Seeing Air in a New Light With LiDAR
Michael Cloos, a University
of Iowa student, adjusts the
On a still, dark evening near Ames, Iowa, about 30 researchers and
helpers mill about a large van parked in the middle of a vast cornfield.
They gaze upward, at a tight, narrow, steady beam of hot, green light
streaming from the vehicle. Hushed voices, carrying well through the
summer air, rise in excited spurts as the beamprojected out into
the star-filled skysuddenly snaps westward, and then southward.
"I hope you're enjoying our light show," says Jerry Hatfield,
director of ARS's National Soil
Tilth Laboratory (NSTL) in Ames. A light show, yes. But what Hatfield
and his colleagues are really doing is exhibiting the uses of LiDAR,
a technology that's been around awhile but is now showing great promise
Hatfield says LiDARfor Light Detection and Ranging"may revolutionize how we monitor the atmosphere around agricultural operations."
He explains that single-point monitors currently used to track tiny airborne particles force operators to assume that measurements represent the entire atmosphere. "LiDAR allows us to see just how accurate these samples are and how much the atmosphere in a given area is fluctuating. It gives us a multidimensional picture of what's going on."
Technician Kenwood Scoggin
samples for microwave-assisted
extraction as part of the
spectrometer process to
identify materials attached to
particulates collected in rural
Developed from laser studies during the 1960s, LiDAR has been used to look at clouds and plumes of gas and pollution, to detect stealthy submarines, to nab speeders, and to prepare topographic elements for land and ocean-floor maps.
Used In and Out of This World
The National Aeronautics and Space Administration (NASA), which in 1994 took LiDAR into space aboard the shuttle Discovery, describes the technology as being similar to radar. But instead of bouncing radio waves off its target, it uses short pulses of laser light to detect tiny particles, gases, or molecules in the atmosphere. Its tight, unbroken beam disperses very little as it moves away from its source. Computers analyze measured data from the reflected light, which scientists later analyze through display and tabulated formats.
"The technology works off of the principle of light-reflectance signaturethat is, being able to identify the reflection that specific particles make when struck by laser light," says Hatfield. "It allows us to accurately determine the location, distribution, and nature of particles."
Laboratory director Jerry Hatfield
and technician Kenwood Scoggin
examine a particulate sampler
during air quality studies
Hatfield says light emitted from LiDARs can vary in color, depending on the type of measurements being made. A complete, portable LiDAR costs between $100,000 and $200,000. Hatfield says his laboratory doesn't own one but has worked out a collaborative agreement with the Los Alamos National Laboratory in New Mexico and the University of Iowa (UI) to use their instruments.
"LiDAR can help us gain a profile of dust particles from mills
and cotton ginsand even of particles that make up odor plumes
that emanate from livestock facilities," says Hatfield.
Hatfield, NSTL soil scientist John Prueger, Los Alamos scientist Dan
Cooper, and UI professor Bill Eichinger have incorporated LiDAR into
ARS studies at various locations. The light exhibition in the cornfield
was part of a soil moisture experiment series that ARS, NASA, the National
Oceanic and Atmospheric Administration, and collaborating universities
are conducting to evaluate how accurately remote sensors on satellites,
aircraft, and land-based towers monitor ground-level moisture.
Hatfield, Prueger, and their team first used LiDAR in 1998 when they
were asked by the U.S. Department of the Interior's Bureau of Reclamation
to study the effect of saltcedaran invasive and prolific shrub
that removes large amounts of soil water while leaving behind soil-damaging
saltson western U.S. riverbanks.
Working along a section of the Rio Grande River south of Soccoro, New
Mexico, the researchers compared LiDAR with two other methods for estimating
water uptake by trees in riparian zones. They evaluated whether LiDAR
could map the source of water loss in an area covered with vegetation.
"It allowed us to measure water loss with a resolution of 25 meters
over an area of several square kilometers as accurately as by other
methods," Prueger says. "This shows LiDAR can help us understand
the dynamics of different land surfaces and the changes to them induced
by management. It also supports the idea of using LiDAR to produce three-dimensional
images of evaporation processes. An application of this is mapping plumes
of water vapor above a riparian zone."
The scientists used a scanning LiDAR that helped produce maps showing the spatial distribution, as well as rates, of evaporation at regular intervals throughout the day. "The three-dimensional character of the data allowed us to detect water vapor anomalies," says Prueger.
Evaluating an Ill Wind
Hatfield, through an agreement with UI, is currently studying LiDAR's
performance in evaluating dispersion dynamics around swine-production
facilities. "Effects of agricultural management practices on air
quality are ill defined," he says. "Many atmospheric componentssuch
as ammonia, methane, nitrous oxide, carbon dioxide, particulates, bioaerosols,
and herbicide vaporsmust be considered. This is complicated by
all the things that can affect an airborne particle, such as wind and
This study, says Hatfield, "can help us place instruments around
livestock production units where they can effectively capture plume
strength. Then, using mathematical techniques, we can estimate where
specific compounds are coming from, how strong they are, and at what
rate they're being emitted."
LiDAR can also be used to validate dispersion models for particulates
such as dust, water vapor, ammonia, and livestock emission gases. "With
it, we can create a data set for each of these particles," says
Hatfield. "We can make precise atmospheric measurements that can
be applied in many beneficial ways."By Luis
Pons, Agricultural Research Service Information Staff.
This research is part of Air Quality, an ARS National Program (#203)
described on the World Wide Web at www.nps.ars.usda.gov.
Jerry L. Hatfield and John
H. Prueger are with the USDA-ARS National
Soil Tilth Research Laboratory, 2150 Pammel Dr., Ames, IA 50011;
phone (515) 294-5723 [Hatfield], (515) 294-7694 [Prueger], fax (515)
"Seeing Air in a New Light With LiDAR" was published in the October 2004 issue of Agricultural Research magazine.