overview of satellite based products for global et matthew mccabe, carlos jimenez, bill rossow,...

OVERVIEW OF SATELLITE BASED PRODUCTS FOR GLOBAL ET

Matthew McCabe, Carlos Jimenez, Bill Rossow, Sonia Seneviratne, Eric Wood and numerous data providers & contributors…

GEWEX LANDFLUX PROJECT“Produce a GLOBAL multi decadal surface flux product”‐ Jimenez et al (2011) “Global inter-comparison of 12 land surface

heat flux estimates” JGR 116(2), D02102 Mueller et al (2011) “Evaluation of global evapotranspiration

datasets: first results of the LandFlux-EVAL project” GRL, 38, LO6402

AVAILABLE PRODUCTS & SCALES

Product Theoretical Basis Spatial Resolution

Temporal Resolution

Temporal Coverage

UMONT-A PM 1km 8-day 2000-2010UMONT-B PM 8km Daily 1983-2006

CSIRO-PML PM 0.5° Monthly 1981-2006PRU-1 PM 1°-2° 3hr/Daily 1984-2007PRU-2 MOST 5km 3hr/Daily 2000-2010PRU-3 PT 1°-2° 3hr/Daily 1984-2007

UCB-JPL PT 1km-1° Monthly 1984-2010GLEAM PT 0.25° Daily 1984-2007ALEXI* MOST 0.25° Daily 2000-2010

UMT/BNU* Empirical-PM 1° Daily 1982-2006Paris-O Neural Network 0.5° Monthly 1992-1999

Max-Planck Tree-ensemble 0.25° Monthly 1982-2008

PRODUCT SIMILARITIESMonin-Obukhov Similarity Theory (MOST)

considering or ignoring stability correction terms + other assumptions lead to different ET formulations (Penman, Priestley-Taylor etc…)

PRODUCT DIFFERENCES Spatial – what does 0.25° (or 1°) ET represent? Temporal – how are values scaled (consistency in EF?) Forcing clearly plays a major role in flux variation

Note that no products use the same forcing!

PRODUCTION & EVALUATIONOutcome of EGU-Vienna meeting (April, 2011: Consensus amongst several product participants Version 0 will be a number of ‘competing’ products Agreement to run using common forcing – but yet to

agree on that format (some problematic variables) Likely SRB 4.0 rad and associated met inputs 3 hourly, 0.5 degree LE & H (common methodology for G??)

When? Need to compile forcings (timing of SRB 4.0)

PRODUCT EVALUATION PLANSProduct assessment requires analysis over a range of regional and global scales: Wood@Princeton: have compared SEBS, PM & PT

using common Aqua forcing for 3 years; 1984-2007 ensemble approach globally

Fisher@JPL (planned): 5 RS-ET models and 3 LSMs using identical forcing data and model protocols. 1 km resolution, validated against 253 sites (La Thuille)

McCabe@UNSW (just started): GEWEX-RHP scale multi-model comparison with common WRF forcing

Sonia@ETH + Carlos@P-O (just heard)

MULTI-MODELS OVER THE MDBUsing common WRF forcing: a) PM, b) SEBS, c) WRF-NOAHshows inherent model differences that need investigation

Latent Heat Flux (W/m2)

4000

a) b) c)

MULTI-MODELS AT TUMBARUMBAUsing common forcing – PM, SEBS, WRF

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WFEBPMAAPTObs

MDB INTERCOMPARISON

MDB INTERCOMPARISON

Dry pixel, 10km resolution

MDB INTERCOMPARISON


MDB INTERCOMPARISON

Dry, Semi, Wet pixels (top to bottom), 50km resolution

MDB INTERCOMPARISON

Observations, Tumbarumba

MULTI-SENSOR ESTIMATESMulti-model/multi-sensor runs from Princeton group: SEBS, PM and modified-PT approach ISCCP and SRB for forcing (and PU forcing) Issues in ISCCP…so used 2 SRB data sets (SRB/SRB-QC) daily time scale/0.5 degree/1984-2007

Input data initially evaluated against PU 50 yr forcing data…resulting in a composite dataset

MULTI-SENSOR ESTIMATES

MULTI-SENSOR ESTIMATESMulti-model/multi-sensor runs from Princeton group: Issues in Ts-Ta between data sets (which is right??) Noted issues in humidity and temp trends (compared

to PU data set)

Uncertainty b/w models > uncertainty in rad forcing Largest uncertainty (absolute) in humid tropics Largest uncertainty (mean) in transitional regions

MODEL EVALUATIONRange of evaluation efforts being undertaken: Tower data (where, when, number) Basin (P-ET-dS/dt) – which P, which dS/dT, accuracy in R Atmospheric water budgets Hydrological consistency

Need a co-ordinated approach to product evaluation Requires identification of high quality data-sets Agreement on spatial and temporal scales Metrics for assessment

CONTINUED EVALUATIONNeed to examine issues of: Model interdependencies (forcing and formulation) Sensitivity of approaches to forcing variables Regional scale (MDB) and daily evaluation of retrievals

- do products represent diurnal variability (3 hourly)

- are spatial patterns reflected at the regional scale

- how consistent are the retrievals with other data

NEEDED DISCUSSIONS Significant uncertainties in radiation Accuracy of all data sets (ET as a Level 4 product) Consistency in ‘stable’ forcing (LULC, basin/land masks) Aerodynamic and surface properties are key: techniques

to derive these? Spatial and temporal scales – who are the users? Accuracy in evaluations (runoff & rainfall data-sets) How to include snow, interception Dual-source models and GEWEX independent datasets Regional scale intercomparisons (diurnal scale)

Overview of Satellite Based Products for Global ET

Matthew McCabe, Carlos Jimenez, Bill Rossow, Sonia Seneviratne, Eric Wood and numerous data providers & contributors…

BREAKDOWN OF APPROACHESPenman-Monteith assumptions: sufficient upwind fetch a uniform saturated surface the canopy satisfies the big leaf assumption approximate the slope of the saturation vapor pressure

curve with ambient temperature and water vapor

Priestley-Taylor assumptions: No advection, wet surface and long fetch, therefore,

wind function in the Penman function tends to zero

GEWEX LANDFLUX PROJECTWhat has been determined so far? Geographic patterns broadly consistent Large range in some regions esp. tropics & rainforests Range in IPCC model simulations not markedly

different from other data

More detailed analysis and interpretation is required! No common data set for algorithm inter-comparison No benchmark with which to compare data Inter-dependence of data sets is an issue

MDB INTERCOMPARISON

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SEBS WRF AMSR-ECLM NOAH



MULTI-SENSOR ESTIMATES

overview of satellite based products for global et matthew mccabe, carlos jimenez, bill rossow,...

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