International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
2. DATA
2. Ikonos Image
Ikonos images are acquired as 1-meter resolution panchromatic
and 4-meter resolution multi-spectral images. While the
panchromatic images represent the visible range of the
spectrum, the four bands of multi-spectral images represent the
red, green, blue and near infra-red range of spectrum.
Sensor Name IKONOS-2
Date and time of acquisition | 05 February 2003
Spatial Resolution 1m. panchromatic, 4m. multi-
spectral
Spectral wavebands 0,45-0,53 um (blue)
0,52-0,61 um (green)
0,64-0,72 um (red)
0,77-0,88 um (near IR)
Nominal collection azimuth | | 7,55?
Nominal collection elevation | 64,87?
Sun angle azimuth 153,62
Sun angle elevation 62,35°
Projection UTM north zone 37
Ellipsoid WGS 84
Bit/pixel/band 11 (stored on 16)
File format Geotiff
Processing Level Standard geometrically
corrected
Table 1. Most important characteristics of the Ikonos Image
(from product metadata file)
2.2 Topographic maps
To get digital elevation model (DEM) of the workspace
topographic state must be known. In this study we used maps of
scale 1:25000 covering the totality of the workspace. Our
workspace is at the intersection of three topographic maps.
These maps which are include our workspace were scanned .
Then contours were digitized by using R2V(Raster to Vector)
program.
2.3 Digital Elevation Model (DEM)
Digital contour lines of the above mentioned 1:25000
topographic map database have been used to calculate DEM of
the study area. The topographic maps contain one contour line
on every 10 meters, with the values of the current elevation
above sea level. After digitizing all of the contour lines of entire
geocoded topographic map database, line coverage has been
created containing every contour line and appropriate elevation
value. By using ERDAS Imagine 8.6. DEM of the area gained
from digitized contour lines. Linear rubber sheeting method was
used for this process. Figure 2. shows DEM of the workspace.
Figure 2. DEM of the workspace
2.4 Software Used
Geometric correction of Ikonos image, creating DEM and
image classification were carried out using ERDAS Imagine
8.6.
2.5 Other Data
We got documents about water height of the river in 2002
Directorate of State Hydraulic Works (Primary executive state
water agency responsible for water resources development in
Turkey.) obtained from hydrographs.
3. METHODOLOGY
3.1 Image Geometry Evaluation
Image rectification is a process by which geometric distortions
in digital remotely sensed data are corrected. (URL 2).
Geometric correction is undertaken to avoid geometric
distortions from a distorted image, and is achieved by
establishing the relationship between the image coordinate
system and the geographic coordinate system using calibration
data of the sensor, measured data of position and attitude,
ground control points, atmospheric condition etc. (URL 3).
In this study firstly image was rectified. The rectification
process was done by using topographic maps scale 1:25000. For
rectification 15 ground control points and 5 check points were
used. The distribution of points is a very important issue during
geometric correction . The distribution must be homogeneous.
But because of physical characteristics of the land, sometimes
it can't be possible to distribute points in a homogeneous
structure. The workspace is also such a place. Because of that
reason, the distribution of points done the most appropriate
position. All the points were carefully selected and positioned
that can be clearly identified both on the satellite image and
topographic maps. Figure 3. shows configuration of points used.
Legend
o Control Point
+ Check Point
Figure 3. The workspace and distribution of points
Simple 1* order polynomial is used for image transformation.
For image, RMS errors for all of the GCPs were calculated.
Table 2 shows RMS errors for control and check points.
POINT X Y “| Total RMS
(Residual) | (Residual) Error
Control Point Error 0,4007 0.5131 0,6510
Check Point Error 0,5452 0,5985 0,8096
Table 2. RMS errors
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