# Ground Displacement in East Azerbaijan Province, Iran, Revealed by L-band and C-band InSAR Analyses
## 1 Introduction  
Since urban growth in recent decades has accelerated on a global scale, migration of the population from rural to urban areas has also increased. This transformation of the population has caused many changes in which the elements of a simple rural life have been gradually replaced by more complex elements that need more resources to meet the demands of a new urban life in an era of complexities. New challenges need to be recognized and modeled before they become problems that can harm other elements or components of environmental systems [1; 2; 3; 4; 5]. The first census of Iran in 1956 reported 201 cities, which increased five times by 2011. According to the 1976 census, Tehran was the only city with a population over 500,000, but in the 2011 census, 14 cities, including Tabriz, Masahad, and Isfahan,had a population of more than 500,000, which means that urbanization and industrialization plans were pursued in recent decades [6].  
Ground subsidence is gradually becoming a major problem for governments and people, especially if not properly planned industrial, mining, and agricultural activities are accelerated [7; 8; 9; 10; 11; 12; 13]. It is a long-term phenomenon in most cases and acts like a \"dark death\" for the Earth. It commonly happens in different parts of Iran. For example, important basins in Tehran, Mashhad, Rafsanjan, Yazd, and Neyshabour have fallen victim to ground subsidence due to a lack of underground water recharge, a lack of supervision, and illegal use of natural resources [14; 15; 16; 17; 18].  
Optical imagery suffers from the presence of clouds and night/day cycle, but synthetic aperture radar (SAR) imagery provides an opportunity to observe the Earth during the day and at night under all weather conditions. New satellite constellations of SAR missions such as Cosmo-SkyMed, TerraSAR-X, and ALOS-2 can guarantee high-resolution SAR data for different applications. SAR interferometry (InSAR) is a powerful technique that uses the phase and amplitude information of at least two SAR images with the same geometry and characteristics to extract the displacement rate of earthquakes [19; 20; 21; 22; 23; 24; 25; 26], ground subsidence [14; 15; 16; 17; 18], volcanic activity [27; 28; 29; 30], mining activities [7; 31], structures [32; 33; 34], and landslides [35; 36; 37; 38; 39; 40; 41; 42]. The technique enables us to overcome the challenges of conventional methods. For example, ground displacements can be monitored by the Global Navigation Satellite System (GNSS) or leveling, which are point-like conventional methods that require more labor and a considerable budget to maintain a network [43; 44]. InSAR has fair spatial coverage without maintenance costs and provides acceptable results for different time spans.  
This study presents the spatiotemporal characteristics of intensity, phase, and coherence of PALSAR-2 L-band images (\(\uplambda\sim\)24 cm) of the ALOS-2 satellite provided by the Japan Aerospace Exploration Agency (JAXA) at different times and focuses on the small baseline subset (SBAS) InSAR technique and principal component analysis (PCA) in NW Iran (East Azerbaijan Province) to monitor the ground subsidence of major basins using 15 PALSAR-2 images.