نوع مقاله : مقاله پژوهشی
1 دانشیار ژئومورفولوژی، دانشکده علوم جغرافیائی، دانشگاه خوارزمی.
2 دانشیار گروه سنجشازدوروسیستم اطلاعات مکانی، دانشگاه تربیت مدرس.
3 دانشجوی دکتری مخاطرات ژئومورفولوژی، دانشگاه خوارزمی.
عنوان مقاله [English]
Earth subsidence is one of the natural hazards under several conditions, including over-exploitation of groundwater, large dams, mining, extraction of fluids from the earth, tectonic and so on. The subsidence causes changes in the geomorphic phenomena of arid and semi-arid regions, which are important due to the occurrence of human complications on different forms, the study of changes due to subsidence in these phenomena is important. Due to the fact that the rate of change in land subsidence as well as the speed of the geomorphological phenomenon is very slow and slow, measuring instruments are of great importance. In this case, static technique is not suitable for monitoring, and dynamic techniques should be used. One technique is the production of radar data. Today, radar interferometry is a common method for measuring the surface deformation of the earth's crust. Global coverage, good resolution of radar images, acceptable accuracy, repeatability, the ability to monitor all areas of study at different time periods, this technique is a powerful technique for studying and measuring land surface changes.
The studied area is Yazd-Ardakan plain which is located in Yazd province. The area of Yazd-Ardakan plain is 11775 square kilometer cover withe longitude are 53º15̍ to54º50̍ east and latitude are 31̊15̍ to31̊15̍ north.
Data and method:
Data used in this study are divided into two general categories, include Scrolling data ( field data for three pilot) and earth observation satellites are data collected from four satellite such as ENVISAT ASAR and Sentinel l satellites from the European Space Agency, Digital Elevation Model ALOS PALSAR Sensor from the University of Alaska, Landsat Satellite from the USGS, survey data from NCC of Iran as well as data from the studied area. And GIS data including Stream, land use, watershed data related to Yazd plain of Ardakan from the NCC of Iran.
This research is based two main steps. The first step is to calculate the amount of land subsidence, for which the images of Sentinel 1 and ENVISAT ASAR satellites were extracted from 2003 to 2018, and using the interferometric method, the amount of subsidence of Yazd plain of Ardakan was calculated and in the second stapes, the geomorphological condition of Yazd plain of Ardakan was studied. To detect changes in geomorphic phenomena digital using with Elevation model ALOS PALSAR Satellite and Landsat satellite imagery that extracted drainage from a digital elevation model using digital stream extraction method. Landsat satellite imagery after preprocessing using edge detection filtering to detect changes in phenomena in specific times series. and last stepe, the relationship between the rate of land subsidence and the changes in geomorphological phenomena was identified.
Stream Extraction from a digital elevation model:
A digital elevation model with a special resolution of 12.5 meters is derived from ALOS PALSAR data for drainage pattern extraction. The extraction of drainage pattern from the aforementioned digitization model was carried out using the Hydrology tool in the ArcGIS software package and based on the value thresholds of different accumulation rates.
Select the Landforms of the study area (Three indicators landform)
Initially, the whole range of Yazd plain of Ardakan was considered and then the water density map for Yazd Plain of Ardakan was produced. In addition, the map of land subsidence was extracted for the study area, and then two maps were automatic superimpose. The highest density of the streams, which corresponded to the subsidence, selected as a pilot. Drainage pattern more over change due specific morphological can be to generate version which local SHAGH (the crack which can font exist in area of subsidence from) drainage pattern furthermore the stream pattern has been change in special form and density level it is important to mention that extraction specific this increases surface erosion.Then Galli's pilot is similar to the previous two pilot automatic superimpose on subsidence map. Largest Galli that was on a descending region was as a pilot selected.
Differential radar interference technique:
This term is used to measure parameters such as topography, surface-displacement and surface displacement due to phase interference of two or more radar images with virtual holes derived from the same region. This method is able to detect surface changes occurring on the ground at different intervals with millimeter precision using at least three (two + DEM + or more radar images).
The interferometer includes the phase difference between two images. The height at each point of the region is determined at the time interval between the two images by the phase difference check. The interferometer is created by the mixed blend of the original image in conjunction of the dependent image. After interferometry method, ENVISAT ASAR and 1 SENTINEL images created the interferometric and, after the final processing, converted to vertical displacement values in meters per meter.
In two times, we had a subsidence of 13 centimeters in the study area, which has occurred in Ardakan, Meybod, Rostaq and Takhzar areas. The highest abandonment rate is in the Ibrahimabad area.
The phenomenon of subsidence causes surface morphological changes such as changes in the pattern of surface currents. On the data processing field study and integration of this data need out that tree phenomena were surface to maximum changing namely SHAGH, GALI and stream pattern .in additionally the reach was shown the change shagh length from 2003 to 2018 rate of increasing 202% from 18 km to 56 km, and the Galli' area increased by 50% from 4 hectares to 6 hectares and the streams increased by 47% from 165 hectares to 241 hectares.