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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 1 | Copyright
Atmos. Meas. Tech., 11, 161-175, 2018
https://doi.org/10.5194/amt-11-161-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Jan 2018

Research article | 10 Jan 2018

Error sources in the retrieval of aerosol information over bright surfaces from satellite measurements in the oxygen A band

Swadhin Nanda1,2, Martin de Graaf1, Maarten Sneep1, Johan F. de Haan1, Piet Stammes1, Abram F. J. Sanders3, Olaf Tuinder1, J. Pepijn Veefkind1,2, and Pieternel F. Levelt1,2 Swadhin Nanda et al.
  • 1Royal Netherlands Meteorological Institute (KNMI), Utrechtseweg 297, 3731 GA De Bilt, the Netherlands
  • 2Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft, the Netherlands
  • 3University of Bremen, Institute of Environmental Physics, Otto-Hahn-Allee 1, 28359 Bremen, Germany

Abstract. Retrieving aerosol optical thickness and aerosol layer height over a bright surface from measured top-of-atmosphere reflectance spectrum in the oxygen A band is known to be challenging, often resulting in large errors. In certain atmospheric conditions and viewing geometries, a loss of sensitivity to aerosol optical thickness has been reported in the literature. This loss of sensitivity has been attributed to a phenomenon known as critical surface albedo regime, which is a range of surface albedos for which the top-of-atmosphere reflectance has minimal sensitivity to aerosol optical thickness. This paper extends the concept of critical surface albedo for aerosol layer height retrievals in the oxygen A band, and discusses its implications. The underlying physics are introduced by analysing the top-of-atmosphere reflectance spectrum as a sum of atmospheric path contribution and surface contribution, obtained using a radiative transfer model. Furthermore, error analysis of an aerosol layer height retrieval algorithm is conducted over dark and bright surfaces to show the dependence on surface reflectance. The analysis shows that the derivative with respect to aerosol layer height of the atmospheric path contribution to the top-of-atmosphere reflectance is opposite in sign to that of the surface contribution – an increase in surface brightness results in a decrease in information content. In the case of aerosol optical thickness, these derivatives are anti-correlated, leading to large retrieval errors in high surface albedo regimes. The consequence of this anti-correlation is demonstrated with measured spectra in the oxygen A band from the GOME-2 instrument on board the Metop-A satellite over the 2010 Russian wildfires incident.

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Estimating aerosol layer height in the atmosphere from satellite data in the oxygen A band (758–770 nm) over land is challenging over land, since the surface is generally very bright in this wavelength region. This paper discusses an interplay between the surface and the atmosphere in their contributions to the top-of-atmosphere reflectance spectrum and the consequent biases obtained while estimating aerosol layer height, using synthetic data and real data from the GOME-2 satellite instrument.
Estimating aerosol layer height in the atmosphere from satellite data in the oxygen A band...
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