How’s the Air Out There on the Farm? LiDAR Can Let You Know Lasers are used for lots of cool things these days. They’re used at supermarket check-out lines to scan the price of items. They’re used by eye surgeons for fixing peoples’ vision, for engraving patterns on glass or metal and for getting the perfect measure of a distance. Lasers also “read” compact discs, helping deliver the music and movies on them to your ears and eyes. Now, Agricultural Research Service (ARS) scientists are using a technology based on lasers to “read” the air around farms and livestock ranches. They hope their studies will lead to the laser-based technology’s widespread use in agriculture. First, About Light Beams and Lasers... Think of the light that comes from a flashlight as regular “white” light. It has a pale color, and spreads out away from its source, fading quickly as it gets further and further away from the flashlight. Now think of the light of a laser beam. In many ways, it’s the opposite of what comes out of the flashlight. Laser light is made up solidly of one color, leaves its source as a solid line that does not spread out, and stays strong, straight and narrow for great distances. Those differences are what make laser light special. Regular light is made up of many colors that blend to create the one color that your eyes see. Colors are actually made up of different waves of light that differ in length. In blending colors, the waves are all different, and they don’t “crest and trough”—go up and down—at the same time or within the same distance. With laser light, all crests and troughs are identical, and they occur at the same time. As a result, you get ONE SOLID color. Also, tiny mirrors are used to ensure that all the light waves go in the same exact direction—that’s what causes the straight beam of light. The word “laser” is actually short for "light amplification by stimulated emission of radiation." Whew—no wonder they just say “laser.” LiDAR, Radar: What’s the Difference? "LiDAR" is the shorthand name for the laser-based technology that the ARS scientists want to use to monitor farm air. The initials LiDAR stand for “light detection and ranging.” If it seems and sounds a lot like “radar,” that’s because LiDAR and radar are similar. Radar, which is short for “radio detection and ranging,” relies on radio waves sent into the air by a transmitter. (A transmitter is something that sends out a signal; it could be a radio signal or a light signal. A receiver is what picks the signal out of the air to make it possible for people to use.) When these waves strike something, they bounce and scatter in all different directions. Some of the bounced waves come back to where they came from, and where they are picked up by a receiver. The waves are then displayed in a way that allows the operator to make out the shape, size, and distance of an object. The Same, Yet Different LiDAR does the same thing as radar. But instead of sending and receiving radio waves, it emits and receives light in the form of laser beams. LiDAR isn’t new. It was first studied during the 1960s. Since then, it’s been used for tracking air pollution and submarines, and for making maps that show how high or low are land masses and ocean depths. It’s even been used aboard one of NASA’s space shuttles. Eeeuuuww—What’s That Smell? Now, says Jerry Hatfield, LiDAR may totally change the way dusty, smelly air around farm and livestock operations is watched. Hatfield leads research at the ARS's National Soil Tilth Laboratory in Ames, Iowa. He says LiDAR can help tell a lot about these agricultural areas, including whether they get enough moisture, whether there’s too much dust of one type or another, or whether they’re causing—or being affected by—air pollution. It can even help tell the size of a stinky plume of odor coming from pig farms, and where it’s going. Once set up and working, LiDAR looks a little like a really simple light show. It has an emitter from which the light beam comes, a receiver that reads the bounced-back light, and a control panel with instruments that collect and display the information. The straight, focused light really stands out against a dark night sky. What It Does Here’s how it works. The LiDAR set emits the light beam into the sky. If it doesn’t hit anything, the beam just keeps right on going into space. But if it does hit something—a fleck of dust, an odor-causing molecule of animal waste, or even a bird in flight—the light scatters, and parts of it come back to the receiver. The really neat trick is telling one thing apart from another. LiDAR does that by being able to read the reflected light’s “signature.” Every particle—and every object—reflects light in its own unique way. LiDAR’s computer program makes it possible to read the unique signatures of many, many things the laser beam strikes. Hatfield says LiDAR would be a great improvement over what is currently used to measure and monitor the air around farm and livestock operations. That’s because today, the best technology for this is sensors that can track particles in the air from only one place. The method forces operators to assume that the measurements they take represent the entire atmosphere. “LiDAR allows us to see just how accurate these limited samples are and how much the whole atmosphere within a given area is changing,” says Hatfield. “It lets us see what’s going on from many dimensions.” -By Luis Pons, formerly Agricultural Research Service, Information Staff To learn more about the use of LiDAR in agriculture, check out a story in the October 2004 issue of Agricultural Research magazine, titled "Seeing Air in a New Light with LiDAR.”
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