1. ESA/ESRIN contract 18348/04/I-LG MERIS land surface Albedo from data fusion with MODIS BRDFs, its validation using MISR, POLDER and MODIS (gap- filled albedo) and Data Dissemination using DDS and OGC Jan-Peter Muller* (UCL) Carsten Brockmann, Marco Z ü hlke, Norman Fomferra (BC) J ü rgen Fischer, R é n é Preusker, Thomas Schr ö der (FUB) Peter Regner (ESA/ESRIN) *Professor of Image Understanding and Remote Sensing MISR & MODIS Science Team Member (NASA EOS Project) HRSC Science Team Member (ESA Mars Express 2003) Chair, CEOS-WGCV Terrain mapping sub-group

2. ESA/ESRIN contract 18348/04/I-LG Overview Context Objectives BRDF/Albedo retrieval approach BRDF/Albedo algorithm details Initial Results Validation approach Preliminary Validation results Future Prospects

3. ESA/ESRIN contract 18348/04/I-LG Context All governments with space agencies agreed in Brussels in February 2005 on a common strategy for Earth Observation called GEOSS (Global EO System of Systems) which has 9 societal benefit areas including climate modelling, biodiversity, ecology and hazard monitoring ESA and the European Union have now established the funding for their GMES (Global Monitoring of Environment and Security) programme which embodies these GEOSS principles CEOS (Committee on Earth Observing Systems) is now the provider of the space segment including setting ISO-level standards for cal/val Main push is to improve interoperability between products from the same agency and products between different space agencies Development of MERIS spectral and broadband albedo is the first example of trying to fuse at the processing chain/algorithm level between products from different space agencies Albedo required for climate GCM model verification by Hadley Centre

4. ESA/ESRIN contract 18348/04/I-LG Objectives Derivation of a one-year (2003) land surface albedo from MERIS for –13 of the 15 MERIS wavelengths (excluding 2 inside O2 absorption bands) –2 broadband albedos (0.4-0.7µm, 0.4-3µm) –16-day and MONTHLY time step for 2003 –Input Level 2 Rayleigh+O3 corrected –0.05º and 10km sinusoidal spatial resolutions »Publication of MERIS albedo browse images (as Web Map Services layers) within the CEOS-WGISS EO Data Portal (http://iceds.ge.ucl.ac.uk)http://iceds.ge.ucl.ac.uk »Publication of the associated albedo files downloadable through a cascaded Web Coverage Server Main driver is to improve the retrieval of atmospheric parameters from MERIS. Hence, spectral albedos at the MERIS wavelengths are required Secondary driver is the production of spectral and broadband albedos for use by the European climate and weather forecasting bureaus Processsing software incorporated into the platform-independent (Java-based) BEAM software so that anyone can produce their own albedo products for any other time periods Validation by inter-comparison with other EO sensors only envisaged at present

5. ESA/ESRIN contract 18348/04/I-LG BRDF/albedo approach(1) Inputs are orthorectified, cloud-cleared, atmospherically-corrected Spectral/Surface Directional Reflectances (SDRs) from level 2 data at 1.2km spatial resolution and a typical sampling of every 2-3 days BRDF retrieval is NOT directly performed on these SDRs as sampling of the bi-directional plane is insufficient for most land surfaces given the narrower swath (1130km) and lower temporal sampling (every 2-3 days at the equator) of MERIS cf. instruments such as MODIS (2550 km and daily sampling) Instead the BRDF shape and BRDF models are taken for the 4 common spectral bands from the MOD43C2 (0.05º) product (see below for an intercomparison). N.B. Bands also common with MISR/POLDER

6. ESA/ESRIN contract 18348/04/I-LG BRDF/albedo approach(2) Using magnitude inversion, MERIS BRDFs are calculated for each set of SDRs which are co-located with the MODIS 0.05º pixel where MODIS returns a value Linear spectral interpolation is performed for the isotropic component of the BRDF for the remaining 9 MERIS spectral bands. (In future, it is planned to use spectral databases such as ASTER or SDRs from CHRIS/PROBA or CAR data to refine this approach) Currently spectral interpolation for the 2 sets of broadband albedos (0.4-0.7µm, 0.4-3µm) is performed using the MISR- equivalent bands. Work is in progress to refine this approach QC information is provided for 4 common spectral albedos and Nadir BRDF Adjusted Reflectances (NBAR) through statistical summaries of intercomparison with MOD43C1 (albedo)/MOD43C3 (NBAR)

7. ESA/ESRIN contract 18348/04/I-LG BRDF retrieval: vegetation Kernel-Driven Semiempirical BRDF Model BRDF Model Linear combination of two BRDF shapes and a constant BRDF shapes described by kernels, which are Trigonometric functions of incidence and view angles Derived from physical models for surface scattering (Ross-Thick Li- Sparse Model Reciprocal (RTLSMR) for leaf “cloud” and shadows) Analytical Form: where is a constant for isotropic scattering ; are trigonometric functions providing shapes for geometric-optical and volume-scattering BRDFs; and are constants that weight the two BRDFs MOD43C2 Product supplies values of f for each 0.05º pixel and separate C code to calculate k

8. ESA/ESRIN contract 18348/04/I-LG BRDF retrieval: vegetation Magnitude inversion We determine a on a per-band basis by a least squares minimisation of the difference between directional reflectances (SDRs) predicted by the MOD43C2 BRDF parameters and those actually measured by the MERIS sensor The predicted measurements are found by running the RTLSMR model in the forward mode using the MOD43C2 BRDF parameters under the same view and illumination angles as the MERIS measurements available Performed on 4 common spectral bands between MODIS (469,555,645,859nm) and MERIS (490,560,665,865nm)

9. ESA/ESRIN contract 18348/04/I-LG Albedo retrieval: vegetation Black-sky, White-sky and solar zenith dependence Direct Hemispherical Reflectance, is given by Black-sky (NO diffuse) albedo, is given by Diffuse bi-Hemispherical reflectance, is given by White-sky (diffuse ONLY) albedo, is given by

10. ESA/ESRIN contract 18348/04/I-LG Albedo retrieval: vegetation Black-sky, Blue-sky and solar zenith dependence The solar angle dependence can be approximated by, Under actual atmospheric conditions given the aerosol optical depth, the blue-sky albedo is given by Where is the fraction of diffuse skylight

11. ESA/ESRIN contract 18348/04/I-LG Albedo retrieval: vegetation Narrow-to-broadband conversion Gao et al. (2003) derived a first approximation to broadband albedo conversion factors based on those from MISR which are taken from his paper with VIS (0.4-0.7µm), NIR (0.7-3µm) and Shortwave (0.4-3µm)

12. Albedo retrieval scheme Meris L2 SDRs MOD43C2 BRDF (0.05º) + QA#1 flags BIN MERIS SDRs (0.05º x 0.05º) over 16-day MOD43C2 MAGNITUDE INVERSION with MOD43C2 INTEGRATE MERIS ALBEDO FOR 16- DAY PERIOD MONTHLY/ SEASONAL AVERAGE RE-PROJECT TO 10Km/0.05º QA#2 Nsamps, ave± stddev, min, max CALCULATE MERIS NBAR 0.05º DAILY CALCULATE NBAR OVER MODIS 16 DAY PERIOD QA3 Nsamps, ± std.dev. MERIS 0.05º 16- DAY NBAR INTERCOMPARE WITH MOD43C3 DIFF STATS MOD43C3 NBAR (0.05º) MERIS 0.05º 16- DAY ALBEDOS INTERCOMPARE WITH MOD43C1 MOD43C1 ALBEDO (0.05º) INTERPOLATE ALBEDO VALUES TO 9 OTHER BANDS + INTEGRATE TO VIS, NIR, SW Broadbands MERIS 10KM/005º 13- SPECTRAL + 4 BROADBAND MONTHLY+ SEASONAL ALBEDOS N.B. Status: Sample products produced for Europe. Global production completion due by end January 2006.

13. ESA/ESRIN contract 18348/04/I-LG First MERIS albedo product: DoY 257 (16- day time period : 14/9/03-29/9/03): all bands

14. ESA/ESRIN contract 18348/04/I-LG First MERIS albedo product: DoY 257 (16-day time period : 14/9/03-29/9/03): Band 5 (green)

15. ESA/ESRIN contract 18348/04/I-LG Validation approach(1) Difference statistics between MERIS-Albedo and MODIS gap-filled albedo product (Moody et al., 2005) for common bands being analysed for the same 16-day time periods Inter-comparisons are also being performed with –MISR 0.5º “true monthly” level-3 product (2003) –POLDER2 0.05º resampled from 6km sinusoidal gridded 30-day products reported on the 15th of each month (Apr03-to-Oct03) –MODIS gap-filled albedo product sampled for weighted average of constituent 16-day time periods within the months of Jan, Feb, Sep, Oct, Nov-03 Initial inter-comparisons follow with POLDER2, MODIS gap-filled and MISR Detailed inter-comparison also shown for MODIS gap-filled and MISR

16. ESA/ESRIN contract 18348/04/I-LG Validation issue: finding temporal coincidences for 16-day products to match them up against monthly climate modelling requirements

17. ESA/ESRIN contract 18348/04/I-LG MERIS (16-day,DoY=257-272) cf. POLDER2 (30-day, DoY=244-273) at 0.05º resolution N.B. Poor atmospheric correction of POLDER-2

18. ESA/ESRIN contract 18348/04/I-LG MERIS (16-day,DoY=257-272) cf. POLDER2 (30-day, DoY=244-273) at 0.05º resolution with coastlines N.B. Very poor geocoding of POLDER-2. Decided NOT to perform any further inter-comparisons with MERIS and MISR until this problem is fixed MERIS: 865nm POLDER2: 865nm

19. ESA/ESRIN contract 18348/04/I-LG MERIS cf. MODIS gap-filled albedo for common bands (16-day, DoY=257-272) at 0.05º resolution N.B. Noticeable differences in colour and bright albedo patterns MERIS: 665, 560, 490MODIS: 665, 560, 470

20. ESA/ESRIN contract 18348/04/I-LG MERIS vs MODIS gap-filled albedo for common bands (16-day, DoY=257-272) at 0.05º resolution N.B. 2D correlation improves with increasing wavelength 490 vs 470 665 vs 665 865 vs 869

21. ESA/ESRIN contract 18348/04/I-LG MERIS (weighted average DOY 241(13), 257(16), 273(1)) cf. MISR (30-day, DoY=244-273) at 0.5º resolution N.B. MISR higher Albedo cf. MERIS MERISMISR 665,560,443nm 865,665,560nm 672,558,443nm 867,672,558nm

22. ESA/ESRIN contract 18348/04/I-LG MERIS [weighted average DOY 241(13/30), 257(16/30), 273(1/30)] vs MISR (30-day, DoY=244-273) at 0.5º resolution N.B. MISR albedo values higher than MERIS but overall good correlation. Plan to compare instantaneous MISR albedo at 1.1km with MERIS 16-day. This requires modification of BEAM ingest for MISR Level 2AS data. This is planned later in 2006. 443 vs 443 867,672,558nm 560 vs 558 665 vs 672 865 vs 857

23. ESA/ESRIN contract 18348/04/I-LG MODIS gap-filled product [weighted average DOY 241(13/30), 257(16/30), 273(1/30)] MINUS MISR (30- day, DoY=244-273) at 0.5º resolution (MODIS-MISR)/MISR normalised difference albedo. MISR always HIGHER than MODIS ±2%±5%±10%±20%±50%±100% 470nm 555nm 859nm 665nm

24. ESA/ESRIN contract 18348/04/I-LG Conclusions First demonstration of data fusion of MERIS and MODIS Substantial interest in user community for monthly (and seasonal albedo products. Little interest in 16-day products Simple weighted average of number of days within a 16-day cycle appears to provide reasonable values of monthly albedos Significant differences between MISR and gap-filled MODIS albedos with MISR consistently higher than either MODIS or MERIS albedos Some differences can be explained due to the derivation of snow-free MODIS gap-filled product Good agreement (as expected) between MERIS and MODIS gap-filled products for common spectral bands

25. ESA/ESRIN contract 18348/04/I-LG Planned Prospects Improvement in POLDER georeferencing so POLDER can be used to compare against MISR and MERIS Intercomparisons of monthly MISR vs MODIS gap-filled albedo for 5 years of data Intercomparisons of MISR L2AS with MODIS gap-filled albedo, POLDER and MERIS Improvement of spectral interpolation using CHRIS/PROBA and GSFC-CAR measurements including development of CHRIS/PROBA processing chain within BEAM based on MERIS Production of further years of MERIS spectral albedos (2002, 2004, 2005, 2006) at current resolutions Development of modified processing chain for production of MERIS 300m spectral albedos for 2005 using MOD43B1 (500m, Collection 5) BRDFs including dealing with snow (explicitly) Publication of MERIS spectral albedo browse products as WMS layers within ICEDS and for use by other WMS browsers as cascaded datasets Publication of underlying MERIS spectral albedos as WCS layers at BC including direct linkage to BEAM and subsetting via WMS

26. ESA/ESRIN contract 18348/04/I-LG CD-ROM, DVD-ROM 1- Physical media 2- Internet USERS ftp or http Near Real Time (NRT): Rolling Archive or On request Near Real Time (NRT): Rolling Archive or On request 3- via telecom satellite (NRT) DDS broadcast (in Europe) ( deployment for Africa ) DDS broadcast (in Europe) ( deployment for Africa ) Product Data delivery : current options Archived data : gradual availability Archived data : gradual availability large capacity media

27. ESA/ESRIN contract 18348/04/I-LG Internet Telecom satellite broadcast 7-days Rolling Archive (ftp or http) 7-days Web File Server (http) Data Dissemination System (DDS) broadcast Complete productGeographical selectionAntenna needed advantages Off-the-shelf Complete product Worldwide access Off-the-shelf User select part of a product and decrease the volume for download Worldwide access Independent of Internet, i.e. of network performances issues inconvenience Rely on Internet (user network performances) Specific equipment needed European reception coverage only (under extension to Africa) cost for usersNo cost (apart from Internet connection) 350 € + 1.2m antenna (DDS-Europe) ENVISAT data access to Near Real Time data

28. ESA/ESRIN contract 18348/04/I-LG Eutelsat W1 footprint Typical 1.2 m DDS receiving antenna Data Dissemination System (DDS) DDS Europe DDS Africa About 2.5 m receiving antenna C-band Dissemination of global MERIS RR Level 1 & Level 2 products

29. ESA/ESRIN contract 18348/04/I-LG ICEDS portal (http://iceds.ge.ucl.ac.uk)