WEATHER SATELLITES

Images

Satellite Images

A variety of weather satellite images are availabe to meteorologist and to anyone with access to the internet. The latest images are updated hourly and some past images, especially ones of significant weather systems such as hurricanes are archived. Two sources of satellite images and other weather information can be found at:

Satellite Image Details

This document contains images generated by a geostationary satellite orbitting 22,000 miles above the equator looking at the United States. This includes visible, infrared and water vapor images and a set of images that concentrate on Indiana. The images are updated once an hour at 50 after the hour.

from: The Purdue Weather Processor, Purdue University

Visible Satellite Image
Sample visible image
This image is the equivalent of taking a black and white photo of the earth. The bright areas show where the sun is being reflected back into space as a result of clouds or snow cover. Clouds and snow show up white. The thicker the cloud, the brighter the color. Land surfaces show up as gray and ocean surfaces nearly black. There is a major limitation to visible imagery in that it is only relevent during daylight.

Infrared Satellite Image
Sample infrared image
This type of image shows heat based radiation. In other words, the warmer the surface, the more infrared radiation it emits. For a satellite image, cooler surfaces are bright whereas warmer surfaces are dark. Since the atmosphere cools as you increase in altitude, clouds would show up as cool bright areas and land surfaces as dark areas. In addition, low clouds will be more gray and higher clouds will show up more white. As a result, tall thunderstorm clouds will show up as bright white and fog will be hard to decern from land areas. A large advantage of IR is that you can view it 24 hours a day.

Enhanced Infrared Satellite Image
Sample enhanced infrared image
This is a modification of the standard infrared image enhancing it to highlight the cloud areas and the coldest cloud tops. Since, IR images could be used to determine cloud height, these images are often enhanced to show those areas which are affected by varing heights of clouds. This is especially helpful in isolating strong thunderstorms which are distinguished by the coldest tops and therefore would be shown by the brightest gray shades in the image. When enhancing, these cloud tops are often shaded differently or colored to reflect approximately how cold the tops are and as a result how tall they are. The enhancement temperatures can be determined from the color bar at the bottom of the image. The tick marks at the top of the bar represent 10 degree Celsius increments starting at 50C on the left and going to -110C on the right. The colored regions represent: 

Colors      Temps (C)      (F)
dark cyan  -32 to -43  -25 to -45  Jet stream and anvil clouds
cyan       -43 to -54  -45 to -65
light blue -54 to -60  -65 to -76  Thick jet stream clouds
dark blue  -60 to -64  -76 to -83  Strong thunderstorm tops
dark green -64 to -70  -83 to -94
green      -70 to -76  -94 to -105 Severe thunderstorm tops
brown      -76 to -81 -105 to -114 Strong Hurricane tops
yellow     -81 to -90 -114 to -130

Composite Visible-Infrared Satellite Image
Sample visible-infrared image
This is a combination of the visible and infrared images. The base image is the visible image. The enhanced portion (T <-32c see above) of the infrared is overlaid on the visible using a stipple pattern. This can be used to detect areas of cold/high cloud tops in the visible image.

Composite Satellite Surface Map
Sample satellite-surface map
This is the surface weather map overlaid on either the visible or infrared image depending on time of day.

Water Vapor Satellite Image
Sample water vapor image
This is slight modification of the IR images which return an integrated amount of water vapor in the atmosphere especially weighted towards the upper atmosphere. Moist areas show up as white dry areas as black. Since jet streams carry large amounts of moisture with them, they generally show up as light gray streaks in this type of imagery.

Take a look at the next page to see videos, current images, and other resources.