Analyses of hyperspectral and directional data for ...

Chris/Proba Workshop April 28-30 2004 No. 1

Analyses of hyperspectral and directional data for agricultural monitoring using a canopy reflectance model

Status of activities in the Upper Rhine Valley additional test-site No. 55

Dr. Heike Bach, Silke Begiebing

Vista GmbH

Gabelsbergerstr.51, D-80333 MünchenTel. 0049 89 523 89 802 / Fax 0049 89 523 89 804www.vista-geo.de, [email protected]


Half swath, 18 m resolution, 37 bands, along track BRDF (5 angles)=> high spectral and full directional capabilities

Acquisition Mode 5:

5 CHRIS acquisitions successful in 2003.3 of them are completely cloud free.3 consist of all 5 observation angles

Good news:


Content

Overview on satellite data

Processing steps:• Radiometric destriping• Geometric corrections and georeferencing• Adjustments of radiometric calibration• Atmospheric corrections

BRDF analyses (TOA and BOA)

Comparison with FourSAIL2 simulation results

Proposed future activities



25 March 2003 02 June 2003 18 July 2003 03 August 2003 11 Sept. 2003

675 nm 713 nm 781 nm



-55° -36° 0° 36° 55° Comments

25.03. + +

02.06. + + + Clouds in the south

18.07. + + + + +

03.08. + + + + +

11.09. + + + + + Heavy clouds


Radiometric destripingStatistical approach compensating striping for each column.

Corrections use the moving averages of the mean gray values for each column. The factor between actual gray value and moving average is used for correction.

Before destriping:

Before Flatfield Calibration

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450 550 650 750 850 950 1050

Wavelength [nm]

Rad

ianc

e [W

/ m² s

r µm

]

646566676869

675, 713, 781 nm


Radiometric destripingExample of results (spatially and spectrally):

After destriping:

After Flatfield Calibration

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450 550 650 750 850 950 1050

Wavelength [nm]

Rad

ianc

e [W

/ m² s

r µm

]

646566676869

675, 713, 781 nm


Georeferencing of the nadir acquisitions

25 March 2003 02 June 2003 18 July 2003 03 August 2003

675, 713, 781 nm


Co-location of the 5 observation anglesColor composite of three observation angles at 780nm

- 36°Nadir+ 36°

03. 08. 2003


Co-location of the 5 observation anglesColor composite of three observation angles at 780nm

- 55°Nadir+ 55°

03. 08. 2003


Radiometric calibration and processing

Observed changes compared to defaults:

1) wavelength calibration: spectral shift of 3.5 nm compared to nominal calibration determined through comparison of position of O2-absorption in CHRIS data with MODTRAN based sensor simulations.

0.0

20.0

40.0

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650 670 690 710 730 750 770 790 810 830 850

Wavelength nm

Rad

ianc

es [W

/m² s

r µm

]

CHRIS measured 1CHRIS measured 2MODTRAN based simulation

2) Adaptation of spectral width: for each band FWHMwas extended by 20% compared to defaults values;

determined through MODTRAN high spectral resolution simulations folded with variable sensor response functions until best fit was achieved.


Radiometric calibration and processing

3) Empirical adaptation of radiometric calibration (vicarious calibration)=> sensitivity drop down in the NIR corrected!

Adapted calibration coefficients (default = 0.01 W/m² sr µm)new calibration

0

0.005

0.01

0.015

0.02

0.025

0.405 0.505 0.605 0.705 0.805 0.905 1.005

wavelength [µm]

calib

ratio

n co

effic

ient

[W/ m

² sr µ

m]

gain


Atmospheric CorrectionBased on MODTRAN 4 radiative transfer simulations using the atmospheric correction scheme PULREF (Bach & Mauser 1995).

e.g. Aug 03 2003, visibility=40km, water vapour factor =1.1

total radiation at 30% albedo

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450 550 650 750 850 950 1050

wavelength [nm]

radi

ance

[W/ m

² sr µ

m]

- 55°- 36°0°+ 36°+ 55° One result:

SNR not adequate for spatial variable water vapour retrieval.


Sample nadir spectra CHRIS 03 Aug 03(1 pixel, no smoothing)

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0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

wavelength [µm]

refle

ctan

ce [%

]

maizedense vegetationbare soilwater forest


Calculated BOA reflectances for bare soil 5 observation angles

bare soil

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450 550 650 750 850 950 1050

w avelength [nm ]

refle

ctan

ce [%

] - 55°

- 36°

0°

+ 36°

+ 55°


BOA BRDF

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-60.00 -40.00 -20.00 0.00 20.00 40.00 60.00

observation angle [°]

refle

ctan

ce [%

] m aize

dense vegetation

fores t

bare soil

water

Spectral analysis of BRDFBOA reflectances at 780 nm

Sun in the back (Solar zenit=32°)


Comparison with modelled spectral / directional reflectances using 4SAIL2(Verhoef & Bach 2003)

Four-stream canopy reflectance model:1. Direct solar flux2. Diffuse downward flux3. Diffuse upward flux4. Direct observed flux (radiance)

Input parameters to 4SAIL2:LAI - leaf area indexAverage leaf slope parameter aLIDF bimodality parameter bHot spot parameter q Fraction brown leaf area fBLayer dissociation factor DSoil BRDF Parameters (b, c, B0, h)Soil moistureCrown coverageOutputs from PROSPECTFraction diffuse sky irradianceDry soil reflectanceSolar zenith angleViewing zenith angleRelative azimuth angle

Input parameters to PROSPECT:Leaf chlorophyllLeaf waterLeaf dry matterLeaf mesophyll structure N


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0.4 0.5 0.6 0.7 0.8 0.9 1 1.1Wavelength [µm]

Ref

lect

ance

[%]

simulated

Simulated directional reflectances BRDF of a bare a soil


Measured directional reflectances BRDF of a bare a soil

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0.4 0.5 0.6 0.7 0.8 0.9 1 1.1Wavelength [µm]

Ref

lect

ance

[%]

measured


Simulated BOA reflectances for maize 5 observation angles

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60

0.4 0.6 0.8 1

wavelength [µm]

refle

ctan

ce [%

] - 55°- 36°0°+ 36°+ 55°


Measured BOA reflectances for maize 5 observation angles

0

10

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30

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50

60

0.4 0.6 0.8 1

wavelength [µm]

refle

ctan

ce [%

] - 55°- 36°0°+ 36°+ 55°


Lessons learned

• Highest spectral resolution (mode 5) required in order to check and correct sensor calibration.

• CHRIS Proba helps to identify BRDF parameters in surface reflectance models (e.g. Hapke parameter of soil BRDF).

• Spatial homogenous pixels must be selected for BRDF parameterisations.

• Application of CHRIS-PROBA data suitable for validation of SPECTRA scene simulations (ongoing ESA contract).


Proposed future activities

• Continuation of spectral and directional analyses of the 2003 data of the Upper Rhine Valley test-site.

• Extraction of agricultural information from hyperspectral directional CHRIS data using the canopy reflectance model FourSAIL2.

• The retrieved agricultural variables will be assimilated in plant production and management models.

Changes compared to earlier workplan• Funding has changed during the years. Therefore a

change of the location test-site is required for 2004.

• Translocated test-site proposed within the pre-agro II project


pre-agro II

• Pre-agro II is Germans largest activity in the field of precision agriculture / precision farming.

• 23 teams in the field of agriculture are collaborating with the goal to support sustainable agricultural production.

• pre-agro II is coordinated by Dr. A. Werner, ZALF.

• The project proposal was accepted this month. It is funded by German Ministry for Research (BMBF).

• Vista is in charge for remote sensing applications of hyperspectral data.

• Multitemporal airborne hyperspectral measurements will be conducted in 2 pilot farms using the AVIS sensor.

• Directional observations with CHRIS would substantially support data analyses.


Proposed translocated „Baasdorf“ test-site

10km x 10km

• Size of farm: 7 km²

• Average field size: 0.5 km² (50 ha)

• Very variable soil fertility (31-94)

• Low precipitation (450 mm/a) => waterstress likely

• Central coordinate:11° 59‘ East51° 42.5‘ North

Pilotfarm for pre-agro II; located central in East Germany


Thanks for your attention!

Dr. Heike Bach

Vista Geowissenschaftliche Fernerkundung GmbH

Gabelsbergerstr.5180333 München+49 (0)89 / 52 38 98 02http://www.vista-geo.de

Analyses of hyperspectral and directional data for ...

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