201
Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
The conception of a project investigating the spectral reflectivity of
plant targets using high spectral resolution and manifold repetitions
F.Boochs
Institute for Photogmmmetry, University of Bom, FR Germany
ABSTRACT: The conception of a project will be shows which investigates the spectral reflectivity of winter
wheat and sugar beets. The collected narrow band spectral information will be correlated with several agronomic
variables decribing the biologic and morphologic situation of the plants. Additionally great effort will be
taken for compensation of exterior influences generally reducing the information content of the spectral data.
The aim of the project is to provide more knowledge about the interaction between radiation and plants to
facilitate and improve the forecats of yield prediction.
INTRODUCTION
In the past the availability of remotes sensing data
mostly collected by satellite sensors has led to an
increasing number of research projects covering a
broad spectrum of different topics.
These investigations handle problems of land use and
its variation, environmental questions like air,
water and soil pollution, special research on the
signature of targets like soil, vegetation or artifi
cial surface components, the inventory of forest
damages, thermal mapping and plant yield estimation
for example. In many cases spectral data from satel
lite sensors serves as basic information for the
interpretational steps or other examination proce
dures.
For some purposes airborne sensors are used, just as
special equipments for ground truth measurements. The
latter often is very helpful for basic investigations
on the reflectivity on selected targets, because it
is possible to provide a lot more and less disturbed
spectral information. This extensive and more accu
rate data is useful to understand the interaction
between radiation and target matter.
The knowledge of the reflection process of the inco
ming radiation at the invested targets is one essen
tial precondition for a succesful examination of
remotely sensed data. Unfortunately the interaction
of radiation and target is very complex and can't be
described by some simple rules. Additionally there
are existing a lot of disturbing influences affecting
the measurements. Therefore most applications using
remotely sensed spectral data are based on statisti
cal procedures, working with empirically determined
relationships between data and target characte
ristics, what leads to a decreasing accuracy of the
interpretation steps.
To avoid empirically oriented interpretation proce
dures some more knowledge on the interactions at the
targets and the influencing factors is necessary.
1 THE REFLECTIVITY OF PLANT TARGETS
For agricultural purposes the measurement of the
reflection of plant targets is of great interest and
importance. A lot of investigations have been started
to discriminate different plant species, to evaluate
plant diseases or to estimate the plant production by
means of spectral data from satellite sensors. The
spectral data is mostly collected in few narrow spec
tral bands ranging from the visible to the middle
infrared region of the electromagnetic spectrum.
This part of the spectrum is very useful for investi
gations at the vegetation, because plants there show
some typical reflection characteristics /Bunnik 1978,
1983, Sanwald 1979, Bauer et al. 1980, Boehnel et al.
1980, Kadro 1980, Goel.Thompson, 1983/.
These reflection characteristics have been compared
to parameters describing the plant target or the
plants themselves like ground cover, leaf area index,
plant height, water content, dry and wet biomass,
pigment content, cell-wall constituents and the in
ternal structure of leaves, for example. For some of
these factors correlations with the spectral signa
ture could be found. But the significance of the
correlations varied with the experiments and never
reproduced that high value found for some measure
ments under laboratory conditions /de Carolis, Amadeo
1980/.
This might be due to the fact that investigations
based on spaceborne sensor data can't take all para
meters into account and, in addition, the characte
ristic of the reflected radiation is reduced on the
way from the target to the collecting sensor.
There also are some exterior parameters like azimu
thal and zenithal illumination conditions, target
geometry and the special atmospheric situation which
may have dominant influence on the reflection mea
surements /Vanderbilt et al. 1980, Guyot 1980, 1983a,
1983b, Lord, et al., 1983/. Therefore the aim of
plant yield estimationm led in the past only under
