This exercise is based on a Landsat Thematic Mapper (TM) scene from July 1997. This scene depicts the Missouri River valley where the states of Kansas, Nebraska, and Missouri meet. Squaw Creek National Wildlife Refuge is included in the scene.
| ||EB/ES/GE 351|
The following files may be downloaded via FTP.These files are in Idrisi Taiga format. Note: download both *.rst and *.rdc files to your personal student directory. Each rst file is ~2½ MB in size.
|Visible bands ||Infrared bands |
|SC97-1 (blue) ||SC97-4 (near-infrared) |
|SC97-2 (green) ||SC97-5 (mid-infrared) |
|SC97-3 (red) ||SC97-7 (mid-infrared) |
| ||SC97-6 (thermal infrared) |
Use the Idrisi Explorer (leftmost icon) to examine the metadata for these image files. Note the general attributes of these files.
Now read about the COMPOSITE module; this is the most important module for processing multispectral images. Use COMPOSITE (4th icon from left) to prepare a standard false-color composite: band 2 = blue, band 3 = green, and band 4 = red. Name the composite image SC97-234. Accept the default selections for contrast stretch, and select the option to create a 24-bit composite with stretched values. Fill in an appropriate title, and click OK. The image will be displayed automatically.
- 1. How many pixels make up this scene? What is the ground area covered by this image? Round your answer to whole km². Hint: multiply max x by max y values.
- 2. What part of the spectrum (wavelength) does each Landsat TM band represent? See bands designations (Landsat TM).
|Standard false-color composite based on TM bands 2, 3 and 4 color coded as blue, green and red. This resembles color-infrared photography in which active vegetation appears in red and pink colors. The asterisk (*) indicates the starting point for the land survey of Kansas and Nebraska (see below). Click on small image for a larger version.
||Survey of the 40th parallel or baseline (40°N latitude) for the Kansas-Nebraska boundary in the 1850s. Photos © Paul Johnston; used here by permission.
The standard false-color composite (above) incorporates two bands of visible light (green and red) along with the near-infrared band. The latter is particularly sensitive for vegetation and water bodies, but many people find this composite confusing because of its strange colors. Now make another composite based on TM bands 3, 4 and 5 color coded as blue, green and red. Follow the same procedure as before.
This composite has a more naturalistic appearance, but it's still false color, as it depicts visible, near-infrared, and mid-infrared bands. Now examine the TM 345 composite in detail. Enlarge the display window--hit "end" key. Use zoom and pan functions to move around the image.
|False-color composite based on TM bands 3, 4 and 5 color coded as blue, green and red. Vegetation appears in green and yellow-green colors; fallow ground and bare surfaces are purple, lavender and pink. Click on small image for a larger version.
Notice a large loop-shaped lake in the middle of the Missouri River valley east of Rulo. This is Big Lake State Park. The lake occupies an oxbow, a former portion of the Missouri River channel that was cutoff when the channel migrated westward. Now look along the Missouri River and find several more oxbox lakes of similar type.
- 3. Describe the colors, sizes, shapes, and patterns displayed by the following features on the TM 345 composite image.
- Interstate highway I-29.
- Falls City, Nebraska.
- Bluffs of the Missouri valley near the survey marker (see above).
- Missouri River.
- 4. Compare agricultural fields in the Missouri River valley (bottomland) with fields in upland areas east and west of the valley.
Squaw Creek National Wildlife Refuge is a major wetland site for migrating shorebirds and waterfowl. It's best known as a site for bald eagle nesting. For more information, see Squaw Creek NWR (ES 341).
- 5. Most of the oxbox lakes are dark blue to almost black. In contrast, the Missouri River and some other water bodies are moderate to bright blue in color. Offer an explanation for this difference in the appearance of water bodies.
- 6. Take a look at the Big Nemaha River in southeastern Nebraska. How have people obviously modified this stream?
- 7. Notice a distinct change in the appearance of I-29 in the southeastern portion of the image. Where does this change take place? Identify the specific highway interchange (see maps). What do you suppose this change in appearance might represent?
Now examine the TM band 6 image with the default palette. This is the thermal band which represents emitted or radiant heat; in other words, band 6 depicts relative ground temperatures. It has lower spatial resolution than the other TM bands and, so, appears somewhat fuzzy. Compare it with the composite images above.
- 8. Describe the appearance of Sqauw Creek NWR paying attention to colors, patterns, sizes, and shapes of objects depicted in the Landsat TM 345 composite image.
- 9. What types of land cover exist for most of the refuge?
- 10. What features appear relatively warm (orange-red)? Explain why these features are relatively hot. What features appear relatively cool (green-blue)? Explain why these features are relatively cold.
Given seven TM bands and three choices for color assignment, it's possible to make more than 200 false-color composite images. Many of these are repetitive, however, and some are rather bizarre in appearance. Experiment now with different false-color composite combinations. You should attempt to create an image that has lots of visual information with naturalistic coloration. Name your favorite result SC97-BEST.
As a final task, prepare a map composition based on your best false-color composite. The composition should have the following elements.
- Title, such as Squaw Creek NWR.
- Subtitle with your name and date.
- Scale bar 10 km long, divided into 5 parts.
- Text inset with brief explanation of band assignments.
- Written answers (1-10).
- Image file for best Squaw Creek composition.
Return to course schedule.
EB/ES/GE 351 © J.S. Aber (2009).