The low-flying planes just south of Ames this month are no cause for concern, said a city official.

The planes, which at times will be flying as low as 100 feet from the ground, are part of a soil-moisture experiment conducted by the United States Department of Agriculture and the Flight Research Laboratory of the National Research Council of Canada.

The purpose of the experiment is to improve the understanding of global water cycles, said Steve Salvo, Public Works Operations Administrator for the City of Ames.

“They’re doing this to understand the exchange of moisture between the ground and the atmosphere,” Salvo said.

The project will run through July 10.

John Aitken, head of flight operations for the Flight Research Center of the National Research Council of Canada, said they are using a Twin Otter (DHC-6) aircraft equipped with sophisticated equipment to measure the moisture in the soil and the humidity in the air, as well as the rate of exchange of the moisture between the ground and the air.

“The area of the experiment is just south of Ames in the Walnut Creek Watershed area,” Aitken said. “It stretches about six or seven miles in the north-south direction and about 15 miles east and west. It’s mostly agricultural land with corn and soybean crops.”

Aitken said there will also be as many as 50 ground sites or “point sites” taking similar measurements on the ground.

“The measurements from the point sites on the ground are valid for 20, 30, maybe 100 feet around the site,” Aitken said.

“We can cover a larger area with the airplanes and then check the accuracy with the ground sites.”

Aitken said the second airplane will be flying at about 5,000 to 7,000 feet with radiometers to see the amount of heat reflected of the ground.

“[The planes] will being measuring the radiant energy bouncing back from the earth,” he said. “There are also satellites whizzing over collecting data 150 to 300 miles up. The idea is to be able to say that these are real numbers coming out of the satellites, but you have to calibrate them with the ground sites. So there is data collection at a number of different levels.”

Aitken said flying so low is a little riskier but isn’t necessarily dangerous.

“The Twin Otter was built for work up in the north country in Canada and to be maneuverable at slow speeds,” he said. “We’re flying slow, so we have time to react. I would say it’s probably less dangerous than driving a car on the highway.”

Salvo said the experiment was only going to be conducted during the day under visual flight rules, meaning there must be a visibility of at least three miles and a ceiling of 1,000 feet. He said the National Research Council of Canada has received clearance from the Federal Aviation Administration to fly at the low altitudes.

Normally, planes are required be at least 500 feet over an unpopulated area and 1,000 feet above a populated area, Salvo said.

Aitken said some people have noticed something unusual going on and have called him with questions, but so far no one has called to complain about the noise.

Aitken said Ames was selected as a site was because the Walnut Creek Watershed is an area the U.S. Department of Agriculture has used to collect data for a number of years.

“They also usually conduct the experiments near agricultural universities,” he said.

Aitken said similar experiments have been done over several different ecological areas in Oklahoma, Kansas, California, the Brazilian rain forest and the Arctic tundra.

“All this data comes together and goes into world models on the relationships between moisture in the ground and in the atmosphere,” he said.

“One offshoot from this is it may improve weather forecasting too.”