Intercomparison of satellite retrieved aerosol optical depth over ocean

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Intercomparison of satellite retrieved aerosol
optical depth over ocean
Mona Johnsrud, Gunnar Myhre, Frode Stordal
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Satellite AOD Past activities
November 96-June 97 AOD over ocean Data from 5
satellite retrievals and 13 AERONET
stations Monthly mean values Satellite data
converted to 550 nm using Ångstrøm
exponent Comparison on 1x1 degrees equal angle
grid
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Paper in JASPoster at EGS

• Gunnar Myhre, Frode Stordal, Mona Johnsrud
• Norwegian Institute for Air Research (NILU),
  Kjeller, Norwayand Department of Geophysics,
  University of Oslo, Oslo, Norway
• Alexander Ignatov
• NOAA/NESDIS/Office of Research and
  Applications/Climate Research and Applications
  Division, Washington, D.C.
• Michael I. Mishchenko, Igor V. Geogdzhayev
• NASA Goddard Institute for Space Studies, New
  York, New York
• Didier Tanré, Jean-Luc Deuzé, Philippe Goloub
• Laboratoire d'Optique Atmospherique, CNRS,
  U.S.T. de Lille, Villeneuve d'Ascq, France
• Teruyuki Nakajima
• Center for Climate System Research, University
  of Tokyo, Tokyo, Japan
• Akiko Higurashi
• National Institute for Environmental Studies,
  Tsukuba, Japan
• Omar Torres
• Joint Center for Earth Systems Technology,
  University of Maryland Baltimore County,
  Baltimore, Maryland
• Brent N. HolbenBiospheric Sciences Branch, NASA
  Goddard Space Flight Center, Greenbelt, Maryland

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Summary of the findings

• Substantial differences in AOD between the
  retrievals
• Best agreement in coastal regions with high AOD
• Largest deviations found over large oceanic
  regions in the southern hemisphere
• Differences in cloud screening probably one of
  the main reasons for the large disagreement

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Current activities, monthly mean values
Data collection is not quite completed. In
addition to the four satellite retrievals for the
entire period we have two more datasets from
AVHRR-1 and a retrieval from VIRS for an eight
month period in 1998. For the same eight months
period data from GOME/ATSR-2 will be made
available for the study. (Dr. Thomas Holzer-Popp,
German Aerospace Center) After the work started
data from MODIS-Terra for the period March to
December 2000 have become available. Presented
TOMS data are just preliminary. AOD for 380 nm
have been scaled to 550 nm by using the average
ratio between 380 nm and 550 nm AOD values for
the nov96-jun97 period.
September 97-December 00 AOD over ocean Data from
4 (7) satellite retrievals and 29 AERONET
stations Satellite data converted to 550 nm using
Ångstrøm exponent Comparison on 1x1 degrees equal
angle grid
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Monthly Global Mean for Sep 97-Dec 00
Sampling problem of AVHRR in 2000 due to orbital
drift of satellite NOAA-14 (2) Second generation
aerosol algorithm (3) Third gen aerosol algorithm
AVHRR-2 AOD over 1.0 is set to 1.0 SeaWiFS AOD
over 0.3 is set to 0.3 VIRS, AVHRR-1 (3QC), and
AVHRR-1 (2QC) for 8 months period only
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Monthly mean AOD for 8 regions
Mineral dust Cape Verde Plateau, Arabian
Sea Biomass burning Angola Basin, Bay of
Bengal Industrial/anthropogenic East Coast USA,
South China Sea, East China Sea Mixed
Mediterranean sea Some of the locations (Angola
Basin, Arabian sea) have a strong seasonal
variation. SeaWiFS misses the peaks (due to
cut-off at 0.3), but seems to have the same
variation as the others TOMS seems to be the
outsider, but this may change when we get better
data for 550 nm.
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AERONET stations 2000
Stations located on Islands and coastlines are
used in the comparison. The number of stations
have increased since the first study. (29 now, 13
in 96-97)
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Monthly mean values for satellite and AERONET data
To compare AOD over ocean with measurements on
land we have picked 3x3 grid squares from the
satellite data, where the AERONET station is in
the middle, and used an average of these grid
squares for the comparison. For stations where
this selection gave no data, we have shifted the
selection away from the coast to get more valid
data. (f.ex. Dakar)
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Scatterplot of AERONET vs. Satellite Retrievals
Each point is one month for one station.
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Scatterplot for different particle groups,
classified by the Ångstrøm coefficient from
AERONET
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Correlations between satellite retrievals and
AERONET data
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Comparison of satellite retrievals for selected
episodes

• Campaigns
• INDOEX, Mar 99
• SAFARI Aug 00
• Major fires
• Indonesia, Oct 97
• Mexico, May 98
• Dust outbreak
• Cape Verde, Jun 99
• Strong anthropogenic influence
• Europe Atlantic Coast, Apr 99
• Mediterranean Sea Aug 99
• China Sea, Mar 00
• East Coast USA May 98
• East Coast USA, May 00

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Current activities, comparison of daily data
Period Nov 96-Jun 97 Focus on periods with high
availability of AERONET data Started analyses for
AVHRR-1 and POLDER data Working to include TOMS,
OCTS, and AVHRR-2
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Scatterplot of daily data
POLDER
AVHRR-1
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Investigation of monthly data

• Period 1 Nov 1996 Jun 1997
• POLDER, OCTS, AVHRR-1, AVHRR-2, TOMS
• Period 2 Sep 1997 Aug 2000
• AVHRR-1, AVHRR-2, SeaWiFS, TOMS others (VIRS,
  GOME/ATSR-2 shorter periods)
• Period 3 Sep 2000 Apr 2002
• MODIS, MISR, AVHRR-1, SeaWiFS
• Period 4 May 2002 gt
• MODIS (Terra Aqua), MISR, AVHRR-1, ENVISAT,
  POLDER others