ارزیابی نظریه ی عدم تغییرات مکانی ریگ زارها با استفاده از سنجش ازدور (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
این تحقیق به ارزیابی نظریه عدم تغییرات مکانی ریگزارها می پردازد. براین اساس ریگزارهای کشور با استفاده از تصاویر ماهواره ای لندست در طول 43 سال و تکنیک های سنجش از دوری مورد ارزیابی تغییرات مکانی قرار گرفتند. در این پژوهش نتایج روشن ساخت که ریگ ها به صورت تثبیت شده می باشند به طوری که ریگزار ها در سال مبدا (1973) وسعتی بیش از 35906 کیلومتر مربع را به خود اختصاص داده اند و سپس در سال 2016 نیز به همین اندازه وسعت داشته اند( 35173.5 کیلومتر مربع). با استفاده از تجزیه و تحلیل آمار بادها و ترسیم گلباد ایستگاههای پیرامونی ریگزار ها روشن گردید که بیشتر ریگزارها تحت تاثیر بادهای محلی چند جهته قرار دارند و وجود تپه های ماسه ای مرکب نتیجه همین امر است. همچنین تغییرات لبه های ریگ نیز با رویهم گذاری تصاویر ماهواری بررسی گردید که بر این اساس نیز لبه دارای تغییرات محسوسی نبوده و در برخی از موارد لبه ها به وسیله انسان دستکاری شده است علاوه بر این تحلیل نتایج آشکار کرد که 68% ریگ ها بر روی پهنه های کویری توسعه یافته اند که به دلیل افزایش خشکی محیطی می تواند باعث تغییر در ریگ ها گردد.. همچنین نتایج این پژوهش روشن ساخت که طرح هایی که مبتنی بر تثبیت ریگزارهای بزرگ صورت می پذیرد کارآیی لازم را نداشته زیرا به طور طبیعی ریگزارها در موقعیت مکانی خود تثبیت شده می باشند. با توجه به این نتایج برای جلوگیری از بروز خسارت های مربوط به تپه های ماسه ای باید به پیرامون ریگزارها توجه شود یعنی مناطقی که مسیر جابه جایی تپه های ماسه ای می باشند چون در مسیر حمل از مبدا به مقصد یا همان ریگزارها ، عوارض ماسه ای فعال مانند برخان ها اکثر خسارات را به بار می آورند.Assessing the Theory of Spatial Stability of ERGs in Iran, Using Remote Sensing data
Introduction
ERGs "Areas covered by sand" are called Rigzar in arid regions in Iran. There are more than 20 large Ergs with an area of 36,000 square kilometers in Iran. According to a study by Farajullah Mahmoodi on Iran's Erg, he believes on stabilization of area and border of ergs. Reviewing this theory is very important because Erg areas are located in arid and desert climates which are associated with wind erosion wind resulted large amounts of desert dusts. Therefore, it is necessary first and foremost before the sand dune control projects to consider whether large Ergs are naturally stabilized or displaced? In This paper we are trying to find the answer to this question.
Materials and Methods
The research method is analytic-descriptive. Thus, all of the Ergs in Iran were studied using Land sat satellite imagery and remote sensing techniques. The satellite data concluded images of 1973 and 2016. Firstly we were prepared false color images (RGB), using Erdas 9.3 software. In the next step, ROI coefficient was determined using sand reflection in satellite imagery. Then, we extracted the polygon future layers of Ergs for morphological evaluation and determination of long term mobility. Finally, we also were studied wind characteristics and its effects on Aeolian landforms.
Discussion and Results
1- Wind characteristics
In this study, the maximum monthly wind velocity was analyzed for recognition of the sand transfer paths as well as effective factors for accumulation of sand particles and growing up sand dunes. We found out that local winds and desert storms are more important agent to form the sand dunes and ergs. Local winds reach to the highest velocity in the summer than other seasons.
2- Spatial variations
In this study, the results showed that the size and area of the Ergs have the same measures in 43-year series (2016-1973). During the study period we only distinguished small changes in the erg edges but the erg areas have been remained constant. However the drought increasing during the last decades affected the salt lands and playas around the Ergs but it probably will impact the ergs for more changes with a long time.
3- Erg edges changes
For more precise considering of moving dunes and erg borders’ extraction, we overlapped satellite images with different dates. The results showed no significant changes in the morphology of the edge Ergs. In recent years due to climate change, physical dryness has increased in parallel with the decrease in humidity. So the Ergs that have been developed on wet playas are likely to change the edge of the Ergs in the future. Accordingly, in 19 large study Ergs, the results showed that more than 68% of Ergs spread on playas and salty wetlands. Also, 11% of the structural plains (LUT and JEN ergs) and 21% have been formed on other areas such as aggraded plains and pediments.
Conclusions
The aim of this paper is assessing the theory of the erg stabilization in space and area. Accordingly, the study areas concluded all of the Ergs in Iran which have been evaluated using Landsat satellite images and remote sensing techniques. We have compared the area and borders of ergs for duration of 1973 to 2016.The results show that Ergs did not have any significant displacement during the study period. Also results show that for preventing damage to the sand dunes dynamic, it is necessary to control the active Barchan in the transport routes. Because Barchans are active sand dunes which cause to damage residential area and agricultural land.
Keywords: ERG, Sand dunes, Spatial variations, remote sensing.
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