# Spaceborne LiDAR Systems: Evolution, Capabilities, and Challenges
## 6 Applications and Outcomes from Spaceborne LiDAR Data
### Vegetation and Ecosystem Monitoring  
Data produced by spaceborne LiDARs allow us to observe Earth's vegetation, especially forest structure [154] and biomass. Forest ecosystems have been one of the most extensively studied applications of spaceborne LiDAR. Missions like NASA's GEDI provide detailed vertical profiles of the forest canopy, allowing estimation of canopy height, biomass, and structural complexity. Such data contribute to a better understanding of carbon cycling and biodiversity [154; 155; 156]. An example of studies can include the following. Ref. [157] investigates the effectiveness of European Protected Areas (PAs) in conserving the vertical structural complexity of forests compared to non-protected forests. The study utilizes over 30 million observations from the GEDI mission. The analysis compares various forest structural metrics, such as canopy top height, Foliage Height Diversity (FHD), and Relative Height (RH) metrics (e.g., RH50 and RH25), inside and outside nearly 10,000 PAs. The findings reveal that forests within PAs are generally taller and more vertically complex than those in unprotected areas, highlighting the positive impact of environmental policies. The study underscores the utility of spaceborne LiDAR for large-scale monitoring of forest attributes essential for conservation and restoration efforts. The study in [45] aims to assess the applicability of GEDI data to characterize the structure of mountain forests. Comparison of GEDI data with Airborne Laser Scanning (ALS) data to estimate key forest structural parameters on the plot scale, considering the trade-off between data density and seasonal/phenological mismatches. The impact of topography on the estimation of structural parameters is also evaluated. Additionally, the study investigates whether GEDI's sampling-based approach can capture forest structure variability at the landscape scale, particularly focusing on rare cases. The effectiveness of GEDI data in educating indicators of ecosystem function, such as avalanche protection, carbon storage, and habitat quality, is assessed in two contrasting mountain landscapes in Germany (Berchtesgaden) and Switzerland (Davos). The study finds that the availability of GEDI data varies between the phenological seasons, with a higher availability during the leaf-on season. The agreement between the GEDI and ALS metrics is highest when the data recording dates are closely aligned, with varying levels of agreement between the different metrics. Ref. [158] leverages 2005 data from GLAS aboard ICESat to create a global map of the height of the forest canopy at a spatial resolution of 1 km. Despite the sparse coverage of the LiDAR shots, the researchers modeled the global canopy height (RH100) by correlating the GLAS-derived values with ancillary variables such as forest type, tree cover, elevation, and climatology maps. The model's accuracy was validated with field measurements from 66 FLUXNET sites, showing a conservative error margin due to measurement uncertainty and sub-pixel variability. The study highlights a global latitudinal gradient in canopy height, increasing towards the equator, and identifies coarse forest disturbance patterns. The findings underscore the challenges in mapping tall canopies, particularly in closed broadleaf forests such as the Amazon. Ref. [159] investigates the applicability of GEDI data to characterize tropical forest aboveground biomass (AGB) on the scale required for REDD+ projects. GEDI, a spaceborne LiDAR instrument on the ISS, provides high-confidence measurements to estimate AGB but does not collect data systematically. The study examines the amount of GEDI data needed to reliably assess AGB forest in tropical Africa, specifically in Mai Ndombe province, Democratic Republic of the Congo. Using good quality GEDI footprint-level AGB data for 31 months, the study analyzes 15 test sites with >80% forest cover.