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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
Techniques developed for accuracy assessment must take into
consideration the factors that are sources of error in image and
the methods used for assessing accuracy in a single image and
for a pair of images.
Serious erosion processes affect the coastal areas. Erosion
monitoring can be best performed using change detection
techniques.
The coastal erosion is a natural phenomenon by which the coast
line advances into the shore, under the continues influence of
the natural factors, (climatic factors and the configuration of the
coastal currents, the winds and hydrological regime and the
waves and also the pollution), the hydro technical and
protection constructions in the coastal aria modified the
currents regime re-directing them and producing an
deceleration of the erosion phenomena in the related zone but in
exchange adjacent areas can be subject to increased erosion
phenomena due to the change in marine currents regime. These
processes have a variable evolution speed in time and space and
are a continuous threat for the human establishments from the
coastal aeries, and also for the ecosystem.
Monitoring of these kind of phenomena can be done only with a
database of an geographical information system (GIS), which
should contain special data (satellite and aerial imagery, maps
etc) and also geographical, geological, socio-economical
information. The Romanian coastal aria stretches on a pretty
long distance. Detecting the changes in the costal line is quite
easy when utilizing images that come from a single sensor.
Sensors operating in the field of microwaves have the advantage
that they do not depend on the visibility conditions and the dry
land and water surfaces appear distinct, each having a specific
response. In the coastal areas the level differences are reduced,
so the geometrical distortions are also reduced, remaining the
ones characteristic to the data used.
CHANGE DETECTION
1. General characterizations of the Romanian Black Sea
shore
Romania is placed in the Northwest side of the Black Sea, with
a 243km shore.
The general orientation of the shore is to the North South, the
northern limit being formed by the Chilia channel (45?12* north
and 29"40'east), which makes the shared border with Ukraina
and the southern limit with Bulgaria being formed by a
conventional line, which passes south of Vama Veche (43?44'
north and 28°35’). The open sea limit of the territorial waters is
considered to be at a 12-mile distance to the shore line; in figure
| is presented the physic-geographical maps of the Romanian
Black Sea shore.
Genetically and especially morphological the Romanian
seashore presents a variety of aspects. Northern sector is an
accumulative shore, formed mainly by littoral lines, sandy and
in submersibile. Southern sector the shoreline is obvious being
formed by a high cliff, which is interrupted by parts, which are
cut off the sea also by sand aeries. To the modification of the
actual morphological aspects of the two existing sectors
contributes in proportions and combinations, factors of different
origins, such as litology the fluvio-marine accumulations,
waves, currents, level fluctuations, seismically activity, winds,
precipitations fauna and flora and also human activities.
The northern sector takes 68% from the Rumanian shore lying
in the eastern extremity of the Danube Delta, between Gura
Musura from the secondary delta, Chilia and Capul Midia.
The existence of positive eustatism of the Black Sea
(0.5cm/year) gave birth to a slight sea transgression shown by
719
swamps in the river marine movment resulted from the
sediments of the delta deposits. At the moment, in the
cordon/Sulina shore sector there is precise demarcation line
because the pre/existing sandy aria is submersed under water
(-0,80m). In the aria of the Sulina channel (behind the dams, the
shore had a rapid forward movement, looking overlay like a
spur adjacency into the sea. Between Sulina and Sf. Gheorghe
there is a sandy belt area almost as a straight line (with different
lengths), with a tendency to move towards west. South in the
mouth of the Sf. Gheorghe channel is developing the island
Sahalin (it appears for the first time on the 1830 and1857 maps,
made by the representatives of the Delta Commission). In the
last 40 years it stretched to the South and moved to the West,
almost closing the Zatoane - Ciotic zone, transforming it into a
lagoon. From Ciotic to Chituc there is a sandy belt/aria
positioned between the sea and the lagoon complex Razelm-
Sinoe, pierced by the Portita mouth through which the strong
storms often produce ruptures in the littoral belt south to Portita.
The littoral belts which border the Danube delta and the Ravel
lagoon to the east are formed from instable dunes, with heights
varying between 0.20m and 1.50m.These sand are often moved
either by the sea waves which cross the belts during storms, or
by the strong winds which blow in these parts. Generally the
littoral belts have variable widths and are in a continuous
displacement, which clearly show the tendency to move to the
west. The southern sector contains 3296 from the Romanian
shore length and has the structural characteristics of a high cliff.
This sector stretches south of Capul Media to the border with
Bulgaria, the land configuration being determined by the
morphology litology and structure of the deposits which form
the Dobrogea Plateau. The shore in this sector has a great
stability and undergoes a continuous but slow process of retreat
because of the erosion accelerated by the action of
atmospherical and biological factors and also of underground
waters which are generating land slides with the aspect of false
terraces. The solutions to diminish the erosion and slide
processes are to build dams to consolidate the cliffs. Today the
zone is characterized by a diminishing process of the beaches.
The aspect of the shore in between Constanta and Vama Veche
is given by the complex geological structure. The combined
action of the waves and marine currents determined the
apparition of small gulfs, which were separated from the sea by
littoral belts.
2. Accuracy assessment aspects for change detection
Accuracy is considered to be the degree of closeness of results
to the values accepted as true. Some of the accuracy assessment
methods are: the variance analysis, minimum accuracy value
used as an index of classification accuracy, spatial error and
class attribute errors, a probabilistic approach for change
detection and land cover classes are abstraction and
generalizations of the real world in order to provide discrete
values for continues To obtain a robust change detection, some
environmental factors and variables must be taken into
consideration, such as atmospheric conditions, soil
characteristics, vegetation cycles, hydrologic cycles and others.
Most of the environmental features are extremely dynamic; in
most of the cases the temporal and geometric resolution of
remote sensed data cannot cover the dynamic domain of the
environmental parameters evolution (atmospheric conditions,
soil moisture, and other environmental related phenomena). In
change detection studies we should have in mind the
differences in the phenological state of different varieties of the
same species and the time the data sets were acquired (most
suitable at the same date of the year).
