بررسي تغييرات توپوگرافي معادن روباز با استفاده از تداخل سنجي راداري الگوريتم PS - مطالعه موردي: معدن سنگ آهن سنگان خواف

Investigation of surface deformation of open cast mines using radar interferometry of PS algorithm - Case study: Sangan khof iron ore mine

معادن منبع اصلي توليد مواد اوليه هستند و استخراج اين منابع طبيعي از معادن براي توليد كالا باعث ايجاد اختلال در تعادل سطحي، تغيير شكل مداوم زمين، افزايش مسائل محيط‌زيست و ايجاد خسارت به زير ساخت ها مي‌شود. از اين رو كنترل و مانيتورينگ جابه‌جايي‌هاي ناشي از معادن سطحي روباز مهم مي‌باشد. در اين مقاله ميزان تغييرات سطح زمين و تأثيرات ژئومورفولوژيكي ناشي از فعاليت‌هاي معدنكاري در معدن سنگ آهن سنگان خواف واقع در خراسان رضوي بررسي شده است. سنگان يك منطقه گرمسيري / خشك با برجستگي بالا 1700 متر ارتفاع در مناطق معدني است. حداكثر دماي 35 تا 40 درجه سانتي‌گراد در جولاي/ آگوست تجربه مي‌شود در حالي كه حداقل دما از5- تا 15- درجه سانتي‌گراد در ژانويه / فوريه رخ مي‌دهد. بلندترين قله، نول خروس، در معدن A، 1719 متر قرار دارد. بررسي‌هاي ميداني انجام گرفته نشان مي‌دهد كه معادن سنگ آهن سنگان به‌علت فعاليت‌هاي شديد معدنكاري به‌ويژه ژئومورفولوژي منطقه دچار تغيير شده است كه اين تغييرات مي‌تواند در روند طبيعي فرآيندها و فرم، مثلاً فرآيند سيلاب تأثير داشته باشد. تداخل‌سنجي راداري ابزار ارزشمندي در پايش جابه‌جايي‌هاي سطح زمين است. براي بررسي و اندازه‌گيري ميزان اين تغييرات در معدن سنگان از روش تداخل‌سنجي راداري الگوريتم PS با 47 تصوير ماهواره‌اي سنتيتل1 مربوط به سال‌هاي 2014 تا 2020، پلاريزاسيون VV با استفاده از نرم‌افزارتجاري SARPROZ در محيط Matlab انجام شده است. تداخل‌سنجي راداري مبتني بر پراكنش‌كننده‌هاي دائمي(PS) جابه‌جايي‌ها را بر روي پيكسل‌هايي كه ويژگي‌هاي پراكنشي آن‌ها در طول زمان تقريباً ثابت است، بررسي مي‌كند. نتايج اجراي سري زماني در اين پژوهش با الگوريتم PS ميزان تغييرات را حدود 30- سانتي‌متر در راستاي ديد ماهواره نشان داد. ميانگين نرخ (سرعت) جابه‌جايي را 4/8- تا 6- سانتي‌متر در سال تعيين كرد. براي ارزيابي نتايج از داده هاي دوربين ترازيابي استفاده شد و در مقايسه با آن مي‌توان گفت تقريباً روند مشابهي را طي كرده است. به‌طور كلي فعاليت‌هاي معدنكاري در معدن سنگان تغييرات توپوگرافي فراواني بر محيط گذاشته است و موجب تشديد فعاليت فرآيندهاي ژئومورفيك مثل لغزش، ريزش، و... بر روي باطله ها شده است. شناسايي و تحليل اين عوارض و فرآيندهاي مرتبط، بيانگر يك چالش براي درك تحول چشم‌اندازهاي زمين است. به‌طور كلي، نظارت بر تغيير شكل معادن سطحي با استفاده از داده‌هاي راداري SAR امكان‌پذير و همچنين نيازمند به اجراي پژوهش‌هاي بيشتر در معادن ايران است.

Extended Abstract Introduction Mining (especially surface) is one of the major causes of land and environmental degradation globally. Environmental impacts such as deforestation, landscape degradation, alteration of stream and river morphology, widespread environmental pollution, siltation of water bodies, biodiversity loss, etc., have been noted to be associated with mining. Surface deformation is the biggest problem in open cast mines and their surrounding areas due to mining activities. Surveying engineers study the amount of displacement in open pit mines by using leveling to calculate the amount of displacement and determine it. These methods are expensive and time consuming. Satellite images are considered as an important tool for land resource management due to the wide view that provide of an area and also due to its regular repetitive coverage. Interferometric Synthetic Aperture Radar (InSAR) is a useful tool in the study of surface displacements. The SAR interferometry concept has been introduced in the last 1980s.The objective of this study as an academic research is monitoring deformation using Persistent Scatterer Interferometry Synthetic Aperture Radar (PS-InSAR) method for managing a very rich iron ore resource in the eastern part of Iran named Sangan, near the Afghanistan boundary. Methodology In this paper, surface deformation calculation based on the processing of PS-InSAR technique (Persistent Scatterers SAR Interferometry) have been carried out. For this study, according to the availability of data for study area 47 SLC images of Sentinel-1A covering the study area during the period of October 7, 2014 –July 7, 2020 are downloaded from European Space Agency website. Sentinel-1A acquired images with a swath width of 250 by 180, with revisiting time 12 days within the IW data acquisition mode, it is reduced to six days if the images acquired by the Sentinel-1B satellite are available. Sentinel-1 has launched on 4th April 2014 by ESA. PS includes following steps: Master image selection, Co-registration data, Reflectivity map generation Amplitude stability index, Persistent Scatterers Candidate selection (PSC), PS point selection, Multi-image sparse grid phase unwrapping, Atmospheric phase screen estimation Removal and PS phased reading Displacement estimation. Study area Sangan Iron Ore Complex (SIOC) is located at latitude N 34°24’ to 34°55’ longitude E 60°16’ to 60°55’ in the Khorasan-e-Razavi Province, North-Eastern Iran. The iron ore deposit is about 20 km Northeast of Sangan town at about 1650 meters above sea level. Sangan Iron Ore Mines (SIOM) is one of the largest mineral areas in Iran, and also considered to be one of the Middle East’s richest deposits which are located in a rectangular area with 26km length and 8km width. Results and Discussion In this paper, the 47 scenes of IW SLC Sentinel-1A images, spanning the period from October 7, 2014–July 7, 2020 are accumulated displacement map and the time series of the deformation derived. The PS were selected on the basis of the ASI threshold value of 0.7, which signifies the stability of target points. The LOS displacement was improved by using APS and atmospheric phase delay correction. Later, the LOS displacement velocity on PS locations was estimated. The temporal coherence of all the selected PS was also tested. The PS points having ASI value of 0.7 and above, and temporal coherence of 0.9 and above, gave a relatively stable estimation of LOS velocity. We have identified 215377 Scatterers points. By imposing the standard threshold of 0.7 on ensemble coherence value, this amount decreased dramatically to 52449 PS points. These factors make the chosen technique suitable for studies of surface deformations. The results showed that the deformation velocity in this area is -4.8 mm/yrs and maximum displacement-30mm. In order to verify the results, we collected the Total Station data and PS data for analysis and comparison. Due to the lack of data in the plain, the Total Station data is related to downslope areas and as a result, uplift of area has been used to validation the results. It has been observed that for the same area the Total Station value shows good agreement with the PS- InSAR result. However, there may be some errors due to the fact that the data are not synchronous and that the nature of the impression is different. Conclusion In the present study, PS-InSAR technique and C-band sentinel-1 data have been used for surface deformation monitoring in open cast mines of Sangan-Khaf, Khorasan Razavi. It can be concluded that monitoring the deformation of mined surfaces using traditional monitoring techniques such as field surveys and using Total Station, especially in large study areas, is time consuming. Since in using the interferometry methods in the study of open pit mines, the area covered by SAR images is much larger, so the use of this method will reduce costs. The results were assessed and validated using leavening data has been observed that, for the same area, the levelling value shows good agreement with the PS- InSAR result.