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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
species” was less than the first species, a mixed type was
obtained (Gorji, Bahri, 2000).
On the basis of the data, resulted from the fieldwork, a vector
ground truth map possessing aforesaid forest types was prepared
using a GIS approach.
In order to assess the accuracy of the maps resulted from forest
classification, the vector GT was then rasterized. In this Process,
cell size of the raster GT was decided to be 5 meters, to keep
the details.
ÜBBBOSQU
B
462000
Figure 1. The ground truth map for 9 forest types
4.2 Digital image processing
It is necessary to be aware of geomatric and radiometric
situation of the image, before performing digital processing
(Darvishsefat, 1994). Therefore, different geomatric and
radiometric distortions such as striping, banding, sweep error,
duplicate pixels and also atmospheric error of existing clouds
were inspected, while any noticeable distortion was found.
Orthorectification was then implemented utilizing 14 GCPs,
ETM4 ;
Y = 0.034937 + 0.999854 X
mi . a
2031
1614
coeff of det (2) = 0.99
H
HH | T4 sdof X (Ex) 318005901
te Fi sdofY (Sy) =31-4027444
1145 se. of estimate = 00575366
se. of beta = 0.0000224
922
t stat forrorbeta = 30831 2101563
$39 | t stat forbeta©>1 = -10.6668125
vs 1 27 n = 3175
ms 1 Ar of 3173
30 T T T T T T T T TU EM
30 254 438 702 926 1150 1374 1598 1822 2046 2270
containing bare soil
ETM3 (X axis) and ETM4 (Y axis)
4.3 Image classification
Based on the divergence between class signatures which is
calculated from the class sample means and the class covariance
matrices, the best band set were selected (Richards, 1999:
Ann., 2001), using training areas. A supervised classification
was then implemented utilizing maximum likelihoo (ML),
Minimum Distanct to Mean (MD), Parallelepiped (PPD) and
Spectral Angle Mapper (SAM) classifieres. In order to eliminate
single pixels deviating from the neighborhood a mode filter
(7x7 pixels) was done on the resulted maps. Ultimately,
accuracy assessment was carried out through a pixel by pixel
comparison of the classified outputs by the ground truth map,
considering overall accuracy, kappa coefficient, user and
producer accuracies.
00 to digital elevation model and ephemeris data using toutin model
; (Ann., 2001). In this regard while performing resampling, pixel 5. Results
ES are size was distinguished to be 5 meters. In order to seperated I- The RMS error resulted from orthorectification was
perus forest types more efficiently, various synthetic bands were 6.9m (0.23 pixed) along with the X axis and 6 m (0.2
ndary created applying band ratioing (Terrill, 1994; Sandison, 1999), pixel) along with Y axis. Desired coincidence
s and principal component analysis, tasseled cap transformation and between the roads and rivers layers of digital
bands fusion (Darvishsefat, 2002). topographic maps and the rectified image indicated
In addition, different vegetation indices such as PVI, SAVI, high precision of the orthorectification.
MSAVII, MSAVI2, TSAVII, TSAVI2 and WDVI were 2- The best result of classifying 9 forest types was
bands produced using soil line parameters, to reduce soil effect obtained by MD classifier with overall accuracy and
digital (Terrill, 1994; Sandison, 1999; Jelenak, 2001). kappa coefficient equal to 18.45% and 11.05%
Iso to The soil line relation was as below: respectively.
3- Because of undesirable separability between pure and
dominant types, understood from Bhattacharrya
Y — 0.034937 + 0.999654 X : (1) distance and trasformed divergence critera and
confusion matrices, these types merged and the
classification was iterated with 5 types. The best
sround Where X= ETM3 overall accuracy and kappa coefficient inferred from
909 ha Y 5 ETMA MD classifier were 47.13% and 22.83% respectively.
in the r=0,99 In this case, separability criteria, user and producer
Large accuracies for amygdalus scoparia were better than
me of those of the others.
ntly 9 4- Finally by merging all of the types except for
|, Acer Amygdalus scoparia, because of its better results, the
ia), 4 classification was performed with 2 types consisting
lanum, Am. Scoparia and the others as a mixed type. The best
e were overall accuracy and kappa coefficient obtained by
es was MD classifier were 92.16% and 67.58% respectivley.
etween
area of
second Figure 2. Scatter diagram of digital numbers of pixels
411