Lesson Plans

Quantifying Land Changes Over Time

Source: https://landsat.gsfc.nasa.gov/about/history/

Purpose

Students identify kinds of land cover (such as roads, fields, urban areas, and lakes) in Landsat satellite images. They decide which land cover types allow the passage of water into the soil (pervious) and which types do not allow it (impervious). They consider some effects of increasing impervious surface area on ecosystem health. This lesson is a modification of the original lesson Quantifying Changes in the Land Over Time with Landsat.

Source: https://landsat.gsfc.nasa.gov/wp-content/uploads/2013/05/Landsat_QuantifyChanges.pdf

Learning Objectives

Students will:

  • Identify some major land cover types in a land remote sensing image
  • Develop maps of land cover at a regional (landscape) scale
  • Quantify land cover change over time 
  • Predict ways and directions that an urban area might grow  
  • Realize that land cover / land use in our country is changing in significant ways;  this has implications for management of the natural resources we depend on
  • Appreciate the value of planning in urban growth to protect natural resources

NASA Phenomenon Connection

Our land is changing. Land covered by forest is changing to farmland, land covered by farmland is changing to suburbs; cities are growing. Shorelines are shifting; glaciers are melting; and ecosystem boundaries are moving. As human population numbers have been rising, natural resource consumption has been increasing both in our country and elsewhere. We are altering the surface of the Earth on a grand scale. Nobel Prize recipient Paul J. Crutzen has said, “Humans have become a geologic agent comparable to erosion and [volcanic] eruptions…”

Land cover change has effects and consequences at all geographic scales: local, regional, and global. These changes have enabled the human population to grow, but they also affect the capacity of the land to produce food, maintain fresh water and forests, regulate climate and air quality, and provide other essential “services.” (See Foley, et. al,) It is critical for us to understand the changes we are bringing about to Earth’s systems, and to understand the effects and consequences of those changes for life on our planet. Landsat satellites enable studies of change at the regional or landscape scale.

The first step in understanding change is monitoring, and the second step is analysis. Doing this activity will enable your students to take these steps at an introductory level.

Essential Questions

  • What is the practical value of remote sensing?
  • How widespread is urban development and what are the impacts on natural resources as land cover changes?
  • How can landscapes change regionally and locally?

Cross-Curricular Connections

  • National Geography Education Standards: The World in Spatial Terms
    • Standard 1: How to use maps and other geographic representations, geospatial technologies, and spatial thinking to understand and communicate information
    • Standard 3: How to analyze the spatial organization of people, places, and environments on Earth’s surface

Technology Requirements

  • Internet Required

Background Information

Near infrared, red, green

One of the most frequently published color combinations used in false-color images is near infrared light as red, red light as green, and green light as blue. In this case, plants reflect near infrared and green light, while absorbing red. Since they reflect more near infrared than green, plant-covered land appears deep red. The signal from plants is so strong that red dominates the false-color view of Algeria below. Denser plant growth is darker red. This band combination is valuable for gauging plant health.

Cities and exposed ground are gray or tan, and clear water is black. In the image below, the water is muddy, and the sediment reflects light. This makes the water look blue. Images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and from the early Landsats are often shown in this band combination because that’s what the instruments measured.

Near infrared, red, and green light were used to create this false-color image of Algeria. Red, plant-covered land dominates the scene. (NASA image by Robert Simmon with Landsat 8 data from the USGS Earth Explorer.)

Credit: https://earthobservatory.nasa.gov/features/FalseColor/page6.php

Near infrared, red, and green light were used to create this false-color image of Algeria. Red, plant-covered land dominates the scene. (NASA image by Robert Simmon with Landsat 8 data from the USGS Earth Explorer.)
Near infrared, red, and green light were used to create this false-color image of Algeria. Red, plant-covered land dominates the scene. (NASA image by Robert Simmon with Landsat 8 data from the USGS Earth Explorer.)

Phoenix, Arizona, and its suburbs are growing rapidly, both in population and area. Landsat images show striking changes in the Phoenix metropolitan area in only a few decades. The most noticeable change is residential areas spreading over agricultural fields, which are shown in the images as bright red squares and rectangles. But in other areas, the urban growth expands over what was once bare desert.

New residents and tourists are attracted to Phoenix by the warm weather and abundant sunshine. Phoenix has maintained rapid and sustained growth, and its location in a wide valley allows neighborhoods to be built with houses that can have a lot of space around them. From 1970 to 2017, the population of the Phoenix metropolitan area grew by about 388 percent.

Phoenix doesn’t have many cloudy days, so it’s perfect for studying urban growth with satellite images. Scientists and city planners study population growth and urban expansion in fast-growing cities like Phoenix to determine the changes that have occurred over time and to see how those changes impact the surrounding environment, affect the availability of natural resources such as water, and alter the landscape and how it’s used. That information can help people plan for future changes as cities continue to grow.

About Pervious and Impervious Surfaces (Land Cover Types)

When rain falls or the snow melts on pervious surfaces such as grassland or fields, that water percolates through the ground, reaching and replenishing our ground-water supply. But when rain or snow falls on surfaces such as pavement and sidewalks, it can’t get through. Those surfaces are impervious to water. The water glides along the pavement and picks up contaminants along the way such as oil, gas, fertilizers, sediment and even bacteria. When the water does finally reach a pervious surface, or a water body, it can be full of all these pollutants. That can introduce a huge surge of contamination into our water supply. On the other hand, when precipitation falls on pervious surfaces, it gradually penetrates the ground, and many contaminants are naturally filtered out before they reach the ground-water supply.

“There is a link between impervious surfaces within a watershed and the water quality within the watershed. In general, once 10-15 percent of an area is covered by impervious surfaces, increased sediments and chemical pollutants in runoff have a measurable effect on water quality. When 15-25 percent of a watershed is paved or impervious to drainage, increased runoff leads to reduced oxygen levels and impaired stream life. When more then 25 percent of surfaces are paved, many types of stream life die from the concentrated runoff and sediments.” (NASA Goddard Space Flight Center News Release, “New Satellite Maps Provide Planners Improved Urban Sprawl Insight.”)

For more information, review the Background on Land Cover change pages found in the student handouts.

Prerequisites Student Knowledge

Students must:  

  • have a basic level of ability to understand and interpret visual representations of Earth’s surface from above, such as maps and aerial photographs;
  • understand the meaning of wavelengths of light;  
  • be able to define “electromagnetic spectrum,” at an introductory level

Student Misconception

Students might think the Landsat images are photographs. They are actually "false color" images. There is information about "false color" images in the lesson.

Procedure

Engage

Step 1 - Watch these video clips:

Why Does NASA Study Earth?

NASA: A Landsat Flyby

Landsat: A Global Perspective (Urban Change is highlighted from 1:52-2:52)

Step 2 - Complete the GLOBE Classroom Activity, Getting to Know Your Satellite ImageryGetting to Know Your Satellite Imagery and GLOBE Study Site

Before starting the activity, discuss as a class: What experiences, if any, have you had of changes in the landscapes where you live? For example, has there been any major construction, such as new housing developments, shopping malls, highways, or bridges? Or, in contrast, are any large areas being allowed to revert to natural land cover?

Explore

Step 3 - Read about False Color Images

How to Interpret Common False Color Images

Though there are many possible combinations of wavelength bands, the Earth Observatory typically selects one of four combinations based on the event or feature we want to illustrate. For instance, floods are best viewed in shortwave infrared, near infrared, and green light because muddy water blends with brown land in a natural color image. Shortwave infrared light highlights the difference between clouds, ice, and snow, all of which are white in visible light.

The four most common false-color band combinations used in analyzing Landsat data are:

  1. Near infrared (red), green (blue), red (green). This is a traditional band combination useful in seeing changes in plant health.
  2. Shortwave infrared (red), near infrared (green), and green (blue), often used to show floods or newly burned land.
  3. Blue (red), two different shortwave infrared bands (green and blue). We use this to differentiate between snow, ice, and clouds.
  4. Thermal infrared, usually shown in tones of gray to illustrate temperature.

Near infrared, red, green

One of the most frequently published color combinations used in false-color images is near infrared light as red, red light as green, and green light as blue. In this case, plants reflect near infrared and green light, while absorbing red. Since they reflect more near infrared than green, plant-covered land appears deep red. The signal from plants is so strong that red dominates the false-color view of Algeria below. Denser plant growth is darker red. This band combination is valuable for gauging plant health.

Cities and exposed ground are gray or tan, and clear water is black. In the image below, the water is muddy, and the sediment reflects light. This makes the water look blue. Images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and from the early Landsats are often shown in this band combination because that’s what the instruments measured.

Near infrared, red, and green light were used to create this false-color image of Algeria. Red, plant-covered land dominates the scene. (NASA image by Robert Simmon with Landsat 8 data from the USGS Earth Explorer.)

Credit: https://earthobservatory.nasa.gov/features/FalseColor/page6.php

Near infrared, red, and green light were used to create this false-color image of Algeria. Red, plant-covered land dominates the scene. (NASA image by Robert Simmon with Landsat 8 data from the USGS Earth Explorer.)
Near infrared, red, and green light were used to create this false-color image of Algeria. Red, plant-covered land dominates the scene. (NASA image by Robert Simmon with Landsat 8 data from the USGS Earth Explorer.)

Step 4 - Explore the 1984 Landsat image.

The image is “false color.” The task for this step is to look over the false color image and identify as many land cover types possible. Students may work with classmates to do this. Lead a class discussion about land cover types in this image. Have students identify as many of them (roads, agricultural fields, urban or suburban areas, etc.) as they can.  

1984

 

2018

 

  

Work with a partner for Steps 5 - 9.

Step 5 - Identify land cover types in the 1990 image.

Students will work with a partner to identify the types of land cover they find in the 1984 satellite image. Have them identify several types. Some examples of land cover types are urban, suburban, water (lake, river, or ocean), forest, grassland, wetland, shoreline, or anything covering significant amounts of the land surface. They should be prepared to share their lists with the class.

If you wish to identify the land cover types for your students before the activity, make that list for them. Each land cover type needs to be represented on the map by a letter or symbol, such as:

  • S Suburban
  • U Urban
  • H Highways and Roads
  • F Forest
  • G Grassland W Water

Now make a class list of the land cover types in the satellite images.

Still working as a class, have students decide which of the land cover types allow water to penetrate the surface (pervious), and which types do not (impervious). Have students keep both a class record and their own individual records of the list of land cover types that are impervious vs. pervious. They will need it later in the activity.

Explain

Step 6 - Visually Comparing 1984 and 2018 Landsat Images

Spend some time examining the two images. Familiarize yourself with the similarities and differences in these images that are about a decade apart. Get a general sense of how much the land cover has changed over that time: where, how, and by how much. Focus on one part of the geographic area at a time to identify specific areas of change.

Use the Student Sheet for Step 6 to write about what you observe and think as you visually assess the changes from 1984 to 2018. Include any questions or concerns you have, or anything you find confusing.

Each student should complete a sheet for this step.

Something you need to be aware of is that the 1984 image and the 2018 image show different months of the year. The 1984 Phoenix image shows the land cover on September 22, 1984, and the 2018 Phoenix image shows the land cover on August 19, 2018. As you compare the two images of land cover, keep the difference in months in mind.

Pointers about the Desert Ecosystem Remember that the natural ecosystem of Phoenix is desert. In the false color image, the desert appears gray/green. Areas that show visible bright red have likely received water recently.  

Landsat Image - Phoenix 1984Landsat Image - Phoenix 2018

Step - 7 Make a map of land cover types in 1984 using the transparency and grid.

Students did a qualitative assessment of about thirty-five years of cover change in Step 6; now they will begin a quantitative assessment of the change.

They should:

  • Place their transparency with grid over the 1984 satellite image.
  • Mark the corners of the image on the transparency so that if it is moved off the satellite image it can be back again exactly where it was.
  • Using the classification scheme for land cover types that your class decided upon in Step 5, make a map of land cover change by tracing carefully around each land cover type with a colored marker.
  • Remember, you decided as a class which kinds of land cover were pervious to water and which kinds were impervious.
  • Label each area with the symbol for its land cover type and also with the symbol for either pervious or impervious (probably P or I).
  • Make a legend for the transparency grid, which is now becoming a map.
  • Be sure to label this map with the year the satellite image was made, and with your name, your partner’s name (if you’re working with a partner), and today’s date.

Elaborate

Step - 8 Recording Land Cover Changes

Comparing the 1984 land cover map to the 2018 Landsat satellite image, count and record the numbers of grid squares representing land cover that have changed from pervious to impervious surfaces, or from impervious to pervious surfaces.

Place the transparent 1984 land cover map over the 2018 Landsat image, and identify the dominant land cover – pervious or impervious — for each grid square on the map.

There are two roles in this step. One student partner compares the 1984 map to the 2018 satellite image and identifies the grid squares that have changed — from pervious to impervious land cover or from impervious to pervious land cover. The other partner marks the equivalent changed squares in the grid provided on Student Sheet for Step 8.

Systematically study each square on your grid map to determine whether or not there has been change so that you include each grid square. One way to do that is to work from upper left to right across each row, one row at a time. Use the row letters (A, B, C…) and column numbers (1, 2, 3…) to keep careful track of the specific grid squares as you communicate with your partner.

You may notice that some grid squares contain more than one land cover type. The most dominant land cover type in that grid square dictates which land cover type to assign to that square. For example if a square is 75 percent Vegetation and 25 percent Water, use the code for Vegetation. Some students may disagree about which type is dominant. Professional land cover analysts occasionally disagree too.

Step 9 - Calculating Percent of Land Cover Type Changes

Use the student sheet for step 9.

Evaluate

Step 10 - Respond to guiding questions provided.

Use the student sheet for step 10.

Use the Student Achievement Record to document student progress.

Sources: 

Extensions

  • Find additional locations at https://earthshots.usgs.gov/earthshots/. Other images can be found by clicking on Cities.
  • If two or more student teams analyze change in the same geographic area, compare teams’ results and comment on any differences.
    • Did your team identify the same kinds of land cover changes as the other team did?
    • If your team did identify the same kinds of land cover as another team, did the two teams arrive at created & produced by the NASA Landsat Education Team 16 Quantifying Changes in the Land Over Time with Landsat the same percent change from pervious to impervious surface area (or from impervious to pervious surface area)? If not, discuss between teams how your perceptions and/or methods of calculating change may have been different.
    • Provide notes about this discussion on the student sheet for Extension - Comparing Different Teams’ Results for the Same Areas of Change.
  • Assuming the same rate and nature of change, make a predictive map of land cover in 2030. Describe and explain the 2030 map and any ecological consequences that might be expected from the change. 
    • Describe the map and any changes you project from pervious to impervious surface or from impervious to pervious surface. (Remember to take the effects of major transportation arteries and geologic features such as mountains and rivers into account.) Explain why you have predicted this kind and amount of change.