Ground Truth Studies Teacher Handbook - Aspen Global Change ...

Continental United States
(image source: EROS Data Center)
Description
This is a satellite image of the continental United States.
Like the previous image, it is a false color composite
mosaic of AVHRR images. The images were collected
over a two year period from 24 May 1984 to 14 May 1986.
The spectral bands displayed are the same, so healthy
vegetation still appears in vibrant reds, but in this image,
much, although not all, water has been specially coded to
blue, making it easier to pick out lakes and waterways. The
resolution in this image is the same as in the previous
image (1 km by 1 km), because it was taken by the same
sensors. Therefore, it also contains the same amount of
information as the previous image, but it is much enlarged,
so it is possible to make out more detail. This image has
also been overlaid with the state boundaries and cropped at
the Mexican and Canadian borders.
Procedure
First of all, if you are in an area covered by this image,
locate the area in which your students live and go to
school. If you aren’t in the continental United States, have
your students pick an area about which they know something,
or would like to learn more. Can they actually pick
out your city? Could our alien now detect any human
activity in your area at this scale?
Indeed, it probably could. Very large cities, such as New
York City, Chicago, Los Angeles, etc. show up as a light
gray or blue-gray spot on the image. Small cities are
unlikely to be visible, yet it is now possible to detect
human influences on the landscape. As noted before,
healthy vegetation shows up vibrant red. In this image, it is
possible to detect human agricultural systems quite easily.
At first, point out bright red areas along major river
systems in the west, such as along the Arkansas River,
running West to East in eastern Colorado, or the area just
south of the Salton Sea, above the Mexican border with
California. There they will see the bright red which
indicates healthy vegetation in well irrigated agricultural
fields. Using these areas as clues, can they find other
areas which indicate agriculture?
What other features can your students identify at this
scale? Watersheds and mountain ranges are more
apparent, and state boundaries follow many watercourses.
Several artificial water reservoirs are also
conspicuous at this scale and resolution. For example,
using a map and the image, ask your students to locate
Lake Powell in Utah, Fort Peck Lake in Montana, or
Lake Sakakawea in North Dakota. Can they locate
natural and artificial features near your area on the
image?
As a writing exercise or discussion, ask your students to
respond to the question: “How do you think state
boundaries were drawn? Do they correspond with natural
features, or do they appear to have been made with other
considerations in mind?” For example, ask them to
compare the state boundaries of Virginia with those of
Colorado.
The student should be able to outline major watersheds
and differences in color and attempt to explain these
differences. For example, why is the western region of
the United States blotched with gray and white, while the
eastern region is so red? What explains the bluish color
of southern Florida, or the bright white patterns in
Colorado, Wyoming, Idaho and other western states?
© ASPEN GLOBAL CHANGE INSTITUTE 1995 GROUND TRUTH STUDIES
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