Implementation activities I
13:30 – 15:00 Technology and Methodology I
Birgit Heese: Capabilities and limits of aerosol measurements with ceilometer
Dietrich Althausen: Automatic operation of lidar systems at remote sites
Constraining lidar retrievals with sunphotometer data:
- Ray Hoff: Leosphere ALS450 extinction retrieval (Klett vs AOD closure)
- Judd Welton: MPLNET approach
Ed Eloranta: HSRL Technique
Giuseppe D’Amico: EARLINET Single Calculus Chain
15:00 – 15:30 Coffee break
15:30 – 17:00 Technology and Methodology II
Ulla Wandinger: Optical particle properties and aerosol typing
Volker Freudenthaler: Depolarization measurement technique: definitions,
calibration, and applications
Detlef Müller: Microphysical particle parameters from multiwavelength
measurements
Nobuo Sugimoto: Determination of aerosol components from
multiwavelength/depolarization measurements
Atsushi Shimizu: Realtime data processing for validation/assimilation of chemical
transport models
Discussion
Optical particle properties and
aerosol typing
Ulla Wandinger
Leibniz Institute for Tropospheric Research, Leipzig, Germany
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
Motivation
• GALION as global network
• spaceborne lidars as global observation systems
→ long-term, global observations
→ global aerosol distribution and climatology
→ long-term trends
→ distinguish natural and anthropogenic aerosols
→ separate “unhealthy” aerosols
→ need to define common aerosol types, distinguish aerosol components
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
Aerosol types vs aerosol components
OPAC (Database on Optical Properties of Aerosols and Clouds, Hess et al. 1998)
Aerosol types
Aerosol components
Insoluble
Water-soluble
Soot
Sea-salt: accumulation mode
coarse mode
Mineral: nucleation mode
accumulation mode
coarse mode
transported
Sulfate droplets
Continental: clean
average
polluted
Urban
Desert
Maritime:
clean
polluted
tropical
Arctic
Antarctic
Mineral transported
Free troposphere
Stratosphere
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
Tools
multi-wavelength, extinction, backscatter and depolarization
lidar instruments
→ retrieval of microphysical properties
- depends mainly on spectral information „3+2“
(backscatter at 355, 532, 1064 nm, extinction at 355, 532 nm)
- depolarization information important for particle shape
(Kernel functions for Mie scatterers or non-spherical scatters)
→ aerosol and cloud type classification relies on intensive particle parameters
- lidar ratios (355, 532 nm)
- color ratios/Ångström exponents (extinction and backscatter)
- particle depolarization ratio
→ knowledge on wavelength conversion factors is required for
single-wavelength lidars or space-borne measurements (see ESA study)
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
aerosol type classification
Pure Saharan Dust
Aged Saharan Dust
Biomass Burning Aerosol + Mineral Dust
Canadian Biomass Burning Aerosol
Industrial Pollution Aerosol
Marine Aerosol
- different aerosol types cluster
and can be distinguished
- spread of the clusters is limited
by natural variations in the end
Petzold et al. ESA -ICAROHS, 2009
Esselborn et al., Appl. Opt., in preparation
BUT:
Inversion of microphysical properties and
determination of aerosol types from intensive optical properties
require high accuracy and precision of the primary optical data!
How do we get such data?
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
Approach for a trustworthy aerosol typing
1) quicklook
→
2) extensive optical data
Backsc.
Extinc.
0.9±0.2
0.9±0.2
1.1±0.3
47±5
50±6
→
3) intensive optical data
Lidar rat.
Angstr.
Depol.
Dust layer
→ layer-mean values:
54±6
46±3
including error bars for all quantities!
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
0.09±0.01 0.06±0.01
0.40±0.07
0.30±0.10
1) Quicklooks are important
- Range-corrected backscatter at the longest wavelength
- Depolarization ratio (if available, volume depol is sufficient for quicklook)
What situation do I deal with?
Are there clouds?
At which height/temperature?
Do they depolarize?
Are they penetrated?
Are there distinct aerosol layers?
At which height?
Do they depolarize?
What is their origin? (dust forecast, fires, smog,…???)
→ select appropriate time intervals (with/without clouds, homogeneous conditions)
→ choose appropriate averaging lengths
- do not mix clouds and aerosols, check carefully for settling crystals and
droplets (rain, drizzle)
- do not mix different aerosol layers
→ look for useful calibration ranges
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
2-3 Aug 2001
22:00 0:00 2:00 4:00
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
SAMUM,
Morocco, 2006,
dust storm
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
2) Evaluate specific „scenes“ (pre-selected time periods)
Calculate the primary data:
Extinction coefficients (355, 532 nm)
Backscatter coefficients (355, 532, 1064 nm)
Particle(!) depolarization ratio
Calculate errors, choose appropriate averaging lengths
Error propagation formulas are valid for errors <20%!!!
Have in mind that further calculations may be performed
with the data (i.e. further error propagation!)
Providing errors is essential!
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
3) Calculate intensive parameters, cross-check the data
Color ratios
b(1064 nm)/b(532 nm)
b(532 nm)/b(355 nm)
a(532 nm)/a(355 nm)
Lidar ratios (355, 532 nm)
Ångström exponents
a-related
b-related
Useful regions only! (error!)
Check whether these data make sense in the present situation!
4) Re-evaluate the data, if you find „strange“ results!!!
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
Always critically check the calibration of the backscatter!
baer (zref) << bmol (zref) is often not valid for long wavelengths!
→ scenes with cirrus clouds (neutral backscatter) are very helpful to train
or to investigate specific problems
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
What are reasonable values for aerosols?
Lidar ratio (355, 532 nm)
Particle depolarization ratio
(355, 532 nm)
25 (marine)….50 (urban)…80 sr (fresh smoke)
<5% („normal“)…10% (mixed dust)…35% (dust,ash)
Color ratios
b(1064 nm)/b(532 nm)
b(532 nm)/b(355 nm)
a(532 nm)/a(355 nm)
0.35 (fresh, small)….0.4–0.5….0.95 (large, sea salt)
0.45 (fresh, small)….0.5–0.7….0.95 (large, sea salt)
0.4 (fresh, small)….0.5…. 1 (smoke, sea-salt)
Ångström exponents
backscatter-related å(532/1064)
backscatter-related å(355/532)
extinction-related å(355/532)
1.5 (fresh, small)….1.4–1.0….0.1 (large, sea salt)
2.0 (fresh, small)….1.4–1.0….0.1 (large, sea salt)
2.0 (fresh, small)….1.4–1.0….0.0 (smoke, sea-salt)
Ratio of lidar ratio
S(355 nm)/S(532nm)
0.8…1.2 ???
Ratio of depolarization ratio
d(355 nm)/d(532 nm)
0.8…1.2 ???
Intensive parameters should remain stable within distinct layers and within time!
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
„Alarm bells“
- Color ratio b(1064 nm)/b(532 nm) < 0.4, Ångström exponent > 2
→ check your calibration at 1064 nm! reference value too small?
- Lidar ratio < 30 sr (under non-marine conditions)
→ check for cloud remnants!
→ check your overlap correction! extinction too low?
- Lidar ratio > 80 sr
→ check your statistical error! sufficient averaging?
→ check your b-calibration! reference value too small?
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
Optical properties, Potenza, 17 May 2008, 20:22 – 20:52 UT
0.90±0.06
0.76±0.07
0.58±0.05
0.96±0.03
0.85±0.03
0.71±0.03
66±7
44±6
75±4
51±5
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
74±8
58±4
1.0 ±0.5
0.4 ±0.1
0.38±0.08
79±5
60±7
1.0 ±0.2
0.30±0.06
0.28±0.02
What information can we use for aerosol typing?
Intensive aerosol parameters:
- particle depolarization ratio (at 355, 532...1064 nm)
- particle lidar ratio (at 355, 532 nm)
- Ångström exponent or color ratio
(backscatter and/or extinction)
Extensive aerosol parameters:
- extinction and backscatter coefficients (thresholds)
Auxiliary information:
- height range (e.g., PBL, stratosphere)
- temperature
- geographical location/surface (arctic, ocean, desert)
- source information + transport modeling
Second GALION Workshop, WMO, Geneva, 20-23 September 2010
per layer
Distribution of major aerosol components
from Tegen et al., JGR, 1997
Second GALION Workshop, WMO, Geneva, 20-23 September 2010