during daylight.

One of the major advantages of visible imagery is that it has a higher resolution (about 0.6 miles) than IR images (about 2.5 miles), so you can distinguish smaller features with VIS imagery.

Infrared Imagery

In the infrared channel, the satellite senses energy as heat. The earth’s surface absorbs about half of the incoming solar energy. Clouds and the atmosphere absorb a much smaller amount. The earth’s surface, clouds, and the atmosphere then re-emit part of this absorbed solar energy as heat. The infrared channel senses this re-emitted radiation.

A major advantage of the IR channel is that it can sense energy at night, so this imagery is available 24 hours a day. This is a disadvantage of the VIS channel, which requires daylight and cannot "see" after dark.

IR images are often colorized to bring out details in cloud patterns.  In the colorized imagery shown to the right, the highest clouds are the coldest and are shown in yellow. Blue and green are lower clouds. Land and water features are shown in gray or black. Forecasters use the temperature data from the IR imagery to estimate cloud-top heights. This is important because taller clouds correlate with more active weather.