The Land Water Vegetation Elevation product (ATL08) derived from NASA’s ICESat-2 Photon Counting Lidar mission provides terrain and canopy height estimates at unprecedented fine spatial scales, enabling improved prospects for the assessment of forest structure worldwide. However, there is a great need to validate these data to determine their usability for forest structure studies. The main goal of this study is to assess the usability of the ATL08 product by comparing its estimates with estimates derived from reference airborne lidar data. We compared mean relative (above ground) and mean absolute (above mean sea level) height metrics from 100-m ATL08 segments with corresponding estimates derived from airborne lidar data at selected sites in Sonoma county, California and coastal range in Oregon using regression analysis.
Results/Conclusions
Our preliminary results show that ATL08 absolute mean canopy heights are highly correlated (R2 > 0.9) with estimates from airborne data in both study sites. However, we observed lower correlations (R2 = 0.4 for California, R2 = 0.3 for Oregon) between ATL08 relative canopy heights and aboveground lidar heights. The lack of agreement is likely driven by the high levels of solar background noise and errors in the deriving the ground reference elevation and in classifying points into respective ground and top of canopy classes. Land cover change including tree growth between airborne lidar and ATL08 data acquisition may also have contributed to the lower observed correlations. In both study sites the agreement between ATL08 and airborne lidar estimates significantly improved (R2 > 0.5) after the removal of outlying predictions. Further work is underway to validate percentile metrics from the ATL08 product and test influences such as biome type and data acquisition time on the quality of derived ATL08 estimates. Overall, the ATL08 product shows great promise for assessment of forest resources but will require continued improvement in the photon classification and relative canopy height estimation.