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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004 
only have hydraulic stations used to determine hydrological 
parameters Hosap river is one of them and the most longest 
river included four runoff gauge station to measure runoff 
value. In the last decade, the water level in Lake Van has risen 
about 2 m; and, consequently, the low-lying inundated along 
the shore are now concerning local administrators and 
government official, and affecting irrigation activities and 
people’s properties.(Kaynak et al,2002)The study region is then 
subdivided into different hydrologic sub-systems for analyze 
characterizing of hydrology. In this study, Hosap river sub- 
basin area is selected to determine runoff value with help of the 
remote sensing and GIS integration included Soil Conservation 
method. (Figure-1) 
  
  
  
  
Figurel. Study area 
3. DATA AND METHODOLOGY 
Data Sources 
In the study, a variety of data including satellite images, digital 
elevation model, soil map, standard 1:25000 scale topographic 
maps and various thematic maps obtained from various sources 
have been used as data sources together with ground truth 
studies that have also been carried out. Landsat TM image from 
May 1987 was acquired and used in the analysis. The Landsat 
TM data have spatial resolutions of 30 m. The thermal band (6) 
was not used in the study because it represents emitted energy 
or radiant temperature and has large spatial resolution (120 m). 
TM bands 1-3 represent visible electromagnetic radiation with 
wavelengths 0.45-0.52, 0.52 and 0.60 and 0.63-0.69 um, 
respectively. Band 4 represents near infrared with wavelengths 
of 0.76-0.90 um, and bands 5 and 7 represents mid-infrared 
with frequencies of 1.55-1.75um, and 2.08-2.35um, 
respectively. The radiometric resolution of all the data was 8 bit 
with 256 levels of brightness. Digital elevation model derived 
from 1: 25000 scale topographic maps to analyze basin area. 
Digital soil maps of basin areas are prepared by KHGM 
(General Directorate of Rural Services) in relation with 
125000-scale topographic maps. Digital soil maps prepared by 
KHGM include several parameters for each polygon existing in 
the map. 
Geometric correction 
Remote sensing data are distorted by the earth curvature, relief 
displacement and the acquisition geometry of the satellites (i.e. 
variations in altitude, aspect, velocity, panoramic distortion). 
The intent of geometric correction is to compensate for the 
269 
distortions introduced by these factors so that the corrected 
image will have the geometric integrity of a map (Lillesand and 
Kiefer 2000). Rectification is the process of projecting the data 
onto a plane, and making it conform to a map projection 
system. Satellite images are rectified using 1:25000 standard 
topographic map and are geometrically corrected to the 
coordinate system using the Universal Transversal Mercator 
(UTM) projection system with 0.5 pixel RMS accuracy. 
Classification 
Image classification is the process of establishing a link 
between a category of interest and a related spectral class. 
Unsupervised classification is based on the fact that most 
remotely sensed image composed of spectral classes that are 
reasonably uniform with respect to reflectance across one or 
more spectral channels, and can therefore be defined .and 
mapped. In this study, the Iterative Self Organizing Data 
Analysis Technique (ISODATA) unsupervised classification 
algorithm was used (Tou et al, 1974). The purpose of 
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 scientist can evaluate the 
landscape in an accurate and cost effective manner(Weber et 
al, 2001) Firstly, Landsat data acquired on May 1987 applied 
pre-processing techniques such as image enhancement to 
increase visual distinctions. Landsat image classified by using 
ISODATA unsupervised algorithm techniques. 
SCS Curve Number Method 
Soil Conservation Model are distributed watershed modelling 
the most widely used in hydrological model. The Soil 
Conservation Service model developed by United States 
Department of Agriculture (USDA) computes direct runoff 
through an empirical equation that requires the rainfall and a 
watershed coefficient as inputs.(T.R.Nayak et.al,2003). The 
general equation for the SCS curve number method is as 
follows; 
F0 
mee (1) 
S P-I 
Where F, actual retention (mm); S, watershed storage (mm); Q, 
actual direct runoff (mm); P total rainfall (mm); I, initian 
abstraction (mm). 
From the continuity principle, 
F=(P-1)-Q (2) 
The SCS method defined the value of the initial abstraction / 
to be approximately equal to 20% of the watershed storage S, 
72=0.25 (3) 
Solving equation ! and 2 simultaneously, 
| ((P-02Sy 
(P2028) (4) 
P+0.8S 
Q