Fig. 2. Outline of the image processing steps to derive dye concentrations from the fluorescence image. Left-hand side panels are images of the fluorescence signal of brilliant sulfaflavine (BF) on horizontal cross sections of four soil cores from the Unterehrendingen soil (upper and lower cores in the panel are taken from the topsoil and subsoil, respectively): A(x) is the raw fluorescence signal; Aff(x) is the flat field corrected fluorescence signal; Affr(x) is the background subtracted fluorescence signal corrected for variations in soil surface reflection; and Ct(x) is the total concentration pattern. Right-hand side panels represent correction factors <F(x)>/F(x) for inhomogeneous illumination (flat field correction); correction factors R0/Rff(x) for variations in excitation light reflection at the soil surface; and calibration relations between corrected fluorescence and total dye concentration, Ct.
