Evaluation of Plant Area Index measurements over crops using
hemispherical images
Sylvie DUTHOIT, Valérie DEMAREZ
CESBIO
2004 : Planimetric technique
- Random selection of 10 plants (at least).
- Removing of the totality of the green leaves of each plant.
- Measurement of the mean green leaf area by plant with a scanning planimeter (Li-Cor 3100).
- Estimation of the mean stem area for sunflowers and corn (height and diameter).
Estimation of the mean PAI from the plants density of the field.
DESTRUCTIVE MEASUREMENTS
LMA for each species
Leaf Mass Area for each crop
Sunflowers 2004
y = 0,008x
R2 = 0,9643
0
1
2
3
4
5
0 100 200 300 400 500 600
Leaf area per plant (cm²)
Dry
wei
gh
t p
er p
lan
t (g
)
Soya 2004
y = 0,0051x
R2 = 0,9504
0
2
4
6
8
10
12
0 500 1000 1500 2000
Leaf area per plant (cm²)
Dry
wei
gh
t p
er p
lan
t (g
)
Wheat 2004
0
10
20
30
40
0 100 200 300 400 500
Leaf area per plant (cm²)
Dry
we
igh
t (c
m²)
Corn 2004
0
10
20
30
40
50
0 1000 2000 3000 4000 5000 6000
Leaf surface per plant (cm²)
Dry
we
igh
t p
er
pla
nt(
g)
June,9,2004
June,26,2004
July,6,2004
July,21,2004
August,3,2004
Wheat 2005, in progress…
Gravimetric technique
- 8 50x50cm squares are removed
- Measurement of the green leaf and stem area of a sub-sample
- The totality of the sample is dried at 65°C
-The Leaf Mass Area of the sub-sample is calculated
The PAI of the total 50x50 cm is calculated from the sub-sample LMA.
Test by scanning the totality of the sample for the 2 first measurements
RESULTS
0
1
2
3
45
6
7
8
9
20 70 120 170 220Julian day
PA
I
Corn 2004 Wheat 2004 Soya 2004 Sunflowers 2004 Wheat 2005
Evolution of the PAI during the growing season
HEMISPHERICAL PICTURES
- Transects of 20 images for each date (except for the wheat parcel)
- One picture every 10 meters
- One between the rows, one under the row.
- From above or below the canopy, depending on its height
Corn parcel
Sunflowers parcel
Soybeans parcel
Wheat parcel
Nikon Coolpix 4500Fisheye 21x
CAN_EYE PROCESSING
Optical centerConsidered field of view : 60°
12 images at the same time
Classification process
Mean gap fraction
COMPARISONDestructive PAI measurements -PAI from CAN_eye software
0
1
2
3
4
5
6
7
8
0 1 2 3 4 5 6 7 8
Destructive PAI
Ca
n_
ey
e t
rue
PA
I
Corn Sunflowers Soya Wheat
r² = 0.955
« USER » CONCLUSIONS
Downward-upward looking imagesPrefer upward looking images when possible.
Illumination conditionsClassification easier by completely cloudy sky.
avoid sunny conditions, particularly when taking downward images.
Distance from the canopyFor wheat, comparison between images at 30 cm and 60cm from canopy.
processing at 60 cm gives best results.
Canopy structure Corn : big green leaves easy to classify.
Sunflowers : dry leaves and flowers, more difficult.Soya: low canopy, very dense with planophyl leaves distribution
saturation effect??Wheat: little and thin leaves, problem of the resolution
RESULTS
True PAIMaïs
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
02/06/2004 12/06/2004 22/06/2004 02/07/2004 12/07/2004 22/07/2004 01/08/2004 11/08/2004
PAI destructif PAI vrai Can_eye PAI vrai Can_eye 57.5°
Tournesol
0
0,5
1
1,5
2
2,5
23/5/04 2/6/04 12/6/04 22/6/04 2/7/04 12/7/04 22/7/04 1/8/04
PAI destructif PAI vrai Can_eye PAI vrai Can_eye 57.5°
Soja
0
1
2
3
4
5
6
22/6/04 27/6/04 2/7/04 7/7/04 12/7/04 17/7/04 22/7/04 27/7/04 1/8/04 6/8/04
PAI destructif PAI vrai Can_eye PAI vrai Can_eye 57.5°