Agricultural aircraft can be flown much lower than larger planes.
"Flying low avoids interference experienced with satellite images,
which requires atmospheric corrections," Thomson says. But low
flights limit the ability to capture images of large areas all at once.
That problem is overcome by "mosaicing," which involves making
multiple flights over the site and assembling many images taken over
different portions. The challenge is to define the altitude that will
result in the best images in terms of size, resolution, and area covered.
Putting New Method to Good Uses
Thomson and colleagues in the ARS Southern Weed Science Research Unit,
also in Stoneville, were able to distinguish between different weed
species and cotton and soybean plants in field studies. This demonstrates
the feasibility of using planes or ground sprayers to apply as little
pesticide as needed. Using digital data, the researchers could spot
weeds among early cotton at an altitude of 65 meters (about 215 feet).
Thermal images of cotton fields may help identify practices that favor
higher soil temperatures. Warmer soil correlates with earlier emergence,
which can benefit crop vigor in early-season cotton.
Water stress is a familiar problem to growers in the Mississippi Delta.
It is more difficult to detect crop water status by remote sensing in
humid climates than in semiarid climates because of limited canopy cooling
by evaporation. At the same time they are being used to spray pesticides,
agricultural planes can be used to obtain canopy heat signatures to
assist in irrigation scheduling.
Another major problem for farmers and ranchers in parts of the Midsouth
are imported fire antsred, black, and a hybrid of the two. Their
painful stings can ultimately lead to death for some people and newborn
livestock. Thomson is helping Stoneville researchers learn more about
the ants' behavior so they can develop more effective biological control
methods. They know that fire ant mounds heat up in morning hours more
quickly than the surrounding soil does. So the researchers are using
thermal cameras to measure infrared emission (heat) and locate the mounds,
which appear as bright spots in images taken from above.
Aquaculture could also benefit from remote-sensing methods. Thomson
and Paul Zimba of the Catfish Genetics Research Unit in Stoneville are
studying a way to detect harmful algal species in catfish production
ponds before the problem gets out of hand. The researchers can now identify
specific types of algae by color, visible on digital video shot during
the low-altitude flights. Unwanted algae are distinguishable by their
chlorophyll and carotenoid compounds. With enough data, the scientists
can predict when certain types of algae are present.
Another project is to find out why double-crested cormorants tend to
pluck catfish fingerlings out of some ponds but not others. Thomson
and Andy Radomski of the Harry K. Dupree National Aquaculture Research
Center in Stuttgart, Arkansas, think pond color and condition may have
some effect.By Jim
Core, Agricultural Research Service Information Staff.
This research is part of Crop Production (#305) and Integrated Agricultural
Systems (#207), two ARS National Programs described on the World Wide
Web at www.nps.ars.usda.gov.
Steven J. Thomson is
in the USDA-ARS Application
and Production Technology Research Unit, P.O. Box 36, 141 Experiment
Station Rd., Stoneville, MS 38776; phone (662) 686-5240, fax (662) 686-5372.
"Agricultural Aircraft Offer a Different View of Remote Sensing"
was published in the March
2005 issue of Agricultural Research magazine.