E. Boegh et al., A remote sensing study of the NDVT-T-s relationship and the transpiration from sparse vegetation in the sahel based on high-resolution satellite data, REMOT SEN E, 69(3), 1999, pp. 224-240
This article proposes a nara approach for estimation of the transpiration r
ate in sparse canopies. The method relies on a combination of techniques; s
ome of which having a successful background of solid experimental and theor
etical justification, while others having only recently been introduced as
promising tools for the extraction of environmental information from satell
ite data. The transpiration rate (lambda E-v) is calculated by applying an
energy balance approach to the vegetation component of the land surface: la
mbda E-v=R-n(v)-H-v, where R-n(v) is the net radiation absorbed by the vege
tation, and H-v is the sensible heat flux between the leaves and the air wi
thin the canopy. R-n(v) is calculated through the use of remote sensing and
standard meteorological data by combining a conventional method for estima
tion of the land surface net radiation with a ground-calibrated function of
NDVI (normalized differential vegetation index). H-v is assessed as a line
ar function of the temperature difference between vegetation (T-v) and the
mean canopy air stream (To) Because the surface temperature (T-s) recorded
by satellite contains combined information of both soil and vegetation, T-v
is evaluated on the basis of the linear NDVI-T-s relationship for individu
al surface types. T-0 is assessed utilizing recent evidence that (T-s-T-0)
is linearly related to the difference in surface temperature and air temper
ature above the canopy (Ts-T-u), with the slope coefficient depending only
on canopy structure. The method is tested using remote sensing data ranging
from ground-based, airborne, and satellite recordings. The modeled transpi
ration rates compared well to measurements of sapflow data and latent heat
fluxes recorded for a wide range of surface types (agricultural crops, natu
ral vegetation, forest vegetation). (C) Elsevier Science Inc., 1999.