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 he first years of the new millennium promise to revolutionize
our ability to see how the natural world is changing and to answer
perplexing questions about mankind's impact on the planet. For
the first time, scientists will be able to peer inside forests
across the world, accurately measure changes in the amount of
ice in the polar caps, and get a global look at how clouds and
airborne dust particles affect global warming.
 Many
of these advances will be made when a new generation of laser-based
sensors make their debut in space, says M. Pat McCormick, co-director
of the Center for Atmospheric Sciences at Hampton University.
In 1999, McCormick was selected by the American Meteorological
Society as the Remote Sensing Lecturer for this year's meeting
in recognition of his outstanding contributions to remote sensing
of the atmosphere.
Three
new NASA Earth-observing spacecraft will launch innovative "lidar"
instruments into orbit beginning this fall. Lidars send pulses
of light energy from a laser through the atmosphere and measure
the speed and the amount of light that returns. The signal's
round-trip time is a direct measure of the distance to the object.
"Most
instruments that scientists use to observe the Earth from space
cannot see through even thin clouds or their view is distorted
by clouds," says McCormick. "Many surface features
and important phenomena in the lower atmosphere are completely
hidden. Lidar can pierce many types of clouds and its very small
beam can pass between clouds."
The
first of these instruments will be launched this September. The
Vegetation Canopy Lidar mission will create the first maps of
the three-dimensional structure of vegetation in the world's
forests. By measuring the height of trees and the amount of leaves
and foliage in a forest, the mission will monitor forest health
and conditions over most of the globe and produce a global estimate
of how much carbon the forests hold.
The
ICESat mission, scheduled for launch in July 2001, will carry
the Geoscience Laser Altimeter System to map the surface of Earth's
ice sheets in unprecedented detail. By comparing how the ice
sheet surface changes over several years, scientists can calculate
how much ice has been lost and how much that ice has contributed
to sea level rise. The ICESat lidar also will detect polar clouds
and haze. A similar instrument, the Mars Observer Laser Altimeter,
recently mapped the surface and ice caps of Mars.
The
Pathfinder Instruments for Cloud and Aerosol Spaceborne Observations
(PICASSO-CENA) mission, scheduled for launch in April 2003, will
provide key measurements of aerosol and cloud properties needed
to improve climate prediction. Hampton University is a partner
with NASA on the PICASSO-CENA mission, and McCormick serves as
a co-principal investigator.
Ground-based
lidar systems were introduced in the early 1960s, and scientists
used them to monitor ozone and small particles (aerosols) in
the upper atmosphere. Airborne lidars were developed in the late
1970s to extend these local views to regional scales. The first
spaceborne lidar flew aboard NASA's Space Shuttle in 1994. The
Lidar In-space Technology Experiment (LITE) provided the first
highly detailed global profiles of the multilayered structure
of clouds. It also was able to follow the movement of airborne
dust from the Sahara Desert and urban air pollution particles
from major industrial centers.
The
new generation of space-based lidar is the result of technological
advances in more power-efficient, long-lived lasers and lightweight
telescopes to collect the returning laser signal. McCormick was
one of the early pioneers in the use of lidars and built the
first airborne system in 1978. He serves as the LITE project
scientist. McCormick led the Aerosol Research Branch at NASA's
Langley Research Center from 1975 to 1996. 
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