ارزیابی دقت آزمایی مدل های رقومی ارتفاعی(Dem)ماهواره های Aster و Srtm با مشاهدات دقیق زمینی(Dgps) مطالعه موردی: از سد آزاد به دشت قروه-دهگلان، سنندج

مدل‌های رقومی ارتفاعی برای بسیاری از اهداف، مهم بوده و در بسیاری از کاربردها و مطالعات جزء الزامات اولیه می‌باشند. هدف این مقاله بررسی میزان دقت و صحت مدل‌های رقومی ارتفاعی حاصل از تصاویر ماهواره aster و داده‌هایsrtm با ابعاد پیکسل 30 و 90 متر و همچنین مدل رقومی ارتفاعی به دست آمده از نقشه‌های توپوگرافی 1:25000 با مشاهدات دقیق زمینی (dgps) در لندفرم‌های مختلف شامل دشت، تپه‌ماهور و کوهستان می‌باشد. میزان انطباق این داده‌ها با استفاده از تحلیل همبستگی پیرسون آزمون شد. دقت و صحت مدل‌های رقومی ارتفاعی مختلف مورد بررسی با استفاده ازrmse، خطای میانگین و انحراف استاندارد بررسی شد. براساس نتایج ضریب تعیین رابطه داده‌های زمینی با مدل‌های رقومی ارتفاعی بین 97 تا 99 بود. بیشترین انطباق مربوط به مدل رقومی مستخرج از داده‌های توپوگرافی 1:25000 و مدل رقومی aster30 متر و کمترین انطباق مربوط به داده‌های srtm90 متر بود. در مجموع با دشوارتر شدن شرایط عرصه یعنی از دشت به کوهستان، انطباق مدل‌های رقومی ارتفاعی با داده‌های زمینی برداشت شده کاهش می‌یافت. نتایج بررسی صحت و دقت مدل‌های رقومی نشان داد که کمترین خطا در وهله اول مربوط به مدل رقومی ارتفاعی استخراج شده از خطوط‌میزان نقشه 1:25000 (27.6=rmse ) و پس از آن مدل رقومی ارتفاعی aster30 متر (43.7=rmse ) است. همواره اندازه پیکسل 30 متر نتایج بهتری نسبت به پیکسل 90 متر داشته است. بر اساس معیار خطای میانگین، کمترین اریبی مربوط به aster30 متر (2 متر اریبی) و پس از آن مربوط به مدل رقومی 1:25000 (2.17) است. بیشترین اریبی مربوط به مدل‌های 30 و 90 متری استخراج شده از داده‌های srtm بود. نتایج خطای انحراف استاندارد منطبق بر نتایج rmse بود که تایید کننده بهتر بودن مدل‌های رقومی ارتفاعی مستخرج از داده‌های توپوگرافی 1:25000 و aster30  متر بود.

Accuracy assessment of Digital Elevation Models (DEM) of SRTM and ASTER satellites with precise ground observations (DGPS)Case study: from the Azad dam to the plain of GhorvehDehgolan, Sanandaj

Extended Abstract Introduction Digital elevation model (DEM) is the raster representation of the ground surface so that the information of each cell on the image has a value equal to the altitude from the sea level corresponding to the same spot on the ground. DEM is an appropriate tool for the generation of topographic maps and contour lines, access to the information of surface roughness, three dimensional vision, etc. (Jacobsen, 2004). The accuracy of the digital elevation model is effective on the accuracy of the information from which it is obtained. This is why researchers are always looking for a way to increase the accuracy of digital elevation models. Among the information resources that are used to generate this model are ground mapping, aerial photography, satellite images, radar data, and Lidar. Some of these data generate the digital elevation model with little accuracy due to the insufficiency of the elevation information. The aim of this paper is to investigate the accuracy of DEMs derived from ASTER satellite images and SRTM data with 30 and 90meter pixel dimensions and the digital elevation model derived from the topographic 1:25000scale maps with Differential Global Positioning System (DGPS) in different landforms including plains, hills and mountains.   Materials and Methods The study area is a part of the project of dam and water transfer system from the Azad dam to the plain of GhorveDehgolan (with the goal of transferring water from the catchments of Sirvan River into the country) in the province of Kurdistan and the city of Sanandaj. In this study, the RealTime kinematic method (RTK) was used to locate the points. In this method, assuming that the coordinates of the reference station are known and comparing it with the location obtained from the GPS receiver, a correction value is obtained that is applied to the coordinates obtained for the Rover Station, which is known as the relative or differential method. In this method, the corrections are calculated asrealtime during the observations and are considered in the determination of the Rover location.The Leica GS10 GNSS receivers were used in this study. First, two reference stations were determined using the Fast Static method and then, the RealTime kinematic (RTK) method was used. In order to investigate the extent of the data compliance and relation, the Pearson linear correlation analysis was used and the accuracy assessment of the extracted digital elevation models was carried out using the RMSE, mean error and standard deviation.   Results & Discussion The statistical parameters such as root mean square error (RMSE), bias (µ) and standard deviation () were used to assess the accuracy of each one of the investigated digital models. By comparing different sources that create DEMs, it can be seen that the minimum error is first related to the digital elevation model extracted from the contour lines of the 1:25000scale map (27/6 = RMSE) and then to the ASTER digital elevation model with the pixel size of 30 meters (RMSE=7.43). The 30meter pixel size DEM has always led to better results than the 90 meter pixel size DEM. Based on the mean error standard, the minimum bias is related to ASTER30 m (bias of 2 m) and then to the 1: 25,000 DEM (2.17). The maximum bias was related to 30and 90meter models extracted from the SRTM data. The results of standard deviation error were in compliance with the RMSE results, which confirmed the superiority of 1:25000scale map and ASTER30 m DEMs. The results showed that the determination coefficient of relationship between the ground data and digital elevation models is between 97 and 99. The maximum compliance is related to the digital elevation model extracted from the 1:25000scale topographic data and the ASTER30 m DEM, while the minimum compliance is related to the SRTM90 m data. In general, the compliance of the digital elevation models with the ground data decreased as the field’s conditions became more difficult, i.e. from plain to mountain.   Conclusion The results of DEMs accuracy assessment showed that the minimum error was primarily related to 1:25000 contour lines DEM (RMSE=6.27) and then, to the ASTER30 m DEM (RMSE=7.43). The pixel size of 30 meters has always been better than the pixels size of 90 meters. Based on the mean error standard, the minimum bias is related to the ASTER 30 m (bias of 2 m) and then, to the 1: 25,000 DEM (2.17). The maximum bias was related to 30and 90meter models extracted from the SRTM data. The results of the standard deviation error were consistent with the RMSE results, which confirmed the superiority of the digital elevation models extracted from the topographic 1:25000scale maps and the ASTER30 m DEM.