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 Zühlke, Norman Fomferra (BC) Jürgen Fischer, Réné Preusker, Thomas Schröder (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
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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 Zühlke, Norman Fomferra (BC)
Jürgen Fischer, Réné Preusker, Thomas Schröder (FUB)Peter Regner (ESA/ESRIN)
*Professor of Image Understanding and Remote SensingMISR & MODIS Science Team Member (NASA EOS Project)
HRSC Science Team Member (ESA Mars Express 2003)Chair, CEOS-WGCV Terrain mapping sub-group
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
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)
» 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
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 MERIS MODIS Spectral Bands (see Table 2)
250m (2 land bands) 500m (5 land bands) 1000m (29 non-land bands)
FoV (swath width) ±34.25º (1150km) ±55º (2330km) Global coverage 3 days 1-2 times/day (both Terra and
Aqua) Repeat cycle 35 days 16 days Orbit Altitude 800km 705km Equator crossing 10am (descending) 10:30am (descending-Terra)
1:30pm (ascending-Aqua) Launch date 1 March 2002
(ENVISAT) 18 December 1999 (Terra)
MERIS MODIS MISR POLDER
490±5 459-479 425-467 443±10
560±5 545-565 543-572 565±10
665±5 620-670 661-683 670±10
865±10 841-876 847-886 865±20
1230-1250
1628-1652
2105-2155
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)
Linear combination of two BRDF shapes and a constantBRDF 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:
R = fiso+ fgeokgeo+ fvolkvolwhere
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
fisokgeo , kvol
fgeo , fvol
MOD43C2Product supplies values of f for each 0.05º pixel and separate C code to calculate k
ESA/ESRIN contract 18348/04/I-LG
BRDF retrieval: vegetationMagnitude 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)
€
RMERIS (θ ,υ ,φ ,λ ) = a • RMODIS (θ ,υ ,φ ,λ )
ESA/ESRIN contract 18348/04/I-LG
Albedo retrieval: vegetationBlack-sky, White-sky and solar zenith dependence
Direct Hemispherical Reflectance, is given by
€
hk(θ )
€
hk(θ ) =1
πK k
0
π / 2
∫0
2π
∫ (θ ,υ ,φ )sin(υ )cos(υ )dυ dφ
Black-sky (NO diffuse) albedo, is given by
€
abS (θ ,λ ) = fk(λ )hkk
∑ (θ )
€
abS
Diffuse bi-Hemispherical reflectance, is given by
White-sky (diffuse ONLY) albedo, is given by
€
H k = hk0
π / 2
∫ (θ )sin(θ )cos(θ )dθ
€
H k
€
awS (λ ) = fk(λ )H kk
∑
€
awS
ESA/ESRIN contract 18348/04/I-LG
Albedo retrieval: vegetationBlack-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
€
abS (θ ,λ ) = fiso(λ )(goiso+ g1iso
θ 2 + g2 isoθ 3 )+ fvol(λ )(govol
+ g1volθ 2 + g2vol
θ 3 )+ fgeo(λ )(gogeo+ g1geo
θ 2 + g2geoθ 3 )
€
gjk for kernel, k k=isotropic k=RossThick k=Li-Sparse
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) VIS-Broadband NIR-Broadband SW-Broadband
Blue 0.3511 0.0 0.1587 Green 0.3923 0.0 -0.2463 Red 0.2603 0.0 0.5442 NIR 0.0 0.6088 0.3748 Intercept -0.003 0.1442 0.0149
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 <MERIS> 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 (16-day,DoY=257-272) cf. POLDER2 (30-day, DoY=244-273) at 0.05º resolution
N.B. Poor atmospheric correction of POLDER-2
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
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, 490 MODIS: 665, 560, 470
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
490vs470
665vs665
865vs869
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 higherAlbedo cf. MERIS
MERISMISR
665,560,443nm
865,665,560nm
672,558,443nm
867,672,558nm
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
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
859nm665nm
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
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
ESA/ESRIN contract 18348/04/I-LG
CD-ROM, DVD-ROM
1- Physical media1- Physical media
2- Internet2- Internet USERS
ftp or h
ttp
ftp or h
ttpNear Real Time (NRT):
Rolling Archiveor
On request
Near Real Time (NRT): Rolling Archive
orOn request
3- via telecom satellite (NRT)3- via telecom satellite (NRT)
DDS broadcast(in Europe)
( deployment for Africa )
DDS broadcast(in Europe)
( deployment for Africa )
Product
Data delivery : current optionsData delivery : current options
