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;, eolian,
alluvial and of other deposits. These are mainly different sands,
sand-loams, clay-loams and loams.
A distinctive feature of the radioactivity released as a result of
the accident at Chernobyl NPP is the fact that the bulk of the
radionuclides belong to one of three forms: small disperse fission
products of nuclear fuel; condensation products of radionuclides
hurled into the air; aerosol absorption products. Within the 30 km
zone, most activity is associated with particles of the first and, in
some places, also the second type. The third plays a minor role.
The term "hot particle" is often used to refer fuel, condensation
or adsorption particles with an activity level in excess of 105
Bq/g or 0.1 Bq/mg. Hot particles from the Chernobyl accident
persist in the atmosphere up to the present day (Chernobyl
disaster, 1995). The majority of these hot particles are oxides of
uranium, and in zone cases iron, lead, titanium, silicon and other
elements, which is most likely due to the introduction of various
extinguishing agents (metallic lead, dolomite, quartz sand, etc.).
It should be pointed out that the properties of hot particles which
determine the dynamics of radioactive fallout have been studied
only very sparsely. Hot particles transported by aerosol transfer,
which played the major role in the first few days after the
accident, by secondary wind transfer, by sheet wash and transfer
in suspensions by waterways and by mechanical processes within
the soil. In watersheds, hot particles are concentrated
in the first 3 - 5 centimeters of soil and in the undergrowth, and
secondary transfer causes their accumulation in depressed
enclosed parts of the relief and in deposits on bends in
waterbodies.
The main danger of this fallout is that it may become caught up
in the geochemical and biochemical cycles of long-lived Cs-137
and Sr-90.
2. METHODS AND RESULTS OF THE
INVESTIGATIONS
At present it doesn't exist universal method of ecological state
research using multiband space images. There are number of
program modules and methods which allow to decide some
problems. Therefore, it had been developed a set supplementary
methods and procedures. In particular, the approaches of
intercalibration of multiband images and spectral reflectance of
vegetation application for pollution indication had been
concerned. Also the software ERDAS IMAGINE had been widely
used in this investigations.
2.1 Intercalibration of multitemporal space images
The thematic interpretation of multispectral and multitemporal
data of air-space surveys essentially raise the efficiency of
ecological monitoring of large territories. It is possible to use
images from different years unless they are adjusted to a standard
level, 1.e. intercalibrated. For this purpose, it is essential to take
into account differences in atmospheric conditions, light levels,
etc., which influence the spectral brightness. With this
purposes, besides of standard calibration devices (so-called
"mir"), also the technical objects as well as different kind of
landscapes could be used. The main requirement is that spectral
characteristics of this objects must be nearly constant in optical
International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998
range of electromagnetic spectrum during the most part of the
year.
A prion this objects are sand formation, concrete plots, water
surface and some others. Within the limits of this test-objects the
test-sites are indicated and coordinates of their position are
determined with accuracy as much as possible. It is necessary for
matching of this objects at multitemporal images. The size of
test-sites must not to be very small to provide statistical
assessment of their reflectance spectra characteristics. The values
of reflectance spectra are used for creation of calibration
relationships, which allow to recalculate reflectance spectra of
landscapes of every image, made at any date, reducing them to
reflectance spectra of base image.
This approach have been used for the problem of the Chernobyl
disaster area ecological monitoring. This was done by correlating
the spectral brightness of objects whose optical properties
remain virtually constant. The objects selected for this purpose
were building structures, water in the cooling reservoir of
Chernobyl NPP and sand from the banks of the River Pripyat. All
images were adjusted to that dating from 6 May 1986.
The investigations show that using of intercalibration allows to
obtain quantitative assessment and maps of ecological
conditions, to estimate the velocity and direction of
environmental changes raising of reliability of ecological control.
It was established that the correlation between the spectral
brightness of the images compared is described by the linear
regression equation;
dn 7 Csc * d * Csh, (1)
where d and dn are the original spectral brightness and that
adjusted to the base image respectively:
Csc and Csh are the scale and shift coefficients in the linear
regression equation, taking into account differences in
atmospheric opaqueness, light conditions, etc.
When calibrating the SPOT images to match each other, it was
established that the Csc and Csh coefficients depend on the
average wavelength in the spectral band.
The analysis of the change in the ecological situation was
conducted by pairing the images (Landsat, 16.04.1984 with
SPOT 6.05.1986, SPOT 6.05.1986 with Landsat, 29.05.1988,
SPOT 6.05.1986 with SPOT 23.05.1995). Shown in different
colors, correspondingly to difference between the same bands, are
the territories where the radioecological situation changed.
Changes in the spectral brightness up to 20 units are generally
due to natural factors. Changes above 20 units are associated
with human impacts on the landscape (felling of forests,
construction dams, etc.).
The image obtained from pair 1984 - 1986 reflects the change in
the ecological situation up to 6 May 1986, when active fallout
from the exploded reactor ceased, as compared with the period
before the accident. None of the forests, including the pine
forests, had yet seen changes over their entire area. Local
yellowing was observed around Chernobyl NPP, where the
forests received lethal doses. Slight changes in the vegetation
were recorded in the town of Pripyat.
Particles of burned graphite from the 4th reactor can be seen
clearly on the surface of the Chernobyl NPP cooling water
reservoir. The release of used process water from the working
