CHRIS Workshop 2005 VISTA - European Space...

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CHRIS Proba Workshop / 21.-23. March 2005 No. 1

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CHRIS Proba Workshop 2005

Analyses of hyperspectraland directional data for agricultural monitoring using the canopy reflectance model SLC

Progress in the Upper Rhine Valley and Baasdorftest-sites

Dr. Heike Bach, Silke Begiebing, Britta Rowotzki, Daniel Waldmann

VISTA GmbH, München

www.vista-geo.deCHRIS image, Baasdorf, Sep. 2004


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Content

Introduction and overview on satellite data

Basic processing steps:• Radiometric destriping and vicarious calibration• Georeferencing• Atmospheric corrections using MODTRAN with

compensation of the adjacency effect

BRDF analyses of various crops

Comparison with SLC simulation results

Parameter retrieval by SLC model inversion

Sensitivity of BRDF on canopy structure

Proposed future activities within preagro

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Georeferenced nadir acquisitions

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

675, 713, 781 nm

Baasdorf 2004: only 1 image ( Sep 9) not masked by clouds

Upper Rhine Valley test-site 2003:


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Adjustments of radiometric calibration

Change of calibration procedure of SIRA for 2004 data set (Baasdorf) showed clear improvement of NIR calibration compared to 2003 data sets (Upper Rhine Valley).

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0.005

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0.015

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wavelength [µm]

calib

ratio

nco

effic

ient

s[W

/m² s

r µm

]

2003

2004

Calibration coefficients 2003 and 2004 derived from vicarious calibration; nominal = 0.01

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Spectral signatures, Upper Rhine ValleyMeasured nadir spectra of different land covers (Aug 03):

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450 550 650 750wavelength [nm]

refle

ctan

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]

maizetobaccopotatomiscanthusforest

Development of maize in 2003 (nadir spectra):

850 950 1050

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450 550 650 750 850 950 1050

wavelength [nm]

refle

ctan

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]

25.03.

02.06

18.07.03.08.


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BRDF analyses of various crops; Baasdorf

Bare Soil 1, 09.09.2004

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0.45 0.55 0.65 0.75 0.85 0.95 1.05

Wavelength (µm)

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lect

ance

(%)

-55°

-36°

0°

+36°

+55°

BRDF, Bare Soil 1

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-60 -40 -20 0 20 40 60

angle (°)

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0.53040.55180.57050.63210.66190.67540.68660.69830.70730.71350.71970.72620.73270.73940.74620.75310.76010.76720.77460.78580.79740.80530.86890.88740.90170.91140.92120.93110.94630.96170.97230.98290.99361.0043

Bare soil; BRDF spectrally not variable

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BRDF analyses of various crops; Baasdorf

Winter Colza, 09.09.2004

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0.45 0.55 0.65 0.75 0.85 0.95 1.05

Wavelength (µm)

Ref

lect

ance

(%)

-55°-36°0°+36°+55°

BRDF, Winter Colza

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0.53040.55180.57050.63210.66190.67540.68660.69830.70730.71350.71970.72620.73270.73940.74620.75310.76010.76720.77460.78580.79740.80530.86890.88740.90170.91140.92120.93110.94630.96170.97230.98290.99361.0043

Rape Seed; BRDF spectrally moderately variable


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Tobacco, 03.08.2003

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0.450 0.550 0.650 0.750 0.850 0.950 1.050wavelength [µm]

refle

ctan

ce [%

]

-55°-36°0°+36°+55°

BRDF, Tobacoo, 03.08.2003

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angle [°]

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0.5300.5520.5700.6310.6610.6740.6850.6970.7060.7120.7180.7250.7310.7380.7440.7510.7580.7650.7730.7840.7950.8030.8660.8840.8980.9080.9170.9270.9580.9680.9780.9891.0001.021

BRDF analyses of various crops; Upper Rhine

Tobacco; red bands with strong BRDF features

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BRDF analyses of various crops; Upper Rhine

Miscanthus(Fiber for biofuel) very weak BRDF in NIR

Miscanthus, 03.08.2003

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0.45 0.55 0.65 0.75 0.85 0.95 1.05

wavelength [µm]

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-55°-36°0°+36°+55°

BRDF, Miscanthus, 03.08.2003

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angle [°]

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0.5304650.5516910.570260.6313570.6609870.6743220.685450.6969950.7059780.7120440.7182430.7246070.731080.7376190.7443830.7512490.7581380.7652480.7725180.7835730.7949550.8027540.8658460.8840320.89811610.9076980.9174220.9272070.9576010.9680170.9784580.9889710.9997831.021387


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Comparison with modelled spectral / directional reflectances using SLC(Verhoef & Bach 2004)

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

Input parameters to SLC: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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Extensions of SLC compared to GeoSAIL

optical properties of leaves calculated based on PROSPECT with improved spectral absorption coefficient for

• chlorophyll (Verhoef, 2005) and • water (Bach, 2003)

integrate soil reflectance and its BRDF function consider crown clumpingconsiders aerosols, water vapour + adjacency effect in the atmosphere using inputs from MODTRANAdditional calculation of albedo, FAPAR and ground coverage

(Verhoef & Bach, 2004)


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Comparison with SLC simulation results

Bare Soil, Aug 03 (simulated)

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470 570 670 770 870 970

Wavelength [nm]

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lect

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[%]

-55°-36°0°+36°+55°

Bare Soil, Aug 03 (1 pixel, no smoothing)

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470 570 670 770 870 970Wavelength [nm]

Ref

lect

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[%]

-55°-36°0°+36°+55°

Bare Soil; Upper Rhine Valley, Aug 2003

Soil moisture: 5%; LAI = 0 optimised to nadir spectrum

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Maize, Aug 03 (1 pixel, no smoothing)

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470 570 670 770 870 970

Wavelength [nm]

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[%]

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Soil moisture: 5%; leaf chlorophyll: 40 µg/cm², LAI = 4.0, leaf water content: 0.02 g/cm², fraction brown: 35% optimised to nadir spectrum

Maize, Aug 03 (simulated)

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Wavelength [nm]

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[%]

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Comparison with SLC simulation resultsMaize; Upper Rhine Valley, Aug 2003


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Measured and simulated BRDF factor

BOA BRDF at 780nm for Aug 03, bare soil

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BOA BRDF at 780nm for Aug 03, maize

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BOA BRDF at 780 nm for Aug 03, maize

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Upper Rhine ValleyBare Soil Maize

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Measured and Simulated BRDF for Maize

BRDF, Maize, 18.07.2003

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0.5300.5520.5520.5700.6310.6740.6850.6970.7060.7120.7180.7250.7310.7380.7440.7510.7580.7650.7730.7840.7950.8030.8660.8840.8980.9080.9170.9270.9580.9680.9780.9891.0001.021

BRDF, Maize, 18.07., simulated, LAI = 5, Cab = 50

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0.5300.5520.5700.6310.6610.6740.6850.6970.7060.7120.7180.7240.7310.7380.7440.7510.7580.7650.7720.7830.7950.8030.8660.8840.8980.9080.9170.9270.9420.9570.9680.9780.9890.9991.021

18.7.2003

LIDF a = -0.10 b = -0.40


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Limitations of SLCMaize photographs; Upper Rhine Valley3rd Aug 2003: FloweringNadir View Tilted View

Limitation: Flowering not considered in SLCExtension of third canopy layer requiredIn nadir view only limited effect, but with increasing observation angle the flowering material on top become more dominant => Room for model improvements!

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Angular reflectance for flowering maize

VIS and red edge, 03.08.2003

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VIS and red edge, Aug 03 (simulated)

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Measured Simulated

Especially the VIS reflectances of the +-55° observation angles show an increase reflectance caused by the flowering that could not be simulated with SLC.


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Simple hyperspectral crop classification

Maize mask (red = maize) Tobacco mask (yellow = tobacco)

NDVI: 0.70 – 0.86 Inflection point red-edge: 727 – 735 nm

NDVI: 0.73 - 0.92Inflection point red-edge: 715-726 nmReflectance: >25 % at inflection point

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Parameter retrieval of CHRIS 18.7.2003


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Retrieval Result LAI of Maize 18.7.2003Histogram of Leaf Area Index

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2 2.5 3 3.5 4 4.5 5 5.5 6LAI

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frequency of occurrence

Leaf Area Index

>2.02.0-2.52.5-3.03.0-3.53.5-4.04.0-4.54.5-5.05.0-5.55.5-6.0a = -0.10, b = -0.40, hot = 0.00

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Retrieval Result Chlorophyll of Maize

> 3535-4040-4545-5050-5555-6060-6565-7070-75

Histogram of Chlorophyll content per leaf area

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a = -0.10, b = -0.40, hot = 0.00

Leaf Chlorophyll [µg/cm²]


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Sensitivity of simulated BRDF with a

BRDF changes with changing LIDF a - parameter for maize at 773nm

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BRDF changes with changing LIDF a - parameter for maize at 773nm

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Model inputs: LAI = 3.5, b = -0.35

a = average leaf angle used in SLC

Absolute reflectance BRDF factor related to Nadir

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Sensitivity of simulated BRDF with b

BRDF changes with changing LIDF b - parameter for maize at 773nm

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BRDF changes with changing LIDF b - parameter for maize at 773nm

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Model inputs: LAI = 3.5, a = -0.65

b = bimodality of leaf angle distribution used in SLC

Absolute reflectance BRDF factor related to Nadir


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BRDF factor for various LIDF a values and a LAI of 3.5

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18.7. measured


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03.08.measured


Retrieval of canopy structure of Maize

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Retrieval Result: leaf angle distribution

LIDF a = average leaf angle

Maize Upper Rhine Valley 18.07.

-0.30-0.20-0.10

a = -0.30 1165a = -0.20 1748a = -0.10 12675

Frequency of occurrence:


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-0.40-0.30-0.20

b = -0.40 9790b = -0.30 1287b = -0.20 4511

Frequency of occurrence:

Retrieval Result: leaf angle distribution

LIDF b = bimodality of leaf angle

Maize Upper Rhine Valley 18.07.

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Preagro is a German project for joint research and development of basics for precision farming:

„Information driven crop production with precision farming as the central scientific and technical precondition for a sustainable development of agricultural land use.“

Proposed future activities within preagro

• Germans largest activity in the field of precision agriculture / precision farming.

• coordinated by Dr. A. Werner, ZALF.• Funded by BMBF.

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

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

• Directional observations with CHRIS substantially supports data analyses.

Baasdorf


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Location of Sitelocation / center: 11.904° East, 51.804° North

Acquisition Mode 1:full swath, half spatial resolution (36m), 62 bands, along track BRDF (5 angles)

Timing of image acquisition: (total: 4 times)15. May to 31. July: 2 times1. August to 15. September: 2 times

675-686nm (blue)713-719nm (green)

785-797nm (red)

test site: Baasdorf Germanydate: 09.09.2005

angle: -55° /-36° /0° /+36° /+55°half swath, full resolution

Proposed aquisitions for 2005

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• green leaf area• fraction brown leaf• soil coverage• leaf chlorophyll• water content of crop • structure of crops•nitrogen uptake

For further assimilation in a crop growth modeldelivering:

• biomass and yield• precision farming planning (seed density, fertilisation, application of fungicides and pesticides)

Planned Crop Parameters to be retrieved


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Conclusions

Basic processing (geometry, atmosphere) of CHRIS data has become a routine effort

The SLC canopy model provides good simulation results concerning both spectral and directional domain

Parameter retrieval by SLC model inversion started, but optimization (e.g. speed) and validation not completed.

Extension of SLC model needed in case of flowering.

Sensitivity of BRDF on canopy structure demonstrated and potential to derive structural information from directional measurements

Future plans within preagro strongly hope for continuation of CHRIS data provision in 2005.

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Acknowledgement

Contact:

Dr. Heike Bach

Vista Geowissenschaftliche Fernerkundung GmbHGabelsbergerstr.51. 80333 München++49 (0)89 / 52 38 98 02http://www.vista-geo.de, [email protected]

Thanks for your attention!

Thanks to Wout Verhoef for SLC model support.

Work funded within a SPECTRA preparatory study of ESA.

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