necessary due to the fact, that the incoming radia
tion doesn't hit the plant homogenously. The upper
parts contribute much more to the reflection than
parts close to the soil. In order to simulate the
interaction between radiation and plant matter the
plants have to be analyzed according to their contri
bution to the reflection.
- 2. Structure parameters
The reflection characteristic of plants depends on
the angular relationships between incoming radiation,
hidden piece of plant material and measuring device.
Due to the heterogenous structure of plants the main
reflection direction may vary. To simulate this it is
necessary to monitor the geometrical shape of the
plants and of the whole target surface.
For wheat the inclination of the leaves and the ear
as their position at the stem will be determined (cf.
fig. 4). For the sugar beets the inclination and
azimuthal orientation of the leaves will be evalu
ated. Due to the rapid changes in the shape and the
inclination of the beet leaves depending on the
turgidity of the plant it is necessary to develop a
statistical model describing the topographic situa
tion.
The structural data will be collected with help of
stereo pictures. Using these photos, corresponding
photogrammetric equipment and software the coordi
nates of object points will be compiled. These then
serve as basic data for the determination of the
parameters in question.
- 3. Meteorologic data
Most of the climatic values will be measured using
corresponding meteorologic sensors and devices. The
I
Figure 4 : Geometric description of a wheat plant
- wind direction
- wind speed
- global air temperature
- global air humidity
- air temperature in the interior of the
field
- humidity in the interior of the field
- light penetration into the field
- spectral, azimuthal and zenithal distri
bution of incoming radiation
Table 2 : Meteorologic parameter
collected values are listed in tab. 2.
The last row notes the distribution of the incoming
radiation. Knowledge about the angular distribution
of the radiation is important for further compensa
tion of the influence onto the reflection readings.
This is of major importance, because very different
weather conditions are to expect for the campaigns,
ranging from dry to cloudy or completely covered sky.
Due to the rapid changes within a partly covered sky,
the recording device has to monitor the whole sky in
short time. Because it is impossible to have high
spectral and angular resolution together with short
registration cycles only the last two components will
be considered. These are registrated using a color
CCD-video camera with 180° field of view, storing the
signals on a videorecorder. The lost of spectral
resolution seems acceptable, because the angular
relations don't change too much with wavelength.
- 4. Radiometric data
As measuring device serves the Minarad SA 100/300
spectro reflectometer. It is a dual channel radiome
ter covering the spectrum from 0.4 - 2.2 pm with a
resolution of 0.002 urn (for 0.4 - l.lyjm) and 0.004
fjm (for 1.1 - 2.2 fjm) respectively. The instrument
works as a reflectometer. It records incoming and
reflected target radiation simultaneously. The inco
ming radiation is integrated over the whole 2irstera-
dian with help of a diffuser disc integrated into the
optics or with a diffuse reflecting plate (BaSO^).
The instrument has the advantage to work in reflecto-
meter-mode with high spectral resolution in a broad
part of the electromagnetic spectrum. However, this
conception results in a relative long measuring time,
which may range from 5 up to 30 minutes for one
complete cycle.
The instrument is mounted on a cherry picker, which
moves it into the position over the plant targets.
With help of some modifications at the cherry picker
the position of the instrument in space is reproduci
ble, so that for each campaign the measured targets
will be identically.
4 DATA PROCESSING
4.1 Data organization
The collected data is of very heterogenous structure
ranging from simple intrinsic values, single measure-
