## 2 Materials and Methods
### Datasets  
Thirty plots were selected based on a stratified random sampling and sampled in September 2017. Each plot was defined as a rectangle sized 20 m \(\times\) 20 m, which is the nominal pixel size for most bands of Sentinel-1 and Sentinel-2. The latitude and longitude coordinates of the center of each plot were recorded with a Global Navigation Satellite System (GNSS) device. Trees with a DBH of more than 8 cm were considered and the species, circumference of the tree trunk at breast height (1.3 m above the ground) and height of each specimen were recorded. A total of 1003 trees were sampled (Table 1). Plots containing more than 90% of a single tree species from all the trees recorded were considered as monodominant. It is worth noting that frequently monodominance is frequently defined as \(\geq\)60% of canopy-level trees belonging to the same species with values regularly attaining 80-100% [76]. Nevertheless, in the current study we set a higher threshold (i.e., 90%) as trees with a very small diameter were excluded from field sampling. The remote sensing dataset used in the current study is comprised of the Sentinel-1 and Sentinel-2 satellites, two twin constellation systems from the Copernicus programme [77]. Sentinel-2 is an optical satellite with 13 spectral bands and 290 km swath width supporting primarily land use and land cover applications [78]. Sentinel-1 is the corresponding C-band SAR satellite mission providing Vertical transmit-Horizontal (VH) and Vertical transmit-Vertical (VV) polarizations. The Sentinel-1 and Sentinel-2 satellite constellations have a revisit frequency at the Equator of 3 and 7 days, respectively, and cover the majority of the Earth, making them unprecedented information sources for frequent monitoring of biophysical parameters at a global scale. Satellite data were selected on the basis of the temporal proximity of the image acquisition and the field data and taking into account the quality assessment of the cloud coverage for the optical data over the area of interest. Sentinel-2 includes a ShortWave InfraRed (SWIR) band at 1.375 \(\upmu\)m dedicated to Cirrus clouds and a respective cloud mask is provided with each delivery. However, cloud coverage is spatially inconsistent in tropical areas; for this reason, the overall cloud coverage statistics provided were disregarded during the selection of the appropriate image. Instead, the visual assessment of the cloud coverage over the area of interest was preferred. A cloud-free Sentinel-2B image acquired on 12 August 2017 was selected and downloaded from the Copernicus Open Access Hub. The image was provided at Top Of Atmosphere (TOA) 1-C level. In addition, a Sentinel-1 image acquired on 4 September 2017 was used; the standard high resolution Ground Range Detected (GRD) product selected was sensed in Interferometric Wide swath (IW) acquisition mode in dual VV and VH polarization. A suitable Sentinel-1 image with dual HH and HV polarization for the area of interest was not found in the Copernicus Open Access Hub. It is worth noting that while the Sentinel-1 image fell within the field data collection time window, the Sentinel-2 image was acquired approximately 3 weeks earlier as a consequence of a worse candidate due to local cloud coverage conditions. Nevertheless, considerable AGB growth is not expectable within 23 days, and, moreover, the climatic conditions remained relatively stable during this time period; the climate is characterized as a tropical monsoon climate (Am in the Koppen-Geiger system), with a short dry season from July to September [79] when the rainfall remains relatively low.