SCIENCE ON THE VIEWING EDGE OF EARTH'S ATMOSPHERE
New NASA instrument to measure ozone, climate change
A new NASA remote-sensing satellite instrument took its first
steps toward monitoring the health of the Earths upper
atmosphere yesterday. The Stratospheric
Aerosol and Gas Experiment III (SAGE III) was launched
successfully from the Baikonur Cosmodrome in Kazahkstan.
Developed and managed by NASA Langley Research Center, Hampton,
Va., SAGE III aboard the Russian Meteor-3M spacecraft lifted off at
p.m. EST on a Ukraine-built Zenit-2 Rocket. SAGE III will make
precise measurements of ozone, aerosols, water vapor and other
gases so researchers can better understand how and why the climate
and ozone are changing. Scheduled for a three-year mission, the
SAGE III/Meteor-3M is a joint partnership between NASA and the
Russian Aviation and Space Agency (RASA).
After so many years of working on the SAGE III project, today
has been a very exciting day for me, Langley and the entire SAGE
III team," said Dr. William Chu, SAGE III project scientist. "So
many people have worked very hard and should feel proud of this
The SAGE III instrument uses a simple technique to provide
complex information on the stratosphere -- its electronic "eye"
watches sunsets, sunrises, moonsets and moonrises. Called
occultation, the light from the sun and moon passes through the
Earths edge or atmospheric limb which SAGE III measures.
"SAGE III locks on to the sun or moon and, as the spacecraft
goes behind the Earth, the instrument measures the dimming of that
sunlight or moonlight caused by the Earth's atmosphere. By making
these measurements in the correct color region, SAGE III produces
accurate profiles of ozone or water vapor," said Dr. M. Patrick
McCormick, SAGE III principal investigator and co-director for the
Center of Atmospheric Sciences at Hampton University. "SAGE III's
role is to provide long-term measurements of key components of the
Earth's atmosphere vital for improved understanding of climate,
climate change, and human-induced ozone chemistry and trends."
Ozone in the stratosphere is destroyed when it combines with
chlorine, forming oxygen and chlorine monoxide. Most chlorine comes
from the decay of human-made compounds known as chlorofluorocarbons
(CFCs). CFCs came into use in the 1930s as refrigerants, later as
blowing agents for creating foam insulation, and as industrial
cleaning agents. The loss of stratospheric ozone means that more
solar ultraviolet (UV) radiation reaches the Earth's surface. Since
UV radiation has been linked to skin cancer, there is a human
health risk posed by ozone depletion.
Long-term record keeping has shown a rise in the average global
temperature over recent decades while other observations show an
increase in greenhouse gases and thinning of the stratospheric
ozone layer. SAGE IIIs accurate, long-term measurements will
be important for understanding the processes involved with climate
"The amount of harmful CFCs emitted into the atmosphere has
lessened," McCormick said. "Are the policies regarding the
reduction or elimination of CFCs that have been agreed to on a
global basis working? Model predictions would say that within the
next few years we should definitely see a slowdown in the thinning
of the ozone layer. During the next ten years, we should start to
see a thickening of this same ozone layer."
The SAGE III mission, a collaboration between NASA and RASA,
extends a long-term working relationship between the United States
and Russia to understand the Earths environment. The SAGE
III, built by Ball Aerospace in Boulder, Colo., is the only U.S.
instrument included on the Meteor-3M payload.
According to Dr. Chip Trepte, SAGE III deputy project scientist
from NASA Langley, working with the Russians has been a technical
and cultural challenge. "Its been rewarding working with the
Russians," said Trepte. "We had different approaches to working
problems. It took additional time and effort to understand and work
through these differences with the language barrier and our
different cultures. In general, we have a common interest to
understand how the climate works and try to find answers to
problems that confront us."
Trepte added that NASA Langley workers are really quite excited
about their role with SAGE IIIs evolution. "We developed the
concept," Trepte added. "We oversaw the entire project from mission
management to integration of the instrument aboard the Russian
spacecraft. Were going to oversee the data collection and the
production, and release the results to the public in a meaningful
In a recent visit to NASA Langley, the RASA Head of the
Department of Space Remote Sensing, Dr. Leonid Makridenko, said the
SAGE III/Meteor-3M mission has been an example of excellent
cooperation between the United States and the Russian Federation.
"This is a fine opportunity to unite the engineering and scientific
skills of NASA and the Russian Space Agency," Makridenko said.
"This optimizes the use of available resources for both sides as we
share data and control of the instruments."
SAGE III will also measure aerosols (tiny particles floating in
the air) from the middle troposphere (the atmospheric layer closest
to Earth) through the stratosphere. Aerosol particles can absorb
radiation from the sun and the Earth causing the atmosphere to warm
or can scatter radiation back to space cooling Earths
atmosphere and surface. Aerosols can also influence chemical
processes, including the control of ozone. SAGE IIIs
predecessor, SAGE II, measured the dispersal of volcanic aerosols
following the 1991 eruption of Mt. Pinatubo. These measurements
were linked to a decline in the global averaged surface temperature
in mid-1992 of about 1 degree Fahrenheit due to the large aerosol
concentrations from the volcanic eruption.
The SAGE III instrument is part of NASA's Earth Science
Enterprise, a long-term research effort being conducted to
determine how human-induced and natural changes affect our global
environment. . A second SAGE III instrument is scheduled to fly
aboard the International Space Station in 2005.
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