The fifteenth expedition of the JASON Project is focused on the rainforests of Panama. In January 2004, students, teachers, and scientists will all travel to Barro Colorado Island, Panama, to make measurements of terrestrial vegetation there and to better understand how natural seasonal climate changes as well as human activities may affect the forest there. In support of the expedition, NASA’s Earth Observatory team is pleased to host this four-part exercise to help teachers and students learn about satellite remote sensing and how scientists use the unique vantage point of space to observe and measure plants.
Exercise 1: The Electromagnetic Spectrum
After reviewing the on-line primer, have your students build true- and false-color images using Landsat multi-spectral data. Bands 3, 2, and 1 correspond to red, green, and blue, respectively--selecting this combination of bands will make true-color image. You will notice that the composite in ICE appears rather dark. This is because much of the light at those wavelengths are scattered and absorbed by gases and particles in the atmosphere, thus diminishing the brightness and clarity of the signal that is actually reflected at the surface. Students can “correct” the true-color composite image by toggling the red, green, and blue sliders beneath each band. Have them experiment to see if they can make the image look “natural color” to their eyes.
Answers to “Questions to consider”:
What features seem to be more prominent, or brighter, in each of the visible (red, green, and blue) bands? What features appear less prominent, or darker? Why do you think so?
Exercise 2: Mapping Vegetation with NDVI
After reviewing the on-line primer with your students, have them take note of the formula for making an NDVI (Normalized Difference Vegetation Index) image using the Image Composite Editor. You can tell them, or let them discover from the primer, that they must use Landsat bands 4 and 3 to make the vegetation index. Upon selecting bands 4 and 3 (as channels 1 and 2, respectively) and clicking “build,” the ICE tool will display those bands in the first two thumbnails and the result of them added together in the third thumbnail. This is half of the NDVI formula already prepared. Now, to complete the operation, students should change the math operation from “add” to “subtract” under the first two thumbnails. (Be careful to leave the numbers set at “1.0” as it is a multiplying coefficient that describes how much of the values in each thumbnail ICE should compute. Leaving it set at 1.0 means “1 times the brightness values currently displayed.”) Next, change the pop-down menu between the second and third thumbnails to “divide” and change the number in the window beneath the third window to “1.0.” After checking to make sure everything is set properly, click “Compute.” In short, you have just used the ICE math tool to compute the result of band 4 minus band 3 divided by band 4 plus band 3. The result is the greenness index value that scientists call NDVI.
Answers to “Questions to consider”:
1. Do you see any differences in the features of the tree in the red and near-infrared photos above? Explain any differences you see and what makes them look different.
2. How is the way a satellite sees Earth’s vegetation similar to the way our eyes see it? How is it different?
3. What kind of “spectral signature” would you expect a rainforest to reflect back to the satellite? Would it have a high NDVI value or a low NDVI value? Explain why you think so.
4. Would the NDVI value of the Panama Rainforest be higher or lower than vegetation in a state park near where you live?
Exercise 3: Limits to Plant Growth
Review the on-line primer with your students and then ask them to review the global-scale movies of solar insolation (or exposure to sunlight at the surface), temperature, and rainfall. Each frame in these movies represents a 1-month average for the month indicated in 2001. Invite your students to notice how the pattern of each variable changes through the course of the year. The changes are usually most extreme at the higher latitudes in the Northern and Southern Hemisphere, while the measurements or more consistent year round near the equator.
Now focus upon the tiny isthmus of Panama. How do conditions change for that region over the course of the year? In January, February, and March, there is good exposure to sunlight and temperatures remain warm, but there is relatively little rainfall. This is the “dry” season and the lack of rain is a limit to plant growth during this time of year. As a result, many of the deciduous trees in Panama shed their leaves at this time. From April through December, the insolation value for the Panama region appears to go down noticeably because rain clouds are almost constantly forming there during this span. The temperatures remain fairly steady. So conditions are ideal for plant growth during this time.
Based upon these global-scale movies of rainfall, surface temperature, and insolation, make a chart of the values for each of these factors for each month of the year. When do you think is the best time of the year for plants to grow in Panama? When do you think is the worst time?
From January through March, conditions are probably too hot and dry for much plant growth. The lack of water during this span causes many deciduous trees to shed their leaves. By May of that year the seasonal rains had returned and remained fairly constant through December. At this spatial resolution (1 degree per pixel) it is hard to see much detail about Panama. Students may pick any month from May to December as the best time for plant growth. The main point here is for them to support their answer with the evidence that they gather.
Which of these limits to growth is the most important for the plants in Panama? Why do you think so?
Do you think this Jason Expedition is taking place during the high or low growing season?
Exercise 4: Vegetation Vital Signs
Review carefully the on-line primer, first by yourself and then with your students. Five different land surface measurements are introduced. There are textual descriptions of each measurement as well as thumbnail images showing what they look like. You can click each thumbnail to view larger versions with color palettes. Have your students read each description and examine the images, and then provide their own answers to the questions given for each.
Leaf Area Index Questions:
1. Which has a greater leaf area, a rainforest or a grassland?
2. What can leaf area tell us about the vegetation in an ecosystem that NDVI cannot?
How is leaf area related to NDVI?
Absorbed Sunlight Questions:
1. Rates of photosynthesis in vegetation can be slowed down by lack of water, cold temperatures, and lack of sunlight. Which of these factors do you think most influences vegetation in the rainforests of Panama? Why do you think so?
Questions for Taking the Tropics’ Temperature, Day and
1. Do you see any relationship between either day or night time temperature and the net photosynthesis (absorbed carbon)?
2. Do you see any relationship between land surface temperature and land cover type?
3. Why would urban areas not cool off as much at night as an area with natural vegetation? (*Hint: Imagine walking barefoot across a blacktop asphalt parking lot on a hot summer day.)
Questions for An Ecosystem’s Net Productivity:
1. Compare Panama’s plant productivity for different times of the year. Do you see any differences? When do you observe the greatest productivity? When do you observe the least productivity?
2. Which land cover type has the biggest change in productivity between the wet and dry season?
3. Why do you think plant productivity in Panama changes over the course of the year?
Questions for Mapping Land Cover Types:
1. What land cover types do you observe across Panama? Which is the most widespread? Which is the least widespread?
2. Compare Panama’s leaf area index map to the land cover map. Which land cover types show the greatest leaf area? Which show the least leaf area?
3. Compare Panama’s plant productivity map to the land cover map. Which land cover types show the greatest productivity? Which show the least productivity?
Comparing these land surface measurements using ICE
You might begin by instructing students to compare measurements taken during February 2001 (the dry season) to measurements taken during July 2001 (the wet season). Once any two of these measurements are displayed in the ICE tool, you can compare the two either by clicking the thumbnail to choose which to display in the large window and then clicking “Probe.” Now, passing your cursor over the large image reveals the unit value for each pixel, for both of the thumbnail images. This way, you can compare the two scenes on pixel-by-pixel basis.
Alternatively, try clicking “Plot Transect” and then clicking and dragging your cursor anywhere on the large image to make a line segment. A new window will open displaying a line graph of the values for every pixel along the line segment, for both scenes. This way, students can quickly compare the values across transects of the landscape for both times of the year.
Teachers might also invite students to use the “Scatter” plot tool in ICE to see if there is a relationship between any of these measurements. For instance, select “Absorbed Sunlight,” “Leaf Area Index,” and “Absorbed Carbon” for February 2001. Pick a region of interest within Panama by hitting “Select Region” and then clicking and dragging anywhere on the large image to draw a box. Then hit the “Scatter” button. NOTE: If no specific thumbnails are selected, then ICE will choose the first two thumbnails by default. To compare, say, the first and third thumbnails, click on each of them both before hitting the “Scatter” button.
If you do not know how to interpret scatter plots, please refer to the ICE User’s Guide.
Additional Slides as Needed (Microsoft PowerPoint files)
- Introduction to
Remote Sensing (5.83 MB)
This presentation is an overview of remote sensing, what it is, why we use it, and how it works. Slides include the definitions of common remote-sensing terms, and examples of images captured by different remote sensing instruments. The presentation also highlights key steps in the history of remote sensing and ends with a spectacular global image of the Earth’s surface combined with ocean temperatures, both of which were captured by the MODIS sensor on the Terra satellite.
Reflectance (3.02 MB)
This presentation addresses how and why vegetation interacts with sunlight the way it does, and how that interaction determines what a satellites “sees” when it looks at vegetation. The presentation includes examples of how vegetation looks different in different parts of the electromagnetic spectrum, and how using “invisible” parts of the spectrum can distinguish vegetated from non-vegetated surfaces as well as one type of vegetation from another. The presentation also includes brief discussion of photosynthesis, including schematic drawings of the process and structures involved, as well as graphs showing the range of sunlight that best drives the process.
- The Human Eye (1.33
This presentation briefly summarizes the main characteristics of the human eye and vision, and makes comparisons to the vision of other creatures. It includes electron micrograph images of the structures of the eye, as well as graphs that illustrate the link between our vision and the energy output of the Sun.