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Cloud and Aerosol Parameter Retrieval

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Parameter  Spectral Window (nm)  Layer  Quantity (column)  Retrieval Algorithm  Retrieval Algorithm Reference 
O3  325 335  troposphere, stratosphere  total  operationalWFM-DOASTOSOMISDOAS  Spurr 2000 Weber et al. 2005 Eskes et al. 2005 Van Roozendael et al. 2006  
NO2  425-450  troposphere, stratosphere  total, tropospheric   operational DOAS SDOAS   Spurr 2000 Richter et al. 2005 Van Roozendael et al. 2006  
BrO  335-347(55)  troposphere, stratosphere  total  DOAS   
SO2  315-327  troposphere  total  DOAS   
HCHO  335-347(55)  troposphere  total  DOAS   
OClO  365-389  stratosphere  total  DOAS   
H2O  688-700  troposphere  total  AMC-DOAS  No l et al. 2004 
CO  2321(24)-2335   troposphere  total  WFM-DOAS IMLMIMAP  de Beek et al. 2006 de Laat et al. 2006 Frankenberg et al. 2005b  
CH4  1627(30)-1671  troposphere  total  WFM-DOAS IMLMIMAP   de Beek et al. 2006 Gloudemans et al. 2005 Frankenberg et al. 2005a  
CO2  1558(63)-1594(85)  troposphere  total  WFM-DOAS IMLMIMAP  de Beek et al. 2006 Houweling et al. 2005 Frankenberg et al. 2005a  

Table 5-1: Atmospheric geophysical parameters and retrieval algorithms – nadir trace gases.


5.3 Cloud and Aerosol Parameter Retrieval

The primary scientific objective of SCIAMACHY is the measurement of atmospheric trace gases in both the troposphere and stratosphere. However, clouds residing in the troposphere do interfere with the retrievals from SCIAMACHY measurements mainly by the shielding and albedo effects. Similarly, tropospheric and/or stratospheric aerosol interferes with the trace gas retrieval, as it alters the light path. Therefore, there is a clear need for cloud and aerosol information. In addition, cloud information from SCIAMACHY will also provide relevant data for cloud research.

In the UV, VIS and NIR spectral regions the solar radiation is strongly scattered by clouds and aerosol, thereby modifying the Earth reflectance spectrum. The presence of clouds and aerosol and their properties can therefore be determined by analysing the top-of-atmosphere reflection function R. It is defined as (equ. 5-6)


image

 


where imageis the cosine of the solar zenith angle, image is the solar irradiance and image is the scattered and reflected light in the direction towards the satellite sensor.

 


Prerequisites for high quality information about aerosol and clouds are high spatial resolution and high calibration accuracy of the reflectance measurements. Typical reflectance spectra for various cloud and surface conditions are shown in fig. 5-7. Various algorithms are required to determine cloud and aerosol properties from SCIAMACHY data. For a summary the reader is referred to table 5-2.

 

click to enlarge

fig. 5-7:

image
Earth reflectance spectra (sun normalised intensity) for various cloud and surface conditions. The inset shows the variation in the reflectance spectrum due to changes in the thermodynamic state of water from liquid water to ice. The large difference in the reflectance spectrum around 1600 nm is used to derive information on the thermodynamical state of water in clouds. (Graphics: IUP-IFE, University of Bremen)
 


Parameter  Spectral Window (nm)  Retrieval Algorithm  Retrieval Algorithm Reference 
CF  PMD (RGB)  OCRA HICRUSPCASPICI  Loyola 1998 Grzegorski et al. 2004 Yan 2005 Krijger et al. 2005  
  reflectance near O2 A-band  FRESCO SACURA  Fournier et al. 2006 Kokhanovsky et al. 2005  
CTH  O2 A-band  FRESCOSACURA  Fournier et al. 2006 Kokhanovsky et al. 2005, 2006  
COT  reflectance VIS-NIR  SACURA  Kokhanovsky et al. 2005, 2006 
CGT  O2 A-band  SACURA  Kokhanovsky and Rozanov 2005 
Reff,cld  reflectance VIS-NIR  SACURA  Kokhanovsky et al. 2005, 2006 
CTP  reflectance NIR-SWIR  SACURA   Kokhanovsky et al. 2005, 2006 Acarreta et al. 2004b  
AAI  340 and 380    de Graaf and Stammes 2005 
AOT  several wavelengths in the VIS  SCIA-BAER  von Hoyningen-Huene et al. 2003, 2006 
Aerosol type  several wavelengths, combination with AATSR  SYNAER  Holzer-Popp et al. 2002a 

Table 5-2: Atmospheric geophysical parameters and retrieval algorithms – nadir cloud and aerosol parameters.

 

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