Characterizing leaf area index (LAI) and vertical foliage profile (VFP) over the United States
نویسندگان
چکیده
Leaf area index (LAI) and vertical foliage profile (VFP) are among the important canopy structural variables. Recent advances in lidar remote sensing technology have demonstrated the capability of accurately mapping LAI and VFP over large areas. The primary objective of this study was to derive and validate a LAI and VFP product over the contiguous United States (CONUS) using spaceborne waveform lidar data. This product was derived at the footprint level from the Geoscience Laser Altimeter System (GLAS) using a biophysical model. We validated GLAS-derived LAI and VFP across major forest biomes using airborne waveform lidar. The comparison results showed that GLAS retrievals of total LAI were generally accurate with little bias (r = 0.67, bias=−0.13, RMSE= 0.75). The derivations of GLAS retrievals of VFP within layers were not as accurate overall (r = 0.36, bias=−0.04, RMSE= 0.26), and these varied as a function of height, increasing from understory to overstory – 0 to 5 m layer: r = 0.04, bias= 0.09, RMSE= 0.31; 10 to 15 m layer: r = 0.53, bias=−0.08, RMSE= 0.22; and 15 to 20 m layer: r = 0.66, bias=−0.05, RMSE= 0.20. Significant relationships were also found between GLAS LAI products and different environmental factors, in particular elevation and annual precipitation. In summary, our results provide a unique insight into vertical canopy structure distribution across North American ecosystems. This data set is a first step towards a baseline of canopy structure needed for evaluating climate and land use induced forest changes at the continental scale in the future, and should help deepen our understanding of the role of vertical canopy structure in terrestrial ecosystem processes across varying scales.
منابع مشابه
Characterizing Leaf Area Index (LAI) and Vertical Foliage Profile (VFP)
Characterizing Leaf Area Index (LAI) and Vertical Foliage Profile (VFP) over the United States H. Tang, S. Ganguly, G. Zhang, M. A. Hofton, R. F. Nelson, and R. Dubayah Department of Geographical Sciences, University of Maryland, College Park, Maryland, USA Bay Area Environmental Research Institute (BAERI)/NASA Ames Research Center, Moffett Field, California, USA Biospheric Sciences Branch, Cod...
متن کاملInteractive comment on “Characterizing Leaf Area Index (LAI) and Vertical Foliage Profile (VFP) over the United States” by H. Tang et al
The referee is correct about the bias introduced by seasonality, and a simple average of GLAS LAI over different months supports this hypothesis: 3.02 for May, 3.14 for June, 2.93 for October and 2.22 for November. However, we did not exclude the leaf flushing/senescence periods because we tried to maximize the usage of GLAS shots. The GLAS/ICESat mission was not operated year round but deploye...
متن کاملTropical Forests of Réunion Island Classified from Airborne Full-Waveform LiDAR Measurements
From an unprecedented experiment using airborne measurements performed over the rich forests of Réunion Island, this paper aims to present a methodology for the classification of diverse tropical forest biomes as retrieved from vertical profiles measured using a full-waveform LiDAR. This objective is met through the retrieval of both the canopy height and the Leaf Area Index (LAI), obtained as ...
متن کاملFirst direct landscape-scale measurement of tropical rain forest Leaf Area Index, a key driver of global primary productivity.
Leaf Area Index (leaf area per unit ground area, LAI) is a key driver of forest productivity but has never previously been measured directly at the landscape scale in tropical rain forest (TRF). We used a modular tower and stratified random sampling to harvest all foliage from forest floor to canopy top in 55 vertical transects (4.6 m(2)) across 500 ha of old growth in Costa Rica. Landscape LAI...
متن کامل