Infrared weather satellite images are produced day and night by the heat sensors on board the satellite. Since the earth is always radiating heat, these satellites interpret the heat emanating from the earth's surfaces and clouds and assigns each pixel (picture element) area a gray scale number from 0 to 255. Zero (0) depicts a value of pure white and 255 indicates a value of pure black.

The warmer the area, the greater the gray scale value, the darker the image. Cloud tops which extend high into the atmosphere are white. This indicates that they are cold. Low lying clouds, water, and land surfaces are varyious shades of gray to black. The warmer the day, the darker the surface color. In fact, one can determine the approximate time of day an infrared image was taken by looking at the surface gray scale color.

The Hurricane Opal infrared image used in this project was taken on October 3, 1995 from a polar orbiting weather satellite. The chart on the upper left of this page indicates the upper and lower end of the DNs with their associated cloud temperatures. Computers can provide an enhanced, colorized infrared view of the storm. The color codes provide information that help meteorologist determine the areas of greatest thunderstorm development. The higher the thunderstorm clouds, the colder their tops become (Look for very low pixel values (DN). Using the scale on the left, above the image (use PC coordinates for Scion and MAC for NIH software):

• Determine where thunderstorms may be occurring within the hurricane (provide three different x,y coordinates).
• If each pixel covers an area of 4 sq. km, determine the estimated sq km are affected by thunderstorms.
• Develop a scale that translates pixel values between 1 and 25 in the image to its associated temperature (degree F)
• What are the temperatures of the clouds at positions (48,146), (66,211), (97,73) if using NIH software; (48,239, (66, 174), (97,312) if using Scion Software

Once the image has been calibrated for the temperature range based upon the above chart, a clear diamond shape will appear next to the name of the image in the title bar. This is an enhanced image with the temperature scale covering pixel values from 1 (-100 degrees F) to 25 (-40 degrees F). Is the scale accurate for pixel values higher than 25? If so, what is the temperature associated with a pixel value of 192? If not what must one do to produce an accurate temperature slope for pixel values greater than 25?

Other Information and Conditions