The black and white image is an early morning picture of the beginning of Tropical Storm Gordon, formed off the Yucatan Peninsula in July of 1995. This is a visible image much like a black and white photograph.

Particle analysis will allow one to highlight certain pixel values and take measurements. In this case I want to determine the area and perimeter of the massive cloud development which I believe will become the center of the storm. Turning on density slicing and highlighting the pixels I'm interested in will give me those measurements.

As a reminder, when working with satellite images, measurements are not entirely accurate. On these types of images, pixel values representing distances have different values directly below the satellite as opposed to those located on the edge of the image. As an example, the image directly below the satellite (nadir) would have a value of 4 miles but at the image edge, the value may be 12 miles.

This activity is done as a technique exercise only, not for actual real-world measurements.

Now try your own hand at density slicing and particle analysis. The activity will allow you to measure the area and perimeter of Lake Okeechobee.

2. Open the Analyze then Option dialog box.

3. Click on Area and Perimeter/Length so that those two boxes are checked.

4. Set the scale to 1 pixel equals 4 miles.

5. Density slice the image so that Lake Okeechobee is highlighted in red. You will need to narrow the range to about 30 pixels.

6 Click on Analyze / Analyze Particles.

7. Check the Label Particles, Reset Measurement Counter, and outline boxes. Set minimum and maximum particle sizes to 50 and 100. Click OK. Setting particle sizes sets the program to measure areas that only contain that quantity of pixels. In this case only areas that contain 50 through 100 pixels of that density will be counted.

8. Click on Show Results

9. Record the results.