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Nov. 8, 1999: To water or not to water? Or fertilize? And how much?
These and dozens of other questions nibble at farmers as they go about the business of raising crops. What could be a simple decision for a single plant cannot be done thousands or hundreds of thousands of times to meet the needs of each plant on the farm.
Of necessity, farmers often wind up with "one size fits all" solutions: an entire field gets the same treatment. Yet nature is viciously random. What we see on a map or from afar as a homogenous field actually has a complex anatomy. "That's the way the real world is put together," said Dr. Doug Rickman, a NASA remote sensing scientist at the Global Hydrology and Climate Center in Huntsville, Alabama.
Rickman is a co-investigator on a project that links remote sensing with precision farming to see if high-altitude images can map the variations in a field and help farmers apply just the right amounts of resources only where they are needed. The co-principal investigator is Dr. Jeff Luvall, also of the GHCC.
"This exciting project brings together NASA scientists and farmers," said Dr. J.M. Wersinger of Auburn University, "soil and plant researchers and Extension specialists - who make sure the technology gets to other farmers so they can use it."
Wersinger is a NASA Space Grant Fellow who is administering and coordinating the program that is funded by the Alabama Space Grant Consortium, the Georgia Space Grant Consortium, Auburn University and the University of Georgia. The current effort grew out of a desire at NASA Headquarters to put remote sensing technology to work helping farmers and others in partnership with Extension people.
Wersinger arranged for Dr. Paul Mask, an Extension specialist and agronomist at Auburn University, and Dr. David Kissel a soil scientist at the University of Georgia to line up farmers who had the right instruments on their harvesting combines, and asked Rickman to develop the remote-sensing end of the project.
"We set up a small pilot project and were wildly more successful than we had expected," Rickman said. In one cornfield, aerial images correlated to 87 percent accuracy with the actual crop yield.
"It's higher than almost anything else I've ever seen in land-based remote sensing," he continued. "There's some interesting physics going on that no one was aware of." Nor does anyone fully understand it yet, but that might not be necessary as far as farmers are concerned. What matters is if it works.
"I don't think we'll understand all of the physics involved in this any time soon," Rickman explained. But in this case, "understanding the science is tertiary. Our end objective is to make an economic difference to the individual farmer."
The individual farmer is starting to benefit from what Rickman calls a "confluence of multiple technologies that are wildly dissimilar in their origins."
Remote sensing is the field of taking images from a distance and making detailed interpretations about what is there. Weather satellites and space probe images of planets are examples of remote sensing. Since the 1970s, though, the term has generally been applied to satellites looking back at Earth and observing the environment.
It's based in the fact that light does more than paint stunning pictures of the world. It also carries information about the object that reflected or emitted the light. The trick is in understanding how to manipulate the light to extract the right messages.
The GHCC's application of thermal remote sensing to precision farming has its foundation in ecological thermodynamics which states that ecosystems develop to maximize energy throughput and maintain the lowest possible surface temperature. In agriculture systems this translates to greater leaf area and greater rates of water evaporating from leaves, which is directly correlated to yield.
The other technology joining the field is precision agriculture, derived from a different aspect of space. Since the mid-1990s, farmers increasingly have used navigation satellites originally designed for the military. By linking sensors that measure yield as crops are harvested with a series of navigational fixes every few feet, and then cranking the data through a computer, a farmer can get an accurate image of how productive different parts of a field are.
Satellite navigation expands the potential value of high-altitude imagery.
"I could do that as early as the '70s," Rickman said of the image that predicted crop yield. "But it wouldn't mean anything because you couldn't match it against ground data."
In addition, ground data was difficult to acquire. Getting 10 soil samples from the field into a lab for analysis was a major effort.
"Basically you couldn't do anything on a subfield basis," Rickman said.
At the same time that satellite navigation became available to the consumer, advanced, low-cost electronics made it possible to add sensors that would sample field conditions as farm combines moved through the field. Coupling the sensors with GPS, farmers now could take dozens or hundreds of soil measurements while planting, fertilizing, and harvesting, and then return days and weeks later to repeat the measurement in the same location.
Still, measuring an entire field is a daunting task, so Rickman, Luvall, and others are testing imagery taken from aboard NASA's Lear 23 jet equipped with the Advanced Thermal and Land Applications Sensor (ATLAS). This is the same system used in the highly successful Urban Heat Island experiments.
ATLAS is sensitive to 15 channels of the electromagnetic spectrum, ranging from visible light (where the human eye is sensitive to three broad channels, red, green, and blue) through near-infrared down to thermal infrared.
A crucial element in ATLAS is the ability to recalibrate itself to ensure that the readings are always accurate and don't drift with time.
Calibration is a key requirement for successful remote sensing. Another is geometric correction so the data taken by the sensor match correctly with elements on the ground. It makes no sense to predict a good harvest from a rock outcrop.
Rickman said that ATLAS meets these and other needs, making it an outstanding selection to meet the requirements for helping precision agriculture.
Working with Auburn University and the University of Georgia, and their respective agricultural extension services, six farms were selected in Georgia, Alabama, and Tennessee where precision agriculture systems are employed on several private farms. Especially valuable, Wersinger said, is precision agriculture directed by Dr. Paul Kvien of the National Environmentally Sound Production Agriculture Laboratory at the University of Georgia.
The geographic variety was needed because, "Just as an individual field varies, you also get significant variations from region to region and area to area," Rickman added.
One of the discoveries from overflights in 1998 and 1999 was that the image, taken two months before harvest, had an 87 percent correlation with the actual harvest yield. Normally in the science community a new correlation is studied in detail until it is fully understood before a paper is written explaining it from start to finish. But the vagaries of climate and farming -- witness this year's drought and its impact on families and the economy -- give Rickman and his colleagues a different perspective.
"We have observed a correlation of a single band of data with a yield that is very high," he said. "We don't understand why it happens, but it happens, and that is enough for us to go forward and tell people that it exists." Especially since it happened more than once.
Wersinger is reluctant to speculate on what it might eventually mean in improved agricultural economics.
"We are in a phase where we are just trying to find out what it can do for people," he explained. "Precision agriculture means different things because fields vary from region to region. The economics are going to depend on the area, on the type of farm, and on what they mean by precision agriculture. However, tailoring the application of chemicals to real needs in the field will certainly benefit the environment, reducing water pollution."
Another discovery was that wind apparently can affect the image collected by a remote instrument. One experiment over Georgia was designed to collect two sets of images 30 minutes apart. Because of the way the flight lines overlapped they acquired four images, two of them just 3 minutes apart.
The details of why the image changed so radically still have to be worked out, but could lie in the elasticity of the plant stalks, interactions between the plant and cooler air, or just the change in the angle between plant and sunlight.
Whatever the cause, "it puts an upper boundary on what you can say about remote sensing images," Rickman said, because winds are unpredictable.
Wersinger agreed that the results are puzzling and said he and students at Auburn are working on a computer model that will try to simulate the crops and try to reproduce the effect.
In addition to measuring crops, remote sensing and precision agriculture can measure the content of organic carbon, minerals, moisture, and other factors in the surface of the soil.
"You can fly over an area and tell a lot about things that are extremely important to the farmer," Rickman said. "You're talking about the field of an individual farmer, and not some nebulous concept of helping farming in general. It makes a difference. It makes it real."