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Ever wondered why so many plants look green? Well, it's because healthy leaves absorb the red and blue wavelengths of sunlight, and they reflect most of the green light back to our eyes. But the sun showers plants with other types of light that we cannot see, like near-infrared light. That light also bounces off plants. And for decades, scientists have used infrared sensors to study those reflections as a proxy for plants' health, among other things.
That gave one artist an idea. Could he use the same technology to play the Joshua tree like an instrument? NPR's Christopher Intagliata explains.
CHRISTOPHER INTAGLIATA, BYLINE: The artist Scott Kildall has spent years revealing hidden natural phenomena through sound. His latest installation transforms the Joshua tree into a shimmering mosaic of tones.
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INTAGLIATA: And that is what brought us to be standing together on a windy day in the high desert, a couple hours outside LA, gazing out at a field full of the iconic scraggly yuccas.
SCOTT KILDALL: I always feel like the Joshua tree just has sort of magical properties when I see it. It is gorgeous, and if I get too close to it, it will prick me and draw blood, and it's done that before.
INTAGLIATA: They're spiky, all right. But today, Kildall is eyeing each and every one of them with the enthusiasm of a kid at Guitar Center ready to pick out an ax.
Well, we're looking now for a really good Joshua tree that is in the sun.
KILDALL: I'm looking for ones that have a mixture of dead parts and live parts that I can actually reach with my hands.
INTAGLIATA: Dead parts and live parts because the bright green buds reflect much more of the sun's near-infrared light than the dead grayish brown bark.
KILDALL: So that one looks pretty good over there. You could go check out that guy.
INTAGLIATA: We walk over lugging a big speaker, a laptop, and a box of electronics. Kildall pulls out a microcontroller just about the size of a credit card. It's got some wires sticking out and an infrared sensor on it.
KILDALL: The sensor's picking up reflections of light that we can't see. And so it's really cool. It's kind of like magic. And the...
INTAGLIATA: Yeah.
KILDALL: ...Magic is just revealing something that's right beyond our levels of perception.
INTAGLIATA: As he runs the device above the rough, shaggy bark, the readings from the sensor are pretty low, in the low 2000s.
KILDALL: Now, if I take the sensor and put it right towards the leaves of the Joshua tree, I'll ask you, Christopher, to tell me what this - numbers say.
INTAGLIATA: Oh, wow. OK, now we're up at 14,733.
These numerical readings are what Kildall translates into sound, using a program on his laptop. And after he boots it up, the performance begins.
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KILDALL: And now I'm playing the tree like a theremin.
INTAGLIATA: Kildall has programmed other instruments to respond to the sensor data, too, and he switches on his favorite.
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KILDALL: And you can hear, as I get to that really kind of sunny, leafy parts - that it's getting this kind of higher-pitched note sounding.
INTAGLIATA: Then, as he caresses the air above the dead parts of the Joshua tree, the infrared readings go down and so does the pitch of the sound.
KILDALL: Like, it's just gotten down to a low rumbling.
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INTAGLIATA: It's a fascinating way to make music. But scientists like Greg Asner at Arizona State University in Hawaii have been studying this interplay between near-infrared light and plants for decades.
GREG ASNER: From our aircraft or satellites, we use it to separate the living vegetation from the dead vegetation.
INTAGLIATA: Asner explains that living, healthy vegetation is packed with water, defense chemicals and other compounds, which is the reason more near-infrared light reflects off a healthy leaf compared to a dead one.
ASNER: And for example, that's very important in a grassland. Is the grassland dry and ready to go up in smoke in a fire, or is it wet and green and living? And so we can translate that to fire fuel load for grasslands.
INTAGLIATA: Asner says he's thrilled to see artists now playing with some of these same ideas.
ASNER: Our studies for decades now have been stuck in the halls of science, and this will help translate what we have come to understand - utilize love as scientists. It's going to translate it to a much wider audience.
KILDALL: Science articles are great. I read them all the time. However, they don't engage people in a more visceral storytelling level as artwork does. I'm hoping that people realize that there is just this invisible layer of data that's just right beneath the surface and get excited about the natural world.
INTAGLIATA: Now, this isn't Scott Kildall's first go at translating science into art. In recent years, he's designed a sound installation that tracks water flow in trees...
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INTAGLIATA: ...And an ambient soundtrack that taps into the electrical signals of mushrooms.
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INTAGLIATA: He's exhibited at the New York Hall of Science, too, among other places. But his latest work took root here in the California desert when he was an artist in residence this spring at Joshua Tree National Park. He calls the work Infrared Reflections.
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INTAGLIATA: Christopher Intagliata, NPR News, the California High Desert. Transcript provided by NPR, Copyright NPR.
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