Atmospheric correction

Atmospheric correction is made using MODTRAN code combining atmospheric temperature and humidity profiles. Lower-level sounding, tethered balloon measurements, standard meteorological radiosounding and middle latitude summer model atmosphere are used for HEIFE subset of ATSR image, while only standard meteorological radiosounding and middle latitude summer model atmosphere are used for IMGRASS subset because of lack of the other measurements. No sounding measurements were available at exactly the same time as the satellite overpass, therefore the closest ones are employed which were acquired at 07:30h and 07h in the morning for HEIFE and IMGRASS respectively. Table 3 gives the results obtained with MODTRAN and atmospheric profiles.

Table 3. MODTRAN results for atmospheric transmission and the path radiance for each channel at nadir and forward view angle( n=nadir,Worward; 11=1 ยก)ini,12-12^m)_

Water vapor Transmission Path Radiance (W cm"2 sr 'jrni1) xlO"1

Site_(gfcm3) 1 In 1 If 12n 12f lln 11f 12n 12f

HEIFE 1.77 0.8603 0.7832 0.7755 0.6702 0.776 1.29 1.31 1.90

IM GRASS 1.52 0.8290 0.7307 0.7346 0.6110 0,942 1.49 1.60 2.36

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