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 Windows version With Teacher Notes 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 Windows computers Purpose To display, observe, and identify elements of land cover change within a section of a satellite image between two time periods using the Multispectral Image Data Analysis System (MultiSpec ) software. Student Outcomes Students gain experience in the use of remotely sensed image data. Students learn how to perform land cover change analysis. Students gain/improve spatial or landscape level perspective of the area around their school. Science Concepts Geography The characteristics and spatial distribution of ground elements surrounding the students school. How humans change their environment and how the environment changes human patterns of land use. How land use patterns change over time. Physics Energy-object interaction and the use of remote sensors to detect the energy reflected from objects. Color formation and color systems. Life Sciences The characteristics of vegetation communities surrounding the students school. The distribution of habitat types surrounding the students school. How the distribution of habitats has changed over time and the potential impacts of these changes. Scientific Inquiry Abilities Identify answerable questions. Conduct scientific investigations. Develop descriptions using evidence. Scientific Inquiry Abilities continued... Communicate results. Other Concepts Mathematics and Computing Math concepts are reinforced, such as average and ranges. Use of algorithms for digital image analysis. Specific Learning Objectives Upon successful completion of this lesson students will be able to: Inspect a section of a Landsat-TM image to observe and identify ground elements. Analyze changes in ground elements between two time periods. National Science Education Standards Content Standard A: Science as Inquiry Abilities necessary to do scientific inquiry Understanding about scientific inquiry Content Standard D: Earth and Space Science Standards Structure of the earth system Content Standard E: Science and Technology Standards Abilities of technological design Understanding about science and technology Content Standard F: Science in Personal and Social Perspectives Populations, resources, and environments Science and technology in society 2

3 National Educational Technology Standards (NETS-S) Creativity and Innovation Apply existing knowledge to generate new ideas, products, or processes Identify trends and forecast possibilities Research and Information Fluency Locate, organize, analyze, evaluate, synthesize, and ethically use information from a variety of sources and media Evaluate and select information sources and digital tools based on the appropriateness to specific tasks Process data and report results Critical Thinking, Problem Solving, and Decision Making Identify and define authentic problems and significant questions for investigation Collect and analyze data to identify solutions and/or make informed decisions Use multiple processes and diverse perspectives to explore alternative solutions Lesson Description Level Grades 9 to 12 Time 60 minutes. Time includes the presentation of the activity and background information, as well as hands-on activities. Materials Computer(s) running Windows operating system (if students will be using Macintosh computers, please refer to the Mac version of this tutorial). Note: we suggest students work as a group, with ideally two students per computer. MultiSpec software: this tutorial was created using MultiSpec version bit for Windows computers. Pre-selected sections of two remotely sensed images acquired by the Thematic Mapper (TM) sensor onboard the Landsat satellite from two time periods and same location. Color printer (optional). Preparation This lesson is designed to follow the Viewing Remote Sensing Imagery with MultiSpec tutorial, also from AmericaView. Before beginning this lesson, students should be familiar with opening and visualizing a satellite image using MultiSpec software. See the accompanying Teacher Preparation Plan document for details. After completion of the Viewing remote sensing Imagery tutorial, MultiSpec should be installed on each computer to be used by the students, and you should be familiar with the software. If some time has passed since you performed the Viewing... tutorial, you may wish to take some time to re-familiarize yourself and students with MultiSpec. Select and download two Landsat-TM images from the same area but separated by 1-20 years depending on the rate of land cover change Make sure images are from the same season. Identify the area to be loaded and observed by students and clip a subset of the downloaded Landsat-TM image representing this area. Make sure the two clipped subset images have a similar size and position so that students can easily compare the two images. 3

4 Preparation (cont.) Save copies of the selected section of the Landsat-TM image on the computers the students will be using. Make sure students will have read and write permissions to access the necessary folders when following the tutorial. Identify ground elements in the selected subsection of the Landsat-TM image. If a printer will be used (optional) verify that it can be accessed by every computer used in this exercise and that the printer has ink. Preparation Time Image preparation time: if the images to be used in the tutorial are part of USGS s image archive (i.e., the images covering your area have already been processed and are available for download), preparation time may take around one hour. If the images covering your area are not available for immediate download, you need to request that USGS processes the images. You will receive a notification from USGS that the images are available for download two to three days after you place the image processing request. MultiSpec software and data copy time (setup time): MultiSpec and the sections of the Landsat-TM images must be available on every computer to be used by this exercise. Setup time per computer is less than five minutes if a computer account with read/write permissions already exists (make sure students will be able to read from/write to the folder where the sections of the Landsat-TM images are stored). The teacher should also consider allocating time to understand the basics of remote sensing, including image acquisition by remote sensors and the characteristics and use of those images. This lesson may be presented in conjunction with the other AmericaView Earth Observation Day MultiSpec tutorials. These tutorials guide students to classify the land cover around their schools through supervised and unsupervised classification methods. For more information on these tutorials, see the AmericaView Earth Observation Day website Lesson Overview This lesson will guide students in the process of analyzing land cover change using Landsat-Thematic Mapper (Landsat-TM) images. Students will use the MultiSpec image processing software and two Landsat-TM images from two different time periods. The image processing will be followed by a qualitative analysis of the magnitude of land cover change during the time period between image acquisitions. The main steps involved in this lesson are: Display and combine sections of images acquired by the Landsat-TM sensor Identify areas of change in ground elements and analyze their spatial distribution in the area around the students school 4

5 Suggested Sequence of Activities Present an overview of the exercise. Present background information regarding remote sensing: the Landsat satellite, spatial resolution (pixel size), spectral resolution (bands), spectral response of ground elements in the satellite image, including vegetation, soil, water and constructed areas. Inform students on where the images to be used (tm1.tif and tm2.tif) are located. Guide students to individually or in groups conduct the image display, observation, and analysis as directed by the tutorial. Students may complete assessment questions individually or in groups to evaluate their achievement of the lesson goals. 1. Why are the colors for the same land cover types so different when I compare my image with the images in the Earth Observation Day Powerpoint presentation? Some difference in color between images is normal. If the color difference is considerable and all other elements of your screen seem to present their normal colors, you may have loaded your image using a color composite different from the suggested color-channel association. Reload the image and in the Set Display Specification dialog box make sure you have 3-Channel Color for Type and the values 4, 3 and 2 associated with the Red, Green and Blue Channels. 2. What if the combined land cover analysis image looks blurry? It may be possible that the combined land cover image will appear fuzzy or blurry. This is most likely caused by the two images not quite lining up properly. The satellite visits approximately the same place as it circles the Earth, but small errors may occur so that the same feature in one image will be slightly offset in another image at a different time. If you feel like this distortion so large that it interferes with students analysis of the images, we recommend trying to use a different set of images that are better aligned. 3. What if I don t see changes when I compare the images that I am analyzing? Land cover change depends on numerous human and non-human factors and can occur at various Frequently Asked Questions rates. A city downtown will likely remain urban while a desert would also likely remain as such. You may try to find an area that is in transition between two land cover types (e.g., forested to agricultural, agricultural to suburban, etc.). Alternatively, try downloading two Landsat-TM images that are separated further in time. Rapidly transitioning areas will show land cover change over a few years while slowly transitioning areas may require a decade or more between image acquisitions. 4. What if I see very little variability in the colors and textures of the image depicting the area around my school? There may exist situations where there is very little variation in the land use and land cover in the area immediately surrounding your students school. This may occur when the area is predominantly covered by one type of vegetation or land use, with very little variability. Under these circumstances, you may wish to present an image with greater variability for your students to view. If you know of another location with which your students may be familiar (a local park, lake, or similar), you may use this location when choosing an image for your students to analyze. Ideally the location of the image you choose would be somewhere that students are familiar with visiting in real life. 5

6 5. What if an area has changed, but the analysis does not show this and vice versa? A common problem with remotely sensed land cover change analysis is using images acquired from different times of the year. Seasonal variations in vegetation growth can dramatically alter how images appear. Vegetated areas may artificially appear to grow or shrink if one image was taken during the winter (i.e., leaf-off) and one image was taken during the summer (i.e., leaf-on). We recommend using two images from approximately the same time of year so that the vegetation will be at approximately the same stage in growth. 6. Where can I find more information about remote sensing and digital image processing? For an introductory approach, we suggest the following books: Remote Sensing of the Environment: An Earth Resource Perspective, by John R. Jensen. Remote Sensing and Image Interpretation, by Thomas Lillesand, Ralph W. Kiefer and Jonathan Chipman

7 Land Cover Change Analysis Earth Observation Day Tutorial Series An introduction to land cover change analysis using MultiSpec for Windows 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. Note to Teacher: Please refer to the MultiSpec Teacher Tutorial preparation guide of this Tutorial Series for instructions on how to create a desktop icon to launch MultiSpec. 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. Note to Teacher: A detailed description on loading and viewing remote sensing imagery is provided in the Viewing Remote Sensing Imagery with MultiSpec tutorial, available from AmericaView. If students need a refresher on how to load and view these images, you may refer them to this tutorial. 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 Set Display Specifications for: dialog box will open (Figure 1 below). 4) In the Display group of the Set Display Specification for: 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. 7

8 Figure 1: Set Display Specification 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. Note to Teacher: Using Step 7 below, students should explore the area around their school in the first time period. If substantial time has passed, or if land cover change has been rapid, students might need help identifying the location of their school and other nearby landmarks. 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). A reset zoom button ( ) is located to the left of the large mountains button and allows you to go directly to a x1 magnification. You can control the magnification also by holding the Ctrl 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. The current zoom magnification is displayed on the bottom right of the MultiSpec application window in the box labeled Zoom=. Note to Teacher: The following steps will deal with visual interpretation and change analysis of the Landsat-TM image section between both time periods. Ground elements that may be present in your images are: bare soil, vegetation, roads, buildings, paved areas, water and 8

9 shadows. We suggest preceding the following steps of the lesson with a review of the Earth Observation Day Powerpoint presentation showing examples of how land cover types and ground elements are depicted by color composites of images acquired by the Landsat-TM sensor and examples of how land cover might logically change from one type to another. An example would be change from forested in time period one to housing in time period two. 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? 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) Before clicking OK, check Link to active image window. Click Open, and the Open dialog box will reappear. Now, click Cancel. The two images are linked together, but must be saved. 9

10 12) From MultiSpec s File menu, choose Processor, then Reformat, and finally, Change Image File Format. The Set Image File Format Change Specifications 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. 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 Set Display Specifications for: 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. Click OK (Figure 3 below). Click OK when the Set Histogram Specifications dialog box appears. 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. Note to Teacher: The following steps will explore how the level of urbanization has changed between the two time periods. To see how a land cover type has changed, you must isolate the bands associated with it. In this case, the Red band from tmi1.tif is set to display as Red, while the Red band from tmi2.tif is set to display as Green. Areas that were built-up in both time periods will display as bright yellow. Areas that have been cleared and built-up since the first time period will display as bright green. Cleared and/or builtup areas in time period one (but not time period two) will display as red. Since urban areas are unlikely to revert back to vegetated areas, red regions most likely represent fields with relatively 10

11 low health in time period one compared to time period two or fields that were cleared in time period one, but vegetated in time period two. This might also be due to climatic variations (e.g., drought) or low agricultural productivity in tmi1.tif. Images collected at similar dates under similar long-term weather conditions will help remedy this issue. Figure 4: Urban land cover change analysis image resulting from step 14. 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. 11

12 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 Set Display Specifications for: 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. 12

13 Note to Teacher: If a printer is available, following the inspection of image students may print their results, ideally in color. To print an image, give the following instructions to your students: a. Click anywhere inside the image window. The image window receives focus. b. Go to the File menu and select Print Preview. The image window then shows how the image will be printed (in case you change your mind and decide not to send your results to the printer, press the Close button on the print preview window and you will be taken back to the image). c. If the print preview looks ok, press the Print button on the image window to print your results. 13

14 Note to Teacher: The following pages contain student questions and the tables used in this tutorial. We suggest printing these pages and providing them to your students as worksheets. 14

15 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? 15

16 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 16

17 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 17