پديد آورندگان :
گورابي ، ابوالقاسم نويسنده استاديار ژيومورفولوژي، دانشكدهي جغرافيا، دانشگاه تهران , , كريمي، مصطفي نويسنده استاديار اقليمشناسي، دانشكدهي جغرافيا، دانشگاه تهران ,
چكيده فارسي :
شناسايي و استخراج لندفرم هاي سطح زمين از داده‌ها رقومي در سالهاي اخير، رشد و گسترش بسيار زيادي يافته اند. در اين راستا مخروط‌افكنه‌ها در مناطق خشك از اهميت بسيار زيادي برخوردارند. هدف اين مطالعه ارايهي روشي بهينه (سريع، دقيق، كم هزينه، و استفاده از حداقل دادهي مورد نياز)، براي استخراج مرز مخروط‌افكنه‌ها از DEM است. بدين منظور با استفاده از DEM و روشي كه در اين پژوهش براي نخستينبار ارايه شده است (مدل قرينهي DEM)، با قرينه سازي داده‌هاي رقومي ارتفاع و روش‌هاي موجود در نرم‌افزارهاي GIS، مخروط‌افكنه بهعنوان يك حوضهي آبريز معرفي و سپس مرز آن استخراج شده است. براي ارزيابي دقت اين روش، مرز استخراجي روي تصاوير ماهواره‌اي (ASTER, QuickBird)، نقشهي توپوگرافي و شبكه‌هايي زهكشي منطقه همپوشاني شده‌اند. نتايج پژوهش نشان مي‌دهند كه روش «مدل قرينهي DEM» از نظر دقتِ نتايج، سادگي، سرعت انجام و بهره‌گيري از حداقل داده‌ها بر روش‌هاي ديگر برتري دارد.
چكيده لاتين :
Extended Abstract
Introduction
Alluvial fans have received great attention in all aspects. They have played important roles in the human societies, especially in arid regions. Many early civilizations and cities are built on alluvial fans in arid regions. In arid regions, alluvial fans are provided ground water and fertile soils for human activities. Likewise, in the Central Iran above 90% population exist nearly on alluvial fans. Alluvial fans are commonly associated with tectonically active mountain ranges. Altogether, alluvial fans show great diversity because of variations in climate, fan history, tectonics, source area lithology, vegetation, and land use. Therefore, recognition of alluvial fans border is significant for remote sensing, geomorphology, hydrology, disaster damage assessment, developmental conformity evaluation and quaternary researches.
Many researchers have used DEM in different fields. They have employed DEM for obtaining the drainage networks, extraction of lineaments or linear features, and analysis of longitudinal and transverse characteristics of watersheds. Notwithstanding its many uses, DEM has been used less for extraction of alluvial. In the beginning and the early stages, the methods were used for extraction of alluvial fans were based on topography maps or aerial photography observations and drawing manually their borders. The purpose of the present research is - demonstarating application of the new technique for extraction of alluvial fans by using SRTM
Methodology
In general, the methods used for extraction of alluvial fans can be classified in three general categories: (1) manual methods; (2) semi-automatic methods; and (3) the new method or automatic methods. The objective of this study is providing an efficient method to extract rapidly, accurately, low cost, and using the minimum data requirements for extraction of alluvial fan boundaries from DEM. To do so, by using the DEM and the method which is presented in this study for the first time (symmetrical model of DEM), with symmetry of the alluvial fan elevation data, and GIS ability, alluvial fan is introduced as a catchment and then its boundary is extracted. To assess the accuracy of this method, the extracted boundary is overlapped on satellite imagery (ASTER, QuickBird), topographic maps and drainage networks of the region.
Results and Discussion
The boundary of alluvial fan extracted in WMS from symmetrical digital elevation model (symmetrical DEM). Therefore, these outlets of basins are in really apex of alluvial fans. Also, symmetric DEM of area was calculated by ArcGis software. It used for extraction of false basin (alluvial fan) in the WMS software. So, this method has bounded the alluvial fans accurately and speedily. For validation of extracted boundaries of alluvial fans base on this technique, the extracted boundaries are overlaid on another images and maps, for example: satellite images, contour and drainages of study area. In a general view, it seems that the extracted boundaries are in full compliance with the land borders of alluvial fans. As the main drainages of alluvial fans are often followed the border of alluvial fans, we use it for validation of boundary of alluvial fan. The result shows this method can be potentially used in various aspects of digital data and methodology.
Conclusion
This method gave appropriate results in extracting alluvial fan and requires only DEM as an input data. Research results show that the "symmetric model DEM» as regards to accuracy, simplicity, speed and performance using minimal data takes precedence over other methods.
