Characterizing leaf area index (LAI) and vertical foliage profile (VFP) overthe United States

[摘要] Leaf area index (LAI) and vertical foliage profile (VFP) are among theimportant canopy structural variables. Recent advances in lidar remotesensing technology have demonstrated the capability of accurately mapping LAIand VFP over large areas. The primary objective of this study was to deriveand validate a LAI and VFP product over the contiguous United States (CONUS)using spaceborne waveform lidar data. This product was derived at thefootprint level from the Geoscience Laser Altimeter System (GLAS) using abiophysical model. We validated GLAS-derived LAI and VFP across major forestbiomes using airborne waveform lidar. The comparison results showed that GLASretrievals of total LAI were generally accurate with little bias (r² =  0.67, bias  =  −0.13, RMSE  =  0.75). The derivations of GLASretrievals of VFP within layers were not as accurate overall (r² =  0.36,bias  =  −0.04, RMSE  =  0.26), and these varied as a function ofheight, increasing from understory to overstory – 0 to 5 m layer:r² =  0.04, bias  =  0.09, RMSE  =  0.31; 10 to 15 m layer:r² =  0.53, bias  =  −0.08, RMSE  =  0.22; and 15 to 20 m layer:r² =  0.66, bias  =  −0.05, RMSE  =  0.20. Significantrelationships were also found between GLAS LAI products and differentenvironmental factors, in particular elevation and annual precipitation. Insummary, our results provide a unique insight into vertical canopy structuredistribution across North American ecosystems. This data set is a first steptowards a baseline of canopy structure needed for evaluating climate and landuse induced forest changes at the continental scale in the future, and shouldhelp deepen our understanding of the role of vertical canopy structure interrestrial ecosystem processes across varying scales.

[学科分类] 地球化学与岩石