Polar Caps: Image Processing Tutorial
Polar caps of Mars and Earth
In this step-by-step tutorial, students will learn to use computer image processing techniques to measure the size of Earth's polar ice caps and analyze various phenomena visible on planetary images. These skills can be used to scale and analyze any image of our Sun, the planets, or any other electronic image found on the Internet. 

Learner Outcomes

By completing this activity, the learner will: 

  • find and download/save an image of a terrestrial planet from the Internet
  • convert a GIF or JPG image to TIFF format
  • use image processing software to view and magnify the image
  • calibrate and scale the viewed image
  • use the computer to measure the diameter and area of polar caps
  • create a surface plot of the planet
National Science Education Standards

National Mathematics Education Standards

Materials and Technology

Scientific Background

Teacher Lesson Plans

Activity 1: Exploration of Earth's north pole.

Activity 2: Downloading, saving, and converting images from the Internet.

Activity 3: Using image processing software for scaling and measurement.

Activity 4: Class is divided up into NASA imaging teams in order to present their discoveries of nearby worlds using image  processing techniques.

Activity 5: Extensions.

Teacher Lesson Plans
Earth's north pole courtesy of NASA
Let's look at a picture of our Earth's north pole.  What do you see in this picture? What do the different colors represent?  Make a sketch of Earth's north pole; label the continents and sketch the extent of the ice coverage.  Predict how the appearance of this area will change in the upcoming months, and add this to your sketch. 

Concept Introduction
The concept introduction portion of this lesson is presented as a step-by-step tutorial.  It is divided into two portions, each requiring one session using the computer.  In the first part of the lesson, students learn how to save images to their computer's hard drive. In the second part of the lesson, students learn how to scale and calibrate images in order to make measurements. 

Go back to Activities.
Part I - Downloading, saving, and converting images from the Internet

Any image that you find on the Internet's World-Wide-Web (WWW) using Netscape or Microsoft Internet Explorer can be saved on your hard drive for analysis.  Even better, the process is almost the same on a Macintosh or a PC. All you have to do is the following:

1. Start your WWW browser (Netscape or MS Internet Explorer, for example) and enter a URL that has lots of images (more information).  A great place to start is the NASA Windows to the Universe site at http://windows.engin.umich.edu/.  Some other fabulous places are NASA's Hubble Space Telescope and Jet Propulsion Laboratory WWW sites.

2. To save an image to your hard drive, position the mouse over the image and hold down the button for a couple of seconds (use the right button if you have more than one).3. A menu will appear and you can select SAVE THIS IMAGE.  This will give you an option about what to call the image and where to save it.  Note where it goes and what it is called.  Choose a different name and location if you like.

 4. The image is now saved on your hard drive and you can open it in the future with your WWW browser or with any image conversion program you might have, like GraphicConverter or PaintshopPro (more information).  With these programs, you can alter the image's size, color, or even add text to the image as you wish.

5. Most images on the Internet are in GIF (pronounced with a hard "g" as in "gift") or JPG ("jay-peg").  Image processing software do not typically use files in this format, so they must be converted to TIFF (which rhymes with GIF).

6. Use either Graphic Converter or Gif Converter (MacIntosh Compatible), or Paint Shop Pro or L View Pro (PC Compatible).  From the file menu, select OPEN.  Find the image that you downloaded and open it using this converter program.

7. From the file menu, select SAVE AS, and, in the format box, select save as TIFF format.  Close your graphics converter program and you are ready to conduct image processing.

Go back to Activities.
Part II - Using Image Processing Software for Scaling and Measurement
1. If you haven't converted your images to TIFF, you need to go back to part one and convert your images to TIFF format. Image Processing Tool Bar

2. Start your image processsing software (MAC or PC or more information).  Using the FILE pull-down menu, select OPEN. Select the TIFF image that you converted in Part I.

3. The first task is to calibrate the image (tell the computer the scale of the image).  If you are looking at an image of Earth, you must know the diameter (you can look this up in a book or on the Internet as 12,756 km).  Using the segment tool (fifth from the top on the right labeled "select lines"), draw a line across the diameter of Earth.

4. Under the ANALYZE menu, select SET SCALE.  Note that the computer has already recorded how many pixels (picture elements) long the line you drew is.  First, change the UNITS to the known diameter units.  Then, enter the known diameter.  For large numbers, like 93 000 000, use 93e6.  Click OK and your image is now calibrated.  (example)

5. Use the magnifying glass in the tool bar to focus in on the ice caps.  The software will remember the scale of the image, so you can get as close as you like to make a good measurement.  To un-zoom, double click the magnifying icon in the tool box, or use the OPT key on the keyboard.

6. Use the segment tool to draw a diameter across the polar ice cap.  From the ANALYZE menu, select MEASURE.

7. From the ANALYZE menu, select SHOW RESULTS.  You might have to grab the bottom left hand corner of the new window and expand the window to see your results. (example)

8. Determine the diameter for ice caps on several planets.  How big are they?

9. You can use the same Freehand Tool to Measure Perimeter and Area.  This image processing program has four tools for selecting regions for study.

  • The first tool in the right hand column of the tool window is used to drag out rectangular areas. 
  • The second tool in the right hand column of the tool window is used to define oval or circular areas. 
  • Using the third tool in the right hand column of the tool window, you can connect a sequence of points with line segments, to create a polygon of your own design.  To close the polygon (connect your last point to your first point), just click the mouse twice in rapid succession. 
  • The fourth selection in the right hand column of the tool window allows you to freehand any curve you want (this is called the Freehand Tool and looks like a heart). 
10. Determine the area of an ice cap using the freehand tool to trace the outside. Select ANALYZE and SHOW RESULTS to view the measured value for perimeter and area.
  Go back to Activities.
Concept Application

Divide up into several NASA imaging teams. Each team needs to analyze a different nearby worlds and create a written technical report, a multimedia presentation, and/or an oral presentation that describes: 

  1. Which images you analyzed.
  2. How the images were analyzed. 
  3. How big are various features compared to things on Earth or beyond? 
Possible Imaging 
Team Assignments 
and Resources
  • Earth's Polar Caps
  • Mars' Polar Caps
  • Mars' Great Volcano
  • Jupiter's Red Spot
  • Saturn's Rings
  • Neptune's Dark Spot
  • Mercury's Great Crater
  • Moon's Maria
  • and many others ..... A great place to start is NASA's Planetary Photojournal
    Go back to Activities.

    The above process will work on ANY image that you find on the Internet.  Try out the following to demonstrate your skills at image processing. 

    How far is it from your hometown to the state capital?  Find a map of your state, calibrate the image using the map scale, and measure the distance by road between the two places.  How big is Jupiter's Red Spot? Use the known diameter of Jupiter to calibrate your image.  How big are Saturn's rings? Use the known diameter of Saturn to calibrate your image.Try the activities Investigating the Dynamic Martian Polar Caps from the CERES Project, Measuring Sunspots at the NASA Yohkoh Public Outreach (YPOP) site, Investigating Olympus Mons, (the solar system's largest volcano) or Focus on Hurricane Andrew (an enormous tropical storm) from the Network Montana Project (NMP).

    Go back to Activities.
    Lesson Debriefing

    How do you determine the scale, in order to analyze an image on the computer?  Most images on the WWW are in GIF or JPG format; what do you need to do in order to use these image processing programs?

    Assessment Strategies