Geoscience Reference
In-Depth Information
Figure 1.
An artist's rendering of the Aura satellite, which is dedicated to collecting data on air
pollutants (image courtesy of NASA).
LAUNCH OF A NEW FIELD
Steady progress in the capabilities of satellites during the 20th century provided
glimpses of the planet from ever higher elevations. With the 1957 launch of the first
satellite, Sputnik, by the Soviet Union, we gained our first view of the Earth from
above the troposphere, the layer of the atmosphere that shimmies around the planet
from the ground to elevations of about 4-12 miles.
The following year the US created NASA. The study of atmospheric pollutants
was far from the fi rst priority in NASA's early years; instead, the program focused
on keeping the US ahead of the Soviets in the Space Race. But the technological
capabilities developed as part of the US space exploration program have provided
critical tools for beginning to observe the complex gyrations of various pollutants in
the atmosphere.
Among the many other countries now involved in satellite programs targeting air
pollutants are Brazil, Canada, China, India, Japan, and the 20 European countries that
are the primary supporters of the European Space Agency (ESA). “More and more
countries are getting aware of this problem all over the world,” says Claus Zehner, an
ESA Earth observation applications engineer. “It is a growing theme in the satellite
world.”
Tracking individual air pollutants can be quite a challenge. Satellite instruments
use the unique spectral signature of a single chemical or class of chemicals to dis-
tinguish it from all the other substances fl oating around it. But scientists must also
account for variables such as clouds, humidity, wind, and landforms; refl ectance from
land and ocean surfaces (which form the backdrop of what the instrument sees); time
of day and season (which can affect formation of various compounds); and chemical
reactions (which can alter the tracked compound before it reaches the ground, making
it diffi cult to predict the exact chemical culprits of environmental health concern). In
addition, there's horizontal and vertical mixing of air masses at a wide range of tempo-
ral and spatial scales, including that caused when the upper troposphere mingles with
