## 2 Study Area and Dataset
### Pre-Processing  
The SAR images were provided as single-look complex (SLC) data with processing levels of 1.1 for ALOS-2 and 1.0 for Sentinel-1. Both images were represented by the complex I and Q channels to preserve the amplitude and phase information [31; 32]. The Sentinel free open source toolboxes were employed for pre-processing. The images were projected on the WGS84 reference ellipsoid. The radiometric calibration of each intensity image was carried out to obtain the backscattering coefficient (sigma-naught, \(\sigma^{0}\)) in the ground range with the decibel (dB) unit, represented by the following equation:  
\[\sigma^{0}=10.0\log_{10}\Bigl{(}k_{s}\cdot|DN|^{2}\Bigr{)}+10.0\log_{10}(\sin \theta_{loc}) \tag{1}\]  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Year** & **1986** & **1991** & **1996** & **2006** & **2011** \\ \hline Population & 6,058,207 & 6,497,238 & 6,758,845 & 7,711,230 & 12,183,391 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The change of population in Tehran [28].  
Figure 1: Location of Tehran and coverage of the satellite images used in this study, including Sentinel-1 (blue frame) acquired on 26 October 2015, ALOS-2 (red frame) acquired on 14 October 2015 and Landsat 8 (green frame) acquired on 7 May 2015.  
where \(DN\) is the digital number of backscattering intensity, \(k_{s}\) is the calibration factor, and \(\theta_{loc}\) is the local incidence angle.  
After this conversion, different processes were applied to the SAR data. To represent the images as geometrically similar to the real world as possible, geometric terrain correction was applied on the ALOS-2 data using the range Doppler orthorectification method. The Shuttle Radar Topography Mission (SRTM) data were introduced as 3 arc second (approximately 90-m resolution) digital elevation model (DEM). Then, the images were resampled using bilinear interpolation after the terrain correction. As the last step, an adaptive Lee filter with a window size of 3 \(\times\) 3 [33] was applied to the original polarized SAR images from ALOS-2 to reduce the speckle noise.  
Since the IW mode images of Sentinel-1 include three sub-swaths, the Terrain Observation with Progressive Scan SAR (TOPSAR) deburst technique was used to produce a homogenous image for each polarization. Then, the orbit state vectors of Sentinel, precise to the third polynomial degree, were applied to provide accurate information on satellite position and data velocity. Afterwards, the same geometric terrain correction and speckle filtering methods applied to the ALOS-2 images were used. During geometric correction, the pixel size of the Sentinel-1 data was changed to the same pixel size as for the ALOS-2 polarized images (6.25 m). Finally, the two SAR images were registered with the nearest neighbor resampling type and bilinear interpolation method, where the ALOS-2 image was selected as the master.  
Additionally, radiometric calibration was applied to the optical image to convert the DN value to the Top of Atmosphere (TOA) reflectance. The image was projected onto the WGS84 reference ellipsoid. Then, the 15-m multi-spectral image was obtained using the pan-sharpening process.