SAT Reading - Khan Diagnostic Quiz level 2 - reading 1

Questions 1-11 are based on the following passage.

This passage is excerpted from Joseph Mascaro, Gregory P Asner, Stuart Davies, Alex Dehgan, and Sassan Saatchi, “These Are the Days of Lasers in the Jungle,” ©2014 by Joseph Mascaro, et al.

Just as the Moon’s history was disrobed by laser ranging
50 years ago, Earth’s tropical forests are giving up their
secrets to the light. Airborne light detection and ranging—
called LiDAR—has over the last ten years become a key
5 tool that ecologists use to understand physical variation in
tropical forests across space and time. Like an MRI of the
human brain, LiDAR probes the intricate three-
dimensional architecture of the forest canopy, unveiling
carbon that forests keep out of the atmosphere, and also
10 the mounting threats to that carbon storehouse: drought,
fire, clandestine logging and brash gold-mining operations.
Even the quintessential natural disturbance of the sun-
filled light gap—long thought to enhance the incredibly
high species diversity of tropical forests—has been
15 deconstructed by laser technology.
Laser ranging in tropical forests is such a game-changing
technology that science results can scarcely get through
peer-review before they are dwarfed by still larger-scale
studies. In a decade, laser power on commercial-grade
20 LiDARs has skyrocketed and costs have plummeted. These
improvements in LiDAR technology allow airplanes to fly
faster, higher and farther, covering more forest area in a
single day than every ground-based survey that has ever
been collected in the history of tropical ecology. To
25 estimate the amount of carbon stored in a 50-hectare
tropical forest monitoring plot on the ground—the largest
field plot in the world—takes a team of 12 people about
eight months: a slog of rain and mud and snakes with tape
measures and data log books. Today’s airborne LiDARs
30 can get you to within about 10% of the same carbon
estimate in eight seconds.
It is this staggering contrast in scale between LiDAR
and fieldwork that led us here: Before this decade is out, we
could directly assess the carbon stock of every single square
35 hectare of tropical forest on Earth. We could do it just as
well as if we were standing there in the flesh with tape
measures in hand. And we could do it for far less than what
we have already spent to offset carbon emissions from
forests. . . .
40 It is easy in principle, though logistically nightmarish, to
measure carbon in tropical forests. A strict constructionist
would cut, dry and weigh the biomass of the world’s
forests. But this is a self-defeating enterprise. As a result, it
is likely that no one has measured carbon over a single
45 hectare of tropical forest, even with the most detailed field
surveys. For a century ecologists and foresters have relied
on allometric1 estimation in lieu of carbon measurements
to translate field surveys of tree diameters, heights and
wood densities into whole-forest carbon estimates. Given a
50 volume with known dimensions and density, one would
estimate its mass in a similar fashion.
As the new kid on the block, LiDAR has been tacked
onto the back end—initially thought of as kind of large-
scale helper to field surveys. Carbon estimates from the
55 field have been treated as something inherently closer to
the real thing than measurements made by LiDAR—
ground “Truth” with a capital “T”. This is perhaps
understandable historically, but vis-à-vis actual carbon,
there is no such thing as ground truth: both field and
60 LiDAR efforts rely on allometry to convert measurements
into carbon estimates. Prior to using these measurements
for carbon estimation, they exist as standardized, spatially
explicit, archivable and verifiable data—the needed
substrate for a REDD2-type accounting program.
65 Due to the constancy of the underlying measurements,
both field and LiDAR data could provide the needed
information if they covered every hectare on Earth. But, in
the case of field surveys, this is impossible. The surveys
that do exist measure a tiny amount of actual forest, and
70 so what might be verified is widely spaced. And to avoid
fraud and protect landowners, many governments keep
their plot locations secret. Satellite LiDAR data remain
sparse, providing only extrapolated, coarse-resolution
carbon estimates with very high uncertainties, and there is
75 no prospect of wall-to-wall coverage in the near future. By
2020, airborne LiDAR could give us a direct measurement
of 3-D forest structure for every hectare in the tropics: a
standardized database from which to build a carbon
economy.

 
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