NRT Product available since Dec 2010
Evapotranspiration (ET) accounts for the flux of water evaporated at the Earth-atmosphere interface (soil + vegetation + water bodies) and transpired by vegetation through stomata in its leaves as a consequence of photosynthetic processes. Evapotranspiration, plays a crucial role in the recycling of precipitation, in soil water availability and consequently on food production. Evapotranspiration is dependent mainly on the solar energy available to vaporize the water and in water content in the soil layers. Because of the dependence on solar energy, ET varies with latitude, season of year, time of day, and cloud cover. It is also an important component of the water cycle and it is associated with the latent heat flux (LE), a key link between the energy and water cycles. Accurate measurements of evaporation rates at large spatial scales are central to understanding land and atmosphere interactions in the context of global warming. It is of great importance in disciplines like weather forecasting, water management, agriculture, hydrology, ecology and global climate monitoring.
This operational product is documented in the Algorithm Theoretical Basis Document (ATBD), Product User Manual document (PUM) and the Product Output Format document (POF) The validation results for this product are available in the (VR) document.
Please see Product Peer-Review publications in References.
The use of LSA SAF products in publications is kindly requested to be duly acknowledged:
ET and DMET were provided by the EUMETSAT Satellite Application Facility on Land Surface Analysis (LSA SAF; Trigo et al., 2011)
Trigo, I. F., C. C. DaCamara, P. Viterbo, J.-L. Roujean, F. Olesen, C. Barroso, F. Camacho-de Coca, D. Carrer, S. C. Freitas, J. García-Haro, B. Geiger, F. Gellens-Meulenberghs, N. Ghilain, J. Meliá, L. Pessanha, N. Siljamo, and A. Arboleda, 2011: The Satellite Application Facility on Land Surface Analysis. Int. J. Remote Sens., 32, 2725-2744, doi: 10.1080/01431161003743199
The evapotranspiration generated in the framework of the LSA-SAF consortium consist on two outputs: the instantaneous ET product (MET) with a time interval of 30 minutes (in mm/h) and the daily evapotranspiration product (DMET) obtained by integrating instantaneous values over the whole day (in mm/d). Both products are generated over the full MSG disc domain, covering Europe, Africa and most of South America at SEVIRI spatial resolution (3 km at sub satellite point) Together with the ET estimates, additional information about the quality of the estimation is provided. In the case of the MET product, the quality flag is calculated based on the quality of input variables, the algorithm performances and pre/post processing manipulations on the estimates. For DMET product, two additional images are provided: the first one contains information on the percentage of missing values for every pixel in the considered day and the second one provides information on the number of missing instantaneous images in the same day.
The methodology adopted for the ET product combines the advantages of satellite remote sensing (high repetition rate, wide area coverage, high spatial resolution) with the ability of Soil Vegetation Atmosphere Transfer (SVAT) models to describe physical and physiological process occurring in vegetation canopy. In this approach, radiative data derived from Meteosat Second Generation (MSG) geostationary satellites together with recent land-cover information (from ECOCLIMAP land cover database + LSA-SAF VEGA products) and ancillary meteorological data (from ECMWF forecasts) are used to drive a physical model of energy exchange between the soil-vegetation-atmosphere systems. The scope of the method is limited to evaporation from terrestrial surfaces and inland water rather than from ocean surfaces. The ET product has been validated on different climatic and environmental conditions, providing evidence that the algorithm is able to produce ET estimates with accuracy equivalent to the accuracy of measurements (validation report -VR-). The approach adopts the tile approach in which each model entity (pixel), is composed of a mix of homogeneous plant functional types (tiles), representing main land-coverage types (bare soil, grassland, crops, forests). The surface energy balance is solved for each tile separately, and the resulting pixel ET value is obtained as the weighted contribution of all tiles in the pixel.
The ET product output and accompanying quality flag, are stored on single files on HDF5 (Hierarchical Data Format, version 5) format. HDF5 is a machine independent standard for storing/sharing scientific data. In this format, each file contains also the necessary information for manipulating the data. For more information on this data format see https://www.hdfgroup.org/
The main sources of uncertainties on the ET product come from: a) the physical formalism of the algorithm itself, b) from the errors associated with each input of the algorithm, in particular from other LSA-SAF components and c) from surface heterogeneity and land cover classification used in the algorithm. From a global point of view, most uncertainties cumulated on the ET results from sensors performance, accuracy of cloudy pixels identification, accuracy of atmospheric corrections which propagates into algorithms using this information, and providing input for the ET algorithm.
Ghilain, N., Arboleda, A., and Gellens-Meulenberghs, F: Evapotranspiration modelling at large scale using near-real time MSG SEVIRI derived data, Hydrol. Earth Syst. Sci., 15, 771-786, doi:10.5194/hess-15-771-2011, 2011.
Ghilain, N., Arbeda, A., Gellens-Meulenberghs, F: Evapotranspiration monitoring in semi-arid areas using MSG/SEVIRI derived data; improvements from the use of leaf area index and land surface temperature, Proceedings of EUMETSAT's user conference, Vienna, Austria, September, 2013.
Gellens-Meulenberghs, F., Ghilain, N. and Arboleda, A: Land surface evapotranspiration as seen from METEOSAT second generation satellites: LSA-SAF developments and perspectives. Proceedings of the IGARSS 2012 conference, IEEE TGRS, IEEE Publisher, ISBN: 978-1-4673-1159-5, 1018-102, 2012.
Trigo, I. F., DaCamara, C. C., Viterbo, P., Roujean, J.-L., Olesen, F., Barroso, C., de Coca, F. C., Carrer, D., Freitas, S. C., Garcia-Haro, J., Geiger, B., Gellens-Meulenberghs, F., Ghilain, N., Melia, J., Pessanha, L., Siljamo, N., & Arboleda, A: The Satellite Application Facility on Land Surface Analysis, Int. J. Remote Sens., 32 , 2725-2744, 2011.
Arboleda, A., Ghilain, N., Gellens-Meulenberghs, F: EUMETSAT's LSA-SAF evapotranspiration: comparisons of operational product to observations and models at hydrological basins scale, proceedings of the EUMETSAT conference 2011, Oslo, Norway, 2011.
RMI, The EUMETSAT Satellite Application Facility on Land Surface Analysis (LSA SAF) Evapotranspiration Validation Report (VR), Evapotranspiration Product User Manual (PUM), Evapotranspiration Algorithm Theoretical Basis Document (ATBD) at : (http://landsaf.ipma.pt)
Gellens-Meulenberghs, F., Arboleda, A. and Ghilain, N: Towards a continuous monitoring of evapotranspiration based on MSG data. Symposium on Remote Sensing for Environmental Monitoring and Change Detection. IAHS, 228-234,. IUGG, Perugia, Italy, July 2007.
Gellens-Meulenberghs, F., Arboleda, A. and Ghilain, N.: Status of development of the LSA-SAF evapotranspiration product. Proc. 2nd LSA-SAF Training Workshop, Lisbon, 8-10 March, 2006.
Arboleda A., Ghilain, N., Gellens-Meulenberghs, F.: The LSA-SAF evapotranspiration product - first results with MSG, Proceedings of the 2005 EUMETSAT meteorological satellite data user's conference, Dubrovnik, Croatia, 19th-23th September, 2005.