The Naval Research Laboratory's
(NRL's) Polar Ozone and Aerosol Monitor III (POAM III) instrument
is scheduled for launch on Monday March 23, 1998, as a follow-on
to the highly successful POAM II experiment, which provided unique
data on ozone depletion in the polar stratosphere.
POAM III, which is sponsored
by the Office of Naval Research (ONR) and the DoD Space Test
Program, will continue this monitoring of the polar stratosphere
and provide valuable information on the way the earth's ozone
layer is responding to decreased abundances of chlorine in the
atmosphere as a result of restrictions in CFC emissions mandated
in the international Montreal Protocol.
POAM III will be placed in the
same orbit as POAM II and, thus, will have identical measurement
coverage. More sensitive than its predecessor, POAM III will
be able to measure deeper into the atmosphere with greater precision.
The launch of POAM III will provide a continuation of the unique
and important measurements of ozone in the polar regions, begun
by POAM II, well into the next decade.
POAM III will be carried aboard
the French Space Agency (Centre National d'Etudes Spatiales (CNES))
SPOT-4 satellite (the newest in the series of SPOT remote sensing
instruments). SPOT-4 will be launched on an Ariane-4 rocket from
the CNES facility in Kourou, French Guiana. (The acronym "SPOT"
stands for "Satellite Pour l'Observation de la
Terre".)
The POAM instruments are space-based
atmospheric sensors that have been developed by NRL to monitor
ozone, and other atmospheric constituents that are important
to the ozone layer in the Arctic and Antarctic stratosphere (the
stratosphere extends from about 6 to 30 miles above the earth's
surface). POAM collects detailed stratospheric information by
scanning through the atmosphere while it follows the sun as it
rises or sets. Each POAM profile of the stratosphere contains
information on the abundance of ozone, aerosol particles, and
other important atmospheric constituents at a vertical resolution
of 1 kilometer.
POAM II was launched in September
1993 on the French SPOT 3 satellite, and operated successfully
until the host SPOT satellite failed in November 1996. During
this three-year period, POAM II made more than 20,000 measurements
of ozone concentrations in the stratosphere in the polar regions,
providing unprecedented detail as it monitored the 1993 through
1996 Antarctic ozone holes. POAM II's simultaneous observations
of ozone, polar stratospheric clouds, and nitrogen dioxide have
allowed scientists at NRL and elsewhere to deliver rich new insightsto
the science community.
POAM is particularly well suited
to the study of the Antarctic ozone hole because it is the only
space-borne instrument to make measurements of the ozone profile
over the polar regions on a continuous basis. The ozone hole
is a remarkable geophysical phenomenon which results in rapid
and severe depletion of the ozone layer over Antarctica in late
winter and early spring. Although the detailed meteorological
and photochemical processes that produce the ozone hole are unique
to Antarctica, ozone depletion in the Arctic has been observed,
by POAM and several other instruments, in the last several winters,
and chemical ozone loss has also been observed at mid latitudes.
According to NRL scientists, this suggests that chemical processes,
similar to but on a smaller scale than those taking place in
the ozone hole, may also be occurring outside of the Antarctic
stratosphere and may have significance for global ozone depletion.
This adds increasing emphasis and importance to studies of the
Antarctic ozone hole, which is the most clear-cut and extreme
manifestation and, therefore, optimum place to study these photochemical
processes.
POAM III is an integral component
of the middle atmosphere science program being carried out jointly
by NRL's Remote Sensing and Space Science Divisions. The objective
of the program is to study the photochemistry and dynamics of
the middle atmosphere using a combined experimental and theoretical
approach. In addition to POAM, the experimental programs include
the Millimeter-wave Atmospheric Sounder (MAS), the Ground-based
Water Vapor Spectrometer (WVMS) and the Middle Atmosphere High
Resolution Spectrograph Investigation (MAHRSI) Information on
these experiments can be found on the following web sites:
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