by radionuclides is substantial rather than energetic for most
parts of the test site.
The radiobiological effects on vegetation for various
exposure levels can be assessed more completely only with
regard to the critical structure at all stages of its hierarchical
organization.
A special „hit“ principle and a „target“ conception allow to
explain the disproportion between the amount of energy
absorbed by the biological system with a radioactive
contamination and the final biological effect (Grodzinsky,
1991).
This indicates that
- radioactive contamination of an area affects significantly
all kinds of vegetation;
- combined action of external and internal exposure
induces an injury of the genetic mechanismus of plants;
in this case a recovery process is obviously absent
against the background of chronic external exposure
under influence of incorporated radionuclides;
- radioactivity affects the photosynthetic cells of plants,
especially the chlorophyll mutation abundance, which
can be revealed in the optical properties of plants.
These changes can be determined by spaceborne remote
sensing and can be applied for the assessment of
radioactive influence on the environment.
3.1 Methods
In order to study the effects of radionuclides on vegetation of
large areas an analysis of the optical properties of wooded
and herbaceous vegetation were carried out. Space
photographs were used as primary data sources for the
investigations. Prior to image processing they had to be
scanned.
The software complex for image processing includes
ERDAS/IMAGINE and an additional program package
implemented by the Centre of Aerospace Research of the
Earth Kiew and the uve Remote Sensing Centre Potsdam,
which enable:
1. superposition of three one-band images into a single file
as a multiband image in order to get a synthetic image
for the visual analysis of landscape making the next
steps more convenient
2. georeferencing of images and rectification into a map
projection
3. inquire digital spectral characteristics at ground truth
measurements points for further studies of the
environmental objects
4. collection and handling of remote sensing and ground
truth data by GIS technology
5. mathematical processing and analysis of measurements.
The determination of spectral characteristics were made on
a window template sized, for example 7*7 pixels, for which
average and dispersion were computed.
The processing and interpretation of multispectral remote
sensing data require the solution of the inverse problem, i.e.
the determination of environmental objects state from remote
sensing data.
The complication of this problem consists in the unknow
functional relations between remote sensing data and the
parameters of environmental object state. Using ground truth
measurements these parameters can be determined by
means of regression analysis.
The authors have treated the problem of defining fe
functional relations between Cs-137 content in soil an
spectral brightness values of the landscape (Lyalko et al
1996). The mathematical formulation of the proper
consists in the description of content as a resultant vey
and of digital spectral brightness values as causing vectors
The mathematical model of linear multifactor regression 5
given by:
m m
Cx,y)m > Su T; G0 T, (y) (l)
j=0 i=0
where
X, Y are the spectral brightness values for two bands
T. (X) is the Chebyshev polynomial of i-th power;
C... are the regression coefficients, usually provided by
1]
means of the least-square method.
For correct processing multispectral remote sensing data
it is nessesary to compare homogenous kinds of
vegetation growing on soils with similar moisture
conditions.
In order to estimate the changes of soil moisture a
remote sensing determination method for soil moisture
(W) and ground water (H) by means of active nadir
soundings in the 0.7 m band were developed and used
by ZAKIZ.
The possibility of estimating soil moisture characteristics
is based on the dependence between reflected radiation
and the dielectric properties of soils determined by the
volume content of water and by peculiarities of its vertical
distribution. To derive W and H from the remotely sensed
value E, the dependencies, which could be received both
experimentally and by analytical calculation, were applied
using the method of replacing real soil with a system ofn
thin layers with piecewise continous W value (Lyalko el
al., 1992).
To improve the efficiency of mapping W, a new method
was offered by joint utilizing microwave airborne nadir
sounding and SAR data from the Space Shuttle (L-Band,
À-21cm, parallel polarization, horizontal).
The main idea of this method consists in segmenting the
test site into homogenous parts according to {he
underlying surface. The dependencies between the
amplitudes of backscatter signal (c) expanded into 2
Fourier series, and E were determined within the limits oi
homogeneous areas using profile data:
o^, =i (E^i) (2)
Therefore the e -6c(W) and
O — O (H) could be applied.
dependencies
Beside gray level intensity each image is characterize!
by the rules of its spatial distribution, which à*
determined by texture.
456
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
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