1. Evaluation of Plant Area Index measurements over crops using hemispherical images
Sylvie DUTHOIT, Valérie DEMAREZ
CESBIO

2. Study area

3. DESTRUCTIVE MEASUREMENTS 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.
LMA for each species

4. Leaf Mass Area for each crop

5. Gravimetric technique
Wheat 2005, in progress…
Gravimetric technique
x50cm 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

6. RESULTS
Evolution of the PAI during the growing season

7. HEMISPHERICAL PICTURES
Nikon Coolpix 4500
Fisheye 21x
- 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

8. Considered field of view : 60°
CAN_EYE PROCESSING
Optical center
Considered field of view : 60°
12 images at the same time
Classification process
Mean gap fraction

9. COMPARISON
Destructive PAI measurements -PAI from CAN_eye software

10. Downward-upward looking images
« USER » CONCLUSIONS
Downward-upward looking images
Prefer upward looking images when possible.
Illumination conditions
Classification easier by completely cloudy sky.
avoid sunny conditions, particularly when taking downward images.
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
Distance from the canopy
For wheat, comparison between images at 30 cm and 60cm from canopy.
processing at 60 cm gives best results.

11. RESULTS
True PAI

12. THANK YOU…