Evaluation of Plant Area Index measurements over crops using

hemispherical images

Sylvie DUTHOIT, Valérie DEMAREZ

CESBIO

Study area

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°

THANK YOU…