SPACE-BASED LIDAR FOR ESTIMATING VEGETATION STRUCTURE

Tropical Dry Forests and Shrublands, also known as "Savannas," cover over 20% of the Earth's land area and represent the third-largest carbon stock after Tropical Rainforest and Moist Forest ecosystems. Savannas contributes to approximately 24% of the global Gross Primary Productivity (GPP). These ecosystems generally have lower Aboveground Biomass Density (AGBD) at levels below 80 Mg/ha. Limited remote sensing studies have focused on the AGBD estimations in savannas since they are characterized by high heterogeneity, short-statured vegetation, which pose a substantial challenge. Models for biomass estimation often rely on sparse field measurements and Airborne Laser Scanning (ALS) data for parameterization, leading to large uncertainties in map products. The vast amount of height and vegetation cover data collected by spaceborne LiDAR missions, especially Global Ecosystem Dynamics Investigation (GEDI) and Ice, Cloud, and land Elevation Satellite-2 (ICESat-2), are expected to significantly improve the accuracy of SAR-based models of AGBD. The study provided the first baseline calibration and validation of spaceborne LiDAR (GEDI and ICESat-2) canopy height and terrain metrics in southern African savannas. This study furthermore developed locally calibrated footprint-level GEDI AGBD products using local field measurements and ALS data. Finally, wall-to-wall AGBD maps were produced by leveraging ALOS PALSAR-1/2 data, with reference data derived from field measurements, ALS, and GEDI. This study also conducted an error propagation analysis to assess the uncertainty of the resultant AGBD products. The AGBD products derived from this research are essential to Monitoring, Reporting and Verification (MRV) and Greenhouse Gas (GHG) emissions mitigation activities under various programs, e.g. Reducing Emissions from Deforestation and Degradation (REDD) +. This research can also make a valuable contribution to the advancement of SAR-based AGBD mapping and monitoring of change in savannas, particularly with upcoming L-band spaceborne SAR missions like NASA/ISRO (NISAR).