# Ground Displacement in East Azerbaijan Province, Iran, Revealed by L-band and C-band InSAR Analyses
## 2 Study Area and Datasets
### Dataset Description  
Previous studies show that using 17 ENVISAT C-band images (\(\lambda\sim\)6 cm), the ground subsidence rate in the Tabriz basin was extracted by the SBAS method for a 7-year period from 2003 to 2010 [45; 46], in which the maximum ground subsidence rate was \(-\)20 mm/year in the line of sight (LOS) of the satellite. Furthermore, these studies reported that the water level during those 7 years declined up to 1.5 m in some of the piezometric wells, which resulted in three oval-shaped subsidence patterns in the Tabriz basin [45; 46]. For Shabestar basin, 14 ENVISAT C-band images from 2003 to 2010 were processed based on the SBAS technique, and the results revealed that the maximum rate of subsidence was about \(-\)40 mm/year in the LOS direction [47]. There are several InSAR techniques, depending on the topographic situation, extent of the study area, and number of images, and different InSAR techniques might be selected for crustal displacement analysis [12]. This work used SBAS InSAR time series analysis for L-band data acquired from 5 December 2015 to 4 April 2020. As shown in Table 1, the PALSAR-2 and Sentinel-1 datasets were used. Generally the continuity of L-band (PALSAR-2) data is lower than C-band (Sentinel-1) data, but L-band data has the advantage of strong intensity correlation and long-lasting temporal coherence in order to perform more accurate time series InSAR analysis [50]. Figure 2 shows the correlation of backscattering values (dB) of all PALSAR-2 images with the super master image (27 January 2018). Overall, the correlation of all images with the super master image is high, but images from the same month or season as the super master image have much higher correlation, indicating that the vegetation effects of the backscattering coefficients are probably similar. For example, the correlation between images 6 (super master image) and 13 is 0.98, since their seasonal difference is only 16 days regardless of what year they were acquired. In addition, Figure 3 shows a histogram of the backscattering coefficients of the target area, in which the majority of images show a normal distribution (bell-shaped curve). The shape of the distribution is important in natural sciences to understand the physical situation of the study area [26]. Figure 3 shows that the peak of the bell curve for all PALSAR-2 images is formed between \(-\)5 and \(-\)15 dB. The normal distribution is generally symmetric near the mean value and is non-zero over the real line. However, some curves in Figure 3 are not exclusively symmetric (red curves). For example, histograms of the images acquired in February, March, and April show sinusoidal behavior in the left shoulder of the bell curve, mainly \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Label (\#)** & **Date (YYYY/MM/DD)** & **Polarization** & **Incidence Angle (\({}^{\circ}\))** & **Band** & **Orbit** & **Track** \\ \hline  
\hline \hline \end{tabular}
\end{table} 
Table 1: Synthetic aperture radar (SAR) images and detailed characteristics of L-band PALSAR-2 and C-band Sentinel-1 datasets used in this study. \({}^{\ast}\) indicates super master image; D and A indicate descending and ascending orbits, respectively. because of considerable rain. Other images, including the master image, that were acquired in dry seasons or months show relatively symmetric bell curves. Although the main focus of this work is SBAS analysis of L-band PALSAR-2 data, conventional differential InSAR (DInSAR) analysis was also applied on the C-band Sentinel-1 dataset, for comparison or validation of the L-band SBAS results. The dual polarized horizontal (H) and vertical (V) PALSAR-2 data (HH + HV) were acquired from ascending orbits (right-looking observations) of track 178, while the dual polarized Sentinel-1 data (VV + VH) were acquired from descending orbits (left-looking observations) of track 79.