Radiance to Reflectance Conversion
This process aims to extract the input Level-1B data and convert the included radiance into reflectance through three main steps.
- Pre-processing for geometry and meteorological parameters: This step is carried out to derive geometry and meteorological parameters (pressure, wind) at each pixel, including invalid ones, from those provided at each tie-point of the Level-1B annotation product.
- Level-1B pixel classification screening. Level-2 pixel identification starts with reading of the INVALID flag of the Level-1B product. If it is set to TRUE, no further processing of the current pixel is performed, the Level-2 product shall contain fixed values for all geophysical products, with the INVALID flag set, and the next pixel is examined. Otherwise, processing of the current pixel is pursued.
- Pixel extraction and reflectance conversion. If the Level-1B pixel is not flagged INVALID, the other Level-1B flags and the top of atmosphere radiances at all bands are extracted from the Level-1B product. Radiances are converted to reflectances using the sun zenith angle cosine interpolated at the pixel and the sun spectral flux, read from the Level-1B product annotations.
Note that this process also includes preliminary processing applied to annotation and measurements data sets (interpolation of annotations from the tie-points grid to the pixel grid and radiance to reflectance conversion respectively).