Land Cover Change Analysis An Introduction to Land Cover Change Analysis using the Multispectral Image Data Analysis System (MultiSpec )

Transcription

1 Land Cover Change Analysis An Introduction to Land Cover Change Analysis using the Multispectral Image Data Analysis System (MultiSpec ) Level: Grades 9 to 12 Macintosh version Earth Observation Day Tutorial Series Developed by The University of Georgia Chapter of the American Society for Photogrammetry and Remote Sensing (ASPRS)

2 Land Cover Change Analysis Earth Observation Day Tutorial Series An introduction to land cover change analysis using MultiSpec for Macintosh computers Lesson Overview In this exercise, you will use the MultiSpec image processing software to display and inspect sections of two Landsat Thematic Mapper (Landsat-TM) satellite images showing your school and surroundings. You will investigate how the ground elements around your school are represented by Landsat-Thematic Mapper imagery and how the ground elements have changed between two time periods. The main steps involved in this lesson are: Display and inspect a section of an image acquired by the Landsat-TM orbital sensor Display and inspect a section of a second image acquired by the Landsat-TM orbital sensor from a later time period and over the same location as the first one Identify ground elements represented in the Landsat-TM image using your knowledge of the area around your school to support your hypotheses on how the land cover has changed. Classroom Instructions: 1) Start by launching MultiSpec using the icon on the desktop. 2) First, we will load a less recent Landsat-TM image into MultiSpec. From MultiSpec s File menu, choose Open Image. An Open dialog box will be displayed, allowing you to select the image file to be loaded. 3) Using the Open dialog box, navigate to the folder where the tmi1.tif file is stored (The teacher will provide instructions on where to find this file). Select the tmi1.tif image and click Open. The Multispectral Display Specifications dialog box will open (Figure 1 below). 4) In the Display group of the Multispectral Display Specifications dialog box, make sure you have 3-Channel Color for Type and the values 5, 4 and 3 associated with the Red, Green and Blue Channels. These choices will display the multiple bands of your satellite image using a combination of three colors, called a color composite. Enter the value 2 for Magnification. Click Ok. If this is the first time this image is displayed, the Set Histogram Specifications dialog box will open.

3 Figure 1: Multispectral Display Specifications dialog box for loading the tmi1.tif image. Your values for Line and Column in the Area to Display group may differ from the ones presented in the figure. 5) In the Set Histogram Specifications dialog box, accept the default options by pressing OK. The tmi1.tif image will load. 6) Repeat Steps 2-5 to open the Landsat-TM image from the second time period, tmi2.tif. This image is more recent. Therefore, the ground elements should more closely resemble the ground elements that are present today. 7) Adjust your image window and practice zooming in and out different areas. You can click and drag the corners of the image window to expand it, so the entire image section can be displayed at once. If necessary, you can also use the scroll controls to display different parts of the image. Notice that MultiSpec s toolbar has two buttons representing large ( ) and small ( ) mountains. You can use these buttons to zoom in (large mountains) or zoom out (small mountains). The current zoom magnification is displayed on the bottom right of the MultiSpec application window. Clicking on this current magnification button resets the zoom level to 1.0 ( ). You can also control the magnification also by holding the Command key down while clicking on the mountain buttons. This will change the degree of magnification by smaller increments, giving you more control over how the image is presented. 8) Visually inspect the displayed images and identify ground elements. Can you locate your school in both images, or just one? How many different ground elements can you identify? Do you see roads and constructed areas? What about vegetation and water? How have those ground elements changed between the two time periods?

4 Figure 2: Landsat-TM images from two time periods summer 1985 (left) and fall 2011 (right). Green indicates healthy vegetation while bluish-white represents buildings. Agricultural fields vary from light green to tan-ish-pink. What do you think accounts for this variation? 9) Rather than simply looking at the two separate images to see how the ground elements have changed, you will now perform a change analysis and combine both Landsat-TM images to identify the changes. Close tmi2.tif. 10) Reopen the more recent Landsat-TM image in MultiSpec. From MultiSpec s File menu, choose Open Image. An Open dialog box will be displayed, allowing you to select tmi2.tif. 11) Select Link selected file(s) to active image window from the drop down menu. Click Open, and the Open dialog box will reappear. Now, click Cancel. The two images are linked together, but must be saved. 12) From MultiSpec s File menu, choose Processor, then Reformat, and finally, Change Image File Format. The Image File Format Change Options dialog box will be displayed, allowing you to select the file type of the new combined image. Be sure that GeoTiff (or TIFF) is selected. (Using the GeoTIFF format will allow the map coordinate parameters to be saved with the image for later display of latitude and longitude coordinates if needed). Click OK. 13) A Save As dialog box will be displayed. Change the Save as type to Multispectral. Navigate to where your Landsat-TM images are saved. Give your new image a meaningful name that ends with.tif such as change.tif. Click Save. 14) Now, we are going to open the combined image. From MultiSpec s File menu, choose Open Image. An Open dialog box will be displayed, allowing you to select the image file to be loaded. Select change.tif and click Open. The Multispectral Display Specifications dialog box will open. For Type, choose 2-Channel Color (R-G). Here we will select Band 3 from each year to display as a combination of red or green. For Channels, choose 3 for Red and 9 for Green. Change the magnification value to 2. Click OK (Figure 3 below). Click OK when the Set Histogram Specifications dialog box appears.

5 Figure 3: Each Landsat-TM image contains six bands (or wavelengths intervals): from blue to infrared. When you combine the two images from both time periods, the resulting image contains a total of twelve bands (six from the older image and six from the most recent image). 15) The resulting image is then displayed with four main colors: yellow, black, green, and red. See Figure 4 below for an example. Figure 4: Urban land cover change analysis image resulting from step 14.

6 Note to Student: The resulting land cover change analysis image shows the red TM band from the earlier image as Red and the red TM band from the later image as Green. Urban areas are highly reflective in all wavelengths, so new urban areas will display as green in change.tif. If you want to analyze the change of a different land cover type, then you must change the display band combination. 16) Follow the example given in TABLE 1 and list the main colors (black, yellow, green, red) you have in your image, associating these colors with ground elements that exist in the area around your school. Use your knowledge of the area around your school to form a hypothesis about how ground elements around your school are represented by different colors in the combined image. 17) Now, you will display other bands from the change.tif image. You will use other color combinations in order to examine change in vegetation land cover instead of urban land cover. From MultiSpec s File menu, choose Open Image. An Open dialog box will be displayed, allowing you to select the image file to be loaded. Select change.tif and click Open. The Multispectral Display Specifications dialog box will open. For Type, choose 2-Channel Color (R- G). For Channels, choose 4 for Red and 10 for Green. Click OK. Figure 5 shows the resulting urban and vegetation land cover change analysis images side-by-side. Figure 5: The left image shows the urban land cover change analysis while the right image shows the vegetation land cover change analysis (both derived from change.tif). New features (urban or vegetation) are displayed as green and features no longer there are displayed as red. 18) Follow the example given in TABLE 2 and list the main colors (black, white, green, magenta) you have in your image, associating these colors with ground elements that exist in the area around your school. Use your knowledge of the area around your school to form a hypothesis about how ground elements around your school are represented by different colors in the change analysis image. 19) Be sure you have answered all the discussion questions at the end of this tutorial. Following your teacher s instructions, you may wish to print your image or discuss your results with the class. Congratulations!! You just finished the land cover change analysis tutorial, using two Landsat-TM images and the MultiSpec image analysis software.

7 Student name/group: Date: / / Land Cover Change Analysis with MultiSpec Tutorial: Discussion Questions Answer the following questions in the space provided below. If you need more space, continue on a spare sheet of paper. 1) Using the original change.tif, describe your school: a. What color is your school in the urban land cover change analysis? b. What color is your school in the vegetation land cover change analysis? 2) Describe how the land cover immediately surrounding your school has changed. a. What color is it in both the urban and vegetation change analysis images? b. What is the texture (example: smooth or rough surface)? c. Can you identify any elements of land cover (example: vegetation, water, soil, buildings, roads) that you recognize? 3) Use what you know about the color display properties of your monitor and the color band combinations used in the change analysis to answer the following questions: a. Why do new features appear green? b. Why is there so much new vegetation in Figure 5 (think back to Figure 2)? 4) What impacts can you see that humans have had on the environment immediately surrounding your school between the two time periods?

8 Student name/group: Date: / / TABLE 1 Urban change analysis image colors (black, yellow, green, and red) and their association with land cover change classes Instructions: (1) Under Change analysis image color, list all the colors of your images as described in step 15 of the Land Cover Change Analysis Tutorial. (2) Under Ground elements enter your best guess, or your hypothesis, for what the colors on the change image really represent in the environment around your school. Urban change analysis image color Ground elements Example: green Example: new construction - roads

9 Student name/group: Date: / / TABLE 2 Vegetation change analysis image colors (black, yellow, green, and red) and their association with land cover change classes Instructions: (1) Under Change analysis image color, list all the colors of your images as described in step 15 of the Land Cover Change Analysis Tutorial. (2) Under Ground elements enter your best guess, or your hypothesis, for what the colors on the change analysis image really represent in the environment around your school. Vegetation change analysis image color Ground elements Example: green Example: new / healthy vegetation growth