## Materials and Methods
### Satellite Datasets
#### 2.2.2 Satellite Image Pre-Processing  
PALSAR-2 images that were used in this study came in Level-1.5 product, which means the range and multilook azimuth compressed data is represented by amplitude data. The range coordinates were also converted from slant range to ground range, and map projection was performed.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Sensor**} & \multirow{2}{*}{**Wavelength**} & **Date of** & \multirow{2}{*}{**Mode/Polarization**} & **No. of** & **Ground** & **Incidence** \\  & & **Acquisition** & & **Scene** & **(m)** & **Angle (*)** \\ \hline \multirow{2}{*}{PALSAR-2} & C-band & Between & & & & \\  & (5.405 GHz) & March and & Fine Beam Dual & & & \\  & (5.405 GHz) & June 2016 & Fine Beam Dual & & & \\ \multirow{2}{*}{Sentinel-1A} & L-band & & & & & \\  & (1.270 GHz) & November & & & & \\ \multirow{2}{*}{Sentinel-1A} & L-band & & & & & \\  & (1.270 GHz) & 2016 & & & & \\ \multirow{2}{*}{Sentinel-1A} & L-band & & & & & \\  & (1.270 GHz) & November & & & & \\ \multirow{2}{*}{Sentinel-1A} & L-band & & & & & \\  & (1.270 GHz) & 2016 & & & & \\ \multirow{2}{*}{Sentinel-1A} & L-band & & & & & \\  & (1.270 GHz) & 2016 & & & & \\ \multirow{2}{*}{Sentinel-1A} & L-band & & & & & \\  & (1.270 GHz) & 2016 & & & & \\ \multirow{2}{*}{Sentinel-1A} & L-band & & & & & \\  & (1.270 GHz) & 2016 & & & & \\  & (1.270 GHz) & 2016 & & & & \\ \multirow{2}{*}{Sentinel-1A} & L-band & & & & & \\  & (1.270 GHz) & 2016 & & & & \\  & (1.270 GHz) & 2016 & & & & \\ \multirow{2}{*}{Sentinel-1A} & L-band & & & & & \\  & (1.270 GHz) & 2016 & & & & \\  & (1.270 GHz) & 2016 & & & & \\  & (1.270 GHz) & 2016 & & & & \\ \multirow{2}{*}{Sentinel-1A} & L-band & & & & & \\  & (1.270 GHz) & 2016 & & & \\  & (1.270 GHz) & 2016 & & & & \\  & (1.  
Level-1 GRD consist of Sentinel-1A products consist of focused SAR data that has been detected, multi-looked and projected to ground range using an Earth ellipsoid model such as WGS84. The ellipsoid projection of the GRD products is corrected using the terrain height specified in the product general annotation. The terrain height used varies in azimuth but is constant in range.  
Ground range coordinates are the slant range coordinates projected onto the ellipsoid of the Earth. Pixel values represent detected magnitude. Phase information is lost. The resulting product has approximately square resolution pixels and square pixel spacing with reduced speckle at a cost of reduced geometric resolution. In addition, the GRD products have thermal noise removed to improve the quality of the detected image.  
Other than these processes, they are two important pre-processing stages, namely, speckle suppression and radiometric terrain correction. Spatial domain Lee Sigma filter with a kernel size of 7 \(\times\) 7 pixels was used to remove speckle effect on the images. Digital Elevation Model (DEM) acquired from SRTM was used to minimize terrain shadowing effect on the images. The presence of this effect on SAR imagery was because the signal strengths were dependent on two variables, which were incidence angle and surface roughness or topography of terrain. If slope is facing the SAR transmitter, the signal will become stronger than the other side of the slope. Semi-empirical method was used for radiometric terrain correction [27] and the processes were performed in ENVI/IDL (Harris Corporation, Melbourne, Australia) following the same approach as found in [PERSON] et al. [28]. This process was necessary to normalize both sides of the slopes and it minimized errors towards the end of AGB prediction.