Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 13, issue 1
Biogeosciences, 13, 239–252, 2016
https://doi.org/10.5194/bg-13-239-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 13, 239–252, 2016
https://doi.org/10.5194/bg-13-239-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 15 Jan 2016

Research article | 15 Jan 2016

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

H. Tang1, S. Ganguly2, G. Zhang2, M. A. Hofton1, R. F. Nelson3, and R. Dubayah1 H. Tang et al.
  • 1Department of Geographical Sciences, University of Maryland, College Park, Maryland, USA
  • 2Bay Area Environmental Research Institute (BAERI) / NASA Ames Research Center, Moffett Field, California, USA
  • 3Biospheric Sciences Branch, Code 618, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

Abstract. 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 (r2 =  0.67, bias  =  −0.13, RMSE  =  0.75). The derivations of GLAS retrievals of VFP within layers were not as accurate overall (r2 =  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: 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. 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.

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This paper provides a unique insight into vertical distribution of leaf area index across North American ecosystems using spaceborne lidar data. This data set of leaf area index and vertical foliage profile can help set up a baseline of canopy structure needed for evaluating climate and land use induced forest changes at continental scale in the future.
This paper provides a unique insight into vertical distribution of leaf area index across North...
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