## Materials and Methods
### Satellite Datasets  
#### 2.2.1 Satellite Images Acquisition  
The satellite datasets that have been used in this study came from two satellites, which are; (i) Advanced Land Observing Satellite 2 (ALOS-2) that carries Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) on-board and (ii) Sentinel-1A that carries C-band imaging SAR sensor. Table 1 summarizes the properties of the data and Figure 2 shows both datasets that have been processed and used in this study.  
ALOS-2 is the successor of the ALOS, but the structure of the new satellite is quite different from its predecessor. ALOS was launched in January 2006 and brought the Phased Array type L-band Synthetic Aperture Radar (PALSAR) on-board. After five years of observations, it stopped transmitting in April 2011. ALOS-2 was then launched on 24 May 2014, which carried the PALSAR-2 sensor. PALSAR-2 is currently operating and producing L-band SAR data, that has similar (with some advancements) characteristics with PALSAR. The data were acquired from Earth Observation Research Center (EORC) under Japan Aerospace Exploration Agency (JAXA). The data was acquired under the Kyoto and Carbon (K&C) Initiative, a research agreement between Forest Research Institute Malaysia (FRIM) and JAXA, whereby FRIM has special permission to access the PALSAR-2 product at all imaging modes and resolutions. JAXA also provides free access of PALSAR-2 mosaic product at 25-meter resolution for public which is available at [[http://www.eorc.jaxa.jp/ALOS/en/PALSAR_fnf/data/index.htm](http://www.eorc.jaxa.jp/ALOS/en/PALSAR_fnf/data/index.htm)]([http://www.eorc.jaxa.jp/ALOS/en/PALSAR_fnf/data/index.htm](http://www.eorc.jaxa.jp/ALOS/en/PALSAR_fnf/data/index.htm)).  
Figure 1: Forest types in Peninsular Malaysia.  
The SENTINEL-1 mission is the European Radar Observatory for the Copernicus joint initiative of the European Commission (EC) and the European Space Agency (ESA). The SENTINEL-1 was launched on 3 April 2014 and its mission operating in four exclusive imaging modes with different resolution (down to 5 m) and coverage (up to 400 km). It provides dual polarization capability, very short revisit times, and rapid product delivery. The Sentine-1A data was acquired in Level-1 Ground Range Detected (GRD) format so that radar cross-section of both distributed and point targets can be easily derived from the data. The data is available at [[https://scihub.copernicus.eu/dhus/#/home](https://scihub.copernicus.eu/dhus/#/home)]([https://scihub.copernicus.eu/dhus/#/home](https://scihub.copernicus.eu/dhus/#/home)) and free to download.  
Another satellite data that was used in this study was the digital elevation model acquired from the Shuttle Radar Topography Mission (SRTM). This data was used to classify the forest into specified elevation categories, according to the type of forests. It was also used for radiometric terrain correction on both PALSAR-2 and Sentinel-1A images. These data are available at the US Geological Survey's EROS Data Center for download at [[http://strtm.usgs.gov/index.html](http://strtm.usgs.gov/index.html)]([http://strtm.usgs.gov/index.html](http://strtm.usgs.gov/index.html)).