AN OVERVIEW OF HAMPTON UNIVERSITY’S 48-INCH LIDAR SYSTEM
Sydney Dianne Paul
Hampton University
Abstract
In 2004 Hampton University was the benefactor, via governmental surplus, of a world-class lidar
system that is built around a 48-inch diameter-receiving telescope. Lidar, is an acronym for Light
Detection And Ranging, which is the optical analog of microwave Radar. The telescope for the lidar
system has been positioned in HU’s Observatory so that data can be taken at the zenith, viewing the sky
through the movable dome roof. The proposed research will develop a new capable lidar at HU for
investigating novel laser remote sensing techniques and devices to strengthen our remote sensing
program. This paper outlines HU’s 48-inch lidar system, and the expected measurements it will make.
Once the 48-inch lidar system is fully operational at HU it will be part of the Cloud-Aerosol Lidar and
Infrared Pathfinder Satellite Observation (CALIPSO) Quid Pro Quo Validation program. The program will
be important in validating the calibration and algorithms for the CALIPSO data. Data will be taken while
CALIPSO overpasses, and comparisons made.
1. Introduction
The 48-inch lidar was developed by NASA
LaRC in 1969-1970 as a state of the art lidar for
atmospheric measurements of aerosols and
clouds. At first, the system was integrated into a
large trailer and measurements were taken at
many remote sites such as Boulder, Colorado and
the NASA GSFC Wallops Flight Facility.
Hampton University has obtained the 48inch lidar as surplus property from NASA and
installed it in an observatory refurbished for the
lidar (figure 1). The lidar is currently positioned at
Hampton University’s observatory so that data can
be taken at the zenith, viewing the sky through a
movable dome roof. The new lidar will develop a
new capable lidar at HU for investigating novel
laser remote sensing techniques and devices to
strengthen Hampton University’s remote sensing
program.
Fig. 1. The 48-inch Lidar System in the
observatory at Hampton University. (Courtesy Of
P. McCormick)
The 48-inch lidar with its enormous
collecting area will provide HU the capability to
investigate distant targets as well as phenomena
with very small backscattering cross-sections. The
48-inch lidar system will be used not only to make
important atmospheric measurements, but also a
test bed for developing new measurement
capabilities or techniques. The latter will allow the
development of small dedicated lidars for various
DOD applications, like the measurement of toxic
or lethal gases.
Although the complete telescope, most of
the steering optics and supporting structure is in
excellent condition, there was no data acquisition
system or detector system included. In addition,
the ruby and Nd:YAG lasers provided with the 48inch lidar needed extensive refurbishment and did
not have the frequency stability, output stability, or
narrow wavelength output required for current
applications, Therefore, a new injection seeded
four-wavelength Nd:YAG laser, detectors, and a
new data acquisition system was recently funded
and purchased through a successful BAA
proposal. Presently they are being installed and
tested by HU students and faculty.
2. LIDAR
Lidar is an instrument for remotely
obtaining information about the atmosphere. This
is done by sending out short pulses of light and
measuring (as a function of time) the amount of
light that is backscattered by the atmosphere. It
has been a powerful technique for measuring
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atmospheric constituents like aerosols, clouds,
and gases.
The basic set up of a lidar system can be
shown in figure 2.
accurate range and real time remote sensing
detection capabilities.
3. LITE
Fig 2. Basic lidar set up
A lidar can consist of a transmitter and a
receiver. At the receiver end, a telescope collects
photons that backscatter from the atmosphere.
This is usually followed by an optical analyzing
system that selects particular wavelengths or
polarization states from the collected light. The
radiation is directed to a detector where the optical
signal can be received and converted into an
electrical signal. The signals intensity is
determined electronically and stored in a
computer.
This system can be defined into a simple
equation and is written as
P(R) = K G(R)  (R) T(R)
where P is the power received from a distance R.
This equation is made up of four factors. The first
factor K is the performance of the lidar system, the
second factor G(R) is the range dependent
measurement geometry. These first two factors
are controlled by the setup and are determined by
the experimentalist.
The measurable quantities are in the last
part of the equation. The β(R) term defines the
backscatter coefficient at a distance R. It is the
ability of the atmosphere to scatter light back into
the direction from which it comes. (Wandinger et
al., 2005) The last term T(R) stands for the
transmission term. This term describes how much
light gets lost on the way from the lidar to
distance R and back. These last two terms are
unknown to the experimentalist.
The lidar equation commonly used to
interpret signals is the one shown here
R
c
O( R)
P( R,  )  P0
A 2  ( R,  ) exp  2  (r ,  )dr 


0

2
R
Lidar’s have provided important
measurement roles in chemical and biological
detection and identification due to their specificity,
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LITE was launched on board the shuttle
Discovery on September 9, 1994. As the first lidar
designed for atmospheric studies to fly in Earth’s
orbit, the goals of the LITE project was to validate
key technologies required for operational space
borne lidars. The raw data showed great potential
for space borne lidars. Everything was seen from
desert dust, biomass burning, pollution outflow off
continents, stratospheric volcanic aerosols, and
many storm systems (McCormick et al., 2005).
The comparison between the pictures that were
taken from the shuttle and from aircraft lidars was
remarkable. They each closely showed cloud
layering and lower troposphere aerosol
distributions. LITE gave a vertical profile of what
the atmosphere looked like. Like the example
below.
Fig 3. An example of LITE data picture shows
LITE observations over the Sahara on September
18, 1994.
This picture shows a plume Sahara dust
about 5 km in the air. The LITE shuttle flight gave
a new era of remote sensing of the Earth’s
atmosphere from space. This flight showed the
importance of space borne lidars in the science
community.
4. CALIPSO
The Cloud-Aerosol Lidar and Infrared
Pathfinder Satellite Observation (CALIPSO) will
provide cloud and aerosol profiles, data important
for climate research and the prediction of future
climates.
Aerosols are known to play significant
roles in the Earth’s atmosphere. They affect the
atmospheric energy balance directly by scattering
and absorbing solar and terrestrial radiation, and
indirectly by serving as cloud condensation nuclei.
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Aerosols act as sinks and catalytic reaction sites
for trace gases and can thereby greatly perturb the
normal atmospheric chemical state (Poole et al.,
1992). The presence of large quantities of
aerosols can also seriously degrade the
performance of satellite instruments designed to
measure other atmospheric constituents (Bandeen
and Fraser, 1982).
CALIPSO is a long duration Earth orbiting
satellite mission designed for continuous
measurements for at least three years and it will
fly on the French satellite, Proteus. The three nadir
viewing instruments are CALIOP a twowavelength polarization-sensitive lidar that
provides high-resolution vertical profiles of
aerosols and clouds, a wide field of view camera
for scene registration on the daylight side if the
orbit, and a French Imaging Infrared Radiometer
(IIR) instrument. These three instruments are
made to operate autonomously and continuously,
except for the wide field camera, it collects science
data only under daylight conditions (McCormick,
2005). CALIOP is a three channel lidar for 1064
nm measurements and 532 parallel and
perpendicular measurements. CALIPSO will make
elastic backscatter measurements in three
channels; 1064nm and 532nm. The depolarization
measurements of CALIPSO will help determine if
clouds contain liquid droplets or ice crystals.
aerosol, cloud and physical properties as shown
before.
CALIPSO is designed to determine the
height of aerosols and clouds, the source of
aerosols, and the presence of sub visible clouds. It
has become a powerful technique for measuring
atmospheric constituents like aerosols, clouds,
and gases.
CALIPSO and CloudSat will be launched
from Space Launch Complex 2W at Vandenberg
Air Force Base, California. As of now they are
installed in the Payload Attach Fitting at
Vandenberg. They will remain there until launch.
CALIPSO will fly in formation with AQUA, AURA,
CloudSat and PARASOL. Combining data from
the instruments on these spacecraft will allow for
countless important characterizations of aerosols
and clouds and their effects on radiation budget.
Five satellites will fly in formation during
the CALIPSO mission. This grouping is known as
the Aqua constellation or “A-train”. It is an
Afternoon constellation and has Aqua in the lead
with Aura in the rear. Each satellite in the
formation offers unique information on clouds and
aerosols. Combining their data will greatly provide
better insight into climate and weather prediction.
The Aqua satellite is focused on
understanding the Earth's water or hydrological
cycle. CloudSat will use a radar to provide vertical
profiles of thick clouds that lidar cannot penetrate.
Aura will monitor atmospheric chemistry and
dynamics and will provide information on the
geographic distribution of absorbing aerosols.
Finally, the PARASOL (Polarization and
Anisotropy of Reflectance for Atmospheric
Science coupled with Observations from a Lidar)
satellite will provide unique information on
aerosols and clouds using a multi-channel, wide
field-of-view, polarization-sensitive camera. The
“A-train” is shown in the figure below.
Fig 4. CALIPSO during its final fabrication stages
at Ball Aerospace and Technologies Corporation.
(Courtesy of Ball)
LITE demonstrated the potential of space lidar for
the observation of clouds and aerosols. This set
up future projects like CALIPSO, showing that it
could be done. The data from LITE gives a test for
CALIPSO simulations. It will provide, from space,
the first global survey of the vertical profile of
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Fig 5. The Afternoon train or better know as “Atrain”. The “A-train comes from the old jazz tune,
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“Take the A-train” composed by Billy Strayhorn
and made popular by Duke Ellington’s band.
(Courtesy of NASA GSFC)
After the 48-inch lidar is fully operational at
HU, it will become part of the CALIPSO Quid Pro
Quo Validation Program. Data will be taken while
CALIPSO overpasses it will make comparisons
and measurements will be made for the validation
of the CALIPSO data product.
This is to link measurements with those
from already ground state instruments all over the
globe. Once the data is compared, there will be a
gain of understanding about weather and climate
from the satellite.
Assessment of Ozone Depletion: 1991, World
Meteorological Organization, Geneva, 1992
Wandinger,U., McCormick, M.P., Weitkamp, C., et
al. (2005). Lidar: Range-Resolved Optical Remote
Sensing of the Atmosphere. Singapore: Springer.
Winker, David M., Jacques Pelon, and M. P.
McCormick, 2002: The CALIPSO mission: Aerosol
and cloud observations from space, 21st
International Laser Radar Conference
Proceedings, 735-738.
5. Conclusion
In addition to hardware and/or technology
issues, the challenges for space borne lidar in the
near future include our ability to incorporate the
data from the constellation of satellites flying in
formation with CALIPSO into a more complete and
understandable data set, and then use the data for
various modeling studies and for a more complete
understanding of various scientific studies
including climate forcing. This effort, if successful,
will serve as a paradigm for and, perhaps, justify
future Earth-orbiting lidar missions.
The above improvements will enable
future applications to be implemented in the
following decades like studies of the carbon cycle,
circulation and forecasting through global
troposphere wind measurements, DIAL for
constituent measurements, and elastic backscatter
for aerosol and cloud measurements. The
implementation of these lidars in space will greatly
enhance our understanding of the Earth and other
planet’s atmospheric chemistry, climate and
geophysical properties. The future is indeed bright
for space borne lidars, which are now taking their
place alongside passive sensors, and fulfilling
countless measurement needs for the study of our
solar system.
REFERENCES
Bandeen, W.R., and R.S. Fraser, Radiative Effects
of the El Chichon volcanic eruption; Preliminary
results concerning remote sensing, NASA TM84959, 1982
Poole, L. R., R. L. Jones, M.J. Kurylo, and A.
Wahner, Heterogeneous Processes: Laboratory,
Field, and Modeling Studies. Chapter 3, Scientific
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