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CEOS/LPV Phenology workshop Dublin
Autonomous ground systems for phenology monitoring: PAR@METER &
PASTiS57
F. Baret, O. Marloie, J.F. Hanocq, B. de Solan, D. Guyon, A. Ducoussou
1/15
CEOS/LPV Phenology workshop Dublin 2
Introduction
• Need for continuous monitoring of foliage development and senescence from ground for:– Phenology modeling– satellite products validation and calibration, including phenology products– Phenotyping tree species
• If possible accessing GAI• LAI: green leaf area (one sided) per unit horizontal ground area• GAI: half the developed area of the convex hull wrapping green vegetation elements
per unit ground area• PAI: half the developed area of the convex hull wrapping vegetation (including non
green) elements per unit ground area
• Based on light transmittance measurements• Need low cost units for better spatial sampling
CEOS/LPV Phenology workshop Dublin 3
The sensors
Criterions Hemispherical PAR
sensors
Directional blue photodiode
sensorsPAI estimates Yes Yes
PAR measurement Yes No
Albedo measurements Yes No
Sensitivity to illumination conditions Yes (sun position, diffuse fraction)
No
Sensitivity to leaf clumping (for PAI estimates) Yes restricted
Spatial sampling Larger (±90°) Restricted (±20°)
Cost 50€ 25€
The recording systems
Wifi network Independent units
Autonomy 1 month (master) 3 months
Ease for data recording +++ +
Realibility + +++
Installation + +++
Synchronization with irradiance meas. +++ ++
Maximum distance with irradiance meas. 400m 1-5 kms
Internet conection Yes No
Cost per recording unit 150€ (for 4 sensors) 100€ (for 6 sensors)
Cost for ESU sampling (12 sensors) 1000€ 500€
CEOS/LPV Phenology workshop Dublin 4
CEOS/LPV Phenology workshop Dublin 5
PAR@METER
• Better suited for agriculture
Incident
Transmited
Albedo
Slave
Master
Absolute calibration based on AERONET measurements
6/
6S
Absolute calibration needed for diffuse fraction estimation
7/
Estimates of the diffuse fraction from irradiance measurements
based on 6S model simulations
y = 0.8636x + 0.0466
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
Diffuse fraction
6s e
stim
atio
n
PARi
Date, Hour
exo-atmosphéricradiation
NNT(6S)
Less accurate when partially cloudy sky
PAI estimation
8/
TransmittancePARt/PARi
Diffuse fraction
Hemispherical extinction coefficient
Directionnal extinctioncoefficient
Adjusting ALA and PAI over a temporal window of few days
PAIALAKPAIhALAK efef ),(),( 1
prior
n
JJ 2
1
The Poisson model is currently used under randomly distributed vegetation elementsThe radiative transfer model may be refined for specific vegetation types
CEOS/LPV Phenology workshop Dublin 9
Some results
1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.60
1
2
3
4
PAI par@meter 03/06
De
stru
ctiv
e G
AI
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
20 30 40 50 60 70
Sun zenith angle (°)
Tran
smitt
ance
/Diff
use
frac
tion
Diffuse fraction
3D canopy simulations
Actual measurements
Poisson model
Wheat at flowering
CEOS/LPV Phenology workshop Dublin 10
Additional results
0
0.2
0.4
0.6
0.8
1
40 60 80 100 120 140 160 180
Time (Julian day)
PA
R b
alan
ce c
ompo
nent
s
TransmittanceReflectanceAbsorptance
0
1
2
3
4
5
6
7
100 150 200 250 300
Time (Julian day)
LA
I
PAR balance over Wheat crop LAI dynamics over maize crops
CEOS/LPV Phenology workshop Dublin 11
PASTiS57
10m 6m 2m 2m 6m 10m
12
Comparison with PAR sensors
CEOS/LPV Phenology workshop Dublin
60 60.5 61 61.5 62 62.5 63 63.5 64 64.5 650
200
400
600
800
1000
1200
1400
1600
020406080100120140160180200
PAR
Time (DoY)
PAR
(µE)
Blue
LED
sig
nal (
mV)
0 200 400 600 800 1000 1200 1400 1600 1800 20000
50
100
150
200
250
PAR (µE)
Blue
LED
Sig
nal (
mV)
Clear skyFull c
loud c
over
Clear sky
Full cloud cover
CEOS/LPV Phenology workshop Dublin 13
Why 57° towards North in the blue?
• Why blue spectral domain?– Better contrast between vegetation (almost black) and sky
(rayleigh and aerosol scattering)– Limits multiple scattering in the canopy
• Interest of 57°– Minimization of leaf angle distribution effect– Minimization of plant clumping effect– Compromise between sensitivity (short path length) and spatial
sampling (longer path length)• Why North orientation?
– Avoids direct sun light– Reverse to South in the southern hemisphere!
14
Some results on phenology: direct ground observations
CEOS/LPV Phenology workshop Dublin
14 April 7 May 22 June
15
Typical dynamics measured by the sensors
CEOS/LPV Phenology workshop Dublin
Incident
Transmitted
Prototype sensors (PAR domain, 40° zenith angle)
CEOS/LPV Phenology workshop Dublin 16
Comparison with visual notations
CEOS/LPV Phenology workshop Dublin 17
Performances of stages estimates
Date of inflection from sensors
Dat
e of
infle
ction
of B
BCH
Sta
ge 1
9
CEOS/LPV Phenology workshop Dublin 18
Conclusion• (Relatively) low cost systems are now available
for ground measurements of leaf development:• LAI• FAPAR• Albedo (PAR or PIR)
• Good performances with regards to visual estimates of phenology (but need confirmation)
• Few 3x3 km² sites are/will be equipped in 2010– Barrax / Crau / Foret de Harth / Hyatt&$@la / Poland
CEOS/LPV Phenology workshop Dublin 19
Questions
• From which product? (NDVI, EVI, @!VI, LAI, fAPAR, fCover
• Which model(s) of dynamics and fitting/smoothing/interpolation?
• Which metrics derived from continuous dynamics
• Propose transfer functions from ground to satellite products– Scaling issue– Measurement/metrics issue
CEOS/LPV Phenology workshop Dublin 20
Need for support for PROBA-V 100m
• Resolution: 300 m every day 100 m every 3 days
• 4 bands (Blue, red, NIR, SWIR (VEGETATION)• Launch in beginning 2014•