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Topic：Small All-range LIDAR
with Optical Fiber Communication
Abstract:
Light Detection And
Ranging (LIDAR) has long been used to map the surface topography of Earth
and planetary bodies from orbit. Conventional lidars measure laser pulse
time of flight one pulse at a time. The received signals are usually very
weak in a space lidar because of the high orbit altitude. At present,
only Q-switched diode pumped Nd:YAG lasers can
give enough output laser pulse energy and nanosecond pulse width to close
the link and operate continuously for years in space. We have recently
developed a new technology to use more efficient and low-cost 1.55 um
fiber lasers so that we can build the lidar with off
the shelf components from industry at a much lower cost. The laser
in this case is modulated by a return-to-zero pseudo-noise (RZPN) code,
like in a communication system. The receiver detects the pattern of the
pulse train instead of individual pulses. This allows the use of
relatively low peak power laser for long distance ranging, just like our
GPS receivers in our phones. The receiver correlates the received signal
with the transmitted code to identify the target return and determine the
target range from the time delay. All signal processing is carried out in
real time inside an FPGA. We also use the latest multipixel HgCdTe
avalanche photodiode arrays which can detect single photons from near to
mid infrared wavelength. Another unique advantage of this lidar is the
wide dynamic range, since the power of the fiber lasers, the detector
gain, and the receiver integration time can all be adjusted according to
the target range. We call this lidar Small All-range LIDAR, or SALI.
Bio:
Xiaoli
Sun is a Research Physical Scientist at the Planetary Geology,
Geophysics, and Geochemistry Laboratory, NASA Goddard Space Flight Center
(GSFC). He was the Lead Engineer in the photodetector development and
receiver performance analysis for the Mars Orbiter Laser Altimeter on the
Mars Global Surveyor Mission and the Geoscience Laser Altimeter System on
the ICESat Mission. He was the instrument
scientist for the Mercury Laser Altimeter on the MESSENGER mission, the
Lunar Orbiter Laser Altimeter, and the one-way Laser Ranging system on
the Lunar Reconnaissance Orbiter (LRO) mission. He has involved
in the development of most space lidars at NASA GSFC in
the area of lidar detectors and instrument performance analysis.
Besides space lidar development, he also led the first two-way laser
ranging experiment between the MESSENGER spacecraft and Earth over 24
million km in 2005, and the first lunar laser communication experiments
from Earth to LRO at lunar distance in 2012. He is currently leading
NASA's effort to develop and deploy small laser retroreflector arrays on
the Moon for lunar exploration. In addition to space flight projects, he
has been leading the research and development of HgCdTe avalanche
photodiode arrays for future space lidars to improve receiver sensitivity
and to extend the laser wavelength to short and mid wave infrared. He is
currently leading the development of a spectroscopic lidar at the 1.6 and 3.0 micron water absorption bands at NASA
GSFC. Xiaoli Sun received his B.S. degree from Taiyuan Institute of
Technology, Taiyuan, China, in 1982, and the M.S. and Ph.D. degrees in
electrical engineering from the Johns Hopkins University, Baltimore, MD,
USA, in 1985 and 1989, respectively.
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