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Can Satellites See Frogs?
May 2005
If you wanted to monitor frogs across the United
States, you probably would not think to use
satellites. After all, the highest resolution,
commercial satellite currently orbiting the earth
cannot map objects that are smaller than 4 ft2.
There are no frogs that large, so how could
information from satellites be helpful for
monitoring frogs?
While it is true that we cannot see frogs directly
from satellite imagery, we can see landscape
changes that tell us something about amphibian
habitat. Habitat loss and alteration are the
principal causes of amphibian declines worldwide.
Because satellites enable us to collect information
over the entire world, we can remotely monitor
much larger areas than could ever be visited in
person.
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Satellite data can
be used to detect
many types of
changes in the
landscape, such as
from wildfire (figure
1), timber harvest
(figure 2), urban
development,
land management,
floods, tornadoes,
and volcanoes, etc.
By monitoring the
landscape, we can
watch for changes
that might be
beneficial or
detrimental to
amphibian habitat.
One type of change
that is important for
amphibians is the
availability of
potential breeding
habitat. Many
species require
wetlands as
breeding sites.
Wetland habitat
can change
drastically due to natural environmental differences from year to year, or due to human-imposed alterations. For example,
differences in annual weather conditions strongly affect the amount of surface water available in the
Great Plains each year (Figure 3). A longer-term effect on available surface water results from the
installation of drain tiles, which promote quicker drainage of agricultural lands.
Satellite imagery offers a means for detecting many types of landscape change over large areas. This can
help ARMI scientists determine how quickly the landscape is changing, the types and locations of change,
and the likely consequences for amphibians. It can also help scientists develop strategies for where
amphibians should be monitored.
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Figure 1. Fire scars (shown in shades of red and pink) in Mesa Verde National Park.
Recent scars are red; older scars are in shades of pink. As scars age, forest regrowth
(green) becomes visible. While forest fires may be hazardous to amphibians at the time
of conflagration, fires also provide benefits. Fires can open up densely-packed, closed canopy
stands, providing a variety of stand ages and structures that afford amphibians
a greater opportunity to move between patches of sunlight and shade to regulate their
internal body temperatures.
[Images are from the Landsat Thematic Mapper sensor.] |
Figure 2. Timber harvest patterns in the Northern California Coast Range. The satellite image on
the left is for a nearly 40 square-mile area in 1991. Lighter-colored patches are where timber has been harvested.
Vegetation cover for the same area, shown on the right, was highly fragmented by the year 2000.
[Images are from the Landsat Thematic Mapper sensor.] |
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Figure 3. These satellite images
show changes in the amount of
standing water (black areas) in
Brown County, South Dakota,
for May 1992 (top image), May
1994, (middle image) and May
1997 (bottom image).
Precipitation in May of 1992 was
little more than half the season's
average amount. Precipitation
received in 1997 was only about
5% above average, but followed
a year of extraordinarily high
precipitation (70% above
average). Habitats that are
subject to high rates of change,
such as these wetlands, provide
a challenge for wildlife biologists
and land managers.
[Images are from the Landsat
Thematic Mapper sensor.] |
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