Landslide detection and monitoring using InSAR, Case study: Ardal and Koohrang Counties, Iran

Landslide is a geological phenomenon that includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows. Landslides are caused by various natural and human causes. Due to its damages, landslide activities must be considered in various construction, industry and agricultural activities. There are several methods for measuring the motion of the earth's crust caused by landslides. These include microgeodesic methods using accurate leveling and GPS observations. It will not be possible to repeat these measurements with this methods due to the high cost and difficulty. Therefore, it is not possible to provide timely and widly information on movements and displacements caused by landslides.SAR interferometry technique is one of the newest remote sensing techniques that by processing radar images has provided the possibility of preparing earth crust movement maps on a large and continuous surface.

One of the principal applications of the SAR technology is represented by the SAR interferometry (InSAR) technique. SAR interferometric techniques combine complex images recorded by antennas at different locations or at different tima to form interferograms which permit the determination of minute differences in the range (distance) to corresponding points of an image pair, on the sub-wavelength scale. By combining three radar images as two pairs of interferograms were able to separate topographic and dynamic effects and thus estimate the coseismic displacement field using radar data alone. The purpose of this study is to evaluate the capability and capability of radar interferometry technique in landslide detection. Radar interferometry processes and the results are presented in order to identify landslides in the study area (Koohrang county). Radar images taken by ASAR (Advanced SAR) sensor, which is one of the ENVISAT satellite sensors, are used for radar interferometry processing and interferogram creation.

Seven interferograms were formed on all pairs of available images. In three cases, fringes indicating landslides were observed. Considering the elimination of the topographic effect in the above interferograms and considering the fact that no earthquake has been recorded in this area during this period, so the fringes formed in this interferograms can be related to the occurrence of landslides. Considering the consistency of the observations of all three interrograms, the approximate average displacement rate has been calculated for each of these landslides.Among the identified sites as landslides, only two cases are located in Chaharmahal and Bakhtiari province. One of them is located in the vicinity of Kofi village and another one is detected in Dehdeli village in Ardal county.

The approximate maximum ground displacement of landslides detected in the range of radar sensor visibility was estimated in centimeters. Extensive coverage of radar images in InSAR technique is one of the important advantages of this technique. Therefore, using this technique, make it is possible to identify active landslides, even in Inaccessible areas. Due to the presence of images in the archives of radar satellites such as ENVISAT satellites, it is possible to monitor landslides over the past years to the present.One of the limitations in using the SAR interferometry technique is that all SAR images taken are not suitable for forming interferrogram. In fact, reducing the correlation of images such as Baseline Decorrelation and temporal decorrelation are important obstacles in using this technique in different situations.Another limitation factor of this technique that can be considered is low spatial resolution of the resulting interrograms. This in turn causes the loss of small displacement ranges, in other words small landslides.Accurate Global navigation satellite system point observations can be used as a complement to InSAR observations (continuously and extensively) in landslide modeling.The following suggestions for using this technique in the study of landslides are presented.A) Since it is possible to identify landslides and calculate the displacement vector for high-precision radar sensor vision using InSAR technique, use this technique to identify and monitor active landslides in order to complete the land database. Slips are suggested.B) Conducting research to extract the dimensions and components of a landslide (including parameters such as canopy, peak, landslide, displaced mass, depletion zone, accumulation zone, etc.) from the results of InSAR technique to model landslide seems necessary It arrives.C) GPS point and sight observations can be used as a complement to InSAR observations (continuously and on a large scale) in landslide modeling.D) Due to the low spatial resolution of the displacement interrogram resulting from the use of the digital SRTM elevation model with a pixel size of 90 m, conduct research to use digital elevation models with better pixel size to reconstruct the topographic phase and finally obtain An interrogram requires better displacement with better spatial resolution. Undoubtedly, in such an interrogram, the probability of identifying landslides that have occurred in small areas will increase.