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Satellite Analysis

Jump to [materials] [getting started] [tools for analysis] [conclusion]

Question: How do you think the rain forests of the Earth are being destroyed? Is it by insects? Drought? Large-scale forest fires?

Question: Do you think the United States lost much of its forests of the 1700s to 1800s in different ways compared to the rain forests?

Now that you see how to analyze vegetation in satellite images, you are ready to use software that has automated calculation and graphing tools: the VegetationAnalysis program. The analysis tools, which include pixel, line, and area tools, are fashioned after those you already used. Clicking and/or dragging the cursor on any of the images allows the selected tool to become active in an identical fashion in the displayed series of satellite images. So if you see an interesting feature in one satellite image and want to study it, you also get the same type of analysis at the same location for each of the time-related satellite images. There are many useful features, and additional information is available in the ‘Help’ menu.

Materials

Download the VegetationAnalysis software and see a brief tutorial.

Use the three satellite images on the right.

Getting Started

First, run VegetationAnalysis and select three satellite images to work from the ‘File’ menu. Open ‘Rondonia_1975.jpeg’ file first, followed by ‘Rondonia_1986.jpeg’ and then ‘Rondonia_1992.jpeg’. Pick the earliest (oldest) picture first, followed by the next oldest, and the most recent image last. You will not be allowed to continue if you pick images that are not of the same area or not in increasing year. A window will pop up that asks you to enter the numerical value of the map scale value visible in the lower left corner of each satellite image.

In Rondonia_1975.jpeg, you will see the box is 6 mi on a side, so type ‘6’ in the available white box. The program will ask separately for the unit (mi). If you type an incorrect value, reload the 3 satellite images with the ‘Select Satellite Images’ button. This calibrates the line and area analysis tools.

Visualize Vegetation

Use the menu button to the right of ‘Visualization’ to toggle between an RGB picture and a NDVI enhancement.
NDVI
Surface Cover
+1
Vegetation
0
Exposed soil or rock
-1
Water, Snow, Clouds

Page Setup and Print

To print the images and graphs, first use ‘Page Setup’ in the File Menu. Select ‘landscape’ printing and set scale to 75%.

Tools for Analyzing Satellite Images

Select one of three tools from the menu button to the right of ‘Analysis Tool.’

Point Analysis Tool

  • Explore intensities of infrared, red, and green light and the vegetation index, NDVI, at the same pixel for each satellite image.
  • Intensities are scaled from 0 to 100%
  • Move the cross hair in three ways:
  • Click the mouse on an area of interest 
    Click and drag the mouse to an area of interest Use the small up and down arrows along the upper-right edge

Line Analysis

  • Click and drag the cursor to draw a line.
  • Move ends of line in similar way as the Point Tool.
  • Automatically calculates number of pixels along the line and length of line
  • NDVI values for pixels along the line are graphed.
  • Average NDVI is calculated and color-coded by the year of each image.
  • Move cursor to each satellite image to see yearly data on the graph.
  • To see all data, move the cursor to the graph window.

Area Analysis

  • Click and drag the cursor to draw a rectangle.
  • Move ends of line in similar way as the Point and Line Tools.
  • Creates histogram (graph) of NDVI values for all pixels inside the rectangles.
  • Histogram shows the percentage of values within narrow ranges of NDVI values.
  • Data viewed year by year when cursor moved to each satellite image.
  • By changing the range of min/max NDVI values to calculate the percent of NDVI values between the selected range. 
  • Automatically calculates number of pixels within area and size of the area.
Rondonia, Brazil in 1975.

Rondonia, Brazil in 1975.

Rondonia, Brazil in 1986

Rondonia, Brazil in 1986

Rondonia, Brazil in 1992

Rondonia, Brazil in 1992.

Questions:

  1. What is the distance between roads that run west to east on the satellite image.
  2. Draw a north-south line across these east-west roads and describe how the vegetation changes along the line. What are the average or mean NDVI values along the line for each of the 3 years?
  3. Create a box with corner #1 at x=363 and y=178 and corner #2 at x=378 and y=190. How many square miles does this box cover? How many pixels are within this box? What surface features appear in this box for the 1986 and 1992 images? What is the average of the NDVI values for all pixels within the box for each of the three images?
  4. Create a box with corner #1 at x=66 and y=14 and corner #2 at x=295 and y=141.
    1. How many square miles does this box cover?
    2. How many pixels are within this box? What is the average of the NDVI values for all pixels within the box for 1975 to 1992?
    3. Change the min NDVI value (white box in upper right corner) to 0.6 and click the ‘Run’ button. From the graph that results, what is the percent NDVI values within the box that fall within this range of NDVI values (0.6 to 1.0) from 1975 to 1992?

Challenge.

Use these satellite images and tools to describe how vegetation is changing in this section of Brazilian rainforest from 1975 to 1992. Examine the many features on the images, such as roads and villages, and explore how vegetation changes within and near these features. Based on these observations, what is your projection for the forest ground cover? In this projection, consider how well the NDVI identifies the type of vegetation covering the ground.

Conclusion

Did your views of deforestation change after working with the satellite data? What additional data would help complete any questions you still have about deforestation in this area of Brazil?

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