The European Space Agency (ESA)
has adopted the direct detection strategy
for the Atmospheric Dynamics Mission (ADM-Aeolus), a spacecraft that
had been planned to launch in 2008
but is now scheduled for 2010. The ESA
experiment will use a 355-nm Nd:YAG
laser to measure wind at the molecular
level. It will operate in “burst mode,” in
which the laser will make one complete
observation consisting of 700 shots over
7 s, followed by 21 s of downtime. The
satellite will travel 50 km during each
The ESA satellite’s high-repetition-rate laser will be at least five times more
powerful than the one on CALIPSO,
but the ultraviolet light is very corrosive,
and contamination inside the laser itself
could be a problem. According to Singh,
the team was awarded the ADM-Aeolus
mission first and then started development of the laser technology. Now the
rest of the mission is ready to fly, but it
still awaits completion of the laser. Thus,
Singh advocates for keeping in-house
development capability for lasers within
NASA because of the space agency’s
“I’m not saying that NASA should be
building all the lasers, but we should have
the knowledge to make space lasers or
how to make the laser appropriate for the
space-based environment,” Singh said.
Singh cited the fate of the Space
Readiness Coherent Lidar Experiment
(SPARCLE), a planned shuttle payload
that was supposed to test the technology
for detecting tropospheric winds. The
project was canceled in its second year
(1999) because the company that was
supposed to build the laser could not do
so, he said.
In 2001, Singh started NASA’s Laser
Risk Reduction Program, which has
been developing better spaceborne-laser
technologies as well as the methods for
testing them prior to launch. According to Singh, NASA Langley has been
developing the 2-µm laser—both new
laser crystals for high power and new
laser diodes for long lifetimes—for using
aerosols as a space-lidar target. Singh
spearheaded an agreement to pursue a
The next frontier of
lidar is getting a better
picture of terrestrial
especially in places
can’t easily place an
anemometer or wind-
speed gauge, like the
middle of the ocean.
Lidar measurements of lunar topography
made by the Clementine mission.
hybrid approach: a spacecraft that will
use 2-µm lidar to investigate the troposphere, up to about 8 km, and 1,064-nm
lidar to study wind movement from
4 km up to 15 or 20 km. The project,
to be called 3D-Winds, is slated for the
2016-2020 timeframe in the U.S. earth
science decadal survey.
Beyond ADM-Aeolus and 3D-Winds,
Europe and Japan are collaborating on
another cloud- and aerosol-monitoring
spacecraft called Earth Clouds, Aerosols and Radiation Explorer (
Earth-CARE), scheduled for launch in 2013.
Plans call for the satellite to carry both
active sensors (backscatter lidar and
radar sounders) and passive detectors (a
multi-spectral imager and a broadband
radiometer). From 450 km above the
home planet, EarthCARE’s lidar will
use its high spectral resolution at 355
nm to discriminate between Rayleigh
scattering from molecules and Mie scattering from aerosols and cloud particles
in the lowest 20 km of the atmosphere.
This spring, NASA is launching the
Lunar Reconnaissance Orbiter (LRO)
with a lidar instrument that will take a
high-resolution map of the moon’s entire
surface with the specific intent of identifying sites for future human landings
and lunar bases. LRO will also search
for laser pulse reflections from the possible water ice deposits in the deep polar
craters; large stores of water, if they
exist, would be a huge boon to human
LRO’s laser pulses will make a new
multiple-spot pattern on the lunar
surface, thanks to a diffractive optical
element that splits the single laser beam
into multiple beams directed downward.
This paves the way for surface lidar to
start imaging topography, instead of
profiling topography and reconstructing
it later from the one-dimensional scans.
Undoubtedly, other lidar-wielding
spacecraft will continue to explore Earth
and its sister planets in the years and
decades to come. t
Patricia Daukantas ( email@example.com) is the
senior writer/editor of Optics & Photonics News.
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