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

Des

truct

ive

GA

I

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)

PAR

bal

ance

com

pone

nts

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

sign

al (m

V)

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

Date

of i

nflec

tion

of B

BCH

Stag

e 19

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•