IEEE Spectrum - North American - March 2015 - 37

harvard forest project

where the height of water is proportional
to the rate of flow.
Nestled in the undergrowth are three Raspberry Pi-powered acoustic sensors. They are
part of a pilot project to survey birds and
insects by detecting their distinctive songs.
Each unit, built for US $100, records every
sound within a radius of 10 to 15 meters, compressing and wirelessly transmitting audio
over the Internet to researcher Erik Sobel's
office on the outskirts of Boston. "Nobody is
going to sit and listen to terabytes of sound
data," says Sobel, whose background is in
target and pattern recognition for defense
applications. He is now working on algorithms to identify different forest species.
"The concept is to develop low-cost technology that can automatically detect when the
first cardinals arrive in the spring and when
the earliest crickets chirp, then correlate
that with temperature and so on."
This process of studying natural cycles is
called phenology, and it is the core of the
Harvard Forest mission. Every year since
1990, Harvard investigator John O'Keefe has
been noting when the leaves of dozens of
tree species first bud in the spring and when they change color
and die in autumn. Now his role is in danger of being usurped
by cameras mounted high above. Harvard biology associate
professor Andrew Richardson first put a digital camera on a
tower at the Harvard Forest in
2005, to "get some pretty pica threefold hybrid
tures to illustrate lectures." But
of wireless technology
he soon realized that by comconnects the forest's
paring colors in time-lapse phofar-flung sensors. Five
towers above the
tos, he could track and identify
treetops communicate via
seasonal changes. The dozens of
5.8-gigahertz radio links
"phenocams" he has installed at
[blue]; other 900-megahertz
radios penetrate leaves
12 locations around the United
and branches [green].
States have captured more than
Several 2.4-GHz Wi-Fi
5 million images. "We're doing
access points at ground
level serve the laptops
what satellite remote sensing
and smartphones of
does," says Richardson. "But
researchers working
we're doing it with cameras that
nearby [red].
cost a couple of hundred dollars
rather than a hundred million."
To be fair, many satellites capture far more than just visible
light. But by comparing phenocam data with images shot from
orbit, Richardson can quantify
uncertainties in the satellite data.
"We're improving satellite
data for the whole world," says
Richardson. He is now using

thermal cameras to follow trees' responses to heat stress,
and he has even installed an aerial tram that scoots over the
canopy on wires. The tram carries sensors that measure the
canopy's height, color, and ability to absorb different wavelengths of light-a key indicator of photosynthesis and plant
health. The tram can be controlled from a Web interface via
its 2.4-GHz ZigBee radio; it returns its data the same way.
a longside the ca mer as-and the main reason for Harvard Forest having towers at all-is a host of atmospheric sensors. Eddy flux devices measure tiny swirls in the wind and,
with the help of infrared analyzers, track the movement of
gases in the air several times a second. There are six of these
systems mounted at different heights on each tower, from the
forest floor to clear air above the canopy. Researchers can
thus follow the absorption of carbon dioxide and the emission of water vapor, as well as the changes in man-made pollutants like ozone and oxides of nitrogen.
Harvard Forest's eddy flux towers have been collecting data
since 1991-"the longest time series like that in the world," says
Richardson. It allowed Richardson and colleagues to prove
last year a long-held suspicion that forests are now doing more
photosynthesis with less water than in the past. As carbon
dioxide levels in the atmosphere rose from the combustion
of fossil fuels, trees actually removed and stored more of it.
This extra carbon sequestration might seem like good news.
But ecologists are trying to understand what the secondary
effects could be. And a few are not prepared to wait decades
to see how climate change might develop: They want to see it
today, with real-world simulations of global warming.

500 m

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