Tóm tắt
The spectral reflectance of leaves from several
Eucalyptus species was measured over the 400–2500
nm wavelengths with a laboratory spectroradiometer. The relationship of
reflectance with the gravimetric water content and equivalent water thickness
(EWT) of the leaves was analysed. The results showed that EWT was strongly
correlated with reflectance in several wavelength regions. No significant
correlations could be obtained between reflectance and gravimetric water
content. It was also possible to confirm theoretically that reflectance
changes of leaves could be directly linked to changes in EWT but not to
changes in gravimetric water content. Several existing reflectance indices
were evaluated for estimation of leaf water content and some new indices were
developed and tested. Two semi-empirical indices developed in this study,
(R850 -
R2218)/(R850
- R1928) and
(R850 -
R1788)/(R850
- R1928), were found to show
significantly stronger correlations with EWT than all other indices tested. It
was also shown that these new indices were least sensitive to the effects of
radiation scatter. The indices
(R850 -
R2218)/(R850
- R1928) and
(R850 -
R1788)/(R850
- R1928) are therefore proposed as
two new indices for the remote estimation of vegetation water content.
