03.21.11

Meteorology 101: Satellites

Posted in Weather Education at 8:00 am by Rebekah

Last week in the weather education series we looked at weather radars; this week we’re going to take a look at weather satellites.

Types of Satellites

There are two major types of satellites: polar and geostationary.

Polar satellites orbit the earth from pole to pole. This allows the satellite to take images of pretty much the entire earth.

Geostationary satellites orbit the earth around the equator, but they are so far out in space (about 36,000 km, or 22,500 miles) that they practically remain stationary above a certain spot on earth.

Most of the U.S. weather satellite images you see are from the GOES series (Geostationary Operational Environmental Satellite), from either GOES-11 (GOES West, at 135°W over the Pacific Ocean) or GOES-13 (GOES East, at 105°W approximately over the Rockies). GOES-12 (GOES South, formerly GOES East at 75°W over the Amazon River, off the East Coast) was placed into standby in April 2010.

Europe and Africa is imaged by the European Meteosat series, operated by EUMETSAT.

The western Pacific, including Australia and eastern Asia, is imaged by the Japan Meteorological Agency’s MTSAT.

Weather Satellite Channels

There are three primary bands: visible, infrared, and water vapor.

  • Visible (0.4 – 0.7 µm) – this band is in the visible range, so this is what the earth would look like if you were in space. It is based on reflected sunlight, so these images are only available during the day. Visible satellite images show cloud tops, and the thicker the clouds, the whiter they appear on the satellite image.
  • Infrared (11 – 12 µm) – this band is in the infrared (longer wavelength) range, so this is in effect sensing heat. From an infrared satellite image, we can deduce the cloud-top temperature. Infrared satellite images are lower-resolution than visible satellite images, but they are available night and day (since they don’t depend on the visible range). The higher the cloud tops, the whiter they appear on a visible satellite image.
  • Water vapor (6.7 µm) – this band detects water vapor in the mid-levels of the atmosphere. This can be helpful for determining winds/troughs/ridges/etc. in the mid-levels. It is important to note that just because you see a stripe across a water vapor image, doesn’t mean there are any clouds there (it could just be moisture in the air). These images also are available night and day. Color schemes depend on the website you’re looking at; if it is a black and white image, the whiter the region, the more the moisture. Water vapor images are often colored, and typically higher moisture content will be shown in purples and/or greens, with drier air shown in reds and/or oranges.

Check out a few satellite sites for examples!

NOAA GOES

College of DuPage (has regional satellite images and my favorite for hi-res visible images)

EUMETSAT (Europe, Africa)

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Next Monday we will talk about lightning detection systems.

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Visible (0.4 – 0.7 µm) – this band is in the visible range, so this is what the earth would look like if you were in space. It is based on reflected sunlight, so these images are only available during the day. The thicker the clouds, the whiter they appear on a visible satellite image.
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