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Remote sensing for resources development and environmental management
Damen, M. C. J.

Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
Application of multispectral scanning remote sensing
in agricultural water management problems
Institute for Land and Water Management Research (ICW), Wageningen, Netherlands
Government Service for Land and Water Use (LD), Utrecht, Netherlands
ABSTRACT: A method has been developed for the automatical mapping of évapotranspiration from digitally taken
reflection and thermal images. This method has been tested in combination with field measurements and agro-
hydrological model calculations. We found that an important improvement of the hydrological description of an
area can be achieved by combining the remote sensing approach with conventional methods. Especially the spatial
variation in soil physical characteristics can be determined more accurately by applying remote sensing
techniques. Satellite and airplane images acquired after a dry period supply information about the occurrence
of drought damage. Because of the fast changing weather conditions in humid areas like the Netherlands remote
sensing in water management will mainly depend on scanning techniques from airplanes.
Remote sensing techniques can be applied to obtain
information about the hydrological characteristics
of an area. In a remote sensing study project per
formed in the eastern part of the Netherlands (East
Gelderland) we developed a method to automatically
derive an évapotranspiration map from reflection and
thermal infrared multispectral scanning images. In
formation about regional évapotranspiration of crops
is important for optimal water management in agri
culture and for the determination of the effect of
man-made changes in the overall hydrological situa
In the framework of the mentioned study project
experience is obtained especially with the detection
of drought damage. From an economical point of view
prevention of damage caused by excess of water is
also important in the Netherlands. Untili now only
Figure 1. Location of the three study areas in the
limited experience has been obtained with remote
sensing like MSS techniques and radar. Probably remote
sensing images taken directly after the winter period
can supply information about the regional distribution
of areas with water excess. At the beginning of the
growth stage information about excess of water might
be obtained through differences in germination.
We are currently testing the usefulness of remote
sensing to solve water management problems. In several
projects we are investigating whether the additional
use of remote sensing is technically and financially
advantageous in determining the effects of hydrolog
ical measures.
In this paper we give an overview of the MSS re
search. The concerning study areas are indicated in
Figure 1.
2.1 Relation between instantaneous crop temperature
and 24 hour évapotranspiration rate
For the translation of instantaneous to daily values
the TERGRA-model has been developed (Soer 1977). In
terpretation of thermal images with the aid of the
TERGRA-model is rather complicated, however, because
of the large number of input parameters that are re
quired. For an operational use of remote sensing
techniques simplified procedures are of importance.
For this aim Jackson et al. (1977) related midday
surface-air temperature differences linearly to 24
hour évapotranspiration and net radiation values. To
estimate the slope of this relationship a crop depen
dent analytical expression has been derived by Seguin
and Itier (1983).
With the approach of Jackson absolute estimates of
crop évapotranspiration are obtained. As heat images
are mainly applied to determine reductions in évapo
transpiration this approach has been adjusted
(Nieuwenhuis et al. 1985).
The surface air temperature difference in the ap
proach of Jackson has been replaced by the temperature
difference that exists between the crop that is
transpiring under the actual restriction of the soil
moisture condition and that transpiring under optimal
soil moisture conditions (T C ~T*). The net radiation
term was replaced by the 24 hour potential évapotrans
piration rate of the crop. With this adjustment they