## 6 Pan-Tropical AGB Mapping  
The quantification and mapping of changes in spatial distribution and patterns of AGB, in tropics, is a key parameter to estimate carbon uptake and emissions induced by the LCLU change and its impacts on global climate changes [105]. Apart from site-specific or localized AGB estimates using a variety of modelling approaches, efforts have been made to develop pan-tropical or global AGB estimates (Tables 2 and 3) by integrating ground inventories and remote-sensing-based forest products (described in sections above). The first pan-tropical map of live biomass was produced at a 1-km spatial resolution in 2011, by combining extensive filed inventory data from 4079 plots and a variety of remote sensing methods acquired by optical, microwave and LiDAR sensors [156]. The total woody biomass of the tropical vegetation was estimated to store 247 PgC, with 78% contribution of carbon stock from AGB, and the remaining 22% of the carbon stock was attributed to below the canopy biomass of roots. Later, in 2012, another pan-tropical AGB map was produced at a 500 m resolution using a multiscale multi-sensor mapping and calibration approach by combining field inventories, GLAS LiDAR data at 70 m resolution and MODIS multispectral surface reflectance images at a 500 m resolution [105]. Moreover, a carbon density map (MgC ha\({}^{-1}\)) was produced for the improved estimation of carbon emissions from tropical deforestation and degradation [105]. The study showed that 228.7 PgC is stored in the tropical woody vegetation, which was 21% higher than the FAO's estimates in the FRA report of 2010, with a net carbon emission of 1.0 PgC yr\({}^{-1}\) from tropical deforestation during 2000-2010 [105]. Measuring and mapping carbon stock and fluxes in tropical areas is challenging, due to uncertainties in canopy structure and height parameters and the advection effect induced by small topographic variations. Therefore, it is difficult to extrapolate plot-level AGB estimations to pan-tropical areas. Considering the challenges in the pan-tropical biomass estimation and limitation of the two previous studies [105, 156, 162], an updated pan-tropical AGB map (Figure 5) was produced by integrating the existing two pan-tropical biomass maps, along with the harmonization and upscaling of field inventories, and additional reference, consolidation, local AGB estimates, and other covariate datasets [163]. The updated map, estimated AGB carbon stock of 375 Pg dry mass in the tropics, which is 9% and 18% lower than the previous dry mass estimates of 413 Pg [156] and 457 Pg [105]. [PERSON] and [PERSON] [164] has produced recent estimates of the global forest AGB at a 100 m spatial resolution as part of ESA's CCI. The algorithm is primarily based on the two SAR products acquired in 2017--a global mosaic from PLARSAR-2 (onboard ALOS-2) operated by JAXA and another set of SAR data acquired by Sentinel-1 operated by ESA--as well as the LiDAR data from the ICESat. Recently, a new approach is developed to harmonized measures of aboveground vegetation biomass and belowground biomass across the globe at a spatial resolution of 300 m for the year 2010 [165]. [PERSON] et al. [166] assessed pan-tropical biomass maps produced at 500 and 1000 m spatial resolutions, and they found substantial uncertainties when compared with the FRA country-level data and with the 100 m biomass map. They found that both pan-tropical maps have higher biomass estimation when compared with a high-resolution map. Large uncertainties are related to the spatial distribution of biomass and spatial pattern of forest landcover change. Similarly, uncertainties and inaccuracies in measuring AGB and carbon emission by different countries were reported by \"forest reference emission levels and forest reference levels\" FREL/FRL 2020 [167]. Between 2014 and 2016, five out of seven countries who submitted national-level carbon stock have aggregative uncertainties.