198 
Wavelength (ntn) 
Figure 8 : Surface leaf water absorption required to achieve an optimized spectral fit for the golf course 
5 - REFLECTANCE INVERSION 
An algorithm has been developed for the inversion of AVIRIS measured radiance to apparent surface spectral 
reflectance using a radiative transfer code (Green et al., 1990b; Green et al., 1991b; Green et al., 1993). 
Currently, the MODTRAN radiative transfer code is constrained with the aerosol optical depth, the pressure 
elevation, water vapor and illumination geometry for each AVIRIS spectrum. MODTRAN is used to calculate 
the atmospheric path radiance and the two-way transmitted radiance for a horizontal surface of 1.0 reflectance 
Computer look-up-tables are used to accelerate these calculations. For each AVIRIS spectrum, the path 
radiance is subtracted and the two-way transmitted radiance divided to calculate the apparent surface 
reflectance. 
Figure 9 : Comparison of the AVIRIS inverted reflectance spectrum and a in situ measured reflectance 
spectrum for the polo field. 
Figure 9 shows 
measured at th 
irradiance sped 
absorption have 
course showing 
1 
0.9 
0.8 
0.7 
S 0.6 
0.3 - 
0.2 - 
0.1 - 
400 
Figure 10 : An 
6 - CONCLUSH 
Radiative transf 
constraining the 
directly from th< 
applied to each 
derived atmospl 
transfer code to 
element. A preli 
situ measured re 
surface reflectai 
characteristics o 
Acknowledgme 
This research v 
contract with th<