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

Comparison of measured and modelled uv indices for the assessment of health risks

The World Health Organisation (WHO) and the World Meteorological Organisation (WMO) have jointly recommended that the UV Index (UVI) should be used to inform the public about possible health risks due to overexposure to solar radiation, especially skin damage. To test the current operational status of measuring and modelling techniques used in providing the public with UVI information, this article compares cloudless sky UVIs (measured using five instruments at four locations with different latitudes and climate) with the results of 13 models used in UVI forecasting schemes. For the models, only location, total ozone and solar zenith angle were provided as input parameters. In many cases the agreement is acceptable, i.e. less than 0.5 UVI. Larger differences may originate from instrumental errors and shortcomings in the models and their input parameters. A possible explanation for the differences between models is the treatment of the unknown input parameters, especially aerosols

Réactions photosensibilisées par le chlore dans les systèmes chlore-oxygène-haloéthanes. Etude du 1,1,1,2-tétrachloroéthane et du 1,1-difluoroéthane

Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe

Chlorine‐photosensitized reactions in the Cl2 + O2 + 1,1,1,2‐C2H2Cl4 system

The gas‐phase photochlorination (λ = 436 nm) of the 1,1,1,2‐C2H2Cl4 has been studied in the absence and the presence of oxygen at temperatures between 360 and 420°K. Activation energies have been estimated for the following reaction steps: (Formula Presented.) (Formula Presented.) (Formula Presented.) The dissociation energy D(CCl3CHClO2) ± (24.8 ± 1.5) kcal/mole has also been estimated from the difference in activation energy of the direct and reverse reactions (Formula Presented.) The mechanism is discussed and the rate parameters are compared to those obtained for a series of other chlorinated ethanes. Copyright © 1976 John Wiley & Sons, Inc.SCOPUS: ar.jFLWNAinfo:eu-repo/semantics/publishe

NOMAD/UVIS sensitivity investigation for Mars observations

The UVIS instrument is part of NOMAD, the “Nadir and Occultation for MArs Discovery” spectrometer suite has been selected by ESA and NASA to be part of the payload of the ExoMars Trace Gas Orbiter mission 2016. This instrument suite will conduct a spectroscopic survey of Mars’ atmosphere in the UV, visible and IR regions. UVIS’s observation modes include solar occultation, nadir and limb observations. The nadir mode will provide detailed trace gas mapping UVIS is an ultraviolet and visible spectrometer (200 – 650 nm) whose main objective is to detect and quantify trace gases’ concentrations but also to study aerosols present in the Martian atmosphere. The main absorbing trace gas in the wavelength range of UVIS is ozone which has already been extensively studied but for which there are still significant discrepancies in present day observations. The high signal-to-noise ratio of the instrument will allow us to measure ozone more precisely. Moreover the instrument could also detect other minor constituents that absorb in this wavelength range, such as SO2 if present. Because aerosols play a major role in the radiative transfer on the red planet, we also plan to investigate the different characteristics of the interaction between aerosols and UV-visible light. The UVIS instrument and its capabilities will be presented. The results of a sensitivity study on the detectability of minor constituents will be shown and discussed. NOMAD is being built by a European consortium led by IASB-BIRA (Belgium) and IAA (Spain), with contributions from OU (UK) and IFSI (Italy)

Studying the Martian aerosols UV properties with SPICAM

International audienceAerosols on Mars have an important impact on the radiative transfer properties of its atmosphere. Today their spectral properties and therefore their interaction with UV radiation are only poorly known. Improving the radiative transfer modeling requires a better knowledge of their characteristics, in particular of their phase function, single scattering albedo and opacity. We have developed a new retrieval algorithm based on the use of the radiative transfer code LIDORT [1], which allows us to simulate the scattering effects of the dust and clouds. The retrieval code, based on the optimal estimation method [2], allows, for the moment, determination of the O3 column, of the albedo of the surface (one constant value over the whole spectral interval), and of the opacity due to the dust (with fixed spectral parameters). In the near future, this code will be adapted in order to take into account the wavelength dependency of all the parameters. Finally, these parameters will also be fitted. We will show how these simulations/methods will improve the knowledge of the aerosol's scattering phase function and single scattering albedo, as well as their opacity as a function of wavelength. We will present preliminary sensitivity studies of the impact of the different parameters investigated using the data of the SPICAM instrument on board MARS-EXPRESS, both in Nadir and EPS (Emission Phase Function) viewing modes. References 1. Spurr, R., T. Kurosu, and K. Chance, A linearized discrete ordinate radiative transfer model for atmospheric remote-sensing retrieval. J. Quant. Spectrosc. Radiat. Transfer, 68, 689-735 (2001) 2. Rodgers, C.D., Inverse methods for atmospheric sounding: Theory and practice. World Scientific, ed. N.J. Hackensack (2000

Studying the Martian aerosols UV properties with SPICAM

International audienceAerosols on Mars have an important impact on the radiative transfer properties of its atmosphere. Today their spectral properties and therefore their interaction with UV radiation are only poorly known. Improving the radiative transfer modeling requires a better knowledge of their characteristics, in particular of their phase function, single scattering albedo and opacity. We have developed a new retrieval algorithm based on the use of the radiative transfer code LIDORT [1], which allows us to simulate the scattering effects of the dust and clouds. The retrieval code, based on the optimal estimation method [2], allows, for the moment, determination of the O3 column, of the albedo of the surface (one constant value over the whole spectral interval), and of the opacity due to the dust (with fixed spectral parameters). In the near future, this code will be adapted in order to take into account the wavelength dependency of all the parameters. Finally, these parameters will also be fitted. We will show how these simulations/methods will improve the knowledge of the aerosol's scattering phase function and single scattering albedo, as well as their opacity as a function of wavelength. We will present preliminary sensitivity studies of the impact of the different parameters investigated using the data of the SPICAM instrument on board MARS-EXPRESS, both in Nadir and EPS (Emission Phase Function) viewing modes. References 1. Spurr, R., T. Kurosu, and K. Chance, A linearized discrete ordinate radiative transfer model for atmospheric remote-sensing retrieval. J. Quant. Spectrosc. Radiat. Transfer, 68, 689-735 (2001) 2. Rodgers, C.D., Inverse methods for atmospheric sounding: Theory and practice. World Scientific, ed. N.J. Hackensack (2000

The absolute solar spectral irradiance from 200 to 2500nm as measured by the SOLSPEC spectrometer with the ATLAS and EURECA missions

International audienceThe SOLSPEC instrument measures the absolute solar spectral irradiance from 200 to 2500 nm. The instrument flew in March 1992, March 1993 and November 1994 with the three ATLAS missions during 10 days. SOSP is the spare unit of SOLSPEC. It flew on the EURECA platform from 11 August 1992 to May 1993. SOLSPEC and SOSP are made of three spectrometers and contains several lamps allowing to check in flight, the instrument stability and its wavelength scale.These two units have an identical design and are made of the same components. However, their detectors have different performance leading to a SOSP responsivity smaller than the SOLSPEC responsivity. As during the ATLAS missions two other spectrometers were also observing in the UV and near visible domain, we took advantage of this situation by choosing SOLSPEC for the three ATLAS missions. Afterward, it appeared that it was also the good choice for the IR channel of SOSP on board EURECA.The calibration of the instrument is performed with the blackbody of the Heidelberg observatory (Mandel et al., 1998). Its temperature is adjusted as a function of the wavelength domain, ranging from 3000 K for UV calibration, down to 2700 K for the IR spectrometer calibration. The blackbody temperature is measured with a pyrometer calibrated by the Physikalisch-Technische Bundesanstalt (PTB) of Berlin (Germany). The mean accuracy of the solar irradiance is estimated to be 2 to 3% in UV and 2% in the visible and infrared domains. In details, it depends on the spectral interval being better in the middle of each spectral domain.We shall present the best data obtained during the ATLAS and EURECA missions, e.g., UV and visible spectra from the three ATLAS missions and the IR results from EURECA.The duration of each ATLAS mission does not allow study of the solar variability. This is why the best spectra are selected. This selection is based on several criteria including the thermal conditions, stability of the pointing, linearity of the measurements, stability of the wavelength scale, position of the Sun in the field of view and tangent height of the line of slight observations greatern than 100 km. The selected spectra are averaged afterward. A similar procedure was also applied to the SOSP infrared data because the solar variability in this domain is very small and is not detectable with SOSP. Special care was dedicated to this channel due to the variable responsivity in the field of view. Spectra which were not measured in the condition of the laboratory calibration, were eliminated