Site Harvard Hemlock

Site 305Site Harvard EMS tower

The LAI estimates are impacted by changes in the occlusion effect at the different scales. 

75 m is considered as the appropriate scale due to the layout of the EVI scans. Modeled G vs. G=0.5: more work is needed to define the transition between the

two in intermediate sites.

Virtual Direct Measurement of Leaf Area Index and Above-Ground Biomass Using Echidna® Terrestrial Laser Scanning

Xiaoyuan Yang1, Crystal Schaaf1, Alan Strahler2, Zhan Li2, Zhuosen Wang1, Tian Yao3, Feng Zhao4, Curtis Woodcock2, David Jupp5, Darius Culvenor6, Glenn Newnham6, and Jenny Lovell7

1Department of Environmental, Earth and Ocean Sciences, University of Massachusetts Boston, Boston, MA2Center for Remote Sensing, Department of Earth and Environment, Boston University, Boston, MA 3Remote Sensing Laboratory, Montclair State University, Montclair, NJ

4Department of Geographical Sciences, University of Maryland, College Park, MD 5CSIRO Marine and Atmospheric Research, Canberra, ACT, Australia6CSIRO Land and Water, Melbourne, VIC, Australia 7CSIRO Marine and Atmospheric Research, Hobart, TAS, Australia

Foliage Area Volume Density & Leaf Area Index Three-Dimensional Forest Reconstruction

Voxelization

Voxelization transform s the irregular, unorganized cloud of data points in the 3-D forest reconstruction into volumetric datasets.

Voxel Based LAI & FAVD Estimation

•FAVD Model for point cloud

•The total effective area of objects in volume V

or

•Leaf area index:

Noted: In the case of multiple observations: the average of LAI is used for each voxel

, ,1, ,

, ,app

t gap

rf r

G P r

G-function Leaf reflectance

Apparent reflectance of the point

Probability of gap

, ,, , , ,

, ,app

Vt gap

rVLA r V f r

G P r

( , , )( , , )

( ) ( , , )app

Vt gap

x y zVLA x y z

G P x y z

, , baseLAI LA x y z A

1 22

max,

21 2 cos 1 sint c H HG f f

Horizontal fraction of canopy cover

Site ID Field LAIVoxel based LAI by Diameter

G=0.550m 75m 100m

Hemlock 4.32±0.27 4.95 4.73 3.66 2.68EMS tower 4.67±0.82 5.30 4.86 3.52 2.83

305 2.03±0.50 6.54 *5.55 4.86 2.77

X. Yang, A. Strahler, C. Schaaf, D. Jupp, T. Yao, F. Zhao, Z. Wang, D. Culvenor, G. Newnham, et al., “Three-Dimensional Forest Reconstruction and Structural Parameter Retrievals Using a Ground-Based Full-Waveform Lidar Instrument (Echidna®)”. Remote Sensing of Environment, submitted.(2012)

A new method for retrieval of leaf area index (LAI; m^2) foliage area volume density (FAVD; m^2 LAI/m^3 volume), and wood volume of forest stands uses voxels derived from a three-dimensional point cloud of scattering events observed in registered forest scans using a full-waveform, terrestrial Echidna® lidar scanning at 1064 nm. The voxelization process uses the attributes of scattering events, including the gap probability to the event, its apparent reflectance at one or both laser wavelengths, and the geometric volume associated with the return of the laser pulse, to produce the volumetric dataset. Classification procedures (Yang et al. 2012), based on the shape of the laser pulse and the ratio of apparent reflectance at the two wavelengths are used to separate trunk from foliage scattering events. Leaf angle distribution is accommodated with a simple model based on gap probability with zenith angle as observed in individual scans of the stand. An important advantage of the method is that coarse-scale clumping (between crowns and within crown interiors) is observed directly and does not require parametric correction. For validation, we compare LAI, FAVD, and biomass profiles retrieved directly from the voxelized 3-D forest reconstructions with those observed in airborne and field measurements.

Voxelized 3-D forest reconstructions can be used to validate large-footprint spaceborne and airborne lidar systems, thus facilitating large-area inventories. The enhanced characterization of leaf area and biomass is of interest to both land biogeoscientists who require bulk vegetation biomass measures and to atmospheric biogeoscientists, who require information on surface roughness, photosynthesis, and respiration processes. Moreover, Echidna-style lidars can be deployed to monitor disturbance and deforestation detected by optical sensors, such as MODIS or Landsat, to provide better calibration of the type and nature of change.

Overview

Site Characteristics

While the two instruments detected the top of the canopy pretty well, LVIS sees more upper canopy component while EVI sees more lower canopy component over the same forest area. (Profiles are compared at 75 m plot diameter.)

Site Harvard Hemlock

Site 305Site Harvard EMS tower

Terrestrial (EVI) vs. Airborne (LVIS) Lidar

Future Direction

The Dual-Wavelength Echidna® Lidar (DWEL), the successor instrument to the EVI, emits simultaneous laser pulses at 1064 nm and 1548 nm wavelengths. DWEL scans provide the capability to separate hits of leaves from hits of trunks and branches because of the reduced response of foliage at 1548 nm due to water absorption by leaf cellular contents.