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Generation the coastline change map for Urmia Lake by TM and ETM+ imagery
Ali A. Alesheikh
Assistant Professor
Dept. of GIS, Faculty of Geomatics Engineering, K.N. Toosi University of Technology, Tehran, Iran
alesheikh@kntu.ac.ir
A. Ghorbanali
MSc in remote sensing
Faculty of Geomatics Engineering, K.N. Toosi University of Technology, Tehran, Iran
alighorbanali@yahoo.com
A. Talebzadeh
Applications & GIS Director, Iran Space Agency, Tehran, Iran
talebzadeh_a@yahoo.com
Abstract
Coast is a unique environment in which atmosphere, hydrosphere and lithosphere contact with each other. Coastline is defined as the line of contact between land and a body of water. Coastline is one of the most important linear features on the earth's surface. Coastlines have a dynamic nature, therefore coastal zone management requires the information about coastline. The study site is the Urmia Lake. Urmia Lake is the 20th large lake and the second hypersaline lake in the world. The Urmia Lake covers an area average of 5,100 square kilometers. The maximum depth and average depth of this lake respectively are 16 and 5 meters. This lake is located between latitude 37°N to 38.5°N and longitude 45°E to 46°E.
In this investigation, Urmia Lake coastlines were extracted from ETM+ and TM imagery (these images have been acquired in 1989, 1998 and 2001). This Coastline map represents 1000 square kilometers lake-area reduction between 1998 to 2001 years .It is necessary to say that the tide-range in Urmia Lake is inconsiderable. Therefore the coastline changes do not derive from the tide. These changes derive from water balance of Urmia Lake.
In this investigation, we have evaluated advantages and disadvantages of some methods for coastline extraction. These methods are histogram thresholding and band ratio technique. In this paper also we have applied a new approach for coastline extraction, in which we have utilized histogram thresholding and band ratio techniques together. To evaluate the accuracy of this approach, we required to compare the extracted coastline from this method with the extracted coastline from a ground truth map. Because of the lack of a reliable ground truth map we utilized a ground truth image. This ground truth image was provided via fusing the ETM+ multispectral bands with ETM+ panchromatic band. Then we extracted coastline from this ground truth image via visual interpretation. Next we compared between two mentioned coastlines. With this comparison, the accuracy of the extracted coastline from this approach was evaluated 1.3 pixels (pixel size=30meters).
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