برآورد مساحت و حجم توده ي لغزشي با استفاده از تكنيك‌هاي InSAR و مشاهدات GPS (مطالعه موردي پهنه لغزشي روستاي گوگرد)

The estimation area and volume of landslide using InSAR techniques and GPS (case study Googerd landslide)

زمين‌لغزش به‌عنوان يكي از مخاطرات ژيومورفولوژيك ممكن است در قلمرو معين، با بزرگي و دوره هاي زماني مشخص رخ دهد. تخمين حجم و مساحت توده ي لغزشي نيازمند اطلاعات زمين‌شناسي و ژيومورفولوژيكي است كه امروزه تنها با روابط تجربي بين حجم زمين‌لغزش‌ها و مساحت زمين‌لغزش، و بكار گيري داده هاي دورسنجي و تكنيك هاي تداخل‌سنجي قابل‌محاسبه مي باشد. توده ي لغزشي روستاي گوگرد در سطحي در حدود 200 هكتار روي يك زمين لغزش قديمي به وسعتي در حدود 876 هكتار اتفاق افتاده است كه روي اين توده ناپايدار 468 خانوار با 2566 نفر جمعيت زندگي مي كنند. در اين پژوهش اطلاعات مربوط به تعداد 26 زمين‌لغزش در منطقه ي قطور، شامل مساحت، حجم و عمق با استفاده از 25 تصوير سنجنده ASAR ماهواره ي ENVISAT و الگوريتم StaMPS و SBAS در تكنيك InSAR تهيه شد. سپس يك رابطه تجربي براي برآورد حجم توده ي لغزشي گوگرد به‌كاربرده شد محاسبات نشان داد كه در طي 7 سال اخير با احتساب متوسط طول، عرض و عمق جابجايي به ترتيب 2600، 800 و 35 متر، مجموع سطح جابجايي و حجم مواد جابجا شده معادل 2 * 106 m2 و 7.3 * 107 m2 مي باشد. استخراج اطلاعات سري زماني جابجايي از اينترفروگرام ها نيز نشان مي دهد كه سالانه 2.1 * 104 m2 مواد با سرعتي معادل ?= 10 mmyr-1 جابجا مي شود. لذا در اين منطقه لغزش ها فعال هستند و ممكن است لغزش هاي جديدي با بزرگي قابل‌ملاحظه به وقوع بپيوندند.

Introduction A significant practical contribution of geomorphology is the identification of stable landforms and sites with a low probability of catastrophic or progressive involvement with natural or man induced processes adverse to human occupancy or use. The slide mass volume estimation, requires to the geological and geomorphological information on discrete slope. It is very difficult and expensive to collect. But if digital form of slide map will be available, calculating volume and surface of all slips is possible. Today remote sensing products can be utilized for deriving various parameters related to landslide controlling factors. And mass movement quantitative properties such as length, wide, slope and displacement can be calculated using SAR data and InSAR approach. The study area is located in the Northwest of Iran, West Azerbayjan province. The application site (Googerdʹs slide mass) lies in ?: 38° 30´ 30" ?: 44° 34´ 00". Data and methods In this research the relationship between Geometric characteristics of the slips and their volume have been evaluated. This equations is provided by Simonett in 1967 and has been evaluated by other experts in the world and Iran. The equations proposed by previous researchers such as Guzzetti used to calculate volume and surface of slip on the Googerd sliding mass. Furthermore, for monitoring and estimation of length, wide and the average depth of landslides and for slope displacement assessment, GPS observations and 25 SAR data from ENVISAT RADARSAT with descending collection has been used. All of this images are in SLC format and has collected from 2003 to 2010 that has processed using interferometry approach. The SAR data has processed using PSInSAR, StaMPS and SBAS techniques. Result and discussion The assessment of Interferograms showed that the average rate of displacement from line of sight (LOS) is 10 mmyr-1. Time series analysis of Interferograms in Googerdʹs landslide represents that downward shift continues. Calculations show that during the past 7 years, with assuming length, width and depth of the movement 2600, 800, 35 meters respectively, the area of displacement is and the volume of this displacement is . Time series information of Interferograms represents that approximately materials shift to downward with velocity. This means that in this area the landslide are active and may be considerably new slips to occur. Conclusion Access to the data from number and size of landslide is important to estimation, assessment and evaluation of landslide susceptibility occurrence. However estimation of landslide volume is difficult and needs to data from geometry of surface and subsurface of broken domain that today can be calculated only with the correlations between landslide volume and area. For monitoring and estimation of length, wide and the average depth of landslides and for slope displacement assessing, GPS observations and 25 SAR data has been used. Calculations show that the area of displacement is and the volume of this displacement is . This volume of materials shift to downward with velocity.