Minimize Gas Correction

The radiative transfer processes in the atmosphere and OLCI measurements are mainly affected by:

  • air molecular scattering
  • ozone absorption
  • water vapour absorption
  • oxygen absorption
  • nitrogen-dioxide absorption
  • chlorine-dioxide absorption
  • aerosols scattering and absorption
  • cloud scattering and absorption.
As a consequence, all the atmospheric constituents have to be investigated to estimate the impact of atmospheric gases on OLCI measurements. The amount of absorption as well as the vertical distribution of each atmospheric gas determines the impact and strategy for correction of its impact.

 

Before being able to fully identify land and water pixels and to perform smile correction, the TOA reflectances need to be corrected for absorption by atmospheric gases (NO2, O2, H2 O and O3). If absorption by nitrogen-dioxide, ozone and oxygen are based on meteorological or climatological data, specific OLCI channels are used to first estimate the atmosphere total water vapour content along the pixel light path to better correct for H2 O absorption.

Functional Block Diagram of Gas Correction