Tree Canopy Size and Density

Assessment with a Laser Scanner

Citrus Research and Education Center

Masoud Salyani and J. Brian Wei

2nd Workshop on

Precision Agriculture for Florida Citrus

January 21, 2004

Citrus grove with dead trees and resets

Spray drift

Ultrasonic sensors

Ultrasonic sensors

Ultrasonic sensors

Photocells

Laser sensor

Laser sensor

CREC Laser system in operation

Scanning system principle

Scan profile

Ground

Window start

α

Li1Li2

Dij

Lij

Lij+1

Hs

D

LG

LLij+1

LLij

Window stop

Ө

132.40

βj

βG

βT

I

II

Sensor

LT

Schematic view of a Distance image

i+1+

ΔW

XL

XR

YB

YT

j

j+1

i

Illustrated in next slide

(1,1)

x

y

Pseudo-color image of a tree

Spatial resolution test

A

HIJK

LM

B

A

HIJK

LMB C D E F G

C

D

E

F

G

A

HIJK

LMB C D E F G

Not continuous

Continuous image lines

Distance image for vertical targets (horizontal resolution)

A

HIJK

LM

B

C

D

E

F

G

Not continuous

Continuous

Distance image for horizontal targets (Vertical resolution)

A

HIJK

LMB C D E F G

WhiteBlack

Signal amplitude image for vertical targets

Ground truth of length measurements in three dimensions

0

200

400

600

w1 w2 w3

Manual measurement

Instrument measurement

0

100

200

300

400

D1 D2 D3

Le

ng

th, c

m.

0

200

400

600

H1 H2 H3

Targets

Std. dev.

Manual vs. laser length measurements

Picture of a test tree

Signal amplitude image

Distance image

Inverted distance image

Smoothing of canopy boundary

Figure 2: Scanning illustration and canopy boundary smoothing

Ground

Lij

Lij+1 LLij+1

LLij

Ө

Sensor

Smoothed canopy

Original canopy

Hs

β

D

Deep gap

Shallow gap

Through hole

Peak-link algorithm

0

50

100

150

200

250

0 50 100 150 200

Distance from tree row plane to canopy, cm

Ve

rtic

al

co

ord

ina

te f

rom

to

p o

f im

ag

e,

pix

el

3rd peak-link

Laser incident point

1st peak-link

Tree row plane

2nd peak-link

Distance image – smoothed by peak-link algorithm

D1a

D2a

Ha

Hb

Hd

Hc

Ground

Level

D2c

D1c

D1b

D2b

Tree

Canopy

Manual Volume Measurement

0

10

20

30

40

50

60

70

80

90

100

D1 L1 L2 L3 M1 M2 M3 H1 H2 H3

Tree

Vo

lum

e, m

3

ManualLaser

Manual- and laser-measured volumes

Std. dev.

Canopy volume at different heights of trees

0

10

20

30

40

50

D1 L1 L2 L3 M1 M2 M3 H1 H2 H3

Tree

Vo

lum

e, m

3

Top 1/3

Middle 1/3

Bottom 1/3

Visual vs. laser-measured densities

0

10

20

30

40

50

60

70

80

90

100

D1 L1 L2 L3 M1 M2 M3 H1 H2 H3

Tree

Fo

lia

ge

de

ns

ity

, %

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Pix

el/

vo

lum

e r

ati

o,

pix

el/

m3

Visual assessment

Laser- Foliage/canopy volume ratio

Laser- Pixel/volume ratio

yB = 1484.3x - 11237

RB2 = 0.74

yA = 0.808x + 10.582

RA2 = 0.96

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Visual density assessment, %

La

ser

me

asu

rem

en

t, %

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Pix

el-

volu

me

ra

tio,

pix

el/m

3

Corr. bet. Visual and laser-measured densities

0

10

20

30

40

50

60

70

80

90

D1 L1 L2 L3 M1 M2 M3 H1 H2 H3

Tree

Fol

iag

e D

ensi

ty, %

South

North

Overall

Foliage density at north and south sides of trees

Std. dev.

Foliage density at different tree heights

0

10

20

30

40

50

60

70

80

90

100

D1 L1 L2 L3 M1 M2 M3 H1 H2 H3

Tree

Fo

liag

e d

ensi

ty, %

Top 1/3Middle 1/3Bottom 1/3

User Interface

Amplitude image of one row

Processed canopy image of the row

Real-time measurements of one row

Real-time run, 1 mph

Real-time run, 3 mph

Thankyou