Answers to Frequently Asked Questions about Satellite Images

What are satellite images?

Satellite images can be used to show current cloud cover or can be shown in sequence loops to depict cloud movement. AccuWeather uses GOES-8, GOES-9, Meteosat and GMS Satellites to make dozens of different satellite sectors available, each showing clouds over a different area.

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What are some of the different types of satellite images?

Although AccuWeather also has satellite images available in visible, 3-D, and water vapor, the sample satellite images shown on our home site are infrared satellites, which are actually based on the temperature of the highest cloud layer, rather than visible light. The primary reason we look at infrared images rather than visible ones is that infrared images are available 24 hours a day, while visible images can only show cloud cover during the daylight hours.

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How are infrared satellite images produced?

The infrared satellite images produced by AccuWeather give an excellent representation of the location and intensity of the actual clouds despite being based upon temperatures. The reason for this is that the temperatures shown are the highest level of clouds above the earth. Since the atmosphere gets colder as you go higher up (at least in the lower part of the atmosphere where clouds typically occur) the colder the temperature that shows up on an infrared image, the higher the clouds that are being sensed by the temperatures. When there are no clouds at all, the temperature of the earth is sensed and this is typically warmer than if there were clouds above the location.

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What problems exist with infrared satellite images?

The problem with this is that sometimes on clear, very cold nights the temperature at the earth's surface is colder than temperatures aloft (this is referred to as an inversion). To correct this problem, complex algorithms are necessary to determine that skies are clear rather than cloudy in this case. Also when low clouds and fog exist, the temperature of low clouds and fog is typically very close to that of the earth's surface so algorithms are also needed to determine that clouds exist in these cases rather than clear skies. AccuWeather meteorologists, programmers and system engineers have devoted more than ten person years of time developing algorithms that determine which areas are cloudy and which are clear in an infrared satellite image.

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How can I get other kinds of satellite images?

AccuWeather's visible, water vapor, and 3-D sattelite images, as well as higher resolution infrared images, are available from AccuWeather's database, AccuData^®, in near-real time, with no delays.

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