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

Remote Sensing & Ground Truth Primer (continued)
display different spectral bands, the image is called a ‘false color’ image. In color infrared photography, the color red is
traditionally assigned to the near infrared band, which results in healthy vegetation showing up as vibrant red, because it
radiates strongly in the infrared region of the spectrum. At first, one may be disoriented by the “false color” of color
infrared images. There is a “standard” color key used in color infrared imagery, but a scientist studying a specific feature
with a particular reflectance or emittance characteristic might choose to highlight these features by assigning different
color codes.
Geographic Information Systems
Geographic Information Systems (GIS) use computers to combine remote sensing data with other information (e.g.,
topographic, political, cultural, economic, ground truth). In essence, a GIS is a way of managing Earth science data to
bring out geographical interrelationships. Such systems provide powerful ways to use and compare remote sensing data.
A satellite image of a country’s vegetation can receive overlays of roads, district or county boundaries, population
statistics, etc. In essence, a GIS is a database management system specifically designed for simultaneous processing of
spatial data with many capabilities similar to automated map making.
Ground Truth
Ground truth refers to field observations and measurements which provide the link between remotely sensed data and the
environmental information that is desired. Satellite data can often be ambiguous, since the information is based on
radiation measurements with limited spatial and spectral resolution. For example, forests can usually be distinguished
from fields, and sometimes the type of trees present (deciduous vs. conifers) can be inferred. Scientists may then visit a
forest to verify that it is composed of pine trees. The field data gathered is called “ground truth.” Such “ground truth”
information may be used calibrate the remote sensing data for local conditions, and to interpret and analyze the data. It
may also be used to validate the results of the interpretation and analysis process. Ground truth observations by students
can be used to analyze aerial photographs and satellite images of their own location.
Teaching Remote Sensing and Ground Truth
Remotely sensed images may be used very successfully as educational tools with students of all ages. It is sometimes
useful to begin with images closest to your neighborhood and progress to images obtained from greater distances. For
example, start with hand-held photos and then move to low-altitude aerial photos, to high-altitude aerial photos, and then
to satellite images. The false color may initially be confusing, but this can be quickly remedied by explaining that it is
similar to assigning a color code to a map. When remotely sensed images are compared to maps, the effects of scale
should be considered to avoid confusion about an object appearing larger on one than the other.
Remote sensing and ground truthing are activities that make use of knowledge and skills which students acquire from
many traditional school subjects. Their improved ability to “see” and understand their world can bring them closer to
experiencing the interdependence of all life and the complex systems of planet Earth.
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© ASPEN GLOBAL CHANGE INSTITUTE 1995 GROUND TRUTH STUDIES