Studying the Impact of the Three Dimensional Canopy Structure on LIDAR Waveforms Evaluated with Field Measurements

Liang Xu, Boston University, bireme@gmail.com (Presenter)
Yuri Knyazikhin, Boston University, jknjazi@bu.edu
Ranga Babu Myneni, Boston University, rmyneni@bu.edu
Alan Strahler, Boston University, alan@bu.edu
Crystal Schaaf, Dept of Geography and Environment, Boston University, schaaf@bu.edu
Alexander Antonarakis, Harvard University, aantonarakis@oeb.harvard.edu
Paul R. Moorcroft, Harvard University, paul_moorcroft@harvard.edu

The three-dimensional structure of a forest – its composition, density, height, crown geometry, within-crown foliage distribution and properties of individual leaves – has a direct impact on the lidar waveform. The pair-correlation function defined as the probability of finding simultaneously phytoelements at two points is the most natural and physically meaningful descriptor of the canopy structure over wide range of scales. The stochastic radiative transfer equations naturally admit this measure and thus provide a powerful means to investigate 3D canopy from space. NASA’s Airborne Laser Vegetation Imaging Sensor (LVIS) and ground based data on canopy structure acquired over 5 sites in New England, California and La Selva (Costa Rica) tropical forest were analyzed to assess the impact of 3D canopy structure on lidar waveform and the ability of stochastic radiative transfer equations to simulate the 3D effects. Our results suggest the pair correlation function is sensitive to horizontal and vertical clumping, crown geometry and spatial distribution of trees. Its use in the stochastic radiative transfer equation allows us to accurately simulate the effects of 3D canopy structure on the lidar waveform. Specifically, we found that (1) attenuation of the waveform occurs at a slower rate than 1D models predict; this may result in an underestimation of foliage profile if 3D effects are ignored; (2) 1D model is unable to match simulated waveform and measured surface reflectance, i.e., an unrealistic high value of surface reflectance needs to be used to simulate ground return of sparse vegetation; (3) spatial distribution of trees has a strong impact on the lidar waveform. Simple analytical models of the pair-correlation function will also be discussed.

Presentation Type:  Poster

Session:  Global Change Impact & Vulnerability   (Tue 11:30 AM)

Associated Project(s): 

• Myneni, Ranga: A Synergistic Study for LIDAR and Passive Optical Remote Sensing of Forest Horizontal Structure in Support of DESDynI Mission ...details
• Myneni, Ranga: Remote Sensing of Forest Canopy Structure Across Multiple Scales from Synergistic Analysis of Lidar, Hyperspectral and Multiangle Data With Time-Dependent Stochastic Radiative Transfer Based Algorithm ...details

Poster Location ID: 295