Development of the SEVIRI Aerosol Retrieval Algorithm (SARA)

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Development of the SEVIRI Aerosol Retrieval
Algorithm (SARA)

• Aerosol retrievals using
• MSG-SEVIRI images

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Outline

• MSG-SEVIRI Instrument characteristics
• Aerosol retrievals over the ocean algorithm
  principles
• Aerosol models and radiative transfer simulations
  
• Cloud screening process
• AOD results over the ocean for 2 case studies
• Conclusions and on-going work

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Instrument characteristics of MSG-SEVIRI
Altitude 36 km Nominal position Equator, 0
Longitude Geographic coverage a full Earth
hemisphere over Europe and Africa Spatial
resolution at the sub-satellite point narrow
band channels 3 km, HRV 1 km Time sampling
15 minutes
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Retrievals over the ocean Equations
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AOD retrievals Equations
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Aerosol models

• Aerosol is considered to be an external mixture
  of a coarse (natural) and a fine (anthropogenic)
  aerosol type with monomodal lognormal size
  distribution
• Expansion coefficients of the scattering matrix
  and single scattering albedo calculated using
• - MIE code for spherical particles De Haan et
  al., 1987
• - TMATRIX code for randomly oriented spheroids
  Mischenko and Travis, 1998

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Radiative transfer simulations

• LUT data generated using DAK radiative transfere
  model Stammes,2001
• - Midlatitude Winter/Summer profile for gases
  McClatchey et al., 1972
• - aerosol layer height 2 km
• - exponentially decreasing concentrations with
  height
• - 15 solar and viewing zenith angles, 37
  azimuth angles
• - 11 aerosol optical depths at the reference
  wavelength of 500 nm
  (ranging between 0.02 and 6).

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Cloud Screening - Method

• Basic principle Clouds are generally colder and
  brighter than most surfaces
• Method based on the cloud screening technique
  used in AATSR aerosol retrieval algorithm
  Robles-Gonzalez, 2003
• ?Treshold technique based on image histogram
  analysis
• Detection tests
• - Infrared Gross Temperature Test (IGTT)
  (over land and sea (T12.0))
• - Dynamic Visible Test (DVT) (over land
  (R0.6) and sea (R0.8))
• - Ratio Test (DRT)
  (over sea only (R0.8/R0.6))
• - Dynamic Spatial Coherence Test (SCT) (over
  sea only (T10.8, R0.6))

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Cloud Screening -Cloud mask comparisons over
Europe
SEVIRI and MODIS
4 week periods in (Jan/May/Aug/Oct) 2006 Most
differences observed on cloud edges, and broken
cloud fields. In general 85 agreement with both
products
SEVIRI and SAFNWC/MF
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Case study 1 (FF)Forest-Fire Smoke from the
Iberian peninsula advected over the Atlantic - 7
August 2006
True color scene from Terra-MODIS 1110 UTC
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SARA results for FF -7 August 2006, 1115 UTC
Fine Mode Weight at 500 nm
AOD at 635 nm
Angstrom 635-870 nm
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Comparison with MODIS (MOD04) for FF

• Comparison with MODIS for FF
• Spatial variations well represented
• SEVIRI-AOD635 lt lt MODIS-AOD660
• underestimation by 50

MODIS - AOD at 660 nm
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Validation with AERONET for FF

• Validation with AERONET for FF
• Diurnal variations well reproduced
• Best results obtained for the visible channels
• MODIS-AOD860 and SEVIRI-AOD810 overestimated

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Case study 2 (DD)Dust Storm across the Eastern
Mediterranean Sea25 February 2006
True color scene from Terra-MODIS 0900 UTC
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SARA results for DD -25 February 2006, 0900 UTC
Fine Mode Weight at 500 nm
AOD at 1640 nm
Angstrom 870-1640 nm
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Comparison with MODIS (MOD04) for DD
MODIS - AOD at 1630 nm

• Comparison with MODIS for DD
• Very good agreement between SEVIRI-AOD1630 and
  MODIS-AOD1630

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Validation with AERONET for DD

• Validation with AERONET for DD
• Time series cloud contaminated
• General trends well represented
• Best results obtained for AOD in the
  near-infrared

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Conclusion and on-going work

• The stand-alone algorithm for cloud detection
  with MSG-SEVIRI provided satisfying cloud masks
  over Europe
• Aerosol retrievals with SARA over the ocean have
  been validated for 2 case studies (FF and DD)
  favorable comparison with MODIS and AERONET data.
• Aerosol retrievals over land is an ongoing work.
  Preliminary results expected in winter 2008...
• Thanks for your attention !