The Middle Atmosphere High Resolution
Spectrograph Investigation (MAHRSI), a remote sensing instrument
developed by the Naval Research Laboratory (NRL), is scheduled
to begin its second data-collecting mission this summer to map
the distribution of two important gases in the middle atmosphere.
In the fall of 1994, MAHRSI obtained the first global measurements
of the hydroxyl radical (OH) in the middle atmosphere, providing
unprecedented information on the chemical family that is believed
to determine the natural balance of ozone in the altitude region
above 35 kilometers (km).
MAHRSI will fly on the German
Space Agency's Cryogenic Infrared Spectrometers and Telescopes
for the Atmosphere -- Shuttle Pallet Atmosphere Satellite (CRISTA/SPAS).
CRISTA/SPAS will be deployed from the space shuttle Discovery's
robot arm during NASA's STS-85 mission, planned for launch on
August 7. During nine days of free flight, MAHRSI will measure
OH and nitric oxide by sensing the ultraviolet (UV) radiation
emitted and scattered by the atmosphere.
MAHRSI's first set of measurements,
which were made in November 1994, provide a detailed picture
of the morning build-up of the OH profile. This second flight
will provide an opportunity to observe afternoon OH levels at
smaller solar zenith angles (the angle of the Sun from overhead).
The new observations will also provide the opportunity to explore
the photochemistry of the summer polar region.
A different instrument on NASA's
Upper Atmosphere Research Satellite (UARS) has seen values of
water vapor (the "parent" molecule of OH) at high altitudes
in this region that are so large that they cannot be explained
by current theory. The MAHRSI science team has found that the
high values observed during the 1994 UARS flight are in excellent
agreement with the MAHRSI OH measurements. Dr. Robert Conway
of NRL's Space Science Division, MAHRSI principal investigator,
notes, "the highest values of water vapor ever observed
by UARS were near the north pole in August so the new OH measurements
should provide an exciting test of the current theory of formation
of OH and its role in ozone photochemistry."
MAHRSI obtains its measurements
by detecting ultraviolet glow (a result of absorbed sunlight)
from gases at high altitudes and repeatedly measuring the brightness
of the glow in long, narrow strips across the horizon. MAHRSI
then forms an image of the glowing gas layers fromwhich the scientists
can make density profiles maps.
To correspond with the CRISTA/SPAS
mission, researchers from all over the world will participate
in the CRISTA/MAHRSI Campaign 2. This three-week cooperative
science campaign includes the collection of complementary and
correlative measurements from ground-based stations, balloons,
rockets, aircraft and satellites. These measurements will become
part of a database that will be used to validate the CRISTA and
MAHRSI observations.
The U.S. Naval Research Laboratory is the Navy's full-spectrum corporate laboratory, conducting a broadly based multidisciplinary program of scientific research and advanced technological development. The Laboratory, with a total complement of nearly 2,500 personnel, is located in southwest Washington, D.C., with other major sites at the Stennis Space Center, Miss., and Monterey, Calif. NRL has served the Navy and the nation for over 85 years and continues to meet the complex technological challenges of today's world. For more information, visit the NRL homepage or join the conversation on Twitter, Facebook, and YouTube.
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