1. LIDAR: Introduction to selected topics
Leibniz-Institut für Atmosphärenphysik
Schlossstraße 6, Kühlungsborn
Michael Gerding

2. LIDAR: What’s it all about?
LIDAR = light detection and ranging (similar to radar, sodar)
light: pulsed laser (nanosecond-range)
scatterer: air molecules and aerosols
detector: telescope and photon detectors
ranging: time-resolved detection
distinction between scatterers by optical properties (e.g. wavelength and scattering cross section)

3. LIDAR: What’s the use of it?
vertical distribution of scatterers
aerosol particles from troposphere to mesosphere
existence, phase, optical thickness (extinction)
particle size, particle number ???
trace gases in troposphere/stratosphere/mesosphere/ thermosphere
concentration of pollutants: NO2, SO2, ..., H2O, O3, OH, metal atoms (Fe, Na, K, Ca, ...), Ca+
temperature of the troposphere/stratosphere/mesosphere/...

4. 2. Lidar Basics 1. Introduction and Overview
3. Lidar Application: Aerosols
4. Lidar Application: Temperature

5. Light Interaction with the Atmosphere
Rayleigh scattering
elastic; atoms or molecules
Mie (particle) scattering
elastic; aerosol particles
Raman scattering
inelastic, molecules
Resonance fluorescence
elastic at atomic transition; large cross section
Fluorescence
inelastic, broadband emission; atoms or molecules
Absorption
attenuation in bands; molecules or particles

6. Light Interactions with the Atmosphere (II)

7. Light Interactions with the Atmosphere (III)
Q branch
total intensity of the rotational Raman bands
Rayleigh/Mie line
pure rotation Raman bands
vibrational Raman scatter
relative intensity
wavelength [nm]
Rayleigh-Raman spectrum
from: A. Behrendt, PhD thesis, University Hamburg, 2000

8. Elastic Lidar Backscatter Signal
M. Gerding, PhD thesis, IAP Kühlungsborn, 2000

9. Basic Lidar Equation background bin width detector sensitivity
total backscatter coefficient
geometric overlap between laser and telescope FOV
transmission between ground and scattering altitude zi
solid angle of visible telescope aperture
emitted intensity at the wavelength 
intensity at the emitted wavelength  received from altitude zi (z=c·t/2)

10. Lidar System: Schematic Drawing
laser
detection
telescope

11. 3. Lidar Application: Aerosols
1. Introduction and Overview
2. Lidar Basics
3. Lidar Application: Aerosols
3.1 Aerosol Determination by “Slope Method”
3.2 Aerosol Determination by “Klett Method”
3.3 Aerosol Determination by “Ansmann Method”
4. Lidar Application: Temperature

12. Aerosol in the Atmosphere
noctilucent clouds
aerosol free
polar stratospheric clouds
Junge layer and volcanic aerosol
clouds
boundary layer and tropospheric aerosol

13. 3.1 Aerosol Determination by “Slope Method” (I)
n: molecule number
density

14. 3.1 Aerosol Determination by “Slope Method” (II)

15. Application of the “Slope Method”
Figure courtesy of M. Alpers

16. NLC photos
photo: P. Parviainen
photo: M Alpers

17. 3.2 Aerosol Determination by “Klett Method” (I)

18. 3.2 Aerosol Determination by “Klett Method” (II)

19. Application of the “Klett Method”: Polar Stratospheric Clouds
Ny-Ålesund, January 20, 2001, 0:21-2:10 UT
Slope (smoothed)
Klett (unsmoothed)

20. Polar Stratospheric Clouds
photo: M. Rex

21. 3.3 Aerosol Determination by “Ansmann Method” (I)
R. Schumacher, PhD thesis,
Alfred Wegener Institute, 2001

22. 3.3 Aerosol Determination by “Ansmann Method” (II)
aAer(lR)
k Ångström-coefficient
No need of “L”!

23. Application of the “Ansmann Method”: Tropospheric Aerosol
LR=25: sea salt
Koldewey Aerosol Raman Lidar KARL
March 12, 2002, 21:00-23:30 UT

24. Methods for Aerosol Determination: A Comparison 
Slope Method
requires only one channel
suitable for weak, noisy signals
no extinction correction
 only suitable for thin clouds
Klett Method
extinction considered
needs assumption on extinction to backscatter ratio (lidar ratio)
Ansmann Method
requires no assumption on lidar ratio
requires additional Raman channel (small cross section)  range limit

25. 4. Lidar Application: Temperature
1. Introduction and Overview
2. Lidar Basics
3. Lidar Application: Aerosols
4. Lidar Application: Temperature
4.1 Temperature Profile from Resonance Lidar
4.2 Temperature Profile from Rayleigh Lidar
4.3 Temperature Profile from Raman Lidar

26. IAP Mobile Potassium Lidar
Potassium Temperature Lidar of Leibniz-Institute of Atmospheric Physics on the
Plateauberget near Longyearbyen (78°N, 16°E)
photo: J. Höffner

27. 4.1 Temperature Profile from Resonance Lidar
IAP Potassium Lidar
atomic K exists in the mesopause region (like Si, Mg, Fe, Na, Ca ...)
investigation by resonance lidar
alkali metals show hyperfine structure of electronic transitions
temperature dependent Doppler broadening of resonant backscatter can be detected by narrowband laser
Figure courtesy of J. Höffner

28. above 80 km: K resonance lidar
Hyperfinestructure and Doppler broadening of a K resonance line
von Zahn and Höffner, 1996

29. km: K resonance lidar
Hyperfinestructure and Doppler broadening of a K resonance line
Measured and fitted shape of the resonance line

30. 22-90 km: Rayleigh lidar hydrostatic equation ideal gas law
relative density profile required -
derived from
(aerosol free) lidar backscatter signal

31. Temperature profile from air density profile

32. 1-30 km: Rotation-Raman lidar
Rotation-Raman spectrum of air for excitation at nm
Alpers et al., 2004

33. 4.3 Temperature Profile from Raman Lidar
Rotation-Raman spectrum depends on temperature
Intensity of transitions to high J-numbers increase with temperature, intensity of transitions to low J-numbers decrease
Intensity ratio between two different wavelengths depends on temperature
For lidar choose narrow fractions of the spectrum
high-J filter
low-J filter
A. Behrendt, Uni Hamburg, 2000
wavelength [nm]

34. 5.3 Temperature Profile from Raman Lidar (II)
Backscatter signal at the different wavelengths depend on temperature, but also on the filter characteristic, the transmission of the detection system, atmospheric extinction
temperature dependence of the signal can (hardly) be calculated or
lidar can be calibrated with
respect to temperature response
(comparison with other methods like
radiosondes)

35. Comparison of temperature sounding principles
range
complexity
limits
Rayleigh-Integration
Strato- and Mesosphere 
aerosol inhibits sounding
hydrostatic equilibrium assumed
Raman-Integration
(Troposphere) Stratosphere
aerosol disturbs sounding
Resonance-Doppler
Mesopause region
( km) 
limited to atomic metal layer
Brilloiun-Doppler
lower troposphere
very weak signal
Rotation-Raman
Tropo- and Stratosphere 
weak signal

36. 5. … add on’s 1. Introduction and Overview 2. Lidar Basics
3. Lidar Application: Aerosols
4. Lidar Application: Temperature
5. … add on’s

40. Detector of the IAP T lidars