Atmospheric scattering adds a “sky radiance”. Haze correction aims at removing sky radiance effects from raw data, and doing so can be beneficial to many applications of space-borne Remote Sensing.
Scattering depends on wavelength: Rayleigh scattering will hardly affect recordings in the red spectral band, while DNs in the blue band may become significantly larger. Reducing haze, therefore, must be done independently for each band of an RS image.
How much to subtract from every DN from a particular band? We can find out if the scene is favourable and contains areas that should have zero reflectance (a spectral-band-specific black body). Deep clear water, for example, should yield pixel values of zero in the NIR band. If not, we attribute the minimum value found for “water pixels” to sky radiance and subtract this value from all DNs in this band.
The alternative is less reliable, i.e. to look at the histogram of the band and simply take the smallest DN found there as the haze correction constant.