Accuracy Assessment of Terrain and Canopy Height Estimates from ICESat-2 and GEDI LIDAR Missions in Temperate and Tropical Forests: Firsr Results

Kurzfassung

Accurate measurements of terrain elevation are crucial for many ecological applications. In this study, we sought to assess new global three-dimensional Earth observation data acquired by the spaceborne LiDAR missions ICESat-2 and GEDI. We conducted our analysis across four land cover classes: bare soil, herbaceous, forest, savanna, and six forest types: temperate broad-leaved, needle-leaved and mixed forests, tropical upland, floodplain and secondary forests. For assessment of terrain elevation estimates from spaceborne LiDAR data we used high resolution airborne data. Our results indicate that both LiDAR missions provide accurate terrain elevation estimates across different forest types with mean error lower than 1 m, except tropical upland forests for both sensors. Here, however, using GEDI alternative algorithms can improve accuracy of terrain elevation estimates. Specific environmental parameters (e.g., terrain slope, canopy height and density) and sensor parameters (e.g., GEDI quality and degrade flags, terrain estimation algorithm; ICESat-2 number of terrain photons, terrain uncertainty) can be applied to improve the accuracy and thus, to select more confident ICESat-2 and GEDI-based terrain estimates. The goodness-of-fit statistics from two spaceborne LiDAR are not directly comparable, since they possess different footprint size (100 x 14 m segment vs. 25 m circle). For instance, there will be much less dense canopies over a 100 m segment than over a 25 m circle. The impact of terrain slope can be also higher for a larger sample. We observed, however, similar trends on impact of terrain slope, canopy density and canopy height. Terrain slope strongly impacts the accuracy of both ICESat-2 and GEDI terrain elevation estimates for forested and non-forested areas. Moreover, dense canopies affect the accuracy of spaceborne LiDAR terrain estimates, while canopy height does not when consider samples over flat terrains. In summary, our study provides analyses of the accuracy and precision of early versions of spaceborne LiDAR products across different vegetation types.