GOME reflectivity and polarisation validation study

P. Stammes (1), I. Aben (2), R.B.A. Koelemeijer (1), 
S. Slijkhuis (3), and D.M. Stam (1,4)

     (1) Royal Netherlands Meteorological Institute (KNMI)
         Postbus 201, 3730 AE De Bilt, The Netherlands
     (2) Space Research Organization Netherlands (SRON)
         Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
     (3) Deutsche Forschungsanstalt fuer Luft- und Raumfahrt (DLR)
         82230 Oberpfaffenhofen, Germany
     (4) Faculty of Physics and Astronomy, Vrije Universiteit
         De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
     
         stammes@knmi.nl


During the GOME validation campaign, which took place from 
mid-1995 until mid-1996,
we have been studying the quality of the GOME measurements
of the Earth's reflectivity (i.e. Earth radiance/solar irradiance)
and polarisation.
Thereto, we performed 
consistency checks on the GOME level 1 data and compared these data with 
radiative transfer model results.

The polarisation validation of GOME is important, because
the accuracy of radiance measurements 
by GOME depends on the correction
for the (strong) polarisation-sensitivity of the instrument.
The three Polarisation Measurement
Devices (PMDs) in combination with spectral channels 2-4 of GOME 
yield the so-called fractional polarisation in three broad bands.
This quantity has been validated by 
comparison with polarised radiative transfer calculations
and by considering the data at special geometries along the orbit.

It has been found that the fractional polarisation measurements 
of the PMDs are generally consistent and accurate
to within a few percent.
The additional measurements of 
fractional polarisation in the channel-overlap regions
are strongly deviating, due to the
serial read-out of the spectral channel detectors.
This serial read-out causes
a shifted scene across a spectral channel.
In the measured reflectivity spectra 
often jumps from channel-to-channel are observed,
which are also caused by the serial read-out.
Reflectivity jumps are especially occurring 
over inhomogeneous (e.g. partially cloudy) scenes. 


Keywords: GOME, validation, reflectivity, polarisation, 
radiative transfer modelling

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry