The atmospheric correction of the AVHRR bands in the solar region includes the correction of the absorbing and scattering effects of atmospheric gases, in particular ozone, oxygen and water vapour, of the scattering of air molecules (Rayleigh scattering) and the correction of absorption and scattering due to aerosol particles.
The transformation of the Top Of Atmosphere (TOA) reflectance data to surface reflectance values is achieved with the help of pre-calculated LookUp Tables (LUTs), which replace the complex computations with a fast array indexing operation. The sensor-specific LUTs were calculated using the radiative transfer model MODTRAN (Berk et al. 2008).
To avoid the LUTs from being too large, the TOA reflectances are normalized to a standard surface pressure, stratospheric aerosol and a fixed ozone value prior the atmospheric correction. The underlying idea is to put an extra layer on top of the standard atmosphere that takes into account the deviation of the standard values from the actual values for ozone, air pressure and stratospheric aerosol.
The atmospheric correction accounts for different levels of water vapour derived from era interim and aerosol type and aerosol optical depth. Currently, a climatology from the aerosol CCI project and the stratospheric aerosol optical thickness data provided by the Goddard Institute for Space Studies, NASA, is used for the correction.
Example of the SDR product from August 1990
Berk, A; Anderson, GP; Acharya, PK ; Shettle, EP: MODTRAN®184.108.40.206 USER’S MANUAL, SPECTRAL SCIENCES, INC. 4 Fourth Ave.Burlington, MA 01803-3304, AIR FORCE RESEARCH LABORATORY Space Vehicles Directorate AIR FORCE MATERIEL COMMAND HANSCOM AFB, MA 01731-3010, available to registered users of MODTRAN5.2.1 from Spectral Sciences Inc. at firstname.lastname@example.org.