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