Description of the software Heliosat-2 for the conversion of images acquired by Meteosat satellites in the visible band into maps of solar radiation available at ground level

This document describes the software Heliosat-II developed by the Groupe Télédétection & Modélisation, Centre d'Energétique, a joint research unit of Armines and Ecole des Mines de Paris. The method Heliosat-II was developed by this research group in 2000-2001, partly with the support of the European Commission (project SoDa, contract DG "INFSO" IST-1999-12245, http://www.sodais. com). This method converts images acquired by the satellite Meteosat into maps of global irradiation received at ground level. Under concern are the images acquired in the visible band of the Meteosat sensor. The software was developed in C for a Unix station. The present document describes the various libraries and procedures. It describes how these can be implemented for the correct execution of the whole method. The procedures described here comprise I/O orders that are to be tailored to the specific format for Meteosat images. The method can be applied to other geostationary satellites offering similar broadband in the visible range (0.4 - 1.1 mm). The input images are geometrically superimposable images. Calibration coefficients exist that convert digital counts into radiances (W m-2 sr-1)

La base de données HelioClim de rayonnement solaire disponible au sol

La ressource solaire disponible au sol est devenue un enjeu majeur dans les nouvelles technologies de développement durable. Les utilisateurs publics et privés de l'énergie solaire ont besoin d'un accès facile et rapide à cette information, sous forme ponctuelle ou sous forme de cartes à l'échelle locale, régionale, ou nationale. Les images satellitaires apparaissent comme les mieux appropriées pour couvrir une grille d'échantillonnage de haute résolution, régulière dans l'espace et dans le temps. Les stations de mesures au sol n'offrent en effet pas ces avantages : répartition irrégulière nécessitant des interpolations ou extrapolations qui diminuent la précision du résultat, dates de mises en service différentes, format des données et unités de mesure non standardisés, accès aux données non centralisé et le plus souvent sous forme non adaptée aux besoins des utilisateurs, rendant finalement leur coût assez important. Mines ParisTech apporte une réponse innovante aux besoins des utilisateurs, d'une part dès 1986 en développant la famille de méthodes Heliosat qui permettent de convertir des images de satellites géostationnaires en carte de rayonnement global incident au sol, d'autre part en implémentant une chaine de traitement opérationnelle en temps réel entre la réception de l'image, son traitement par Heliosat-2, et son exploitation dans le système de base de données HelioClim

Using reduced data sets ISCCP-B2 from the Meteosat satellites to assess surface solar irradiance

International audienceThis paper explores the capabilities of a combination of the reduced data set ISCCP-B2 from the Meteosat satellites and the recently developed method Heliosat-2 to assess the daily mean of the surface solar irradiance at any geographical site in Europe and Africa. Firstly, we discuss the implementation of the method Heliosat-2. Secondly, B2-derived irradiances are compared to coincident measurements made in meteorological networks for 90 stations from 1994 to 1997. Bias is less than 1 W m-² for the whole set. Larger bias may be observed at individual sites, ranging from -15 to +32 W m-². For the whole set, the root mean square difference is 35 W m-² (17%) for daily mean irradiance and 25 W m-² (12%) for monthly mean irradiance. These accuracies are close to those of similar data sets of irradiance, such as Medias and NASA Surface Radiation Budget. It is concluded that B2 data can be used in a reliable way to produce long-term time-series of irradiance for Europe, Africa and the Atlantic Ocean

The method Heliosat-2 for deriving shortwave solar radiation from satellite images

International audienceThis article presents the method Heliosat-2 that converts observations made by geostationary meteorological satellites into estimates of the global irradiation at ground level. This new version integrates the knowledge gained by various exploitations of the original method Heliosat and its varieties in a coherent and thorough way. It is based upon the same physical principles but the inputs to the method are calibrated radiances, instead of the digital counts output from the sensor. This change opens the possibilities of using known models of the physical processes in atmospheric optics, thus removing the need for empirically defined parameters and of pyranometric measurements to tune them. The ESRA models are used for modeling the clear-sky irradiation. The assessment of the ground albedo and the cloud albedo is based upon explicit formulations of the path radiance and the transmittance of the atmosphere. The method Heliosat-2 is applied to Meteosat images of Europe for the months of January 1995, April 1995 and July 1994. Pyranometric measurements performed by thirty-five meteorological stations are used to assess the performances that are close to those of Heliosat-1 found in the literature. Possible improvements are discussed

Twelve monthly maps of ground albedo parameters derived from MODIS data sets

International audienceThe National Aeronautics and Space Administration (NASA) of the USA is making available to anyone worldwide maps of ground albedo parameters that are derived from the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument. The first parameter fiso describes the isotropic part of the bidirectional reflectance distribution function (BRDF); the two other parameters fvol and fgeo are linked to the viewing and illuminating geometry and describe the anisotropic part of the BRDF. These maps exhibit missing values. This communication describes a series of 12 monthly maps of the BRDF parameters with no missing values available on the Web. In addition, a method for computing the ground albedo is proposed that does not require the a priori knowledge of the ratio of the direct to the global irradiance

The operational calibration of images taken in the visible channel of the Meteosat-series of satellites

International audienceA method and its implementation are presented for the automatic calibration of the images taken in the visible channel of the Meteosat series of satellites. The method performs on a daily basis and is based on a statistical analysis of two images: one when the sun illuminates the entire field of view of Meteosat, the other during nighttime. This approach does not require any information about atmospheric and surface parameters, and therefore can be easily performed either on archived data, or in quasi-real time when receiving the images. Daily calibration coefficients were obtained since 1985 and are available on the Internet. The results are fully consistent with previous studies

The HelioClim Project: Surface Solar Irradiance Data for Climate Applications

URL : http://www.mdpi.com/2072-4292/3/2/343/International audienceMeteosat satellite images are processed to yield values of the incoming surface solar irradiance (SSI), one of the Essential Climate Variables. Two HelioClim databases, HC-1 and HC-3, were constructed covering Europe, Africa and the Atlantic Ocean, and contain daily and monthly means of SSI. The HC-1 database spans from 1985 to 2005; HC-3 began in 2004 and is updated daily. Their quality and limitations in retrieving monthly means of SSI have been studied by a comparison between eleven stations offering long time-series of measurements. A good agreement was observed for each site: bias was less than 10 W/m² in absolute value (5% in relative value) for HC-3. HC-1 offers a similar quality, though it underestimates the SSI for latitudes greater than 45° and less than −45°. Time-series running from 1985 to date can be created by concatenating the HC-1 and HC-3 values and could help in assessing SSI and its changes

Developing a database using Meteosat data for the delivery of solar radiation assessments at ground level

International audienceAn information system, called HelioClim, is offered for answering the needs for long-term time-series of solar radiation data. These data originate from the processing of spaceborne observations made in the visible range by geostationary satellites to derive solar radiation available at ground level. The recent method Heliosat 2 is used. It offers several improvements in operation and accuracy with respect to previous methods. Typical bias for irradiance for a month is 3 W m(-2). A database is being produced, covering the Eastern Atlantic Ocean, Europe and Africa from 1985 onwards and for each day. This database is accessible through the SoDa service on a free basis (http://www.soda-is.com)