Remote sensing gives satellite’s view of water use - trivalleycentral.com: Farm And Ranch

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Remote sensing gives satellite’s view of water use

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Posted: Wednesday, October 9, 2013 1:00 am

MARICOPA — Farmers are very good at irrigation, said Andy French, a research physical scientist with the U.S. Arid-Land Agricultural Research Center.

They wouldn’t be in business if they didn’t know what they were doing, he said. “The question is: If you don’t have enough water, then how do you do it?” How do you decide which fields get water now and which have to wait?

Scientists have been using remote sensing since March 1, 1984, when NASA launched Landsat 5 to record land surface conditions on earth. It circled the earth for more than 25 years, recording data and sending home information about natural disasters, climate variations, land-use practices, urbanization and other changes.

“Can you imagine building a computer and having it work for over 25 years?” French asked. “My PC crashes once a week.”

Landsat 8 is orbiting now. Any farmer can go to the U.S. Geological Survey website and look at multispectral images of his farm, taken at the same time of day every 16 days.

“The fantastic thing about NASA policy is that the data are all free,” he said. “Anybody can get it.”

NASA did a smart thing by making it free, he added, because it has the whole world using the data. “And that means the science is really huge.”

Healthy plants reflect near-infrared light, French said. Landsat 8’s near-infrared sensors allow farmers and scientists to evaluate plant health more accurately than they could with the naked eye and look at several thousand acres at once.

“We want somebody — NASA or somebody — to build high-resolution, accurate, thermal infrared instruments into the satellites, so we can do this on a routine basis and have a really good way of measuring crop water use.”

But farmers need information about their crops more frequently than once every 16 days, so French is testing proximal sensing instruments. One four-year experiment has four thermal infrared radiometers in two fields. One field is well watered. The other gets the drought treatment.

There should be a big difference in the temperature of the plants’ leaves, he said, because plants cool themselves with water. When they don’t have enough water, they get hot.

The sensors are calibrated to 1/10 of a degree Celsius. Each sensor has four thermal infrared radiometers, one pointed down in each direction because the sun moves east to west, changing the sunny and shady parts of the plants. The wireless system records the temperatures at 15-minute intervals, and French can access it with a Web browser.

Even wind, blowing across a field, changes the temperatures and can be seen as a wave passing through the crop, he said. It all affects how much water the plant uses.

Farmers are not using a lot of remote sensing now, he said, because they are reluctant to use a new technology unless it shows a return on their investment.

“And I am completely with them on this,” he added. They need a system that is affordable, reliable, accurate and not time-consuming to use.

Farmers and scientists have known since the 1980s that they can monitor the temperature of crops, he said. “What is new is that technology has made it easier, cheaper and more capable of data processing.”

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