867 
-ering signals from the 
constraints, including 
irements, wavelength 
wavelengths near (but 
:iency of chlorophyll 
inear effects (singlet- 
tons/pulse/cm^ (i. e . 
telescope with a large 
;s. We describe in the 
; fluorescence lifetime 
sts of this LIDAR has 
¡-locked Nd-Yag laser 
) ps (FWHM) and the 
the JRC (Ispra, Italy). 
400 mm. The optical 
e (670 < X < 750 nm) 
ly. The laser beam is 
;ists in a Sylvania 502 
a few hundreds mV, 
t digitizer and further 
has a bandwidth of 1 
luring a time window 
nder saturating light 
nee quantum yield, 
irescence decay of a 
ise function recorded 
Although the laser 
:ant actinic effect is 
ited area (=35 cm^). 
i in the presence of a 
fferent experimental 
conditions have been compared: low ambient light (< 1 pEm-2s-l, Fo fluorescence level) and saturating light 
(>5000 |iEm-2s-l, Fm). In each case, the fluorescence lifetime can be computed if we consider that the 
measured fluorescence decay Fex(t) is the convolution product of the instrumental function Dex(t) with the 
actual fluorescence decay F(t): 
Fcal(t) = F(t) <S> Dex(t) 
F(t) is modeled as a sum of m exponential components: 
m 
F(t) = X A , exp(- U 
1=1 ' 
Deconvolution of the former expression, or the determination of parameters Aj and Xj, is performed 
with a least squares method using the Marquardt search algorithm for non-linear parameters [12], [24]. The 
average lifetime of fluorescence can be computed by: 
t * A if 
We obtain x(Fo)=0.37 ns and x(Fm)=1.87 ns for the Fo and Fm levels respectively which compares fairly well 
with previous results obtained at near contact. [ 21 ] 
52. Effect of water stress on fluorescence lifetime 
FIG. 5. Effect of water-stress on fluorescence lifetime. Comparison with contact measurements with a PAM 
fluorimeter 
Water supply is one of the major environmental constraints of natural conditions prevailing on hearth. 
Irreversible damages induced by water deficiency occurs when dehydration decreases the water content by more 
than 50%. Mild water deficit essentially induces stomata closure in patches. It determines a decrease in internal