Lesson 5: "Hard" Data from Space



	Lesson 5: "Hard" Data from Space

	Objectives:

	Students will be able to: Visually interpret a satellite image Construct a land cover map from data on a satellite image Estimate the percentage of imperviousness for Baltimore City using a satellite image Understand the environmental impacts of impervious surfaces
	Core Learning Goals:

	Science: Goal 1 - Skills And Processes: The student will demonstrate ways of thinking and acting inherent in the practice of science. The student will use the language and instruments of science to collect, organize, interpret, calculate, and communicate information. Expectation 1.4: The student will demonstrate that data analysis is a vital aspect of the process of scientific inquiry and communication. Expectation 1.5: The student will use appropriate methods for communicating in writing and orally the processes and results of scientific investigation. Science: Goal 2 - Concepts Of Earth/Space Science: The student will demonstrate the ability to use scientific skills and processes to explain the physical behavior of the environment, earth, and the universe. Expectation 2.1: The student will use a variety of resources to identify techniques used to investigate Earth and the Universe. Science: Goal 6 - Environmental Science: The student will demonstrate the ability to use the scientific skills and processes and major environmental science concepts to understand interrelationships of the natural world and to analyze environmental issues and their solutions Expectation 6.3: The student will analyze the relationships between humans and the earth’s resources.
	Materials/Resources:

	For each group: Satellite image of Baltimore City Road map of Baltimore City 1 blank transparency (or tracing paper) Transparency with grid Markers (or colored pencils) Ground Truth Field Data Sheet A, B, C, D, E, or F (provided)
	Background:

	Impervious surfaces are part of the urban landscape. They include surfaces such as roads, sidewalks, rooftops, and parking lots that are constructed from impervious materials such as asphalt, concrete, brick, and stone. These materials do not allow the natural infiltration of water from rain or snow and effectively seal the surface. This can harm water quality and habitat in nearby streams and rivers by increasing the amount and velocity of runoff, which can lead to severe bank or channel erosion. In addition, groundwater supplies can be diminished because less water can infiltrate from the surface. Pollutants on an impervious surface can be washed into a river system by runoff and are a major source of nonpoint water pollution. The lack of vegetation on paved surfaces reduces the amount of evapotranspiration in the area and causes a localized increase in temperature called a heat island. This heat island effect, where the impervious area is warmer than the surrounding countryside, contributes to poor air quality in areas of high imperviousness, such as cities.

	Some impervious cover is necessary to our modern way of life. Our roads need to shed water efficiently to allow safe driving, our roofs need to keep water from falling on our heads, and sidewalks allow us to stay out of the mud when it rains. It is not desirable to rid ourselves of all impervious surfaces, and it is equally undesirable to pave over every natural area we see. A balance must be reached. Research has shown that when the impervious surface area of a watershed reaches about 10%, habitat degradation effects begin to show. (See below)


	(From http://www.chesapeakebayfromspace.net)
	http://136.160.141.178/chesapeake/

	New development adds to the impervious surface within its watershed. As new communities are developed, new roads are built, shopping centers are constructed (with parking lots), and storm drains are installed. Minimizing impervious surface can help reduce both the cost for associated governmental services and damage to the environment. For example, new construction in already established communities is preferable as these communities already have the physical infrastructure of government services in place. In addition, by concentrating development within cities and small towns, planners can preserve large areas of natural land and avoid fragmentation of habitats.

	Satellite images are one tool that local planners use to plan for growth and protect sensitive areas. They show land cover -- the type of feature present on the surface of the earth, such as lakes, forests, mountains, and urban areas. These different cover types influence the biodiversity that can be found there. Land cover information can be directly interpreted from appropriate remote sensing images. Different degrees of detail can be obtained from different remote sensing products, depending on the sensor system and image resolution. Satellite images allow for monitoring of changes in land cover, which becomes increasingly valuable as long-term studies and planning continue.

	About the Image:

	The image is a Landsat Thematic Mapper image of Baltimore City, Maryland, acquired by Landsat on March 24^th, 2000. Each pixel (small square within the image) represents an area of land that is thirty meters by thirty meters. The image is made from three wavelength bands, 4, 5, and 3, which cover the near-infrared, the mid-infrared, and the red portions of the visible spectrum. Each color in the image was assigned to one of the three wavelength bands. The red in the image was assigned to the reflected near-infrared, green was assigned to the mid-infrared, and blue was assigned to the visible red. The relative ratios of each color contained in each pixel was calculated and combined by computer and a final color was determined for each pixel.

	The colors indicate:
	Red: vegetation with high photosynthetic activity (e.g. growing grass or trees in full leaf) Orange: vegetation that is not currently photosynthetically active, lawns Green: deciduous forest areas Blue/Purple: concrete, roads, cities, other impervious surfaces Black: water Burnt/Brownish Orange: mix of deciduous trees and lawns; suburban areas
	Preparation:

	Photocopy the grid transparency onto an overhead transparency, one for each group. Choose the group size so that there are satellite images for each group. It is recommended that six groups are formed, one for each set of ground truthing data. You may color copy the satellite image for each group.

	Activity 1: Image Interpretation

	Ask students to analyze the patterns of development within Baltimore City. Your goal is to illustrate the prevalence of impervious surfaces around Baltimore, as this is a key indicator of environmental health. Tell students they will prepare a land cover map for Baltimore City and estimate the percentages of each type of land cover. Students shall use the satellite imagery to prepare the land cover map and justify their cover descriptions with actual ground truth field data from several sites around Baltimore. Later they can do the same for their own counties. Distribute one copy of the satellite image to each group of students. Give each group of students five to ten minutes to discuss what they see in the image. Can they identify key features? To help them, write on the board examples such as water, roads, parks, stadiums, forests, and piers. What color corresponds to each land feature? Ask students how they identified the key features. Have them compare the satellite image to the view from an airplane window. Have students list all visual clues that help identify different kinds of land cover. Mention that geometric shapes usually indicate human-made areas. After the discussion, have each group present one feature they identified in the image and write the results on the board or chart paper. Explain that they have begun image interpretation, the initial stage of land cover mapping.
	Activity 2: Analyzing Land Cover

	Hand out blank transparencies and the markers and explain that each group will first make a map of the information on the satellite image. They will lay the blank transparency over the satellite image and use markers to outline the boundaries of areas that appear different. (Tracing paper may be substituted for transparencies.) They should include features such as high density urban, parks, forest, water, and roads. Using the road map of Baltimore, add information that relates to the land cover (road, park, and river names). The result is a land cover map. Next ask students to design a legend for their maps by assigning a symbol or label to each land cover type. Areas with the same characteristics should be coded with the same symbol or pattern. Hand out the grid transparency to each group. Have students calculate the area that is covered by each type of land cover. Explain that they can lay their grid over their map and simply count the number of squares in each kind of land cover. (Actually this process produces a relative area.) Note that they should keep track of fractions of squares. Make a table on the board to show the class results. Average the area of each kind of land cover. ( A note about the scale of the image: the horizontal distance across the top of the image, from east to west, is 51,110 feet 9.68 miles). Students can measure the distance on their images using the unit of their choice and convert units to miles or kilometers Ask students if they were studying this area, how would they check their interpretation of land use shown by the image? Explain that ground truthing is a technique that uses field observations to determine the accuracy of a land cover map made from a satellite image. Several locations would be chosen (depending on what the objective of the research is) using the satellite image and land cover map. The researcher would go to each location and survey or census the area. Data from the field are provided on the Ground Truth Field Data Sheet handouts, which you can hand out at this time. It is recommended that each group receive a different data sheet. Assign each group an area on the image to ground truth (A, B, C, D, E, or F). Give each group one of the matching Ground Truth Field Data Sheet to work with. Each data sheet gives information about the actual ground conditions at the corresponding point indicated on the image. Have students work together to ground truth their assigned area. Compare the ground data to their map for the same area and present their findings to the class. Using the satellite image, can they find other areas around Baltimore with the same spectral signature (and thus same ground cover) as the ground truthed area? What conclusion can they draw about these other areas? Ask why ground validation is so important for interpreting satellite imagery. (The only way to check the interpretation of satellite images is to compare them to sample measurements made on the ground.) Students can then use a topographic map to determine where the water falling on their site will go. Using the relative areas that were calculated for each ground cover, calculate the percent coverage for each type of ground cover as compared to the entire image. Use the averages previously calculated for the ground cover areas. Write the results on the board. What is the total percentage of imperviousness in Baltimore City? Is this surprising? Why or why not? Are the impervious surfaces clumped together or spread out? Is there any pattern to the imperviousness? Why is it important to study the land cover of our area? Repeat the above activity with satellite images of the area around your school or neighborhood, which you can find at the Chesapeake Bay from Space website at http://www.chesapeakebayfromspace.net Would their area be classified as mainly urban, suburban, or rural? If possible, ground truth some points on the image by visiting these sites and photographing and describing these sites. Have students determine the percentage of impervious surfaces in this area? What kinds of patterns of imperviousness are visible? Ask them to compare and contrast their area with Baltimore City.



	Assessment/Evaluation:

	Have students write a report describing the types of land cover found in Baltimore, the relative percentages of these land covers to the total area of Baltimore, and the general pattern of imperviousness in the city.

	Extending the Lesson:

	Discuss the issue of working with images of the same area acquired at different times of the year, for example, Spring and Fall. The image used in this activity was taken in the early Spring (March). How would an image of the same area acquired in the summer or fall affect the interpretation? (Many features change with a seasonal regularity.)





	Contents \| "Hard" Data from Space \| Ground Truth Field Data Sheet A, B, C, D, E, or F (provided) Satellite image of Baltimore City Previous Lesson \| Next Lesson



	© 2001, Timothy Kerr, Baltimore City Public Schools.
	Thanks to the Center for Geographic Information Sciences, Towson University, and the Smithsonian Institution's Reflections on Earth: Exploring Planet Earth from Space.