آشکارسازی مکانی- زمانی تغییرات ارتفاعی یخچال های طبیعی علم کوه با استفاده از داده های لیزراسکنینگ هوایی (LiDAR) و عکسبرداری با پهپاد (UAV) (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
یخچال های طبیعی و تغییرات کوتاه مدت و بلند مدت آن ها، از مهم ترین سنسورهای اقلیمی برای پایش روند تغییرات آب و هوایی هستند. در تحقیق حاضر به منظور آشکار سازی مکانی- زمانی تغییرات ارتفاعی دماغه یخچال؛ مدل های رقومی ارتفاعی حاصل، داده های لیزراسکنینگ هوایی (LiDAR) سال 1389و تصاویر پهپاد سال های 1397 و 1399 مورد استفاده قرار گرفتند. دقت مدل های رقومی ارتفاعی (DEM) استخراج شده از پهپاد، در سال های 1397 و 1399 به ترتیب با استفاده از حدود 40 و 20 نقطه کنترل زمینی تقریباً 15 سانتی متر برآورد شد. همچنین دقت برآورد تغییرات ارتفاعی بر اساس ارزیابی تغییرات ارتفاعی در منطقه غیر یخچالی در این بازه زمانی نشان دهنده دقت بالای نتایج است. بطوری که مقادیر میانگین و انحراف معیار در منطقه غیریخچالی به ترتیب برابر با 0.05± و0.34 سانتی متر است که مقادیری قابل قبول در مطالعه تغییرات ارتفاعی یخچال به شمار می روند. نتایج حاصل از تفریق دو به دوی DEM های یاد شده نشان دهنده تغییرات ارتفاعی بسیار زیاد دماغه یخچال علم کوه از سال 1389 الی 1399 است. چنانچه میانگین نرخ تغییرات ارتفاعی شکاف اصلی دماغه یخچال در این مدت حدود 0.8 – متر در سال (.m/yr) و بیشترین مقدار نرخ تغییر ارتفاعی حدود 2.31- (.m/yr) است. عمده تغییرات ارتفاعی این منطقه در بازه زمانی 1389 تا 1397 بوجود آمده و میانگین نرخ تغییرات ارتفاعی شکاف اصلی یخچال در این مدت 1.03- (.m/yr)و حداکثر آن 2.77- (.m/yr) است. تغییرات ارتفاعی در بازه زمانی 1397 تا 1399 کمتربوده و میانگین نرخ تغییرات ارتفاعی 0.1+ (.m/yr)و حداکثر آن 1.85- (.m/yr)است. با توجه به اینکه این منطقه به عنوان خروجی و محلّ تخلیه یخچال نیز شناخته شده و حجم زیادی از واریزه ها و یخرفت ها ی یخچالی را به ارتفاعات پایین تر سرازیر می کند، تغییرات ارتفاعی شدید این منطقه ناشی از ذوب برف و یخ است و همین امر، عامل اصلی وقوع سیلاب عظیم تیرماه سال 1390 در رودخانه سردآبرود بوده است.Use of UAVs and Lidar to identify the spatiotemporal elevation changes of AlamKooh Glacier
IntroductionGlaciers and their short-term and long-term elevation changes are among the most critical environmental hazard indices for monitoring climate change and evaluating geomorphology, perpetually posing risks to climbers, environmentalists, and tourists. The Alamkooh glacier’s snout is known as one of the most dynamic parts of glaciers in Takht-e-Soliman height due to the yearly advance and retreat of glacier movement causing substantial volumes of various glacial deposits to collapse into their downstream areas. Nowadays, the advancements of satellite imagery, aerial photos, and Unmanned Automated vehicles (UAV) pave the path for accurately extracting and evaluating these changes. Therefore, the objectives of this research are: (a) evaluating the use of new and cost-effective technologies (UAVs) in comparison to satellite imagery for monitoring glacier changes, (b) identifying spatiotemporal glacier elevation changes, and (c) evaluation of the elevation change rate of the Alamkooh glacier snout from 2010 to 2020 using high spatial resolution remotely sensing data. In this context, the elevation changes of the snout of Alamkooh Glacier, as the hazardous activist part of this glacier, were assessed using Digital elevation models (DEMs) differences of 2010, 2018, and 2020.Materials and MethodsAlamkooh Glacier is located on the northern hillside of Alamkooh Summit in the Takht-e-Soliman region. The snout of this glacier is situated in a steep valley known as Lizbonak and its high activity changes the shape and morphology of this area. In this paper, spatial and temporal elevation changes of Alamkooh Snout were identified and evaluated using DEMs subtraction derived from aerial laser scanning (LiDAR) data in 2010, and from images captured by UAV in 2018 and 2020. Before elevation change analysis, the DEMs obtained through UAVs in 2018 and 2020 were carried out using approximately 40 and 20 ground control points, respectively. The resulting outputs displayed a reliable accuracy of around 15 cm for these DEMs. In addition, for assessing elevation changes precisely, the all of extracted DEMs were preprocessed and orthorectified and then subsequently subtracted pairwise. Then after, the accuracy of elevation changes was appraised based on non-glacial area elevation change. The outcomes of elevation change in this region signify a high level of accuracy in the 10-year time span. According to the results, the average and standard division elevation change of non-glacial area was ±0.05 cm and 0.34 cm respectively. Moreover, the average error assessment on the non-glacial area indicates that within eight years from 2010 to 2018 the average error was ±0.16 cm, and within two years it was ±0.11 cm from 2018 to 2020.Result and discussionResults of DEMs pairwise differences show significant elevation changes in this part of Alamkooh Glacier from 2010 to 2020. The average and the maximum elevation change rates in this period are -0.8 (m/yr.) and -2.31(m/yr.) respectively. The major elevation changes in the snout of Alamkooh happened in the initial period from 2010 to 2018 where the yearly and the maximum mean elevation change rates were -1.03 (m/yr.) and –2.77 (m/yr.) respectively. On the contrary, the elevation changes from 2018 to 2020 were lower than the first period whereas the yearly mean elevation change was about +0.1 (m/yr.) and the maximum elevation change rate was -1.85 (m/yr.). The positive rate of elevation change from 2018 to 2020 is due to debris and ice cubes flowing from upstream and accumulation downstream. Moreover, the Spatial analysis of elevation changes results show a heterogeneous distribution whereas the most significant elevation change in the snout of Alamkooh glacier has occurred predominantly across and along the largest existing valley rather than being evenly spread out across the entire area. The elevation change domain in this valley is between +1.3±0.05 to -23.05±0.05 and the average elevation change of in ten years from 2010 to 2020 is about -8.01 ± 0.05 meters. These changes mostly were negative with decreasing and eroding rates. In contrast, the elevation changes in other valleys only occurred at the exit area of the glacier and just the entrance of the snout area, and the margins did not show a considerable change. When considering all valleys in the snout of Alamkooh the elevation changes distribution across the snout varies between +0.45 to -13.2 (m) with an average of -7.8 (m) which is less than alongside changes at the main valley.ConclusionThe results show elevation changes in the Almakooh snout do not have constant rate and largely fluctuate in different years and regions. The maximum elevation changes occurred from 2010 to 2018 and along with the main steepest valley. The main valley plays a vital role in elevation change analysis and flowing debris down. This area is also known as the depletion area of the Alamkooh glacier and its drastic elevation changes are caused due to ice and snow melt. The tremendous historical flood of the SardAbrood River occurred in June 2011 was created and affected by elevation changes in this area. Therefore, the tongue of Alamkooh Glacier is considered one of the most dangerous areas regarding natural hazards, and morphological change studies require precaution regarding approaching or visiting this area. This research also confirms that using time-series of remote sensing data such as UAV and Lidar images is very helpful and cost-effective data for identifying, extracting, and monitoring the spatiotemporal changes of glaciers, debris flow directions, and natural hazards.
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