This set of satellite images comes from the same Landsat 5 scene of Gary Wagner's farm on July 13, 2005. In the left panel, four of his fields are shown in natural color. The bottom left is a bare field. The top left is a spring wheat field. The top right two fields are sugar beets, and the bottom right is a confectionary sunflower field. The center panel shows the fields in bands 4-3-2 (the near infrared, red, and green bands), the standard near infrared composite combination used for vegetation where darker patches show stressed plants. The right panel shows just the near infrared band processed so that the yellow, green and teal colors show stressed plants and the blue and purple show healthier plants.
Farmers are using maps created with free data from NASA and the U.S.
Geological Survey's Landsat satellites that show locations that are good
and not good for growing crops.
Farmer Gary Wagner walks into his field where the summer leaves on
the sugar beet plants are a rich emerald hue -- not necessarily a good
color when it comes to sugar beets, either for the environment or the
farmer. That hue tells Wagner that he's leaving money in the field in
unused nitrogen fertilizer, which if left in the soil can act as a
pollutant when washed into waterways, and in unproduced sugar, the
ultimate product from his beets.
The leaf color Wagner is looking for is yellow. Yellow means the
sugar beets are stressed, and when the plants are stressed, they use
more nitrogen from the soil and store more sugar. Higher sugar content
means that when Wagner and his family bring the harvest in, their farm,
A.W.G. Farms, Inc., in northern Minnesota, makes more dollars per acre,
and they can better compete on the world crop market.
To find where he needs to adjust his fertilizer use -- apply it here
or withhold it there -- Wagner uses a map of his 5,000 acres that span
35 miles. The map was created using free data from NASA and the U.S.
Geological Survey's Landsat satellites and tells him about growing
conditions. When he plants a different crop species the following year,
Wagner's map will tell him which areas of the fields are depleted in
nitrogen so he can apply fertilizer judiciously instead of all over.
A farmer needs to monitor his fields for potential yield and for
variability of yield, Wagner says. Knowing how well the plants are
growing by direct measurement has an obvious advantage over
statistically calculating what should be there based on spot checks as
he walks his field. That's where remote sensing comes in, and NASA and
the U.S. Geological Survey's Landsat satellites step into the spotlight.
The Sensors in the Sky "Trip the Light Fantastic"
Providing the longest, continuous record of observations of Earth
from space, Landsat images are critical to anyone -- scientist or farmer
-- who relies on month-to-month and year-to-year data sets of Earth's
changing surface. Landsat 1 launched in 1972. The Landsat Data
Continuity Mission (LDCM), the eighth satellite in the series, will
launch in 2013 and will bring two sensors -- the Operational Land Imager
(OLI) and the Thermal Infrared Sensor (TIRS) -- into low orbit over
Earth to continue the work of their predecessors as they image our
planet's land surface.
Land features tell the sensors their individual characteristics
through energy. Everything on the land surface reflects and radiates
energy -- you, your backyard trees, that rocky outcropping, and a field
where a farmer is growing a crop of sugar beets. The sensors on LDCM
will measure energy at wavelengths both within the visible spectrum --
what people can see -- and at wavelengths that only the sensors, and
some other lucky species, such as bees and spiders, can see.
OLI will measure energy in nine visible, near infrared, and short
wave infrared portions, or bands, of the electromagnetic spectrum, and
TIRS will measure energy in two thermal infrared bands. And that's what
makes them such powerful tools.
Jim Irons, NASA Project Scientist for LDCM at NASA's Goddard Space
Flight Center, Greenbelt, Md., says that the instruments will deliver
data-rich images that tell a deeper story than your average photograph
of how the land changes over time.
Wagner's map -- a special kind of map known as a zone map -- shows
the difference between healthy and stressed plants by representing the
amount of light they're reflecting in different bands of the
electromagnetic spectrum. To display this information on his map, the
visible colors of light -- red, green, and blue -- are each assigned to a
different band. Red, for example, is assigned to the near-infrared band
that isn't visible to humans. Healthy leaves strongly reflect the
invisible, near-infrared energy. Therefore green, lush sugar beets pop
out in bright red on Wagner's map while the yellow-leaved stressed
plants appear as a duller red. Wagner can use this map to track and
document changes in his crop's condition throughout the season and
between seasons. As a tool, this map supports and enhances his
on-the-ground crop analyses with independent and scientific observations
from space.
Different band combinations tell farmers -- and scientists, insurance
agents, water managers, foresters, mapmakers, and many other types of
users -- different information. Additionally, since the Landsat data is
digital, computers can be trained to use all the bands to rapidly
recognize and differentiate features across the landscape and to
recognize change over time with multiple images.
"Therein lies the power of the Landsat data archive," says Irons. "It
is a multi-band analysis across the landscape and over a 40-year time
span."
Both OLI and TIRS use new "push-broom" technology, in which a sensor
uses long arrays of light-sensitive detectors to collect information
across the field of view, as opposed to older sensors that sweep mirrors
side-to-side. The new technology improves on earlier instruments
because the sensors have fewer moving parts, which will improve their
reliability.
OLI will also be more sensitive to electromagnetic radiation than
previous Landsat sensors, which is akin to giving users access to a new
and improved ruler with markings down to one-sixty-fourth of an inch
versus markings at every quarter inch. For Wagner, this means that next
summer with LDCM in orbit, he will be able to better discriminate the
degree of stress on his sugar beets, giving him a more finely tuned view
of what his plants need across the field.
The View of the Field is the Right Fit for its Purpose
Each step of the way, OLI will look at Earth with a 15-meter (49
foot) panchromatic and a 30-meter (98 foot) multispectral spatial
resolution along a ground swath that is 185 kilometers (115 miles) wide.
TIRS will measure two thermal infrared spectral bands with a spatial
resolution of 100 meters (328 feet) and cover the same size swath as
OLI.
Different scale resolutions -- low, moderate, and high -- deliver
different levels of detail in remote sensing images, and each has its
purpose. The 30-meter (98 foot) resolution of the Landsat images Wagner
uses allows him to see what is happening on his spread, quarter-acre by
quarter-acre. He doesn't need a view so narrow that the high resolution
image tells him who's sitting in the combine parked in his field, or a
view so big that it shows him smoke from forest fires drifting over the
North American continent with no detail on his farm.
The moderate resolution also means Landsat satellites are able to fly
over the same piece of real estate more frequently than high resolution
satellites. Once every sixteen days, Landsat 7 in orbit now or LDCM
after it launches, will revisit Wagner's farm, and every other place on
Earth, too, for global coverage. "We're looking forward to having a real
quality instrument in space," says Irons, who is excited about having
OLI and TIRS come online. He says the Landsat 30-meter resolution has
been assessed in the scientific literature as being a suitable
resolution for observing land cover and land use change at the scale in
which humans interact with and manage land. The sensors will record 400
scenes a day, giving users 150 more scenes than previous instruments.
Data from both of the sensors will be combined in each image.
The Legacy in the Landsat Mission is its Continuity
In daily operations on his farm, Wagner has used Landsat data in near
real time. He's anxious for the launch of LDCM and NASA's newest
sensors, OLI and TIRS, because not having the remote sensing data really
puts him in a bind. A lack of current satellite data disrupts Wagner's
understanding of what his plants need, what the soil needs, the
long-term performance history of his place, and his budget.
For now, with his zone map in hand, Wagner adjusts his care for his
sugar beet crop, allowing the plants to deplete fertilizer in the soil
so he can change the bright red on the satellite image to the yellow of
sweet beets in his field.
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