From the Top Down

Objectives:

identify features on a remotely sensed image (RSI) then match locations pinpointed on the image with pictures taken on the ground

match locations on a remotely sensed image with an oblique photo taken at those locations

rationalize student matches in a class discussion

Grade: 4- 6

Time Duration: one class period

Subjects:
geography, language arts, science, observation, spatial relationships

Vocabulary:
oblique, vertical, landforms, remote sensing imagery

Materials:

remotely sensed image of your local area

5 slides or photographs taken from the ground at locations pinpointed on the remotely sensed images (RSI)

chart of color codes for interpreting the RSI

slide projector if slides are being used

butcher or chart paper for each group

pencils or markers

Background:
A remotely sensed image can give us data about an area and its relationship to the areas around it or to areas anywhere that we choose to compare with it. But can we identify places that we know or recognize on an RSI? Imagine that you are flying over your town or neighborhood in an airplane. How could you find your hose? Your school? Where you shop? On an RSI we also use landforms and other features to help us pinpoint locations that we would like to study.

In order to accurately understand the relationship between colors and images on the RSI and the locations that they represent, scientists send teams to "ground truth" areas in the image. These teams travel to locations on the image and take photos and other readings of the area in order to set standards to interpret the differences on the RSI. For example, in the study of the Kesterson Reservoir , scientists discovered that the cattail population around the reservoir that show up as light green on an RSI that uses specific wavelengths have absorbed polluting minerals whereas the cattails that show up as dark green have not.

The first step to using an RSI is to be able to picture the type of area that is represented by given colors on the image. (Many RSI are not taken in visible light and so are displayed in false color which require false-color keys to interpret.) To start, students will identify features on a remotely sensed image then match locations pinpointed on the image with oblique images taken at each spot.

If you decide to take oblique photos of your area or another area for which you have obtained an RSI, then choose varied locations. At each location, take the photos near the same time of day and from the four cardinal compass points (N, W, E, W). When selecting photos to be used in class, choose images with the same orientation at each location. Students can then keep one orientation in mind when matching oblique images with points on the RSI.

Procedure:

Brainstorm with students possible landforms and environments. Show students the remotely sensed images you have obtained for your locale. What landforms can they identify? Have students explain how they know what these landforms are. Chose a color and tell what type of environment it represents. Discuss the differences between environments and between colors.

Refer to your RSI and have the students note specific locations on the image. Have the students tell what these locations might look like from the ground. Show slides or photos taken from the ground. Discuss features in each photo.

Show the ground-level photos again one at a time (save one for assessment). Have students discuss in groups the location from which the RSI is taken. Group will write reasons for their choices on butcher paper then share their rationalizations with the class.

Refer to the Kesterson Reservoir image. Explain to students why the difference in color of the cattails around the lake is significant. The class can brainstorm other possible reasons for subtle differences in colors. Groups brainstorm a list of ways remotely sensed images can be useful then share these ways with the class.

Assessment:
Look at a ground-level photo of an area shown in your local RSI. Find one or more possible locations on the RSI where it could have been taken. Have students explain their choice.

Extensions:

Project an RSI onto a grid. Count the number of boxes of each color. Calculate the percentage or fraction of each color represented in the image. How might this have been different one hundred years ago? How might this be different one hundred years from now?

Walk to locations in your area and decide what color these locations would be on an RSI using the same color code as the above exercise.

Obtain an RSI of another location. Have students discuss and identify features. Pinpoint locations on the image and have students make drawing of what that location could look like from the ground.

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