Introduction to High Spectral Resolution Lidar
Introduction to High Spectral Resolution Lidar
Introduction to High Spectral Resolution Lidar
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<strong>Introduction</strong> <strong>to</strong> <strong>High</strong> <strong>Spectral</strong><br />
<strong>Resolution</strong> <strong>Lidar</strong><br />
Matthew Hayman<br />
ASP Research Review<br />
April 25, 2012
Laser<br />
Telescope/Detec<strong>to</strong>r<br />
Power<br />
Time
Power<br />
Time
Power<br />
Scattering Event<br />
Time
Power<br />
Time
Power<br />
Time
Power<br />
Time
Power<br />
Time/Range<br />
Range =<br />
Time x Light Speed<br />
2
Molecular Density:<br />
Scattering from molecules = Number of Molecules x Scattering from 1 Molecule<br />
Power<br />
Time/Range<br />
Range
Aerosol Detection/Properties:<br />
Total Scattering = Molecular Scattering + Aerosol Scattering<br />
Molecular Density<br />
Power<br />
Time/Range<br />
Range
Aerosol Detection/Properties (Backscattering)<br />
Molecular Density<br />
Aerosol Properties (Extinction)<br />
Molecular Scattering x Extinction<br />
Power<br />
Time/Range<br />
Range
Detected Power = Aerosol Transmission x (BS Mol. + BS Aerosols)<br />
How do we know aerosols<br />
are not also present?<br />
Fewer aerosols or Extinction?<br />
Power<br />
Time/Range
Backscatter Profile
<strong>High</strong> <strong>Spectral</strong> <strong>Resolution</strong> <strong>Lidar</strong><br />
• Pioneered by Ed Eloranta (U.<br />
Wisconsin)<br />
• Designed for aerosol detection<br />
and characterization<br />
Aerosol Motivation<br />
•Major uncertainty in radiative transfer<br />
•Aerosol RT properties<br />
•Condensation Nuclei<br />
•Indica<strong>to</strong>r for Boundary layer height<br />
•Background signal for other instruments
Doppler Shift and Thermal Motion<br />
Spectrum
Doppler Shift and Thermal Motion<br />
Spectrum
Backscatter Spectrum is Doppler<br />
Broadened
1<br />
2<br />
mv 2 =<br />
3<br />
2<br />
k B T<br />
Aerosols<br />
Molecules
<strong>High</strong> <strong>Spectral</strong> <strong>Resolution</strong> <strong>Lidar</strong><br />
Backscattered Signal<br />
Spectrum of Backscattered Signal
<strong>High</strong> <strong>Spectral</strong> <strong>Resolution</strong> <strong>Lidar</strong><br />
Beam Splitter<br />
Iodine Cell<br />
Mol. + Aerosol Channel<br />
Iodine<br />
Transmission
<strong>High</strong> <strong>Spectral</strong> <strong>Resolution</strong> <strong>Lidar</strong><br />
Beam Splitter<br />
Iodine Cell<br />
Molecular Channel<br />
Mol. + Aerosol Channel
Detected Power = Aerosol Transmission x (BS Mol. + BS Aerosols)<br />
How do we know aerosols<br />
are not also present?<br />
Detected Power = Transmission x Backscattering<br />
Fewer aerosols or Extinction?<br />
Power<br />
Time/Range
Detected Power 1 = Aerosol Transmission x (BS Mol. + BS Aerosols)<br />
Detected Power 2 = Aerosol Transmission x BS Mol.<br />
Aerosol Backscatter<br />
Power<br />
Molecular Backscatter Channel<br />
Total Backscatter Channel<br />
Aerosol Extinction<br />
Time/Range
HSRL Profile
HSRL Profile
Polarizing Beam Splitter<br />
1. Transmit Vertical Polarization
1. Transmit Vertical Polarization<br />
2. Scattering Couples Some<br />
Vertical Polarization in<strong>to</strong><br />
Horizontal
P<br />
P<br />
1. Transmit Vertical Polarization<br />
2. Scattering Couples Some<br />
Vertical Polarization in<strong>to</strong><br />
Horizontal<br />
3. Polarizing Beam Splitter<br />
Separates Vertical and<br />
Horizontal Polarizations<br />
Depolarization Ratio<br />
δ = P<br />
P<br />
How much did scattering change the polarization?
Spheres do no change backscattered light’s polarization state<br />
Under MOST conditions, everything else does
Conclusions<br />
•<strong>High</strong> <strong>Spectral</strong> <strong>Resolution</strong> spectrally analyzes backscattered light<br />
•HSRL provides quantitative information on aerosol properties such as<br />
•Aerosol Backscatter<br />
•Aerosol Extinction<br />
•Aerosol Depolarization Ratio<br />
•Characterizes and classifies aerosols<br />
•Sand<br />
•Soot<br />
•Water Phase<br />
•Ice Crystal Orientation<br />
•Temperature and Winds?
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