CHRIS Proba Workshop 2005 II

Transcription

1 CHRIS Proba Workshop 25 Analyses of hyperspectral and directional data for agricultural monitoring using the canopy reflectance model SLC Progress in the Upper Rhine Valley and Baasdorf test-sites Dr. Heike Bach, Silke Begiebing, Britta Rowotzki, Daniel Waldmann VISTA GmbH, München CHRIS image, Baasdorf, Sep. 24 CHRIS Proba Workshop / March 25 No. 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 CHRIS Proba Workshop / March 25 No. 2

2 Georeferenced nadir acquisitions Baasdorf 24: only image ( Sep 9) not masked by clouds Upper Rhine Valley test-site 23: 675, 73, 78 nm 25 March 23 2 June 23 8 July 23 3 August 23 CHRIS Proba Workshop / March 25 No. 3 Adjustments of radiometric calibration Change of calibration procedure of SIRA for 24 data set (Baasdorf) showed clear improvement of NIR calibration compared to 23 data sets (Upper Rhine Valley) calibration coefficients [W/m² sr µm] Calibration coefficients 23 and 24 derived from vicarious calibration; nominal = wavelength [µm] CHRIS Proba Workshop / March 25 No. 4

3 Spectral signatures, Upper Rhine Valley Measured nadir spectra of different land covers (Aug 3): 6 reflectance [%] maize tobacco potato miscanthus forest 5 Development of maize in 23 (nadir spectra): wavelength [nm] reflectance [%] wavelength [nm] CHRIS Proba Workshop / March 25 No. 5 BRDF analyses of various crops; Baasdorf Reflectance (%) Bare Soil, Wavelength (µm) BRDF, Bare Soil Bare soil; BRDF spectrally not variable angle ( ) CHRIS Proba Workshop / March 25 No. 6

4 BRDF analyses of various crops; Baasdorf Reflectance (%) Winter Colza, Wavelength (µm) BRDF, Winter Colza Rape Seed; BRDF spectrally moderately variable angle ( ) CHRIS Proba Workshop / March 25 No. 7 BRDF analyses of various crops; Upper Rhine reflectance [%] Tobacco, wavelength [µm] BRDF, Tobacoo, CHRIS Proba Workshop / March 25 No. 8 BRDF factor to nadir Tobacco; red bands with strong BRDF features

5 BRDF analyses of various crops; Upper Rhine reflectance [%] Miscanthus, wavelength [µm] BRDF factor to nadir BRDF, Miscanthus, Miscanthus (Fiber for biofuel) very weak BRDF in NIR CHRIS Proba Workshop / March 25 No. 9 Comparison with modelled spectral / directional reflectances using SLC (Verhoef & Bach 24) Input parameters to SLC: LAI - leaf area index Average leaf slope parameter a LIDF bimodality parameter b Hot spot parameter q Fraction brown leaf area fb Layer dissociation factor D Soil BRDF Parameters (b, c, B, h) Soil moisture Crown coverage Outputs from PROSPECT Fraction diffuse sky irradiance Dry soil reflectance Solar zenith angle Viewing zenith angle Relative azimuth angle Four-stream canopy reflectance model: Input parameters to PROSPECT:. Direct solar flux 2. Diffuse downward flux Leaf chlorophyll 3. Diffuse upward flux Leaf water 4. Direct observed flux (radiance) Leaf dry matter Leaf mesophyll structure N CHRIS Proba Workshop / March 25 No.

6 Extensions of SLC compared to GeoSAIL (Verhoef & Bach, 24) optical properties of leaves calculated based on PROSPECT with improved spectral absorption coefficient for chlorophyll (Verhoef, 25) and water (Bach, 23) integrate soil reflectance and its BRDF function consider crown clumping considers aerosols, water vapour + adjacency effect in the atmosphere using inputs from MODTRAN Additional calculation of albedo, FAPAR and ground coverage CHRIS Proba Workshop / March 25 No. Comparison with SLC simulation results Bare Soil; Upper Rhine Valley, Aug 23 Bare Soil, Aug 3 ( pixel, no smoothing) Bare Soil, Aug 3 (simulated) Reflectance [%] Wavelength [nm] Reflectance [%] Wavelength [nm] Soil moisture: 5%; LAI = optimised to nadir spectrum CHRIS Proba Workshop / March 25 No. 2

7 Comparison with SLC simulation results Maize; Upper Rhine Valley, Aug 23 Maize, Aug 3 ( pixel, no smoothing) Maize, Aug 3 (simulated) Reflectance [%] 3 2 Reflectance [%] Wavelength [nm] Wavelength [nm] Soil moisture: 5%; leaf chlorophyll: 4 µg/cm², LAI = 4., leaf water content:.2 g/cm², fraction brown: 35% optimised to nadir spectrum CHRIS Proba Workshop / March 25 No. 3 Measured and simulated BRDF factor Upper Rhine Valley Bare Soil Maize BOA BRDF at 78nm for Aug 3, bare soil.4.3 BOA BRDF at 78nm for Aug 3, maize measured simulated measured measured simulated simulated CHRIS Proba Workshop / March 25 No. 4

8 Measured and Simulated BRDF for Maize BRDF, Maize, BRDF, Maize, 8.7., simulated, LAI = 5, Cab = LIDF a = -. b = -.4 CHRIS Proba Workshop / March 25 No. 5 Limitations of SLC Maize photographs; Upper Rhine Valley 3rd Aug 23: Flowering Nadir View Tilted View Limitation: Flowering not considered in SLC Extension of third canopy layer required In nadir view only limited effect, but with increasing observation angle the flowering material on top become more dominant => Room for model improvements! CHRIS Proba Workshop / March 25 No. 6

9 Angular reflectance for flowering maize Measured Simulated VIS and red edge, VIS and red edge, Aug 3 (simulated) reflectance [%] reflectance [%] wavelength [nm] wavelength [nm] Especially the VIS reflectances of the + observation angles show an increase reflectance caused by the flowering that could not be simulated with SLC. CHRIS Proba Workshop / March 25 No. 7 Simple hyperspectral crop classification NDVI:.7.86 Inflection point red-edge: nm NDVI: Inflection point red-edge: nm Reflectance: >25 % at inflection point Maize mask (red = maize) Tobacco mask (yellow = tobacco) CHRIS Proba Workshop / March 25 No. 8

10 Parameter retrieval of CHRIS CHRIS Proba Workshop / March 25 No. 9 Retrieval Result LAI of Maize Histogram of Leaf Area Index 4 Leaf Area Index 35 frequency of occurrence frequency of occurrence LAI a = -., b = -.4, hot =. > CHRIS Proba Workshop / March 25 No. 2

11 Retrieval Result Chlorophyll of Maize Histogram of Chlorophyll content per leaf area Leaf Chlorophyll [µg/cm²] 5 45 frequency of occurrence 4 frequency of occurrence cab a = -., b = -.4, hot =. > CHRIS Proba Workshop / March 25 No. 2 Sensitivity of simulated BRDF with a a = average leaf angle used in SLC Absolute reflectance BRDF factor related to Nadir BRDF changes with changing LIDF a - parameter for maize at 773nm 7 BRDF changes with changing LIDF a - parameter for maize at 773nm reflectance [%] Model inputs: LAI = 3.5, b = -.35 CHRIS Proba Workshop / March 25 No. 22

12 Sensitivity of simulated BRDF with b b = bimodality of leaf angle distribution used in SLC Absolute reflectance BRDF factor related to Nadir BRDF changes with changing LIDF b - parameter for maize at 773nm BRDF changes with changing LIDF b - parameter for maize at 773nm reflectance [%] Model inputs: LAI = 3.5, a = -.65 CHRIS Proba Workshop / March 25 No. 23 Retrieval of canopy structure of Maize BRDF factor for various LIDF a values and a LAI of observation measured CHRIS Proba Workshop / March 25 No. 24

13 Retrieval Result: leaf angle distribution Frequency of occurrence: a = a = a = LIDF a = average leaf angle Maize Upper Rhine Valley 8.7. CHRIS Proba Workshop / March 25 No. 25 Retrieval Result: leaf angle distribution Frequency of occurrence: b = b = b = LIDF b = bimodality of leaf angle Maize Upper Rhine Valley 8.7. CHRIS Proba Workshop / March 25 No. 26

14 Proposed future activities within preagro 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. Baasdorf 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 hyperspectral measurements will be conducted in 2 pilot farms using the AVIS sensor. Directional observations with CHRIS substantially supports data analyses. CHRIS Proba Workshop / March 25 No. 27 Proposed aquisitions for 25 Location of Site location / center:.94 East, 5.84 North Acquisition Mode : full swath, half spatial resolution (36m), 62 bands, along track BRDF (5 angles) Timing of image acquisition: (total: 4 times) 5. May to 3. July: 2 times. August to 5. September: 2 times test site: Baasdorf Germany date: angle: / / / / half swath, full resolution nm (blue) 73-79nm (green) nm (red) CHRIS Proba Workshop / March 25 No. 28

15 Planned Crop Parameters to be retrieved 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 model delivering: biomass and yield precision farming planning (seed density, fertilisation, application of fungicides and pesticides) CHRIS Proba Workshop / March 25 No. 29 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 25. CHRIS Proba Workshop / March 25 No. 3

16 Acknowledgement Thanks to Wout Verhoef for SLC model support. Work funded within a SPECTRA preparatory study of ESA. Thanks for your attention! Contact: Dr. Heike Bach Vista Geowissenschaftliche Fernerkundung GmbH Gabelsbergerstr München ++49 ()89 / Bach@vista-geo.de CHRIS Proba Workshop / March 25 No. 3