Wouter Verhoef Christiaan van der Tol

Wouter Verhoef

Christiaan van der Tol

University of Twente, Faculty ITC Enschede, The Netherlands

e-mail [email protected]

Contents SCOPE model Database design Forward propagation to TOA Retrieval model: SAIL_light Optimization loop Results Conclusion

5th Intl. Workshop on Remote Sensing of Vegetation Fluorescence, Paris, 22-24 april 2014 2

SCOPE model Soil-Canopy-Observations of radiance spectra

including Photosynthesis and the Energy balance Spectral range 0.4 – 50 microns Spectral sampling 400 – 2400 nm @ 1 nm, 2400 –

15000 nm @ 100 nm and 15000 – 50000 nm @ 1000 nm Fluorescence from Fluspect model Outputs 4 BRDF reflectances, directional and

hemispherical fluorescence


Database design Standard case for SCOPE and MODTRAN ± variations from standard case in 15 parameters 13 MODTRAN situations (altitude, visibility, humidity, aerosol type, profile, solar zenith angle) SCOPE pars: soil brightness, leaf Cab, Cw, Cdm, Cs,

Vcmax, Ball-Berry, LAI, LIDF, Tair Tair, p, H2O, CO2, O2 linked to MODTRAN 31 cases total


Forward propagation to TOA Four-stream radiative transfer T-18 system of atmospheric transfer functions Incorporate BRDF and adjacency effects Sampling by FLORIS spectrometers of FLEX, OLCI

and SLSTR sensors of Sentinel-3, using ISRFs Noise models for these instruments Output 187 bands WBS (wide-band spectrometer) 288 bands NBS (narrow-band spectrometer) 21 bands OLCI, 9 bands SLSTR


Importance of BRDF in O2-A


740 745 750 755 760 765 770

0.3

0.32

0.34

0.36

0.38

0.4

Wavelength (nm)

Ref

lect

ance

R pureRac

Apparent reflectance after best possible atmospheric correction, including Fs

Same, without Fs

Spectral resolution 1 cm-1 ~ 0.06 nm, simulated with T-18 system

Output layers (in 505 bands) LTOA noisy LTOC after AtCor (applied to LTOA noisy) LWLR after AtCor LTOA noise-free LTOC noise-free LWLR noise-free TOC Pure reflectance TOC Fluorescent radiance


BRDF-atmosphere interaction for 31 cases in the O2-A band


740 750 760 770 7800.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

Wavelength (nm)

Surface pure reflectance

740 750 760 770 7800.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

Wavelength (nm)

Surface apparent reflectance

740 750 760 770 7800.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

Wavelength (nm)

Best reflectance after AtCor

BRDF effects (BRF,HDRF,DHRF,BHRF)


650 700 750 800 8500

0.1

0.2

0.3

0.4

0.5DB case 3

Wavelength (nm)

Ref

lect

ance

rsordorsdrdd

650 700 750 800 8500

0.1

0.2

0.3

0.4

0.5DB case 8

Wavelength (nm)

Ref

lect

ance

rsordorsdrdd

650 700 750 800 8500

0.1

0.2

0.3

0.4

0.5DB case 15

Wavelength (nm)

Ref

lect

ance

rsordorsdrdd

650 700 750 800 8500

0.1

0.2

0.3

0.4

0.5DB case 16

Wavelength (nm)

Ref

lect

ance

rsordorsdrdd

650 700 750 800 8500

0.1

0.2

0.3

0.4

0.5DB case 17

Wavelength (nm)

Ref

lect

ance

rsordorsdrdd

650 700 750 800 8500

0.1

0.2

0.3

0.4

0.5DB case 18

Wavelength (nm)

Ref

lect

ance

rsordorsdrdd

650 700 750 800 8500

0.1

0.2

0.3

0.4

0.5DB case 30

Wavelength (nm)

Ref

lect

ance

rsordorsdrdd

650 700 750 800 8500

0.1

0.2

0.3

0.4

0.5DB case 31

Wavelength (nm)

Ref

lect

ance

rsordorsdrdd

Surface – atmosphere RT


3

1817137

3

11101491

156821TOA

1)]([

1)(

)()(

TrrTrTrTTLF

TrrTrTrrTTT

TTLFrTTTL

dd

dddodosdd

dd

ddsddosd

sosso

−++++

+

−+++

+

++++=

ε

ε

• Four-stream BRDF effects for reflectance and fluorescence • Adjacency effect and multiple scattering • Thermal emission included • MODTRAN5 spectral sampling at 1 cm-1

T2 – T14 transfer functions obtained from 4 MODTRAN runs


400 500 600 700 800 900 1.000 2.000 3.000 4000 5000 10000 200000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Wavelength (nm)

T2T3T4T5T6T7T8T9T10T11T12T13T14

Sensor noise model


baLLNE +=∆

FLEX’s noise in the NIR

SAIL_light model Spherical leaf angle distribution No hot spot effect, LAI is only canopy parameter PROSPECT leaf model with 5 parameters (Cab, Cs,

Cdm, Cw, N) included Lambertian soil reflectance, modelled with GSV3

basis spectra (3 parameters), soil moisture effect added Model is only intended to provide realistic reflectance

spectra in the 400 - 2400 nm fluorescence range Spectral range 400 - 2400 nm, 1 nm resolution Matlab function, with output of Jacobian



LAI 5 Leaf pars 4 Soil pars

SAIL light

Reflectance

+ Jac.

Atmospheric propagation

T-18 transfer

functions

Read MODTRAN case data

FLEX / S3 database

case

Sampling by sensors

FLORIS OLCI

SLSTR data + J

Compare

TOA Radiance Spectrum

+ J

Update rule

2 Fs pars

Optimization loop

Cost function to minimize


∑∑

∑∑

==

==

−+

−+

−+

−=

6

1

221

1

2

288

1

2187

1

2

lSLSTRl

DBl

SLSTRl

kOLCIk

DBk

OLCIk

jNBSj

DBj

NBSj

iWBSi

DBi

WBSi

NLL

NLL

NLL

NLLC

Updating rule Newton algorithm with damping factor µ Box-constrained (min and max for every parameter) If crossing a border, use line search along the gradient

direction up to the border and find a minimum Newton step only applied when staying inside the box Transformed LAI is used = 1 - exp(-0.2LAI)


LΣJIJΣJp ∆+=∆ −−− 1T11T )( µ

Iteration steps, standard case


1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

0

100

200

300

400

500

600

700

800

900

1000

1 3 5 7 9 11

LAI

Cab

Cs

Cw

Cdm

N

GSV1

GSV2

GSV3

SM

F1

F2

Error (right scale)

Retrieval of vegetation parameters


Parameter “True” (database) Retrieved

LAI 2 2.06

Cab 40 40.9

Cs 0.1 0.095

Cw 0.02 0.0193

Cdm 0.005 0.0065

N 1.5 1.52

LTOA residuals


400 500 600 700 800 900 1000 1500 2000-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

Wavelength (nm)

TO

A ra

dian

ce e

rror

(mW

m-2

sr-

1 nm

-1)

FLORIS WBSFLORIS NBSOLCISLSTR

Retrieved fluorescence case 19


640 660 680 700 720 740 760 7800

0.5

1

1.5

2

2.5

3

Wavelength (nm)

Fs

(mW

m-2

sr-

1 nm

-1)

NBS retrievedNBS "true"WBS retrievedWBS "true"

Retrieved vs. true fluorescence in 5 subregions of O2-B and O2-A


0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Fs true (mW m-2 sr-1 nm-1)

Fs re

triev

ed (m

W m

-2 s

r-1 n

m-1

)

O2-B1O2-B2O2-B3O2-A1O2-A2

RMS errors in 5 regions for all 31 cases


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 310

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Database case #

Fs

RM

S e

rror

(m

W m

-2 s

r-1

nm-1

)

O2-B1O2-B2O2-B3O2-A1O2-A2

Cdm high

planophile

erectophile

visibility 5 km

Conclusion Retrievals of F and R by model inversion fairly successful Small number of model parameters (12) Data from S3 sensors OLCI and SLSTR included Sensor noise included in the cost function About 11 iterations on average are needed Forward atmospheric modelling allows including BRDF and

adjacency effects Propagation of reflectance, fluorescence and Jacobians through

the atmosphere takes most of the computational effort SAIL_light model does not accommodate LIDF variations No good model solution found for planophile and erectophile

canopies Perfect atmospheric knowledge assumed


Wouter Verhoef Christiaan van der Tol

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