طبقه بندي خودكار لندفرم هاي حوضه آبخيز با استفاده از سيستم اطلاعات جغرافيايي (مطالعه موردي: حوضه آبخيز بروجن در استان چهارمحال وبختياري)

Landforms Automatic Classification Using Geographic Information System (Case Study: Borujen Watershed in Chaharmahal va Bakhtiari Province)

لندفرم يك عارضه ژيومرفيك از سطح زمين است كه خصوصيات ظاهري خاص وشكل قابل تشخيص دارد. بنيان واساس شناسايي وطبقه بندي لندفرم ها برپايه ژيومرفومتري است، ژيومرفومتري به كميت عناصر اصلي ريخت شناسي زمين ازجمله شيب،جهت شيب، ارتفاع واختلاف ارتفاع نسبي عناصر، موقعيت مكاني عناصر نسبت به هم، وضعيت شبكه زهكشي و ميزان تحدب يا تقعر عناصر مي پردازد. در حال حاضر طبقه بندي لندفرم ها عموما" مبتني بر تشخيص كارشناسي است كه به طريق دستي وبا استفاده از عكسهاي هوايي ،نقشه هاي توپوگرافي و برداشت هاي صحرايي انجام مي گردد كه روشي است زمان بر،پرهزينه،كم دقت وغير قابل تكرار ،اما در اين تحقيق با استفاده از سيستم اطلاعات جغرافياي و سه معيار شاخص TPI،شيب وموقعيت مكاني عوارض سطح زمين، اقدام به طبقه بندي خودكار لندفرم هاي حوزه آبخيز بروجن گرديده است. نتايج نشان داد كه اين روش توانايي خوبي در جداسازي وطبقه بندي لندفرم ها دارد به گونه اي كه 9 لندفرم در حوزه آبخيز بروجن شناسايي وطبقه بندي گرديد و بدين ترتيب رهيافتي براي طبقه بندي خودكار لندفرم هاي يك حوزه آبخيز ارايه گرديده به اين منظور كه زمينه انجام مطالعات جامع براي ارايه روش هاي كمي ودقيق براي شناسايي وطبقه بندي خودكار لندفرم ها در حوزه هاي آبخيز فراهم گردد .

Introduction Landform is physical factor of land surface with recognizable form and Particular the morphological characteristics. Landforms describe the affect Earthʹs surface processes in the past and present and it provide important information about the characteristics and potential of land (Etzelmüller and Sulebak, 2000). Due to the complexity of the land, innovation of methods to classification of land by smaller units but more uniform based on quantitative methods are necessary. Foundation of identification and classification of landforms is based on geomorphometry. Geomorphometry survey quantify of the major elements morphology such as slope, aspect, elevation and relative elevation, condition and degree of convexity or concavity of the drainage network(Gercek, 2010). In this study, landforms of a large area with semi-arid climate Identified and classified automatically using geographic information systems and digital topographic maps. Study Area Borujen watershed is located in Chaharmahal va Bakhtiari province, northern Karoon, Iran. The area of this case study is approximately 92565 hectares. Methodology Digital topographic maps as the basic data used in this study with 1:25000 scale and 10 meters interval contour lines. Boundary of study area was extracted and merged by categories of TAMAB in 5 levels (National Geographic Center of Iran, 1372). Then, a buffer of 500 meters was considered. Then, in the study area, streams, elevation points and couture lines were separated from the main map and then digital elevation model (DEM) with a 10 m pixel size was produced using extension of Topo to Raster in ArcGIS9.3 software. TPI and Slope raster maps by the neighborhood analysis with radius of 250 meters and the neighborhood analysis with radius of 50 meters of DEM map were produced. TPI Index is the height difference of each cell to the average height of neighboring cells that positive values show that the cell is taller than adjacent cells while negative values of the cells is lower than adjacent cells (Jenness, 2005). For identification and classification of geomorphology units used combination of slope and a circular neighborhood index with radius of 250 meters. Then, TPI index were used for landforms classification into each geomorphology unit with a circular neighborhood distance and radius of 50 and 250 meters. Slope factor were used for separation of landforms if and when there is an overlay. Results and Discussion In this paper, Landforms are classified as automatic form by three criteria of TPI index, slope and relative spatial features using geographic information systems in Borujen watershed. Borujen watershed has semi-arid climate with low rainfall. Results showed that this method has a good ability in classification Landform, and 9 Landform within the Borujen watershed was classified. Thus, an approach for automatic classification of landforms within a watershed is presented. Conclusion Landform classification is very important in watershed studies on the other hands GIS software and digital data are very important for users because analysis and process of digital spatial data are easy and useful. Therfore, it is necessary that geomorphologic units classification traditional and manuall methods developed to digital data . Results of this paper show that this method has a good applicability to landforms separation and classification in a watershed scale.