Improving evapotranspiration in a land surface model using biophysical variables derived from MSG/SEVIRI satellite

Monitoring evapotranspiration over land is highly dependent on the surface state and vegetation dynamics. Data from spaceborn platforms are desirable to complement estimations from land surface models. The success of daily evapotranspiration monitoring at continental scale relies on the availability, quality and continuity of such data. The biophysical variables derived from SEVIRI on board the geostationary satellite Meteosat Second Generation (MSG) and distributed by the Satellite Application Facility on Land surface Analysis (LSA-SAF) are particularly interesting for such applications, as they aimed at providing continuous and consistent daily time series in near-real time over Africa, Europe and South America. In this paper, we compare them to monthly vegetation parameters from a database commonly used in numerical weather predictions (ECOCLIMAP-I), showing the benefits of the new daily products in detecting the spatial and temporal (seasonal and inter-annual) variability of the vegetation, especially relevant over Africa. We propose a method to handle Leaf Area Index (LAI) and Fractional Vegetation Cover (FVC) products for evapotranspiration monitoring with a land surface model at 3–5 km spatial resolution. The method is conceived to be applicable for near-real time processes at continental scale and relies on the use of a land cover map. We assess the impact of using LSA-SAF biophysical variables compared to ECOCLIMAP-I on evapotranspiration estimated by the land surface model H-TESSEL. Comparison with in-situ observations in Europe and Africa shows an improved estimation of the evapotranspiration, especially in semi-arid climates. Finally, the impact on the land surface modelled evapotranspiration is compared over a north–south transect with a large gradient of vegetation and climate in Western Africa using LSA-SAF radiation forcing derived from remote sensing. Differences are highlighted. An evaluation against remote sensing derived land surface temperature shows an improvement of the evapotranspiration simulations

Validation et modélisation de l'évapotranspiration sur la Belgique

Le processus d’évapotranspiration (ETR) reste actuellement difficile à évaluer. L’objectif poursuivi par cette recherche est de proposer une méthode suffisamment robuste pour pouvoir être appliquée à l’échelle pluriannuelle tout en permettant un suivi à pas de temps fin au cours de la journée. En s’appuyant sur l’état de l’art, l’étude s’intéresse successivement au cas idéalisé des surfaces homogènes puis à celui des surfaces hétérogènes. Depuis quelques années, l’IRM a entrepris d’automatiser son réseau de stations synoptiques. Un sous-ensemble de stations a été choisi afin d’être doté d’un équipement plus complet comprenant un mât météorologique destiné à effectuer des mesures de la température et de la vitesse du vent à plusieurs niveaux. Ces nouvelles données sont exploitées dans la méthode préconisée. Celle-ci combine la théorie de Monin-Obukhov et l’évaluation du bilan énergétique de surface pour calculer les flux turbulents de chaleur sensible et de chaleur latente ainsi que le flux d’ETR. La télédétection offre quant à elle la possibilité d’observer de vastes territoires. Un modèle diagnostique est proposé pour estimer les flux turbulents de surface et l’ETR sur l’ensemble de la Belgique. Il s’agit d’une variante simplifiée du schéma « Isba » de transfert sol-végétation-atmosphère. Des flux radiatifs déduits d’images du satellite Meteosat sont exploités en entrée. La résolution spatiale est celle du capteur infra-rouge utilisé jusque Meteosat-7 (5*9 km). L’application est réalisée sur la période 1994-2003 avec un pas de temps horaire ce qui représente une première dans le domaine. Des comparaisons sont effectuées avec les résultats obtenus aux stations automatiques de l’IRM et avec des données récentes des stations belges du réseau Fluxnet. Les résultats sont très satisfaisants. Le travail s’achève sur des perspectives de développements futurs, la recherche en la matière étant encore en pleine évolution.(PHYS 3) -- UCL, 200

Evapotranspiration and surface heat fluxes over Belgium: outcome and perspectives

The assessment of the evapotranspiration and of the related surface turbulent heat fluxes is of major importance for atmospheric modelling and for practical applications in the field of agronomy and environment management. A method of assessment of these variables has been elaborated. As geostationary satellites can provide spatial information with a fairly short time step, the method combines ground meteorological data and Meteosat data. Hourly archives of evapotranspiration and surface turbulent fluxes covering the Belgian territory are now available for more than four years. Monthly means for the different years may be compared to characterise the climate variability. An outcome of the procedure is drawn and some statistics on the obtained results are presented. New perspectives offered by the next generation of meteorological satellites are outlined. In the following years, it is intended to further develop the method in the framework of the Land-SAF set up by EUMETSAT.Évapotranspiration et flux de chaleur en surface sur la Belgique : bilan et perspectives. L'estimation de l'évapotranspiration et des flux turbulents de chaleur qui lui sont associés présente un grand intérêt pour la modélisation atmosphérique et pour les applications pratiques dans les domaines de l'agronomie et de la gestion de l'environnement. Une méthode d'estimation de ces variables a été mise au point. Afin de tirer parti de la possibilité offerte par les satellites géostationnaires de fournir des informations spatiales avec des pas de temps relativement courts, la méthode combine des données météorologiques observées à partir du sol et des données Meteosat. Des données d'archive horaires de l'évapotranspiration et des flux turbulents en surface couvrant le territoire de la Belgique sont actuellement disponibles pour plus de quatre années. Les moyennes mensuelles peuvent être comparées d'une année à l'autre pour caractériser la variabilité du climat. Un bilan de la procédure est esquissé et des statistiques sont établies sur les données obtenues. Les perspectives offertes par la nouvelle génération de satellites météorologiques sont soulignées. Il est prévu de poursuivre le développement de la méthode dans les prochaines années dans le cadre de la "SAF-Land "d'EUMETSAT

Improving evapotranspiration in a land surface model using biophysical variables derived from MSG/SEVIRI satellite

Monitoring evapotranspiration over land is highly dependent on the surface state and vegetation dynamics. Data from spaceborn platforms are desirable to complement estimations from land surface models. The success of daily evapotranspiration monitoring at continental scale relies on the availability, quality and continuity of such data. The biophysical variables derived from SEVIRI on board the geostationary satellite Meteosat Second Generation (MSG) and distributed by the Satellite Application Facility on Land surface Analysis (LSA-SAF) are particularly interesting for such applications,as they aimed at providing continuous and consistent daily time series in near-real time over Africa, Europe and South America. In this paper, we compare them to monthly vegetation parameters from a database commonly used in numerical weather predictions (ECOCLIMAP-I), showing the benefits of the new daily products in detecting the spatial and temporal (seasonal and inter-annual) variability of the vegetation, especially relevant over Africa.We propose a method to handle Leaf Area Index (LAI) and Fractional Vegetation Cover (FVC) products for evapotranspiration monitoring with a land surface model at 3–5 km spatial resolution. The method is conceived to be applicable for near-real time processes at continental scale and relies on the use of a land cover map.We assess the impact of using LSASAF biophysical variables compared to ECOCLIMAP-I on evapotranspiration estimated by the land surface model HTESSEL. Comparison with in-situ observations in Europe and Africa shows an improved estimation of the evapotranspiration, especially in semi-arid climates. Finally, the impact on the land surface modelled evapotranspiration is compared over a north–south transect with a large gradient of vegetation and climate inWestern Africa using LSA-SAF radiation forcing derived from remote sensing. Differences are highlighted. An evaluation against remote sensing derived land surface temperature shows an improvement of the evapotranspiration simulations.status: publishe

Continuous Daily Evapotranspiration with Optical Spaceborne Observations at Sub-Kilometre Spatial Resolution

Evapotranspiration (ET) is a key parameter in the description of the energy and water fluxes over land. Continuous and spatially detailed ET simulations are thus required for a number of scientific and management-related purposes. These conditions are determined by the modelling approach and the composition of the forcing dataset. This study aimed at simulating daily ET in a diversity of climate and land cover conditions at a spatial resolution of ∼1 km and higher. The modelling approach was based on the algorithm driving the ET product developed and set in operations in the framework of the Satellite Application Facility on Land Surface Analysis programme (LSA-SAF). The implemented algorithm allowed the ingestion of biophysical parameters derived from SPOT-V and PROBA-V observations developed by the Copernicus Global Land Programme, as well as other model parameters at a similar spatial resolution. The model was tested at an ∼1 km spatial resolution in over 40 sites located in different climate and land cover contexts. The implementation at ∼300 m was tested in the upper Biebrza basin, in Poland. The simulations correlated well with the validation dataset (r2 > 0.75 in 80% of sites) and exhibited root mean squared values lower than 1 mm/day in 80% of the cases. The results also pointed to the need for refining the accuracy of soil moisture data sources, especially in dry areas. The results showed the ability of the modelling approach and the SPOT-V/PROBA-V missions to support the generation of long ET time series. They also opened the gate to incorporate Sentinel-3 in ET continuous modelling

Combining remote sensing imagery of both fine and coarse spatial resolution to estimate crop evapotranspiration and quantifying its influence on crop growth monitoring

peer reviewedThis study has been carried out in the framework of the GLOBAM -Global Agricultural Monitoring system by integration of earth observation and modeling techniques- project whose objective is to fill the methodological gap between the state of the art of local crop monitoring and the operational requirements of the global monitoring system programs. To achieve this goal, the research aims to develop an integrated approach using remote sensing and crop growth modeling. This paper concerns the use of MSG geostationnary satellite data for the calculation of Actual Evapotranspiration and its integration into a crop growth model