NASA Satellite Switches to Second Laser

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					A space-borne lidar mission developed by NASA and the French space agency
Centre National d'Etudes Spatiales (CNES) has successfully made the
switch from its first laser to its back-up, guaranteeing a continued
stream of data that is allowing scientists to better understand the
complex roles clouds and aerosols play in Earth's climate. The extended
data set will help capture the pattern of year-to-year variations in
cloudiness and the distribution of elevated dust layers that have been
difficult to predict in climate models.      The Cloud-Aerosol Lidar and
Infrared Pathfinder Satellite Observations (CALIPSO) mission is now
operating on its redundant laser, which was designed as a contingency in
case of a problem with the primary laser. A slow pressure leak in the
canister that housed the primary laser, which the CALIPSO team had been
aware of since launch, made the switch necessary. The backup laser, which
stood ready for nearly three years, sent back its "first light" image on
March 12. The instrument is now operational and undergoing a review of
its calibration. The release of standard data products from CALIPSO
should resume in late April. Eventually data from mid-March on will be
processed and the total gap in data products will be limited to about 10
days in early March. CALIPSO makes unique vertical profile measurements
of clouds and aerosols. Aerosols are suspended particles from fires,
industrial activities and natural processes that are one of the least
understood weather and climate variables. CALIPSO's lidar instrument
measures the altitude and thickness of aerosol and cloud layers in the
atmosphere. It also measures particles' size, whether they are spherical
or non-spherical and whether they are composed of water or ice. CALIPSO's
observations complement data recorded by four other satellites flying in
formation called the A-Train, which provide an unprecedented
comprehensive global view of atmospheric chemistry and composition within
eight minutes of one another over the same ground track.    First
operational in June 2006, CALIPSO's primary laser generated more than 1.6
billion pulses of light and 20 terabytes of data that scientists from
around the world are using to investigate our global integrated Earth
system. More importantly, the CALIPSO data are giving scientists new
insight into processes that control how aerosols are formed and
dispersed, how clouds form and dissipate, and how aerosols and clouds
interact. The CALIPSO team became aware before launch that the pressure
canister that housed the primary laser had a slow leak. The decision to
launch was made because it was expected the primary laser could still
complete the three-year prime mission. If it could not, the back-up
instrument could take over. Early this year the laser showed unstable
behavior consistent with low canister pressure. An investigation
determined that turning on the backup laser now was the best solution.
"We designed the system with the ability to change to a back-up laser,"
said Chip Trepte, CALIPSO's project scientist at NASA's Langley Research
Center. Trepte compared building in the second laser to carrying an extra
flashlight on a long camping trip. Very few lasers of the type used in
CALIPSO had been flown in space before. It was unknown how it would
perform in the hostile space environment. The back-up laser provided
assurance that the mission would meet its objectives.    "The good news is
we turned on the second laser that had been idle for three years, and
it's working as well as the primary laser did early in the mission,"
Trepte said. "The pressure in the second laser canister is quite high,
and it should be able to operate for many more years." Throughout the
CALIPSO mission, NASA and CNES have worked closely, from developing the
mission, building the satellite platform and integrating the payload to
monitoring the instrument and processing its valuable measurements.
"Even though we are on each side of the Atlantic, we work as a single,
integrated NASA-CNES team," said Nadege Queruel, mission operations
manager with the CNES team. CALIPSO is a joint effort between NASA and
CNES. NASA and Ball Aerospace designed the lidar instrument; CNES and
Thales Alenia Space, previously Alcatel Space, built the Proteus
satellite platform.


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posted:10/21/2011
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