Light Detection and Ranging LIDAR

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Light Detection and Ranging(LIDAR)

• Presented by Dana Tilley

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History of Light Detection and Ranging (LIDAR)

• 1950s - First used searchlights for measuring
  stratospheric aerosals and molecular density
• 1960 - First laser invented (ruby laser)
• 1963 First use of lasers for atmospheric
  studies, beginning of LIDAR
• Initially only aerosol densities in air
  determined
• Only scattering intensity measured, not spectrum

http//superlidar.colorado.edu/Classes/Lidar2007/L
ecture03.pdf
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Essentials of LIDAR

• Similar to a radar but uses short laser pulses
• Depending on laser, can utilize a large range of
  wavelengths
• Get intensities of light beam reflected back as
  well as a spectrum
• Detection range and what can be studied via LIDAR
  is dependent on the laser and detector being used

4
Various Laser Sources For LIDAR

• Carbon dioxide
• Copper vapour
• Dye
• HeNe
• Nd YAG
• Ion

• Nitrogen
• Ruby
• Semiconductor lasers
• Ultrashort pulses

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Schematic of LIDAR
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Common Current Uses of LIDAR

• Topographical scans via aircrafts
• Officers use for traffic control
• Can tell if speeding in ½ second
• Atmosphere scans for weather conditions
• Velocity of air/clouds
• Composition of air and or clouds
• Aerosals in the air (such as dust or pollutants)
• Air temperature
• Air density
• Air pressure (derived from temp. and density)

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Obtaining Results from LIDAR

• To determine distance use D ct / 2
• c speed of light in medium t time for
  signal to return to detector dividing by 2
  accounts for round-trip travel of photons
• Velocity of particles determined by doppler shift

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Obtaining Results from LIDAR

• Air temperature determined by broadness of
  spectrum returned
• narrower peaks colder broader peaks warmer
• Air density determined by integral magnitude of
  the return signal
• Denser the region of air, more particles to
  scatter light back to detector

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Example Aerial LIDAR

• Operational Altitude
• 65 to 900 feet 
• Air Speed 
• nominally 93 miles/hour
• Accuracy/Resolution
• 6 inches
• Swath Width
• Approx. 1.1 x flight altitude 
• Data Density
• Up to 7,000,000 data pts/sq. mile 

Aerial scan of Mt. St. Helens
http//www.advlidar.com/details.htm
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Typical Atmosphere Lidar Profile
http//superlidar.colorado.edu/Classes/Lidar2007/L
ecture03.pdf
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A General Problem with LIDAR

• Generally restricted to the detection of one
  substance at a time
• Must use different laser sources for detection of
  different substances
• Lack of intensity for specific lasers may inhibit
  studies
• Not well suited to study aerosols

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Fluorescence LIDAR

• Use the laser to induce fluorescence
• Further increases the application of LIDAR

http//superlidar.colorado.edu/Classes/Lidar2007/L
ecture03.pdf
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Use of White Light Filaments for Atmospheric
Studies

• Desired to create a laser induced plasma focus in
  the atmosphere for aerosol studies and possible
  lightning control
• To do this scientists used high-powered
  femtosecond laser pulses with an initial chirp
• Used a negative chirp caused slight delay so
  shorter wavelengths of light emitted before
  longer wavelengths of light

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White Light Filaments for Atmospheric Studies
(Contd)

• Used NdYAG laser
• Pulse width 70 femtoseconds
• Peak Power 5 terawatts
• Wavelength 800 nm
• Repitition Rate 10 Hz
• Used High-resolution spectrometer
• Can process signals in a wavelength range of 190
  nm to 2.5 µm

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Set-Up Used
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White Light Filaments for Atmospheric Studies
(Contd)

• Fundamental wavelength covered the entire visible
  range (from UV to IR)
• Signal could be detected from altitudes over 10
  km

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White Light Filaments for Atmospheric Studies
(Contd)

• Applied laser to a fog chamber
• Caused water to coalesce into laser path
• Chirped laser may be used to probe atmosphere at
  various distances
• Can use to determine if clouds are supersaturated
  leading to better prediction of rain, hail, or
  snow

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White Light Filaments for Atmospheric Studies
(Contd)

• High-power femtosecond laser pulses create
  ionized plasma channels with large electron
  densities
• This is beyond the power requirement for
  lightning initiation in the air

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White Light Filaments for Atmospheric Studies
(Contd)
Free electrical discharge across 3m gap
Electrical discharge across 3m gap in conjunction
with a high-powered femtosecond laser pulse
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Conclusions

• New area of research with White Light Filaments
• High-powered femtosecond laser pulses have
  current primary aims
• Can be used to determine information about
  aerosols other than velocity and distance
• Potential use in controlled lightning strikes

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References

• Kasparian, J. Rodriguez, M. Mejean, G. Yu, J.
  Salmon, E. Wille, H. Bourayou, R. Frey, S.
  Andre, Y.B., Mysyrowicz, A. Sauerbrey, R. Wolf,
  J.P. and Woste, L. White-Light Filaments for
  Atmospheric Analysis. Science Magazine. 2003.
  301. 61-64.
• United States Geological Survey. Mount St.
  Helens, Washington Eruption 2004 LIDAR. 5/3/05.
  Visited 11/25/07. http//vulcan.wr.usgs.gov/Volcan
  oes/MSH/Eruption04/LIDAR/
• Advanced LIDAR Technology Inc. Lidar information.
  Visited 11/25/07. http//www.advlidar.com/details.
  htm
• Michigan Aerospace Corporation. Lidar. 2000.
  Visited 11/25/07. www.michiganaero.com/business_un
  its/lidar/lidar.shtml

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I Would Like to Thank

• YOU, the audience

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Questions?

• How can LIDAR be used to determine distances of
  objects/molecules?
• (Hint See slide 7)