abstract 
Most Earth 
spectrally cc 
of the direc 
distribution 
challenging 
presented, a 
surfaces frc 
suggested c< 
Primarily, e 
biometric p; 
of vegetatioi 
models. 
KEY WOF 
1 - INTRO 
Measuring 
would be tr 
vegetative e 
Marlatt, 19 
1989, Deeri 
the several 
conditions) 
characterize 
surface albe 
of the comp 
such orbiti 
scheduled t 
which is si; 
Th 
(LAI), are e 
between th< 
must be esi 
biophysical 
reflectance 
biophysical 
generally v 
to maximal 
understand: 
viewing gr 
TI 
observing : 
regional tc 
photosynth 
sensing tha 
scientists n