Geostationary Satellite Weather Images

Visible images:

Visible satellite image of cumulonimbus clouds (thunderstorms) with overshooting tops.

The satellite measures sunlight reflected by the clouds and surface of the earth. Water absorbs a lot of sunlight (it reflects just a little) so it appears dark. The percent of sunlight reflected by the land is called the surface albedo. The albedo of land ranges from about 10-30%, except for snow covered surfaces where the albedo is much higher. A cloud's albedo is generally high, but can vary with its thickness and composition. Thick clouds have high albedos and show up bright in the satellite image. Thin cirrus clouds have low albedos and are usually semi-transparent to sunlight. The structure of clouds in the satellite image can tell the meteorologist a lot about the weather and animations tell him about the movement of weather systems.

Infrared imagery:
The satellite also measures the temperature of the clouds and the surface of the Earth with an infrared sensor. This allows for the detection of changes in the temperature of clouds and that of the surface during the day and at night. Clouds are usually colder than the surface (land or water). The temperature of the clouds also indicates how tall they are since temperature is inversely proportional to height in the atmosphere. When the satellite meteorologist processes the infrared data, he/she makes the warm clouds gray, the cool clouds whiter, and the very cold clouds bright white. Meteorologists may also color code infrared imagery in order to more easily interpret the data.

Colorized infrared imagery. Gray is relatively warm, blues cooler, red indicates clouds that are the coldest, tallest, and most likely to produce rain.

The colder the cloud the more likely it is to produce rain. The temperature structure of clouds also tells the meteorologist how hard it may be raining and whether the storm may be producing severe weather. In the absence of clouds, the satellite measures the temperature of the surface, which could be land or ocean. In the infrared image, warm temperatures are dark and cold temperatures are lighter. In the image, arid regions are hot and therefore dark, while regions at higher latitudes are usually cooler and brighter. The infrared image can also be used to monitor sea-surface temperature (SST). Since about 70% of the Earth is ocean, this allows the scientist to study how changes in SST (such as El Nino and La Nina) are related to global weather events (such as droughts, hurricanes, and floods).

Water vapor imagery:

Water vapor image of the jet stream indicated by the elongated contrasting region of dark and light.

This imagery represents a special kind of infrared measurement which measures the temperature of clouds and water vapor in a layer of the atmosphere about 6-10 km above the surface. At this altitude, steering currents such as jet streams control the movement of weather systems around the Earth. The water vapor imagery therefore captures these jet streams (elongated dark regions with adjacent clouds and bright regions), "dry" blocking high pressure systems (dark regions), and other weather systems (gray and bright white cloud patterns). By studying these features and tracking them over time, meteorologists can produce more accurate weather forecasts.

Responsible Official: Dr. James L. Smoot (james.l.smoot@nasa.gov)
Page Curator: Paul J. Meyer (paul.meyer@nasa.gov)