Measuring weather

The visible channel measures sunlight that is reflected in the visible part of the electromagnetic spectrum. This, of course, is only really helpful during daylight hours. Just like the hand-held infrared thermometers that we can use on the ground, the GOES imager observes infrared radiation from Earth that gives information about its temperature. This sensor works at night as well.

Typical visible and infrared images from GOES look like black and white photos of the Earth as shown to the right. If you look at the visible channel, the image is not too far off from reality. Clouds appear white and the land surface is darker unless it is covered in snow. You can see daylight to the right side and darkness of night to the left of the image, away from the sun. On the surface, desert sands appear the brightest, and vegetated forests and the ocean appear much darker due to albedo.

Looking at visible satellite images, it is most often impossible to discern whether the clouds are thin or thick, low or high. This is where the infrared images can be particularly helpful. In these images, white refers to cold, and black refers to warm, so the brighter a cloud appears, the more likely it is high in the atmosphere, where it is coldest. Taller clouds correlate to more active weather, such as stronger thunderstorms or heavier snow. In some infrared images, colors are added to accentuate these cold regions. In cloud-free regions, we can also observe the temperature of the land or sea surface.

In both of our infrared and visible images to the right, a hurricane may be seen. Can you find it?

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