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“Lidar applications to atmospheric studies. "
Dr. Juan Carlos Antuña Marrero
Senior Researcher, Grupo de Óptica Atmosférica de Camagüey (GOAC),
Instituto de Meteorología, Cuba
Winter College on Optics: Light: a bridge between Earth and Space
The Abdus Salam
International Centre for Theoretical Physics
February,16th 2015
Summary
1. Brief Lidar history2. Lidar equation & solutions3. Lidar applications:
• Stratospheric aerosols• Cirrus clouds
4. Space Lidars• LITE• CALIPSO
Conference:Lidar applications to atmospheric studies.
Winter College on Optics
Light: a bridge between Earth and SpaceThe Abdus Salam International Centre for Theoretical Physics
1. Brief Lidar history
Radar: RAdio Detection And Ranging
Electromagnetic
Spectra
1887: Heinrich Herzt began experiments with radio waves
1920 – 1930: Renew efforts for creating an emitter-receptor
WW II: Accelerated military applications (Because clouds Interference)
From 1945 Development of the Meteorological Radar
Range = C * (time/2) C: Light speed
In the 30’s began efforts to measure density profiles in the high atmosphere using dispersed signals from searchlights
Synge, E. H. Phil. Mag. 9, 1014, 1930.
1938: Cloud base measured by 1st time using pulsed lightBureau, R. La Meteorologie, 3, 292, 1946.
Acronym LIDAR coined in 1953Middleton W.E.K. and A.F. Spilhaus, Meteorological Instruments (University of Toronto Press), Toronto 1953.
Between 40’s & 50’s renewed efforts using searchlights to measure high atmosphere density, temperature and aerosols profiles
Elterman, L. , Seasonal trends of temperature, density and pressure to 67.6 km obtained with the searchlight probing technique. J. Geophys. Res., Vol. 59(3), pp. 351-358, 1954.
Ruby laser invented in 1960: a better emission source
Lidar atmospheric studies phases:
1960s – 1970s: Innovation (many pioneering demonstration experiments)1970s – today : Development (improved lasers, hardware and theory)1970s – today : Application (many lidar developed and working getting important and often unique data)
What is a Lidar?
LIght Detection And Ranging
Simple Lidar design
Lidar Systems• Laser System • Optical System • Register System (Detection)• Control &
Operation System
Main laser features:Monochromatic: Only one wavelengthCollimated: Beam of light which has a low beam divergence, so that the beam radius does not undergo significant changesCoherent: Constant relative phases between radio wave pulses
LASER: Light Amplification by the Stimulated Emission of Radiation
Solid state laserActive Medium: Cristal YAG (Yttrium Aluminum Garnet)
Y2Al5O12
Dopant YAG: Nd Y+3 ions replaced by Nd+3 ions Emission Wavelength: 1064nm
Nd:Yag Laser
2. Lidar equation & its solutions.
Lidar Equation (Simplest form):
r
02 )dr'α(r'2β(r)exprC
P(r)
C: Calibration constant (depends on laser power, laser pulse with, receiver area, instrument optical transmission and detector efficiency)
Considering the aerosol and molecular components of the atmosphere:
(r) = par(r) + mol(r) and (r) = par(r) + mol(r)
P(r): Received power(r): Volume backscatter coefficient at range r(r): Volume extinction coefficient at range r
EXTINCTION-BACKSCATTER RATE (LIDAR RATE)
rβrα
rLR
Unlike and , LR doesn’t depend on aerosol amount, but only on aerosol typeExamples: ~ 10 sr (ice crystals); ~ 20-30 sr (maritime aerosols);
~ 60-70 sr (urban aerosol) ~ 100 sr (heavy polluted air)
parameter strongly related to the microphysical aerosols properties
- aerosol type - size distribution relative humidity
Processing Algorithms :
1. Slope Method 2. Total Integrated Backscatter3. Inverse Modeling 4. Analytical Inversion An important simplification: no multiple scattering accounted for
Slope Method:
Based on the assumption of a homogeneous atmosphere: (r)
Calculating the logarithm of the range corrected backscatter signal Z:
r
0
2 )dr'α(r'2CβlnP(r)rlnZ(r)
The extinction coefficient = par + mol can be derived from the gradient:
dr
dlnβ
dr
dZ
2
1α Because of the initial assumption could be
calculated from the slope of the range corrected signal Z
Total Integrated Backscatter:
Requires calibrated lidar system and information about the backscatter/extinction ratio k= 1/LR. The total integrated backscatter signal (U) is defined as:
dr'Pr'U(r)r
0
2 It can be shown that: dr
dU
Ck2U
1Ck
1α
Inverse Modeling:
Well known method for retrieving physical parameters in remote sensing.Main idea: make use of a forward model to model the observed signal, depending on a set of parameters, to be retrieved.
The difference between observed and modeled parameters is minimized in general using iterative procedures. Two particular methods are: Iterative algorithm (Kästner, 1987)
Information-theoretic method (Yee,1989)Analytical Inversion:
Most frequently used method because it is the exact mathematical solution of the lidar inversion problem.
It could be performed in two ways: forward and backward integration.Considers the existence of the lidar ratio (LR)
Algorithm known as refined scattering ratio (Russell et al, 1979: Methodology for error analysis and simulation of lidar aerosol measurements. App. Opt., 18, pp. 3783-3797).
Forward Integration Method
Advantages Disadvantages References
Boundary value can be replaced by lidar calibration constant
Unstable in turbid atmosphereNear-end boundary value or calibration necessary
Fernald et al., 1972Fernald, 1984Kovalev & Moosmüller, 1994
Backward Integration Method
Advantages Disadvantages References
Stable in turbid atmosphere
Far-end boundary value generally can not be determined
Klett, 1981; 1983; 1985Sasano & Nakane, 1984Fernald, 1984Kovalev and Moosmüller, 1994
3. Lidar applications:• Stratospheric aerosols• Cirrus clouds
Mt. Pinatubo stratospheric aerosols
tropopau
se
“Cirrus clouds lidar measurements”
4. Space Lidars
Space Based Lidars Functionality
2006
2016
LITE : LIdar Technology Experiment
LITE on board STS-64 Discovery mission
September 9-20 1994
First sucesful mission using a lidar for atmospheric research
Aerosols and clouds measured
Tomado de: http://www-lite.larc.nasa.gov/
5 minutes LITE measurementSahara overpass September 18, 1994.
Mount Atlas separate dense aerosols mass east of a clear west
More west over the desert a complex massmass of aerosols reaching 5km altitude
Mount Atlas
Tomado de: http://www-calipso.larc.nasa.gov/
CALIPSO: Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation
PICASO-CENA:Pathfinder Instruments for Cloud and Aerosol Spaceborne Observations– Climatologie Etendue des Nuages et des Aerosols
Mission for measuring clouds and aerosols
Designed for 3 years
Operative 2006 to the present
Tomado de: http://www-calipso.larc.nasa.gov/
CALIPSO
Sistemas de Control y Operación del CALIPSO
Muchas Gracias.
