Assessment of Several Empirical Relationships for Deriving Daily Means of UV-A Irradiance from Meteosat-Based Estimates of the Total Irradiance

International audienceDaily estimates of the solar UV-A radiation (315–400 nm) at the surface, anywhere, anytime, are needed in many epidemiology studies. Satellite-derived databases of solar total irradiance, combined with empirical relationships converting totals into daily means of UV-A irradiance I UV , are a means to satisfy such needs. Four empirical relationships are applied to three different databases: HelioClim-3 (versions 4 and 5) and CAMS Radiation Service—formerly known as MACC-RAD—derived from Meteosat images. The results of these combinations are compared to ground-based measurements located in mid-latitude Europe, mostly in Belgium. Whatever the database, the relationships of Podstawczynska (2010) and of Bilbao et al. (2011) exhibit very large underestimation and RMSE on the order of 40%–50% of the mean I UV. Better and more acceptable results are attained with the relationships proposed by Zavodska and Reichrt (1985) and that of Wald (2012). The relative RMSE is still large and in the range 10%–30% of the mean I UV. The correlation coefficients are large for all relationships. Each of them captures most of the variability contained in the UV measurements and can be used in studies where correlation plays a major role

Solar UV radiation in Saint-Denis, La Réunion and Cape Town, South Africa: 10 years climatology and human exposure assessment at altitude

International audienceSolar ultraviolet radiation (UVR) monitoring is important since it depends on several atmospheric parameters which are associated with climate change and since excess solar UVR exposure and has significant impacts on human health and wellbeing. The objective of this study was to investigate the trends in solar UVR during a decade (2009-2018) in Saint-Denis, Reunion Island (20.9°S, 55.5°E, 85 m ASL) and Cape Town, South Africa (33.97°S, 18.6°E, 42 m ASL). This comparison was done using total daily erythema exposure as derived from UVR sensors continuously at both sites. Climatology over the 10-year period showed extreme UVR exposure for both sites. Slight changes with opposite trends were found, +3.6% at Saint-Denis and −3.7% at Cape Town. However, these two sites often experience extreme weather conditions thereby making the trend evaluation difficult. Human exposure assessment was performed for hiking activities at two popular high-altitude hiking trails on the Maïdo-Grand Bénare (Reunion) and Table Mountain (Cape Town) with a handheld radiometer. Extreme exposure doses of 64 SED and 40 SED (Standard Erythemal Dose, 1 SED = 100 J.m −2) were recorded, respectively. These high exposure doses highlight the importance of raising public awareness on the risk related to excess UVR exposure at tourist sites, especially those at high altitude

Validation of TROPOMI Surface UV Radiation Product

The TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor (S5P) satellite was launched on 13 October 2017 to provide the atmospheric composition for atmosphere and climate research. The S5P is a sun-synchronous polar-orbiting satellite providing global daily coverage. The TROPOMI swath is 2600 km wide, and the ground resolution for most data products is 7.2x3.5 km2 (5.6x3.5 km2 since 6 August 2019) at nadir. The Finnish Meteorological Institute (FMI) is responsible for the development and processing of the TROPOMI Surface Ultraviolet (UV) Radiation Product which includes 36 UV parameters in total. Ground-based data from 25 sites located in arctic, subarctic, temperate, equatorial and antarctic areas were used for validation of TROPOMI overpass irradiance at 305, 310, 324 and 380 nm, overpass erythemally weighted dose rate / UV index and erythemally weighted daily dose for the period from 1 January 2018 to 31 August 2019. The validation results showed that for most sites 60–80% of TROPOMI data was within ±20% from ground-based data for snow free surface conditions. The median relative differences to ground-based measurements of TROPOMI snow free surface daily doses were within ±10% and ±5% at two thirds and at half of the sites, respectively. At several sites more than 90% of clear sky TROPOMI data were within ±20% from ground-based measurements. Generally median relative differences between TROPOMI data and ground-based measurements were a little biased towards negative values, but at high latitudes where nonhomogeneous topography and albedo/snow conditions occurred, the negative bias was exceptionally high, from -30% to -65%. Positive biases of 10–15% were also found for mountainous sites due to challenging topography. The TROPOMI Surface UV Radiation Product includes quality flags to detect increased uncertainties in the data due to heterogeneous surface albedo and rough terrain which can be used to filter the data retrieved under challenging conditions

Analyse des mesures de l'expérience satellitaire SAGE III (algorithme d'inversion et validation des résultats)

Le dernier rapport du GIEC souligne que le rôle de la stratosphère dans le changement climatique est mal connu et invite à poursuivre son étude. Les mesures d'occultation solaire et in situ sont appropriées à cette étude mais il est nécessaire de les valider. Nous avons tout d'abord développé notre propre algorithme d'inversion des transmissions de SAGE III et avons comparé nos produits (profils verticaux des concentrations en O3 et en NO2 et coefficients d'extinction des aérosols (CEA)) à ceux issus de l'algorithme officiel et d'un troisième algorithme. De bons accords ont été obtenus entre ces inversions pour toutes les espèces. Nous avons poursuivi avec des comparaisons à des mesures corrélatives obtenues à l'aide d'instruments spatiaux et d'un instrument sous ballon (SPIRALE) déjà validés. Si on exclut les CEA, les résultats sont satisfaisants. Toutefois, la comparaison aux mesures in situ de SPIRALE obtenues aux abords du vortex polaire donne un désaccord pour NO2 démontrant ainsi les limites de l'occultation solaire dans la mesure d'espèces réactives dans des conditions dynamiques complexes. Une fois ces validations réalisées, nous nous sommes intéressés aux intrusions dans la stratosphère d'aérosols issus de feux de forêt et nous avons montré qu'elles conduisent à une forte augmentation du nombre de particules. Enfin, dans un cadre international, nous avons participé à la validation des instruments de la mission ACE (FTS, MAESTRO, Imager) à l'aide de SAGE III et de SPIRALE. Cela nous a permis de valider certains produits (O3 et NO2 de FTS et MAESTRO), d'en invalider d'autres (CEA d'Imager) et de confirmer le désaccord pour NO2 entre mesures in situ et à distance.One of the conclusions of the last IPCC reports is that the role of the stratosphere in the current climate change is not weil known. Consequently, stratospheric studies must continue. Solar occultation and in situ measurements are weil suited to these studies but it is necessary to validate them. First, we have developed our inversion algorithm of the SAGE III transmissions and we have compared our products (vertical profiles of O3 and N02 concentrations and of aerosol extinction coefficients (AEC)) to those from the officiaI algorithm and from a third algorithm. Good agreements are obtained between these inversions for ail species. Then, we have compared our products to those from correlative validated measurements obtained by satellite and balloon borne instrument (SPIRALE). Except CEA, results are satisfying. However, the comparison with in situ measurements from SPIRALE obtained on the edge of the polar vortex exhibits a disagreement for NO2 proving that the solar occultation method are not weil suited for reactive species in complex dynamical situation. Once these validations carried out, we have studied the stratospheric intrusions of aerosols resulting from forest fires and we have shown that they lead to a strong increase in the number of particles. Finally, in an international framework, we have taken part in the validation of the instruments of the ACE mission (FTS, MAESTRO and Imager) with SAGE III and SPIRALE data. That enabled us to validate sorne products (O3 and NO2 from FTS and MAESTRO), to invalidate others (CEA from Imager) and to confirm the discrepancy for NO2 between in situ and remote measurementsLILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

Analyse des mesures de l'expérience satellitaire SAGE III (algorithmes d'inversion et validation des résultats)

LILLE1-BU (590092102) / SudocSudocFranceF

Caractérisation du contenu atmosphérique en ozone et en aérosols au moyen de mesures spectrales dans l'UV (validation de l'instrument spatial OMI / AURA)

Depuis la découverte d'une diminution de la quantité d'ozone stratosphérique au milieu des années 1980, une surveillance de la couche d'ozone et de l'éclairement UV s'est mise en place à l'aide d'instruments au sol et spatiaux. Les mesures de rayonnement UV permettent d'une part de surveiller l'intensité de ce rayonnement arrivant au sol, et d'autre part de caractériser certains composés atmosphériques comme la quantité d'ozone et les aérosols. L'essentiel de ce travail concerne l'analyse et l'utilisation des mesures d'éclairement UV spectral effectuées sur deux sites de mesures au sol, à Villeneuve d'Ascq (VdA) et à Briançon. Nous avons poursuivi la restitution de la colonne totale d'ozone, ce qui nous a permis de disposer d'une série temporelle de plusieurs années. Nous avons également déterminé deux paramètres aérosols, l'épaisseur optique (AOT) et l'albédo de diffusion simple; les comparaisons avec les mesures photométriques du réseau AERONET/PHOTONS se sont révélées très satisfaisantes. Les données obtenues à partir de septembre 2004 nous ont permis de participer dans le cadre d'un projet de l'ESA, à la validation de l'instrument spatial OMI, destiné à effectuer une surveillance globale de l'ozone et de l'UV. Ce travail a permis d'établir que les produits ozone d'OMI sont bien restitués, alors que les éclairements UV spectral et érythémateux sont à utiliser avec précaution. A VdA, les comparaisons entre les AOT-OMI et les AOT restituées au sol sont peu satisfaisantes. De meilleurs accords ont été obtenus sur les sites photométriques impliqués dans la campagne AMMA en Afrique de l'Ouest, cette région étant sous l'influence de contenus élevés en aérosols absorbants.Since the discovery of the stratospheric ozone reduction in the middle of the 1980's, a monitoring of the ozone layer and UV irradiance was organized, using ground-based and satellite instruments. Measurements of UV radiation allow both to monitor the intensity of this radiation reaching the surface and to retrieve atmospheric compounds as content of ozone and aerosol characteristics. The main part of this work concerns the analysis and the use of UV spectral measurements performed at Villeneuve d'Ascq (VdA) and at Briançon. We continued the restitution of the total column of ozone that provides a multi-year record of this quantity. We determined two aerosol parameters, the aerosol optical thickness (AOT) and the single scattering albedo; comparisons with photometric measurements from the AERONET/PHOTONS network appeared very good. The data obtained from September 2004 enabled us to be involved within the framework of an ESA project in the validation of the OMI/AURA instrument, which is dedicated to a global monitoring of ozone and UV. We have established that the OMI ozone products are very well retrieved, whereas spectral and erythemal dose UV have to be used with caution. At VdA, the comparisons between OMI-AOT and those derived fram graund-based measurements are not satisfying. Better results were obtained at six sites located in WesternAfrica region during the AMMA campaign, this region being influenced by high loads of absorbing aerasols.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

A preliminary assessment of the quality of UV data derived from the database HelioClim-3

The database HelioClim-3 contains 15-min values of surface downward solar irradiance for Europe, Africa and Atlantic Ocean. These values result from an appropriate real-time processing of Meteosat data, which started in 2004. The database HelioClim-3 is widely used by the scientific community as well as companies working in the solar energy field. Its performances have been assessed in several occasions and have been published. Interest in spectral distribution of solar irradiance is increasing for various reasons, e.g., photovoltaic systems, biomass production, glazing material, and so on. An algorithm was proposed by the Belgian Royal Institute of Meteorology in the European Solar Radiation Atlas (2000) to derive spectral distribution every 10 nm from observations of total irradiance. It makes use of the sunshine duration and we adapt it to the total irradiance by the means of the Angstrom relationship. This revised version can then be applied to the HelioClim-3 total irradiances to obtain time-series of spectral distribution of irradiance for any pixel in the field-of-view of Meteosat. The communication presents this algorithm and investigates the quality of such spectral data. For the time being, it focuses on the UV-A, UV-B and erythemal bands. This assessment is made by comparison with ground measurements considered as reference. Several time-scales are considered: hour, day, and month. Two years of data: 2005 and 2006, are used. Hence, consistency with time in quality results is investigated. Two ground stations are used: Lille (North France) and El Arenosillo (South Spain), to study effects of climate. Quality is assessed for various types of skies: clear, overcast, and intermediate. The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under Grant Agreement no. 218793 (MACC project)

Spectroradiométrie du rayonnement solaire UV (mesures et analyses)

Le rayonnement solaire atteignant le sol a un impact important sur le monde du vivant (animal et végétal) ; ses effets sont d'autant plus importants que les photons incidents sont plus énergétiques (courtes longueurs d'onde). Le rayonnement UV solaire atteignant le sol ne représente environ que 5% du rayonnement solaire total mais à ces courtes longueurs d'onde, son efficacité biologique est importante. L'ozone, situé pour 90% dans la stratosphère entre 15 et 40 km d'altitude, constitue une véritable barrière du rayonnement. Une diminution de la quantité d'ozone stratosphérique est observée aux latitudes moyennes induisant une augmentation du rayonnement UV B. Divers réseaux de surveillance du rayonnement solaire UV B se mettent en place à travers le monde, avec pour but de mesurer cette évolution. L'ozone n'est pas le seul élément modulant la quantité d'UV B et par conséquent la puissance érythémale. L'altitude et l'enneigement ont aussi un rôle important. L'objectif de cette thèse est de créer deux stations de mesures automatisées du rayonnement UV et d'initier une analyse des paramètres qui influent sur ce rayonnement. Nous présentons les instruments utilisés et leurs caractéristiques techniques, et plus particulièrement celles du second spectroradiomètre développé au cours de cette thèse. Nous présentons également les méthodes et protocoles utilisés pour garantir la qualité des mesures. Après validation des instruments, nous avons débuté les mesures automatisées du rayonnement UV dans deux stations: la première à Villeneuve d'Ascq (59), et une seconde à Villard Saint Pancrace (05). A partir des mesures des éclairements spectriques UV, nous déterminons la colonne totale d'ozone. Par comparaison des mesures à des modèles d'éclairements, nous avons également évalué la réflectance d'un sol enneigé en milieu alpin. Cette thèse s'inscrit dans le cadre des projets européens SUVDAMA et CUVRALILLE1-BU (590092102) / SudocSudocFranceF

Night light polarization: modeling and observations of light pollution in the presence of aerosols and background skylight or airglow

Aurorae and nightglow are faint atmospheric emissions visible during night-time at several wavelengths. These emissions have been extensively studied but their polarization remains controversial. A great challenge is that light pollution from cities and scattering in the lower atmosphere interfere with polarization measurements. We introduce a new polarized radiative transfer model able to compute the polarization measured by a virtual instrument in a given nocturnal environment recreating real world conditions (atmospheric and aerosol profiles, light sources with complex geometries, terrain obstructions).The model, based on single scattering equations in the atmosphere, is tested on a few simple configurations to assess the effect of several key parameters in controlled environments. {Our model constitutes a proof of concept for polarization measurements in nocturnal conditions, that calls for further investigations. In particular, we discuss how multiple-scattering (neglected in the present study) impacts our observations and their interpretation, and the future need for inter-calibrating the source and the polarimeter in order to optimally extract the information contained in this kind of measurements. The model outputs are compared to field measurements in five wavelengths. A convincing fit between the model predictions and observations is found in the three most constrained wavelengths despite the single scattering approximation. Several applications of our model are discussed that concern the polarization of aurorae, the impact of light pollution, or aerosols and air pollution measurements