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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B-YF. Istanbul 2004
The satellite images were corrected for the influence of
atmosphere and topographic relief. These data were geo-coded
by the help of rectified SPOT data according to the European
Datum (ED50) and a UTM projection to combine and analyse
with the other data. In the end, the atmospherically, radio
metrically and geometrically corrected / geo-coded images were
supplied by ERDAS software.
The purpose of digital land cover classification is to link the
spectral characteristics of the image to a meaningful
information class value, which can be displayed as a map so
that resource managers or scientists can evaluate the landscape
in an accurate and cost effective manner (Weber and Dunno,
2001). In this study, the Maximum Likehood supervised
classification algorithm was used (Lillesand Kieffer, 2000). The
best way to compare images from different dates is to classify
the two images separately and to compare the statistical results.
The classification of satellite images were utilised in land cover
analyses and in determining change between the land use before
the fire and that after the fire.
In order to obtain effective and more accurate conclusions,
mathematical operations in the GIS analysis were formed. The
input information on forest fire influencing factors indicates the
weights in the fire risk in an area. The factors were analysed in
the following order of importance: vegetation type, slope,
aspect, distance from roads and settlements. First classes
represent high risk places and last classes represent the minor
risk place. Each class has different weights.
The vegetation types were classified according to the moisture
context that has an influence on breaking out forest fire. For
example, the vegetation type that is very dry is the most
flammable whereas the fresh type is inflammable.
Slope influence behaviour of fire was evaluated the second
highest weight. Fire travels most rapidly up-slopes and least
rapidly down-slopes. Slope classes were created according to
this rule. Aspect was assigned equal weight with slope. Since
the sunlight is much more reflected on the slopes in the south,
fire breaks out fast and spreads in the south sides.
Distance from roads and settlements were evaluated the third
highest weight. The risk factor decreases farther from these
places. It means that a zone close to these places were evaluated
a higher rating.
Water bodies areas do not affect the forest fire risk. These
zones have no weights in determination of fire rating class.
The equation used in GIS to determine forest fire risk places is
shown in equation I.
. RC=T*Vr+ 5%(S+4) + 3%(Dp+Dy) (1)
In this equation, RC is the numerical index of forest fire risk
zones where Vr indicates vegetation type with 5 classes, S the
slope factor with 5 classes, A the aspect variable with 4 classes,
D, and Ds indicate distance factor from road and settlement.
Finally, based on these analysis carried out, a fire risk zone map
was produced.
35
3.3 GIS
Geographic Information System (GIS) has also developed
functions such as analyzing available information and using
them as a decision and a support system as well as it compiles
the information as a whole and stores it.
In that way, GIS analyses show the spatial distribution of the
observed forest condition and also may help to find cause
parameters for the observed — and classified — forest decline
phenomena. The link between remote sensing results and an
efficient forestry GIS can therefore work as a tool for an
operational and practically oriented monitoring system for
forest damage assessment and management. It may play an
important role as a planning tool for forest and land-use affairs
in a broader sense (Faber et al., 1994).
Parameters Weight Classes Factors Fire Rating
classes
Vegetation 7 Very dry 5 Very High
Dry 4 High
Moist 3 Medium
Fresh-like 2 Low
Fresh 1 Very Low
Slope 5 >% 35 5 Very High
% 35-25 4 High
% 25-10 3 Medium
% 10-5 2 Low
<%5 1 Very Low
Aspect 5 South 5 Very High
West 4 High
East 3 Medium
North 2 Low
Distance from 3 < 100m 5 Very High
roads
100-200m 4 High
200-300m 3 Medium
300-400m 2 Low
> 400m l Very Low
Distance from 3 « 1000m 3 Very High
settlements
1000- 4 High
2000m
2000- 3 Medium
3000m
> 3000m 2 Low
Table ! The weight of parameters in determination of fire risk
areas.