494 research outputs found
Improving the solar zenith angle dependence of broadband UV radiometers calibration
International audienceThis paper focusses on the proposal of a new method for the calibration of broadband ultraviolet radiometers. The advantage of the method proposed is the accurate modelling of the dependence on the solar zenith angle. The new model is compared with other one-step calibration methods and with the two-step method, which requires the knowledge of the actual response of the broadband radiometer. For this purpose, three broadband radiometers are calibrated against a spectrophotometer of reference. The new method is validated comparing its predictions with the spectrophotometer measurements using an independent data set
Synthesis, Structure and Antitumour Properties of a New 1,2-Propylenediaminetetraacetate-Ruthenium(III) Compound
A novel complex formed by ruthenium (III) and the sequestering ligand
1,2-propylenediaminetetraacetic acid (PDTA) has been synthetized and characterized. The structure
of the monomeric compound, studied by X-ray diffraction , shows an almost symmetric octahedral
geometry around the metal ion, with two chlorine atoms in a cis conformation. The antitumour
activity against a variety of murine and human cancers is reported
Measurements and estimation of the columnar optical depth of tropospheric aerosols in the UV spectral region
International audienceWe report values of the columnar tropospheric aerosol optical depth at UV wavelengths based on experimental measurements of the direct spectral irradiances carried out by a commercial spectroradiometer (Li1800 of Licor company) covering the range from 300?1100 nm at two stations with different climate characteristics in Spain. The first station is located in a rural site in north central Spain with continental climate. The data extend from March to the end of October of 1995. The other station is a coastal site in the Gulf of Cádiz (southwest Spain) of maritime climate type. This study is mainly focused on the capability of estimating aerosol optical depth values in the UV region based on the extracted information in the visible and near infrared ranges. A first method has been used based on the Ångström turbidity parameters. However, since this method requires detailed spectral information, a second method has also been used, based on the correlation between wavelengths. A correlation has been established between the experimental aerosol optical depth values at 350 nm and 500 nm wavelengths. Although the type of aerosol seems to be the key factor that determines the quality of these estimations, the evaluation of the associated error is necessary to know the behaviour of these estimations in each area of study
Comparative measurements of total ozone amount and aerosol optical depth during a campaign at El Arenosillo, Huelva, Spain
A one week field campaign took place in September 2002 at El Arenosillo, Spain. The objective was to compare total ozone column (<I>TOC</I>) and aerosol optical depth (<I>AOD</I>) from near ultraviolet to near infrared, measured by several Spanish and French instruments. Three spectroradiometers, Brewer, SPUV02, and LICOR, and a CIMEL photometer, have been used simultaneously and the results are presented for four clear days. <I>TOC</I> values are given by the Brewer instrument, and by SPUV02, using two different methods. The ground instruments compare satisfactorily (within 5&nbsp;DU) and the values are consistent with TOMS data (within 10&nbsp;DU). <P style="line-height: 20px;"> <I>AOD</I> from the various instruments are compared at seven different wavelengths between 320 nm and 1020 nm: the agreement is very good at 350, 380, and 870 nm; at the four other wavelengths the difference is smaller than 0.03, which can be explained by a relative difference of 4% only between the calibrations of the various instruments. Larger <I>AOD</I> diurnal variations were observed at short wavelengths than in the visible and near infrared; this is most likely due to changes in aerosol size along the day, during the campaign
Intercomparison of erythemal broadband radiometers calibrated by seven UV calibration facilities in Europe and the USA
International audienceA bi-lateral intercomparison of erythemal broadband radiometers was performed between seven UV calibration facilities. The owners calibrations were compared relative to the characterisation and calibration performed at PMOD/WRC in Davos, Switzerland. The calibration consisted in the determination of the spectral and angular response of the radiometer, followed by an absolute calibration performed outdoors relative to a spectroradiometer which provided the absolute reference. The characterization of the detectors in the respective laboratories are in good agreement: The determination of the angular responses have deviations below ±4% and the spectral responses agree within ±20%. A "blind" intercomparison of the erythemally weighted irradiances derived by the respective institutes and PMOD/WRC showed consistent measurements to within ±2% for the majority of institutes. One institute showed slightly larger deviation of 10%. The differences found between the different instrument calibrations are all within the combined uncertainty of the calibration
Comparison of UV irradiances from Aura/Ozone Monitoring Instrument (OMI) with Brewer measurements at El Arenosillo (Spain) – Part 2: Analysis of site aerosol influence
Several validation studies have shown a notable overestimation of the clear
sky ultraviolet (UV) irradiance at the Earth's surface derived from
satellite sensors such as the Total Ozone Mapping Spectrometer (TOMS) and
the Ozone Monitoring Instrument (OMI) with respect to ground-based UV data
at many locations. Most of this positive bias is attributed to boundary
layer aerosol absorption that is not accounted for in the TOMS/OMI
operational UV algorithm. Therefore, the main objective of this study is to
analyse the aerosol effect on the bias between OMI erythemal UV irradiance
(UVER) and spectral UV (305 nm, 310 nm and 324 nm) surface irradiances and
ground-based Brewer spectroradiometer measurements from October 2004 to
December 2008 at El Arenosillo station (37.1° N, 6.7° W,
20 m a.s.l.), with meteorological conditions representative of the South-West of
Spain.
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The effects of other factors as clouds, ozone and the solar elevation over
this intercomparison were analysed in detail in a companion paper (Antón
et al., 2010). In that paper the aerosol effects were studied making only a
rough evaluation based on aerosol optical depth (AOD) information at 440 nm
wavelength (visible range) without applying any correction. We have used the
precise information given by single scattering albedo (SSA) from AERONET for
the determination of absorbing aerosols which has allowed the correction of
the OMI UV data.
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An aerosol correction expression was applied to the OMI operational UV data
using two approaches to estimate the UV absorption aerosol optical depth,
AAOD. The first approach was based on an assumption of constant SSA value of
0.91. This approach reduces the OMI UVER bias against the reference Brewer
data from 13.4% to 8.4%. Second approach uses daily AERONET SSA values
reducing the bias only to 11.6%. Therefore we have obtained a 37% and
12% of improvement respectively. For the spectral irradiance at 324 nm,
the OMI bias is reduced from 10.5% to 6.98% for constant SSA and to
9.03% for variable SSA. Similar results were obtained for spectral
irradiances at 305 nm, and 310 nm.
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Contrary to what was expected, the constant SSA approach has a greater bias
reduction than variable SSA, but this is a reasonable result according to
the discussion about the reliability of SSA values. Our results reflect the
level of accuracy that may be reached at the present time in this type of
comparison, which may be considered as satisfactory taking into account the
remaining dependence on other factors. Nevertheless, improvements must be
accomplished to determine reliable absorbing aerosol properties, which
appear as a limiting factor for improving OMI retrievals
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