In: Bretar F, Pierrot-Deseilligny M, Vosselman G (Eds) Laser scanning 2009, IAPRS, Vol. XXXVIII, Part 3/W8 – Paris, France, September 1-2, 2009
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ESTIMATING VERTICAL LEAF AREA DENSITY PROFILES OF TREE CANOPIESUSING THREE-DIMENSIONAL PORTABLE LIDAR IMAGING

F. Hosoi, K.Omasa

Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku,
Tokyo 113-8657, Japan- aomasa@mail.ecc.u-tokyo.ac.jp
KEY WORDS: Broad leaf, Canopy, Leaf area density, Lidar, Point cloud, 3D, Voxel
ABSTRACT:In this paper, a new method for estimation of vertical leaf area density (LAD) profile of tree canopy using portable scanning lidar is
proposed. In this method, which we refer to as the voxel-based canopy profiling (VCP) method, several measurement points
surrounding the canopy and optimally inclined laser beams are adopted to facilitate full laser beam illumination of whole canopy up
to the internal. After the scanning, each data obtained from each measurement point are co-registered and the 3-D information isreproduced as the voxel attributes in the 3-D voxel array. Based on the voxel attributes, contact frequency of laser beams on leaves
is computed and LAD in each horizontal layer is obtained. In addition, influence of non-photosynthetic tissues and leaf inclination
angle on the LAD estimation are corrected. Using the method, good agreement between estimated and actual LAD was obtained in
an individual tree of Camellia sasanqua. Next, the method was applied to broad leaved woody canopy of Japanese zelkova (Zelkova
serrata (Thunb.) Makino). In the experiment, LAD profiles had different accuracy depending on each quadrat established on themeasurement plot and on the laser incident angles. From the results, it was shown that the number of laser beam incidences N andG(c) (the mean projection of a unit leaf area on a plane perpendicular to the direction of the laser beam) are the factors to influence
the accuracy of LAD estimation.
assumption that the foliage distribution is random, which leads
to the errors when the foliage distribution is nonrandom.

1. INTRODUCTION
The plant canopy plays important functional roles in cycling ofmaterials and energy through photosynthesis and transpiration,
maintaining plant microclimates, and providing habitats forvarious species. Determining the vertical structure of the
canopy is thus very important because the three-dimensional(3D) composition of the canopy helps to sustain thosefunctional roles. Researchers often represent the vertical foliage
structure using the leaf area density (LAD) in each horizontal
layer, where LAD is defined as the total one-sided leaf area perunit of layer volume. The leaf area index (LAI), which isdefined as the leaf area per unit of ground area covered by the
projected area of the crown, is then calculated by verticallyintegrating the LAD profile data.

Recently, lidar (light detection and ranging) has been applied to
canopy measurements (Omasa et al., 2000, 2003, 2007; Hyyppä
et al, 2001; Lefsky et al., 2002; Popescu et al., 2003; Næsset etal., 2004; Hosoi and Omasa, 2006, 2007, 2009). Portableground-based scanning lidar has been utilized to obtain plantstructural properties such as canopy height, above groundbiomass (Radtke and Bolstad, 2001; Omasa et al., 2007).
Portable scanning lidar has several beneficial features for LAD
and LAI measurements. For instance, it is nondestructive and,because it is an active sensor, measurements are not affected by
the light conditions in the field. The high ranging accuracy andfine resolution allow to capturing detailed structural informationof a canopy. In addition, it can record many 3-D data for a
canopy quickly and automatically as 3-D point-cloud data. Thus,
this technology promises to overcome the shortcomings of theconventional means of measuring LAD profile of the canopy.

Although there are several ways to measure LAD and LAI,
these measurements remain difficult. Stratified clipping of
biomass samples is one direct measurement method. However,its application in the field is limited because of its destructive
and laborious nature. Indirect methods have thus become apopular alternative. The first indirect method that wasdeveloped is the point-quadrat method (Warren-Wilson, 1960),
in which a probe with a sharp point is inserted into the canopy
at a known inclination and azimuth angle, and the number oftimes the point contacts leaves or stems is counted. LAD and
LAI can then be estimated by calculating the contact frequency.
However, this method is also very laborious (Norman andCampbell, 1989). Another indirect method, the gap-fraction
method, is widely applied in field surveys and uses
commercially available tools such as cameras with a fish-eyelens and optical sensors (e.g., the LI-COR LAI-2000 Plant
Canopy Analyzer; Norman and Campbell, 1989). This method
allows automatic estimation of LAI or LAD without destructionof the plants and is less laborious. However, it depends on theBased on the features, we developed a practical method for
accurate LAD estimation of a canopy using portable scanninglidars, which we refer to as the voxel-based canopy profiling(VCP) method. In this paper, the methodology and theapplications to an individual tree and broad-leaved canopy arepresented.
2. METHODS
2.1 3-D data acquisition and registration
In the VCP-method, several measurement points surrounding
the canopy and optimally inclined laser beams are adopted. Thissetting facilitates full laser beam illumination of whole canopy
up to the internal (Fig.1(a)). The measurements offer accurate152

In: Bretar F, Pierrot-Deseilligny M, Vosselman G (Eds) Laser scanning 2009, IAPRS, Vol. XXXVIII, Part 3/W8 – Paris, France, September 1-2, 2009
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that are assigned neither attribute value are omitted from thefollowing LAD computation.

and precise 3-D point cloud images of whole canopy. The
complete data set is composed of several point cloud data, one
obtained from each of the several measurement positions. These
data with their individual coordinate systems are registered intoa single-point cloud data set with a common coordinate system
by using the iterative closest point algorithm (Besl and McKay,
1992).
(a)
Laser
beam

Target

k

Lidar

(b)
Δθ

θC

Trace oflaser beamZij
Voxel array

Lidar position

Lidar position

Intercepted (Attribute value = 1)
Passed (Attribute value = 2)
Not reached by any laser beams

Figure 1: Schematic illustrations of lidar measurements (thecase in an individual tree).(a): Typical lidar positions around atarget tree. (b): Laser beam inclination represented by thecentral zenith angle of laser beam (θc) and the zenith scan angle(Δθ).

Figure 2: Schematic illustration of assignment of voxel
attributes (Lidar positions were placed in the corners for better
visualization of laser beam traces).

2.2 Removal of non-photosynthetic tissues

2.4 LAD computation

In addition to the leaved canopy measurement, the leaflesscanopy is also measured and the data are co-registered by thesimilar ways as above described. Non-photosynthetic tissues
such as trunks and branches are excluded by subtracting theleafless image from the leaved one.

Based on the attribute values, LAD is computed in eachhorizontal layer of the canopy using the following equation:
LAD(h, H ) (2)

where  is the zenith angle of a laser beam, H is the horizontal
layer thickness, and mh and mh+H are the voxel coordinates on
the vertical axis equivalent to height h and h+H in orthogonal
coordinates (h = k × mh). nI(k) and nP(k) are the numbers ofvoxels with the attribute values of 1 and 2 in the kth horizontal
layer of the voxel array, respectively. Thus, nI(k) + nP(k)represent the total number of incident laser beams that reach thekth layer and nI(k)/(nI(k) + nP(k)) represents contact frequencyof laser beams on the canopy. G() is the mean projection of aunit leaf area on a plane perpendicular to the direction of thelaser beam at  (Norman and Campbell, 1989). The termcos()[G()]-1 is a correction factor for the influence of leaf
inclination angle and laser beam direction. Eq.(2) is analogous
to the equation of radiation transfer through canopy in the caseof neglecting the scattering term (Ross, 1981). nI(k) + nP(k) andnI(k) in Eq.(2) correspond to the radiation intensity and theattenuation of the radiation intensity in the radiation transfer
equation. cos()[G()]-1 is determined using the distribution ofleaf inclination angles. Also, constant value of 1.1 can bechosen for cos()[G()]-1 in the case of the laser beam angle of
57.5º, at which the value can be considered nearly independentof leaf inclination (Warren-Wilson, 1960).

2.3 Voxelization
A voxel is defined as a volume element in a 3D array. All
points within the registered data are converted into voxel
coordinates by the following equations.
 Y  Ymin  X  X min   1i  Int   1 j  Int i , j  ,n I (k )cos θ 1 mh  H
G (θ) H k  mh n I (k )  n P ( k ) Z  Z min k  Int  1(1) k 

where (i, j, k) represents the voxel’s coordinates within thevoxel array, Int is a function that rounds off the result of thecalculation to the nearest integer, (X, Y, Z) represents the point
coordinates of the registered lidar data, (Xmin, Ymin, Zmin)
represent the minimum values of (X, Y, Z) and (i, j, k)represent the voxel element size. The voxel element size isdetermined, dependeding on the range and scan resolution of
the lidar (e.g., I = j = k =1mm, in the case of highresolution lidar with the resolution of about 1mm). Voxels
corresponding to coordinates converted from points within theregistered data are assigned 1 as the attribute value. A voxel
with the attribute value of 1 represents a voxel in which atleast one laser beam is intercepted by leaves. All laser beams
emitted from the lidar positions are then traced within thevoxel array in accordance with the actual laser beam angles(see Fig.2). If voxels that do not have an attribute value of 1
are intersected by at least one laser beam trace, the voxel was
assigned 2 as the attribute value. A voxel with an attributevalue of 2 therefore represents a voxel through which one ormore laser beams passed without touching a leaf. Other voxels

3. EXPERIMENTS
3.1 LAD estimation for an individual tree
At the first step, we tested our VCP-method on an individual
tree of Camellia sasanqua with the height of 1.60m (Hosoi andOmasa, 2006). A fine-resolution portable scanning lidar (TDS130L 3D laser scanner, Pulstec Industrial Co., Ltd), that

153

In: Bretar F, Pierrot-Deseilligny M, Vosselman G (Eds) Laser scanning 2009, IAPRS, Vol. XXXVIII, Part 3/W8 – Paris, France, September 1-2, 2009
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calculates distances based on trigonometry, was used for themeasurement. The range accuracy was about 2 mm, and thescan resolution was about 1 mm. A rotating mount run by abuilt-in stepping motor and a galvano-mirror within the lidar
head facilitated horizontal and vertical scanning by the
instrument. Four azimuth symmetrical lidar positions were set
around the specimen (see Fig.1(a)) and 3-D point cloud data ineach position were recorded. Several central zenith angles oflaser beams (the definition is in Fig.1(b) ) from 37.5 to 180 ºwere tried to know the optimum angle. After the lidar
measurements, voxelization was conducted with the voxel sizeof 1 mm  1 mm  1 mm and LAD was computed. For
obtaining validation data, actual LAD and LAI values in eachhorizontal layer of the specimen were measured by stratified
clipping after the lidar measurements.

was near to the particular angle of 57.5 º above described , andthus the constant value of 1.1 could be given for the correction
factor of cos()[G()]-1 without using leaf inclination angle data.
The optimum angle could have a different value depending on
canopy structure. In the case of the optimum angle different
from the particular angle of 57.5 º, leaf inclination angle data isrequired for the LAD computation.

Figure 3 shows the co-registered 3-D point cloud lidar image.
As shown in the image, the whole canopy was reproduced
precisely at the individual leaf scale. The best result of LAD
estimation was obtained at the central zenith angle of laser
beam of 57.8 º as shown in Fig.4. Good agreement between theestimate and the actual was observed in the result with the mean
absolute percent error (MAPE) of 17.4%.

The experiment was conducted in a mixed plantation in Ibaraki
Prefecture, 40 km northeast of central Metropolitan Tokyo,
Japan. The topography was nearly flat. A 4  8-m measurement
plot was established at the site (Fig. 5 (a)), and the Japanesezelkova canopy within the plot was used for the experiment.
The plot was divided into eight 2  2-m quadrats (Fig. 5 (b))
and each vertical region within each of the quadrats was divided
into 16 cells (each 2  2  0.5 m) between heights of 5 to 13 m
above the ground, as shown in Fig. 6. The entire canopy within
the measurement plot was thus divided into 128 cells.

3.2 LAD estimation for broad-leaved woody canopy

(b)

(a)
Side A

1
1 Side A2m

22m

At the next step, the VCP-method was applied to broad-leaved
woody canopy. In the experiment, the LAD estimates were firstcompared with actual values to validate the approach. The
factors that contributed to the accuracy of the estimates werethen investigated (Hosoi and Omasa, 2007).

2

1-1

2-1

1-2

2-2

1-3

2-3

1-4

2-4

3

3

Y

Side B

X

10 m
1

1
Side B2

2

3

3

Figure 5: Study area. (a):Aerial photograph (b): A measurement
plot established beneath the zelkova canopy. Arrows in (b)show the directions in which lidar scanning was performed(modified from Hosoi and Omasa, 2007).
2m

Cell reference number= (l,m,n)Figure 3: Co-registered 3-D point cloud lidar image of Camellia
sasanqua. Each color (R,G,B,Y) represents data obtained fromeach measurement positions.

0.5 m

2m
Cell

1.6
1.4

MAPE=17.4%

Height (m)

1.2

13 m

1.0
0.8

Z

0.6
0.4

5m
Side A
1-1
2-1
1-2
2-2
1-3
2-3
8m
1-4
2-4
4m
Quadrats
A
Side B

m

θc

0.2
0.0
0.0

2.0

4.0

6.0
8.0
LAD (m2 m-3)

10.0

12.0

Beam
direction
Z

Figure 4: Comparison of LAD profiles for C. sasanqua between
the lidar-derived estimates (white square) and actual values(black square). MAPE=mean absolute percent error (Hosoi andOmasa, 2006).
The corresponding LAI absolute error was 0.7 %. In addition,
the optimum angle of 57.8 º was beneficial because the value

Y
X

Lidar

Figure 6: Illustration of the cells established within themeasurement plot. θc: the central zenith angle of laser beam(modified from Hosoi and Omasa, 2007).

154

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tissues and understory were excluded by extracting
corresponding points between the 3D lidar data in the leaflesscondition and the one in the leafy condition. Then, voxelization
process was applied in each angle data and LAD in each cellwithin the measurement plot was computed using following
equation.

To measure the leaf inclination angle, the canopy within themeasurement plot was scanned by the same portable highresolution scanning lidar as used in section 3.1. Each leaf wasdistinguishable from the acquired 3D point cloud image
because of the fine resolution (see Fig.7). After randomly
selecting 200 leaves in the image, each leaf was manually
extracted and approximated as a plane and normals to theplanes were estimated. The distribution of leaf inclination
angles was derived from the angles of these normals withrespect to the zenith (see Fig.8).

LADlmn cos lmn 1 mh  HnI ( k ).
G ( lmn ) H k  mh nI ( k )  nP (k )(3)where (l, m, n) represents the cell reference number, lmn is themean zenith angle for all laser beam incidences within a cell,H is the vertical thickness of a cell (= 0.5 m). Other
parameters are same in Eq.(2). This equation is modification ofEq.(2) for LAD computation of each cell. The correction factorcos(lmn)[G(lmn)]-1 was calculated from the leaf inclination
angle distribution obtained by high-resolution lidar describedabove (Fig. 8 ).
Figure 9 shows 3D lidar images of the zelkova canopy after
registration of the images. Trees in the measurement plot wereextracted as shown in Figure 9(b-1) from the overall image
shown in Figure 9 (a), and then the non photosynthetic tissues,
including undergrowth (Fig. 9 (b-2)) and the leaves (Fig.9(b-3))
were separated. Each tissue was clearly distinguishable becauseof the fine resolution of the images.

Figure 7: Close-up view of the 3-D point cloud image ofJapanese zelkova canopy taken by high-resolution portablescanning lidar.

(a)

(b)
1

0.18
0.16

Proportion

0.14

2

Mean : 18.6°
S.D. : 12.7°

0.12
0.10

3

A-1

0.08
A-3

0.06
0.04

Figure 9: Co-registered 3-D point cloud lidar images of theJapanese zelkova canopy at this site. (a): A section of the
canopy. The area enclosed by the white broken line corresponds
to the measurement plot. (b) : Separation of the image into its
components. (1): Trees in the measurement plot. (2):Separationof non-photosynthetic tissues including undergrowth. (3)Separation of leaves (Hosoi and Omasa, 2007).

0.02
0.00
5

15

25

35

45

55

65

75

A-2

85

Leaf inclination angle (degree)

Figure 8: Distribution of leaf inclination angles in Japanesezelkova canopy derived from a high-resolution portablescanning lidar image (Fig.7) (Hosoi and Omasa, 2007).

The lidar-derived LAD profiles were compared with the actual
stratified clipping values. Figure 10 shows the examples of the
LAD profiles. The estimates for quadrat 1-1 (Fig. 10(a)), which
was close to the lidar position on side A (see Fig.5(b)), showed
good agreement with the actual values at all central zenith
angles, while the LAD estimates at quadrat 2-3 underestimatedthe actual values at greater heights, except at a central angle of
90.0º (Fig. 10 (b)); this quadrat was in the middle of themeasurement plot. The same tendency was observed in theother quadrats; that is, the closer the quadrats were to the lidar
positions, the smaller the underestimation of the actual LAD
value, except at the 90.0º central angle. The mean root meansquare errors (RMSEs) of the LAD estimates for each quadrat
were 0.50, 0.64, 0.78, and 0.44 m2 m-3 at central zenith anglesof 47.2, 57.8, 71.3, and 90.0º, respectively. The mean absolute
errors of LAI for each quadrat were 21, 37, 57, and 12.7% atangles of 47.2, 57.8, 71.3, and 90.0°, respectively. More laser
beams could reach the quadrats close to the lidar positions,compared with the ones in the middle of the measurement plot

Another type of portable scanning lidar (LPM-25HA, RIEGL,
Austria) was used for the application of the VCP method. The
portable lidar was able to obtain the distance to the surface ofan object between 2 and 60 m from the sensor by measuring theelapsed time between the emitted and returned laser pulses (the“time of flight” method). The lidar had an accuracy of ± 8 mm
when computing the range of each sample point. The Japanesezelkova canopy within the measurement plot was scanned by
the lidar from several ground positions (see Fig. 5 (b)) in
August 2005. The central zenith angles of the laser beams c(Fig. 6) was 47.2º, 57.8º, and 71.3º at each measurement
position. The canopy was also measured from positions 10 m
above the ground using a cherry picker. The central zenith
angle of the laser beams was 90.0º (i.e., horizontal direction).
After the measurements during the leafy condition in August
2005, the same canopy was measured from the ground in
February 2006, during the leafless condition. After theregistration in each of the lidar-data sets, non-photosynthetic155

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because path length of the laser beam was shorter at the former
quadrats than the latter ones

A(a)

8.0
2

-3

RMSE ( m m )θθCm = 47.2° : 0.41
57.8° : 0.36
71.3° : 0.45
90.0° : 0.29

4.0
0.00
1.00
B(b)
12.0

2.00

3.00

4.00

57.8°
71.3°
90.0°

10.0
8.0

2

0.0 10-3

RMSE ( m m )57.8° : 0.95
71.3° : 1.05
90.0° : 0.24

1.00

2.00

3.00
2

4.00

LAD (m m )RMSE of LAD ( m2 m-3 )Figure 10: Comparison of LAD profiles in two quadrats
between the lidar-derived estimates with different central zenith
angles (θc) and the actual value. (a) Quadrat 1-1 and (b) quadrat
2-3 (Hosoi and Omasa, 2007).
This would have caused the difference in LAD estimation
accuracy among quadrats. The relationship between the LAD
estimation accuracy and the number of incident laser beams (N)is shown in Fig. 11, in which larger N offers less RMSE of
LAD for all zenith angles. In addition, it was observed that theslope of the regression lines in Fig.11 increases as the central
zenith angle increases. In particular, the rate of decrease of
RMSE with increasing N is higher at the 90.0° angle than at theother angles. This means that the 90.0° angle offers moreaccurate estimates than the other angles when the value of N
exceeds a certain value, i.e., N > 0.3  104 incidences m-3,
estimated from the intersection points of the regression lines inFig. 11(a) to (d). This explains the better LAD estimates at the
90.0° angle then the other angles because N exceeded 0.3  104
incidences m-3 at most of the cells.

RMSE = 5.721 N -0.257

0.1

B
(b)

1

10

100

RMSE = 8.343 N -0.294
R 2 = 0.843

1.0 1

0.1

1

10

100

C
(c)
RMSE = 18.885 N

m )RMSE of LAD (m2 2m-3-3)

0.10.110100.01-0.3722

R = 0.870

RMSE of LAD ( m

Fig.7

11

0.10.110100.01-3

RMSE of LAD ( m 2m -3)

2

The relationships in Figure 11 were fitted well using a powerfunction:
RMSE  aN(a)

R 2 = 0.903

0.10.110.0100.01

5.00

-3

b

A

1.0 1

θCm = 47.2° : 0.66

6.0
4.0
0.00

5.00

ActualθCm = 47.2°

LAD (m2/m3)

2
RMSE
ofLAD
LAD( (mm-3-3))RMSE of
m 2m

6.0

(5)

From Eqs. (4) and (5), the RMSE at each central zenith angle
was expressed as a common function of N and G(c). Here, apossible reason why G(c) is one of factors to affect LAD
estimation accuracy is the presence of obstructed leaves. In thiscontext, “obstructed” refers to leaves that the laser beams
cannot reach as a result of obstruction by other leaves. The
presence of these leaves causes an error in LAD estimation, andthe degree of obstruction would differ among the central zenith
angles. The degree of the obstruction might be assessed byprojection of leaf area on a plane perpendicular to the directionof the laser beam. The mean is G(c), and thus G(c) would
affect the estimation accuracy.

RMSE of LAD (m2m-3)

Height (m)10.0Height (m)a  22.484 lnG(θ c )  5.808 , b  0.183 lnG (θ c )  0.171

ActualθCm = 47.2°
57.8°
71.3°
90.0°

RMSE of LAD (m m )12.0

relationships could be expressed as functions of G(c) as
follows:(4)

This function is characterized by the coefficient a and thescaling exponent b. Figure 11 indicates that a increased and b
decreased as the central zenith angle increased. We
hypothesized that the change in a and b for each central zenith
angle relates to the change in G(c) that accompanies theincrease in the central zenith angle. Then, we calculated G(c)in each central zenith angle by using leaf inclination angle
distribution data and related the result to the corresponding
values of a and b. As shown in Figure 12(a) for coefficient aand Figure 12(b) for the scaling exponent b, the resulting

0.1

4

1

-2

Np ( ×10 shots m )

10

100

Number of laser beam incidences, N
D
(d)
4
-3

(×10 m )RMSE = 30.569 N -0.464
R 2 = 0.763

11

0.10.1

0.01

0.1
1
10
N ( ×10 4 shots m-2 )Number ofp laser beam incidences, N

100(×10 4 m-3)

Figure 11: Relationships between the root-mean-square error(RMSE) of the LAD estimates and the number of laser beamincidences in each cell (N). The central zenith angles are (a)47.2º, (b) 57.8, (c) 71.3º, and (d) 90.0º. Error bars are standard
deviations (Hosoi and Omasa, 2007).

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Hosoi, F., Omasa, K., 2007. Factors contributing to accuracy inthe estimation of the woody canopy leaf-area-density profile
using 3D portable lidar imaging. Journal of Experimental
Botany, 58 (12), pp.3464-3473.

40.00

A
(a)

a = -22.484Ln[G (θCm))] - 5.808
2

R = 0.992

Coefficient, a

30.00

20.00
10.00

0.00
0.000.10
Scaling exponent, b

Hosoi, F., and Omasa, K., 2009. Estimating vertical plant area
density profile and growth parameters of a wheat canopy at
different growth stages using three-dimensional portable lidar
imaging. ISRPS Journal of Photogrammetry and Remote
Sensing, 64 (2), pp.151-158.

-0.10

0.20

B
(b)

0.50

1.00

Hyyppä, J., Kelle, O., Lehikoinen, M., Inkinen, M., 2001. A
segmentation-based method to retrieve stem volume estimatesfrom 3-D tree height models produced by laser scanners. IEEE
Transactions on Geoscience and Remote Sensing, 39 (5),pp.969-975.

G(θ)
b = 0.183
Ln [G (θ(θmC))] - 0.171
R 2 = 0.999

-0.20
-0.30

Lefsky, M.A., Cohen, W.B., Parker, G.G., Harding, D.J., 2002.
Lidar remote sensing for ecosystem studies. Bioscience 52 (1),19-30.

-0.40
-0.50
0.10

0.20

0.50

1.00

Næsset, E., Gobakken, T., Holmgren, J., Hyyppä, H., Hyyppä,J., Maltamo, M., Nilsson, M., Olsson, H., Persson, Å.,
Söderman, U., 2004. Laser scanning of forest resources: theNordic experience. Scandinavian Journal of Forest Research,
19 (6), pp.482-499.

G (θm
C))

Figure 12: Relationship between the mean projection of a unit
leaf area on a plane perpendicular to the direction of the laser
beam at c (G[c]) and the parameters a and b in Eq. (5). (a)G(c) vs. coefficient a. (b) G(c) vs. scaling exponent b. crepresents the central zenith angle (Hosoi and Omasa, 2007).

Norman, J.M., Campbell, G.S., 1989. Canopy structure. In:
Pearcy, R.W., Ehleringer, J., Mooney, H.A., Rundel, P.W.
(Eds.). Plant physiological ecology: field methods andinstrumentation. Chapman and Hall, London, pp.301-325.

4. CONCLUSIONSThe VCP method for accurate estimation of LAD wasdemonstrated using portable scanning lidars. The essential
points of the method are: (1) determining measurement
positions that surround a target tree (2) Optimizing laser beamincident angle (3) Voxelization of obtained lidar data andcomputation contact frequency of laser beams on leaves basedon the attributes of voxels (4) Correction of non-photosynthetic
tissues and leaf inclination angle. Based on the method, good
agreement between estimated and actual LAD was obtained in
the individual tree. The method was also applied to the canopyof broad leaved trees. In the experiment, estimated LAD
profiles had different accuracy depending on each quadrat
established on the measurement plot and on the laser incident
angles. From the results, it was shown that the number of laser
beam incidences N and G(c) (the mean projection of a unit leaf
area on a plane perpendicular to the direction of the laser beam)
are the factors to influence the accuracy of LAD estimation. By
considering these factors in the lidar measurements, moreaccurate LAD estimates can be obtained. In the future, moreworks should be conducted for more species, in particularconiferous species or crops, to well take advantage of thepresent method.

Omasa, K., Akiyama, Y., Ishigami, Y., Yoshimi, K., 2000. 3-D
remote sensing of woody canopy heights using a scanninghelicopter-borne lidar system with high spatial resolution.
Journal of Remote Sensing Society of Japan, 20 (4), pp.394-406.
Omasa, K., Hosoi, F., Konishi, A., 2007. 3D lidar imaging fordetecting and understanding plant responses and canopy
structure. Journal of Experimental Botany, 58 (4), pp.881-898.
Omasa, K., Qiu, G.Y., Watanuki, K., Yoshimi, K., Akiyama, Y.,
2003.Accurate estimation of forest carbon stocks by 3-D remotesensing of individual trees. Environmental Science &Technology, 37 (6), pp.1198–1201.
Popescu, S.C., Wynne, R.H., Nelson, R.F., 2003. Measuring
individual tree crown diameter with lidar and assessing its
influence on estimating forest volume and biomass. Canadian
Journal of Remote Sensing, 29(5), pp. 564–577.
Radtke, P.J., Bolstad, P.V., 2001. Laser point-quadrat samplingfor estimating foliage-height profiles in broad-leaved forests.
Canadian Journal of Forest Research, 31 (3), pp.410-418.
Ross, J., 1981. The radiation regime and architecture of plant
stands. Dr. W. Junk, The Hague, Netherlands.

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Warren-Wilson, J., 1960. Inclined point quadrats. New
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Hosoi, F., Omasa, K., 2006. Voxel-based 3-D modeling ofindividual trees for estimating leaf area density using highresolution portable scanning lidar. IEEE Transactions on
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