Atmospheric Probing using Lidar Systems at

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Atmospheric Probing using Lidar Systems at NPL,
New Delhi A Review S. L. Jain  Radio and
Atmospheric Sciences DivisionNational Physical
LaboratoryNew Delhi 110 012, India E-mail
sljain_at_nplindia.ernet.in 14th Coherent Laser
Radar Conference Snowmass, CO, USA July 09-13,
2007
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• OUTLINES OF THE TALK
• Introduction Mother planet the earth Green
  house gases, Ozone Problem ( Good Bad )
• Ozone Hole over Antarctica
• Different types of lidars 
• NPL activities in the area
• Laser Heterodyne system
• Differential Absorption LIDAR (DIAL)
• Micro pulse lidar
• Results
• Conclusion

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• Background
• The earths environment is constantly changing.
• The scientific evidence indicates that these
  changes are result of a complex
• interplay among a number of natural and
  human related systems.
• Important issues of serious concern for the life
  on the mother planet earth are, global green
  house warming, urban and regional atmospheric
  pollution, regional increases in tropospheric
  ozone, the decrease in stratospheric ozone etc.
• The reporting of ozone depletion in general and
  ozone hole over Antarctica in particular
  witnessed an unprecedented surge of interest in
  Atmospheric monitoring.
• In Antarctica contamination sources are distant,
  the air is very well mixed, extremely clean and
  is far removed from spatial and seasonal
  changes.It is truly the background air of the
  planet compared to measurements made elsewhere
  around the glob. Therefore, special conditions
  prevailing over Antarctica makes it an ideal
  sight for the monitoring of various atmospheric
  parameters.
• NPL has envisaged these problem in early eighties
  and launched new programmes and played lead role
  in IMAP, IGBP, INDOEX etc.
• The new activities started were UV-B, trace gases
  such as ozone, water vapour, CH4, aerosol etc (
  Laser based system and MM wave, Sodar etc) and
  also Antarctica Participation.

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18-20 ppt/yr
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• LIDAR
• Lidar is an acronym for Light Detection and
  Ranging. It is the direct, optical analog to
  Radar using radio waves. In Lidar experiment,
  laser light is transmitted into the atmosphere.
  The beam can interact with the atmosphere in a
  number of different ways
• Different types of Lidars used for atmospheric
  probing such as aerosol, cloud, temperature,
  trace gases, wind etc (ground as well as space
  based)
• Raman Lidar
• Resonance Lidar
• Flourence Lidar
• Rayleigh Mie Lidar- Monostatic and Bistatic,
  MPL
• Laser Heterodyne
• Differential Absorption Lidar (dial)
• Coherent Doppler Lidar

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An inversion technique has been developed based
on inverse solution of radiative transfer
equation Jain J. opt. 28,1999,185. In this
analysis, Lorentz profile was used below 25 km,
while above 25 km, Voigt profile was used where
Doppler broadening is dominant, for computation
of line parameters such as line half width,
line strength etc. for a strong ozone
absorption line, 1053.96 cm-1 using HITRAN data
base. In all, sixteen channels, one at line
center and fifteen in the wing of the line,
were chosen to resolve the line and hence to get
proper height resolution (1 to 3 km). The
inverted profiles compares well with the model
ozone profile.
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SUN
SQUARE LAW DETECTORS
LIQUID NITROGEN COOLED HIGH SPEED Hg Cd Te
DETECTOR
FILTERS
LOCK IN AMP
POWER METER
HELIOSTAT
SPECTRUM ANALYSER
PC
A/D
1
1
CHOPPER
2
2
MONITOR
S
AMP
3
3
ALTITUDE
M
1090
-
4
PRINTER
B
Zn Se LENS
BIAS BOX
n
5
CHANNELS
B
TUNABLE CO2 WAVEGUIDE LASER
CONC
SPECTRUM ANALYSER
S
BLOCK DIAGRAM OF LASER HETERODYNE SYSTEM
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Laser Heterodyne System Specifications
  Laser CO2 (Tunable) Wave Length 9 11 µm
(60 Lines)  Power 2 3 Watt (Refill
Facility) Detector LN2 Cooled HgCdTe (High
Speed 1200 MHz) Spectral Resolution 0.00016
Cm-1 (5 MHz) High S/N 40 Db High
QDE 70 Profiles Measured O3, N2O, H2O, NH3
First of its kind 1GHz AOS as Back-end LHS
Over Antarctica Due To Ultra High Spectral
Resolution Interference Problem Is Minimized
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NPL
Heliostat
Maitri
Fig. 17 LHS Laboratory and Heliostat
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Fig. 7 LHS Liquid Nitrogen Plant
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0
February 10, 1994
-10
-20
-30
-40
-50

Fig. 6 Observed ozone absorption line spectra
near P(24) CO2 laser Line at Maitri
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February 10, 1994
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_____ Retrieved ozone profile
- - - - Guess ozone profile
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20
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Fig. 5 Ozone profile obtained by laser
heterodyne system on February 10, 1994 over
Maitri, Antarctica
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February 17, 1995
30
20
10
10
1
Ozone volume mixing Ratio in ppm
Fig. 6 Ozone profile obtained by laser
heterodyne system on February 17, 1995 over
Maitri, Antarctica
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DIAL BLOCK DIAGRAM
DIAL Equation
Where L is path length ??(ON) is absorption
coefficient at ON wavelength ??(OFF) is
absorption coefficient at OFF wavelength PT(?ON)
is power transmitted at ON wavelength PT(?OFF)
is power transmitted at OFF wavelength PR(?ON)
is power received at ON wavelength PR(?OFF) is
power received at OFF wavelength
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Comparison of surface ozone measured by DIAL
ozone analyzer
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Temporal variation of surface ozone at NPL, New
Delhi during 1997-2006
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Fig. 5 Variation of water vapour ethylene at
NPL, New Delhi on march 22, 1999
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Variation of ethylene and water vapour.
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• Aerosol and climate change
• Aerosols have great impact on global and
  regional climates.
• 
  
• Global radiative forcing by Aerosols (0.3 to
  2 Wm-2) is comparable to that due to
  greenhouse gas increases.
• Lidar plays important role in measurements of
  aerosols with high vertical and temporal
  resolution. Since the invention of laser by
  Maiman , a large number of lidar systems have
  been developed to study aerosols, including
  clouds, atmospheric composition, wind etc in
  the troposphere and lower stratosphere

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• The conventional lidar systems are not eye-safe
  and are quite large, complex and costly.
  Therefore these lidars are extremely difficult
  to deploy for regular monitoring in field.
• Micro pulse lidar proved to be an important
  state of art tool providing a detailed picture
  of the vertical structure of boundary layer and
  elevated dust or tiny aerosol.
• Micro-Pulse Lidar Networks such as MPLNET,
  EURONET etc has been established for long term
  observations of aerosol and cloud vertical
  structure at key sites around the world.

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• The movement of the pollutants can be tracked
  or mapped out as a function of time with the
  help of Lidar which is very important to
  understand the dynamics of particulate matters.
  
• Keeping above in view a Micro-pulse lidar
  with facility of measurement of depolarization
  ratio has been set up at National
  Physical Laboratory, New Delhi for the
  study of vertical profiles of aerosol,
  their characterization, transportation,
  radiation forcing etc.

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Micro Pulse Lidar at NPL The principal
components of the lidar system are transmitter
and receiver. The transmitter is a rugged Diode
pumped solid state NdYAG laser coupled with a
half wave plate and a beam splitter, optics and a
telescope as beam expander for beam collimation
and minimizing divergence. The receiver fore
optics is a 200 mm Schmidt Cassegrain zenith
pointing fixed telescope with 3.048 meter focal
length and f/10 focal ratio. All main parts viz
transmitter, receiver, optics and relevant
hardware is mounted in rugged chassis.
Polarization analysis is performed by
simultaneously collecting backscatter by two PMT
detectors placed at right angles to beam at the
receivers end. The MPL will be mounted on a van
for the study of aerosol loading in different
regions of the country covering rural, urban and
semi- urban areas.
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Block Diagram of micro pulse lidar
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Photograph of Micro Pulse LIDAR at National
Physical Laboratory (NPL), New Delhi, India
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Micro Pulse lidar, NPL, New Delhi, India
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Typical raw data taken on 20th July 2006 using
MPL during testing
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• Conclusions
• Laser based systems such as LHS, DIAL and MPL
  has been developed and used for atmospheric
  studies at NPL, New Delhi
• LHS was deployed at Maitri, Antarctica for the
  first time for ozone profiles during normal and
  ozone hole period.
• Ozone was found to deplete by 3 to 68 in
  the height range 10 to 20 km during ozone hole
  period.
• Effect of planetary waves has been observed on
  ozone hole over Antarctica.
• A considerable day-to-day variation has
  been observed in ethylene concentration.
  As high as 67 ppb and as low as 8 ppb ethylene
  concentration has been observed. The ethylene
  was also f ound to be higher during morning and
  evening peak traffic hours

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• The concentrations of water vapour and
  ethylene is found to be anti- correlated. The
  anti- correlation may be attributed to the fact
  that water vapour is the primary source of OH
  radicals.
• Measurements showed that hourly surface
  ozone concentration frequently reaches above
  80 ppb in summer and autumn, especially during
  April - May and October November. The surface
  ozone as high as 140 ppb has been observed
  during summer months at Delhi which is a health
  hazard and is of serious concern. The daytime
  increase in ozone concentration is a pronounced
  feature of an urban polluted site, which is
  basically due to photo-oxidation of the
  precursor gases such as CO, CH4, and NMHCs in
  presence of sufficient amount of NOx.
• The Ammonia was found to be varying from 1 ppb
  to 65 ppb on different days except some
  occasions when it is as high as 120 ppb depending
  on the wind direction.
• MPL has just been setup and preliminary data
  obtained.

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Calling for Antarctic explorers, circa
1900 --Ernest Shackletons newspaper
advertisement Men wanted for
hazardous journey. Small wages, bitter cold,
long months of complete darkness, constant
danger, safe return doubtful, honor and
recognition in case of success.
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The best day in Antarctica is the day you
arrive. The next best day is the day you leave.

-Steven leaven
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Thanks for your kind attention