Getzewich, Brian

Tackett, Jason L.

Vaughan, Mark

Winker, David

NASA Technical Reports Server

Jason L. Tacketta, Brian Getzewicha, Mark Vaughanb, David Winkerb
(a) Science Systems and Applications, Inc., (b) NASA Langley Research Center; Contact: Jason.L.Tackett@nasa.gov
Aerosol extinction profiles & aerosol optical depth 
Monthly-averaged
Equal-angle gridded
Near-global coverage (82°S to 82°N) below 12 km
Derived from CALIPSO level 2 aerosol extinction
Resolution: 2° latitude x 5° longitude x 60 m vertical
Sky Conditions
All Sky
Cloud Free
Cloudy-Sky, Transparent
Cloudy-Sky, Opaque 
Recent Improvements to CALIOP Level 3 Aerosol Profile Product 
for Global 3-D Aerosol Extinction Characterization
http://www-calipso.larc.nasa.gov/LIDAR SCIENCE WORKING GROUP
Overview of the Level 3 Aerosol Profile Product Motivation for Improvements
Product Release Dates:
Version 3: September 2015
Version 1 Beta: December 2011
In the Version 1 Beta release of the Level 3 Aerosol Product:
• Sky conditions are confusing and misrepresentative 
• Due to Level 3 averaging, Column AOD Mean is biased low
• Dust-only averages are biased high (Amiridis et al., 2013)
• Artifacts exist in extinction profiles near surface
The Version 3 release improves these aspects of the product.
References: Ma et al., 2013, “Comparison of AOD between CALIPSO and MODIS: significant differences over major dust and biomass burning regions”, Atmos. Meas. Tech., 6, 2391-2401
Amiridis et al., 2013, “Optimizing CALIPSO Saharan dust retrievals”, Atmos. Chem. Phys., 13, 12089-12106
Winker, et al., 2013, “The global 3-D distribution of tropospheric aerosols as characterized by CALIOP”, Atmos. Chem. Phys., 13, 3345-3361
“Sky condition” defines cloud cover in aerosol extinction profiles that are averaged together. 
Above, aerosol extinction profiles in white are excluded for the given sky condition. 
Cloud
Aerosol
Opaque
Latitude (°)
Cloudy, Transparent Cloudy, Opaque
All-Sky Cloud-Free
Latitude (°)
All profiles averaged, 
regardless of cloud 
cover. 
Provides view of 
entire column.
Only profiles with 
transparent clouds 
averaged. 
Inaccessible to 
passive 
observations or 
cause biases in 
passive retrievals.
Only profiles 
without clouds 
averaged.
Roughly 
comparable with 
passive 
observations.
Only profiles with 
opaque clouds 
averaged.
Inaccessible to 
passive 
observations. Useful 
for aerosol above 
cloud studies.
Data Availability
New in Version 3
August 2007, All-Sky, Night
Two methods to compute monthly-mean column AOD from level 2 aerosol extinction profiles:
Method 1: Average column AODs Method 2: Integrate averaged extinction
A
O
D
 M
et
h
o
d
 1
AOD Method 2
All-Sky
Averaging column AODs (method 1) causes a strong low bias in monthly-mean AOD because columns 
have unequal geometric depths due to cloud cover or quality screening, yet they are weighted 
equally in the average. The low bias exists because the Level 3 averaging method 1 is inappropriate –
not because of biases in Level 2 aerosol extinction itself.
Mean AOD in Version 3 correctly uses integrated monthly-mean aerosol extinction (method 2).
Used in Version 1 Used in Version 3
Corrected Column AOD  Computation
With proper weighting, level 3 
aerosol extinction for “all-sky” (black 
line) equals the sum of the other 
three sky conditions (red dashed 
line), making the four sky conditions 
internally consistent.
τV1 = 0.128
τV3 = 0.121
AOD Difference: Version 3 – Version 1, Aug. 2008 @ Night
0 0.05 0.1–0.05–0.1
ΔAOD
When computing mean extinction for single aerosol species, 
extinction from other aerosol species can be either:
2. Set to 0 km-1 (i.e. for dust-only, assume marine aerosol has σdust = 0 km
-1)
1. Ignored (incorrect – Version 1 implementation)
Data is August 2008 @ Night over Atlantic Saharan dust transport region.
Version 3 Dust AOD, Aug. 2008 @ Night
Version 3 ->
Version 1 ->
Dust-Only Extinction (km-1) Fraction
σdust overestimated where 
other aerosol types exist marine aerosol 
dominates < 2 km
Atlantic Saharan Dust Transport Region
Version 1 Dust AOD, Aug. 2008 @ Night
Version 1 overestimates 
dust-only AOD where other 
aerosol types exist.
Version 3 dust-AOD lower and 
more realistic where multiple 
aerosol types coexist.
Version 3 uses convention 2, above.
Extinction and AOD reported separately:
• All aerosol species
• Dust
• Polluted dust
• Smoke
New in 
Version 3
Improved Single Aerosol Species Averages
Level 3, Version 3 now available for the entire 
CALIPSO mission (Jun 2006 to current month-1)
Input Data: 
CALIOP Level 2, Version 3.x
Data and documentation:
https://eosweb.larc.nasa.gov
Winker et al., 2013 ACP
Aerosol
Cloud
Surface
Opaque
Level 2 Vertical Feature Mask over Pacific Ocean
marine aerosol
Base of marine aerosol not detected entirely to surface in Level 2. These gaps 
of “clear-air” would bias mean Level 3 extinction low if assigned σ = 0.0 km-1. 
Level 3 Extinction (km-1)
No correction
High bias with 
2.5 km threshold
Low bias we 
want to 
correct
Level 3 Extinction over Pacific Ocean
Mitigation Strategy: Ignore all “clear-air” below lowest aerosol base that is…
(Version 1) Below 2.5 km
(Version 3) Below 250 meters
Too high, leads to high bias in mean Level 3 extinction
Lowered in V3 to focus mitigation where needed
Undetected Surface-Attached Aerosol
Negative Signal Anomaly Mitigation
Ver. 3 Mitigation Strategy:
Ignore Level 2 extinction 
within 60 meters of 
surface prior to generating 
Level 3 average.
Occasional anomalously 
negative backscatter at 
surface can cause very 
negative or low-biased 
extinction in lowest range 
bin.
σ (km-1)
0
1
2
0−0.2 0.1−0.4−0.6
A
lt
it
u
d
e 
(k
m
)
Level 2 Aerosol Extinction
Profile 1
Profile 2
Profile 3
Anomalously negative 
extinction at surface
Eliminates sharp 
decrease in mean 
Level 3 extinction
Level 3 Aerosol Extinction
σ (km-1)
Version 1
Version 3
Improved Profiles Near Surface
• All-species extinction profile changes are confined to lowest 
2-3 km. Largest difference in 1-2 bins near surface.
• Updated averaging strategy recommended by Amiridis et al. 
2013 greatly reduces high bias in V1 dust extinction profiles.
0 0.2 0.4 0.6 0.8
AOD
AOD Version 3, Aug. 2008 @ Night
All aerosol 
species
Dust
Overall, the revised averaging 
scheme and mitigation of near-
surface artifacts yield 
improvements in aerosol extinction 
profile shape, albeit at the cost of a 
slight decrease in Level 3 mean 
AOD.
Revised single-species averaging 
scheme corrects overestimates in 
dust AOD and extinction profile 
shape due to previous Level 3 
averaging scheme.
Global AOD for 2008, All-Sky
V1 V3 % change
AOD, night 0.132 0.125 −5.3%
AOD, day 0.099 0.095 −4.0%
Changes in Extinction and AOD Relative to Version 1
New Sky Conditions
Incorrect Correct
Makes small corrections to Level 3 aerosol extinction profile in lowest 2 km. 
Global Dust AOD for 2008, All-Sky
V1 V3 % change
AOD, night 0.045 0.027 −40%
AOD, day 0.033 0.023 −30%
https://ntrs.nasa.gov/search.jsp?R=20160006701 2019-08-31T02:37:19+00:00Z


Recent Improvements to CALIOP Level 3 Aerosol Profile Product for Global 3-D Aerosol Extinction Characterization

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