The image above is a NOAA 15 infrared satellite image, The shades of gray represent temperature values. Can you locate the outline of the United States? What about locating the Atlantic Ocean, the Gulf of Mexico, or the state of Florida? Click on the image (300K) itself for a processed / enhanced view,

Can you identify those areas now? If you know your geography, you can also find Haiti and the Dominican Republic.

There will come a time when you have the real-world measurement values of a few pixels in the image but not the entire range. This is most common with satellite infrared images (temperatures), altitudes (digital elevation maps), etc. Density calibrating an image will mathematically relate the values of one pixel to other pixels.

As with previous activities, make sure you choose Analyze/Reset from the main menu bar to clear any previous measurements:

1. Click on Mean Density Perimeter, and Area under the Analyze/Option menu.
2. Select a small area of the image, using the selection tool, for whose area you know the actual measurement.
3. Once again use the Analyze/ Measure menu.
4. Repeat steps 2 and 3 for another area for which you know the actual measurement.
5. Click on Analyze/Calibrate.
6. Type in the known measurements
7. Click the check box for straight line.
8. Type in the Unit of Measurement and click OK
9. After clicking OK, a plot box will open and you will be presented with the line equation and the line. Close that box..
10. Analyze/Measure and Analyze/Show Results in the same manner as the measuring activity.
11. Knowing the value of the least and greatest pixel value in an image will provide the greatest accuracy.

1. Follow steps 2 and 3 from the above list.
2. As you hold down the Option Key, click on Analyze/Calibrate.
3. Change the measured values and type in the known quantity.
4.  The calibrate box will also present a menu list of check boxes. Make sure you click on the first one, straight line.
5. After clicking OK, a plot box will open and you will be presented with the line equation and the line. Close that box.
6. Analyze/Measure and Analyze/Show Results in the same manner as the measurement activity.

Download and save this commcld.tif.sit image in your designated folder. This infrared image of the Eastern United States shows a comma cloud formation (same as the image to the left).

1. A pixel value of 141 is associated with a 60 degree Fahrenheit temperature.
2. A pixel value of 38 is associated with a -68 degree Fahrenheit temperature.

Once this task has been completed, use the line/measurement selection tool to outline an area to determine its average temperature. Follow the same procedure to record measured values as you did in the measurement activity. The smaller the outline the more accurate the temperature will be for that area.

You can also determine the temperature of an individual pixel by using the line measurement tool, and clicking on a pixel in the image. Temperatures will be listed under the Mean column of the Analyze/ Show Results window. There is also another way to determine the temperature value of the pixels in this image. Can you discover the method. (Hint: It involves the procedure used in the next paragraph.)

Determine the temperatures for the following pixel locations. Use the Info window of NIH to help in locating X & Y positions.

1. X = 61 / Y = 190
2. X = 161 / Y = 240
3. X = 84 / Y = 425