The use of InSAR and DInSAR for detecting land subsidence in Albania

INTRODUCTION. InSAR or Interferometric Synthetic Aperture Radar is a technique for mapping ground deformation using radar images of the Earth's surface collected from orbiting satellites. DInSAR or Differential SAR Interferometry is an active remote sensing technique based on the principle that, due to the very high stability of the satellite orbits, it is possible to exploit the informative contribution carried by the phase difference between two SAR images looking at the same scene from comparable geometries.

AIM. In this setting, the main objective of this study is to evaluate the region near the closed rock salt mine in the south of Albania. Our input for this exercise will be two images of the land near the former rock salt mine in Dhrovjan near the Blue Eye (Saranda, Albania).

RESULTS. By combining the phases of 2 images we produce an interferogram where the phase is correlated to the terrain topography and deformation so if the phase shifts related to the topography are removed from the interferogram, the difference between the resulting products will show surface deformation patterns or cure between the two acquisition dates and this methodology is called differential interferometry Processing, Phase Unwrapping, and at the end creating the displacement map. We use in our study the difference in time with the algorithm which consists of working step by step with these operators: Read the two split products, Applying Orbit files, Back-Geocoding, Enhanced Spectral Diversity, Interferogram, TOPSAR Deburst, and Write. The resulting difference of phases is called an interferogram containing all the information on relative geometry. Removing the topographic and orbital contributions may reveal ground movements along the line of sight between the radar and the target.

The next algorithm we worked with these operators: Read the debursted interferogram, TopoPhaseRemoval, Multilook, Goldstain Filtering, and Write. At the same time from Goldstain Filtering, we add the Snaphu Export operator.

Correct phase unwrapping procedures must be performed to retrieve the absolute phase value by adding multiples of 2π phase values to each pixel to extract accurate information from the signal. In this study, we will use SNAPHU, which is a two-dimensional phase unwrapping algorithm consists of working step by step with these operators: read (the wrapped image) and read (2) the unwrapped image, Snaphu Import, PhaseToDisplacement, and Write. We can display it in Google Earth after saving it as .kmz and also make a profile of the displacements.

DISCUSSION AND CONCLUSIONS

One of the SAR Interferometry applications is deformation mapping and change detection. This work demonstrates the capability of interferometric processing for the observation and analysis of instant relative surface deformations in the radar LOS direction. When two observations are made from the same location in space but at different times, the interferometric phase is proportional to any change in the range of a surface feature directly. All three stages of the work are important and require accurate interpretation knowledge, especially when working with the Snaphu program.

KEY-WORDS

InSAR, DInSAR, Interferogram