Measurements Of Ultraviolet Irradiance Research Articles

Simultaneous Measurement of Ultraviolet Irradiance and Temperature by Employing Optical Fiber SPR Sensor With Ag/ZnO/PDMS Coating

It is a challenging and valuable work to design and manufacture temperature-compensated all-fiber ultraviolet (UV) sensor. In this article, we creatively use a simple and compact optical fiber sensor based on surface plasmon resonance (SPR) for simultaneous detection of UV and ambient temperature. Different coatings [Ag/polydimethylsiloxane (PDMS) and Ag/ZnO/PDMS] are used to split a length of no-core optical fiber (NCF) into two sensing regions, which generates a transmission spectrum with two distinct SPR dips. The proposed sensor achieves a temperature sensitivity of −2.542 nm/°C in the 15 °C–35 °C range and a UV sensitivity of −0.605 nm/(mW/cm2) in the range of 0–17.20 mW/cm2. The matrix established by the wavelength shift of two dips can demodulate UV and temperature changes, and provide temperature compensation for UV detection. In addition, even in surroundings of complex and changeable UV intensity and ambient temperature, the sensor shows excellent stability and repeatability, as well as great potential in UV sensing, providing a reference for the development of multiparameter optical fiber sensors.

Design and Construction of Ultraviolet and Incoming Solar Irradiance Sensing Device

In-situ measurements of ultraviolet (UV) and solar irradiance is very sparse in Nigeria because of cost; it is estimated using meteorological parameters. In this work, a low-cost UV and pyranometer device, using locally sourced materials, was developed. The instrument consists of a UV sensor (ML8511), a photodiode (BPW34) housed in a carefully sealed vacuumed glass bulb, the UV and solar irradiance sensor amplifiers, a 16-bit analog-to-digital converter (ADS1115), Arduino mega 2560, liquid crystal display (LCD) and microSD card for data logging. The designed amplifier has an offset voltage of 0.8676 mV. The sensitivity of the irradiance device is 86.819 Wm-2/mV with a correcting factor of 27.77 Wm-2 and a maximum range of 1200 Wm-2. The instrument validation error is 9.67% and a correlation coefficient of 0.89 when compared with a standard SRS100 pyranometer. The UV sensor showed a close response with a correlation of 0.99 in comparison with a standard Skye instrument. From 08:00 to 16:00 local time (LT), there is a very close agreement between the standard device and the developed counterpart, with marginal differences of about 9.6% observed at the two extremes.

Relationship between ozone and biologically relevant UV at 4 NDACC sites.

Clouds and aerosols, as well as overhead ozone, can have large effects on ultraviolet (UV) irradiances. We use statistical methods to remove cloud effects and mean aerosol effects from spectral UV irradiance measurements to investigate the relationship between UV and total column ozone. We show that for fixed solar zenith angles (SZA), seasonal changes in ozone lead to marked changes in clear-sky UV irradiances. Such effects are larger at mid-latitudes than in the tropics. At mid-latitudes, the minimum ozone amount over the course of a year can be about 50 percent of its maximum, with the lowest values in autumn and the highest values in spring. These seasonal ozone changes lead to UV Index (UVI) values in autumn that can exceed those in spring at the same SZA by nearly a factor of two. Differences are even larger for UV spectra weighted by the action spectra for DNA-damaging UV, and for cutaneous previtamin D production. In some cases, the seasonal increase exceeds a factor of 4. The analysis experimentally demonstrates the limits of applicability of the concept of constant Radiative Amplification Factors (RAFs) for estimating effects of changes in ozone for some weighting functions. Changes in DNA-weighted UV and erythemally weighted UV are well represented by the published RAFs. However, there are large SZA dependencies in the case of UVB and vitamin D-weighted UV. For all weightings considered, RAFs calculated from the observations as a function of SZA show similar dependencies between sites, in good agreement with published values, independently of the ozone data source. High quality measurements show that natural variations in ozone are responsible for huge variations in biologically damaging UV, with seasonal changes at fixed solar zenith angles sometimes exceeding a factor of four. The measured changes from thousands of spectra agree well with calculations over a wide range of solar zenith angles.

SOLAR-v: A new solar spectral irradiance dataset based on SOLAR/SOLSPEC observations during solar cycle 24

Context. Solar spectral irradiance (SSI) is the wavelength-dependent energy input to the top of the Earth’s atmosphere. Solar ultraviolet (UV) irradiance represents the primary forcing mechanism for the photochemistry, heating, and dynamics of the Earth’s atmosphere. Hence, both temporal and spectral variations in solar UV irradiance represent crucial inputs to the modeling and understanding of the behavior of the Earth’s atmosphere. Therefore, measuring the long-term solar UV irradiance variations over the 11-year solar activity cycle (and over longer timescales) is fundamental. Thus, each new solar spectral irradiance dataset based on long-term observations represents a major interest and can be used for further investigations of the long-term trend of solar activity and the construction of a homogeneous solar spectral irradiance record. Aims. The main objective of this article is to present a new solar spectral irradiance database (SOLAR-v) with the associated uncertainties. This dataset is based on solar UV irradiance observations (165−300 nm) of the SOLAR/SOLSPEC space-based instrument, which provides measurements of the full-disk SSI during solar cycle 24. Methods. SOLAR/SOLSPEC made solar acquisitions between April 5, 2008 and February 10, 2017. During this period, the instrument was affected by the harsh space environment that introduces instrumental trends (degradation) in the SSI measurements. A new method based on an adaptation of the Multiple Same-Irradiance-Level (MuSIL) technique was used to separate solar variability and any uncorrected instrumental trends in the SOLAR/SOLSPEC UV irradiance measurements. Results. A new method for correcting degradation has been applied to the SOLAR/SOLSPEC UV irradiance records to provide new solar cycle variability results during solar cycle 24. Irradiances are reported at a mean solar distance of 1 astronomical unit (AU). In the 165−242 nm spectral region, the SOLAR/SOLSPEC data agrees with the observations (SORCE/SOLSTICE) and models (SATIRE-S, NRLSSI 2) to within the 1-sigma error envelope. Between 242 and 300 nm, SOLAR/SOLSPEC agrees only with the models.

Production of hydrogen negative ions in an ECR volume source: balance between vibrational excitation and ionization

The operation of an ECR-driven (2.45 GHz) hydrogen negative ion source is studied. Electron densities and temperatures are investigated with electrostatic probes and negative ion densities are measured with laser photodetachment. Vacuum ultraviolet irradiance measurements are focused on molecular transitions to the ground state while high-resolution visible emission spectroscopy is used to study the transitions between excited states for both molecules and atoms. The standalone operation of the source is found to be more efficient in higher pressures (12 mTorr) where negative ion densities are as high as 4 × 109 cm−3. Further investigation on the operation of the source reveals a rich vibrational spectrum. On the other hand, a limitation on the production of negative ions which is attributed to a lack of low-energy electrons becomes apparent. The underlying mechanisms that lead to this behavior are discussed along with possible solutions to this issue. Finally, the rates of different negative ion destruction processes are estimated and compared.

The molecular products and biogeochemical significance of lipid photooxidation in West Antarctic surface waters

The seasonal depletion of stratospheric ozone over the Southern Hemisphere allows abnormally high doses of ultraviolet radiation (UVR) to reach surface waters of the West Antarctic Peninsula (WAP) in the austral spring, creating a natural laboratory for the study of lipid photooxidation in the shallow mixed layer of the marginal ice zone. The photooxidation of lipids under such conditions has been identified as a significant source of stress to microorganisms and short-chain fatty acids altered by photochemical processes have been found in both marine aerosols and sinking marine particle material. However, the biogeochemical impact of lipid photooxidation has not been quantitatively compared at ecosystem scale to the many other biological and abiotic processes that can transform particulate organic matter in the surface ocean. We combined results from field experiments with diverse environmental data, including high-resolution, accurate-mass HPLC-ESI-MS analysis of lipid extracts and in situ measurements of ultraviolet irradiance, to address several unresolved questions about lipid photooxidation in the marine environment. In our experiments, we used liposomes—nonliving, cell-like aggregations of lipids—to examine the photolability of various moieties of the intact polar diacylglycerol (IP-DAG) phosphatidylcholine (PC), a structural component of membranes in a broad range of microorganisms. We observed significant rates of photooxidation only when the molecule contained the polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA). As the DHA-containing lipid was oxidized, we observed the steady ingrowth of a diversity of oxylipins and oxidized IP-DAG; our results suggest both the intact IP-DAG the degradation products were amenable to heterotrophic assimilation. To complement our experiments, we used an enhanced version of a new lipidomics discovery software package to identify the lipids in water column samples and in several diatom isolates. The galactolipid digalactosyldiacylglycerol (DGDG), the sulfolipid sulfoquinovosyldiacylglycerol (SQDG) and the phospholipids PC and phosphatidylglycerol (PG) accounted for the majority of IP-DAG in the water column particulate (≥0.2 µm) size fraction; between 3.4 and 5.3% of the IP-DAG contained fatty acids that were both highly polyunsaturated (i.e., each containing ≥5 double bonds). Using a broadband apparent quantum yield (AQY) that accounted for direct and Type I (i.e., radical-mediated) photooxidation of PUFA-containing IP-DAG, we estimated that 0.7 ± 0.2 µmol IP-DAG m−2 d−1 (0.5 ± 0.1 mg C m−2 d−1) were oxidized by photochemical processes in the mixed layer. This rate represented 4.4% (range, 3–21%) of the mean bacterial production rate measured in the same waters immediately following the retreat of the sea ice. Because our liposome experiments were not designed to account for oxidation by Type II photosensitized processes that often dominate in marine phytodetritus, our rate estimates may represent a sizeable underestimate of the true rate of lipid photooxidation in the water column. While production of such diverse oxidized lipids and oxylipins has been previously observed in terrestrial plants and mammals in response to biological stressors such as disease, we show here that a similar suite of molecules can be produced via an abiotic process in the environment and that the effect can be commensurate in magnitude with other ecosystem-scale biogeochemical processes.

Ultraviolet spectral irradiance measurements: an intercomparison of spectroradiometers in laboratory combined with a workplace field test

Ultraviolet (UV) irradiance measurements are usually associated with large inaccuracies and uncertainties complicating the comparability of corresponding measurement equipment and its data. For supervisors or safety experts, though, it is mandatory to measure reliable UV irradiances with regard to occupational safety regulations. The following work aims at an intercomparison of five different types of spectroradiometers regarding their wavelength alignment and irradiance accuracy in the UV spectral region that provides the reader with information on how to determine and compare the measurement accuracies of their own devices. In a first step, measurements of two UV irradiance standards, a deuterium and a halogen lamp, were carried out. The percentage deviations of the measured total UV irradiances from their calibrated ones are smaller than ±10% for all spectroradiometers. The quality of wavelength accuracy as well as of the spectral bandwidth, both investigated by means of a low pressure mercury argon lamp are consistent with those stated by the manufacturers. In a second step, UV radiation from a metal active gas welding arc was examined at three distances in combination with a variation of welding current and arc length to check the behaviour of UV irradiance accuracy in field. The overall averaged standard deviation of these field measurements for all CCD array detectors is given by ±8%. For high welding currents this accuracy decreases to ±21%.

Out-of-Range Stray Light Characterization of Single-Monochromator Brewer Spectrophotometers

ABSTRACTStray light in single-monochromator Brewer instruments increases the uncertainty of solar ultraviolet spectral irradiance measurements and ozone retrievals. To study how spectral irradiance within and outside the measurement ranges of the instruments affects stray light, two Brewer MKII instruments were characterized for the level of in- and out-of-range stray light at multiple laser wavelengths. In addition, several solar-blind filters utilized in single-monochromator Brewers to limit out-of-range stray light were characterized for spectral and spatial transmittances. Finally, the measurement results were used to simulate the effect of stray light and stray light correction on spectral irradiance and ozone measurements at different wavelength regions. The effect of stray light from wavelengths above 340 nm was found to be negligible compared with other sources of uncertainty. On the other hand, contributions from wavelengths between 325 and 340 nm can form a significant portion of the overall stray light of the instrument, with 325 nm being the upper limit of the nominal measurement range of the instrument.

Solar Ultraviolet Attenuation during the Australian (Red Dawn) Dust Event of 23 September 2009

Abstract The large dust event of 23 September 2009 is recognized as the most significant on record in Australia since the 1940s. At its peak, reported hourly average particulate concentrations exceeded 15,000 μg m−3, significantly exceeding the Australian National Air Quality Standard of 50 μg m−3 and daily September averages of 20–25 μg m−3. Measurements of the spectral surface ultraviolet irradiance monitored continuously before, after, and during the event of 23 September 2009 are presented. These measurements highlight the significance of extreme dust load on the ultraviolet irradiance, and exceed previously published UV attenuations measured in Saharan and Chinese dust events. Measured spectral attenuations of up to 99.5% in the ultraviolet B and 97.6% in the ultraviolet A were associated with the arrival of low-altitude cumuliform cloud and the dust plume ahead of an approaching cold front on the morning of 23 September 2009. The data presented cover the period of maximum attenuation and the afternoon, which had no cloud cover. This research characterizes for the first time the influence of a frontal desert dust storm on the surface ultraviolet irradiance in the naturally high ambient ultraviolet climate of subtropical Australia.

Traceability of solar UV measurements using the Qasume reference spectroradiometer.

One major objective of the European Joint Research Project "Traceability for surface spectral solar ultraviolet (UV) radiation" was to reduce the uncertainty of spectral UV measurements. The measurement instrument used for this work was the portable UV European reference spectroradiometer Qasume. The calibration uncertainty of this instrument was decreased and validated by a comparison of direct calibrations against a primary standard for spectral irradiance, a high temperature blackbody radiator, and against a reference detector using a spectrally tunable laser as a monochromatic source. The spectral irradiance responsivity of the reference detector is traceable to the primary standard of optical power, realized through a cryogenic radiometer, and to the SI unit of meter. The measuring technique was improved by the construction of a new reference spectroradiometer, QasumeII. An improved input optics removes the dependences of the measured solar irradiance on the angle of incident for solar zenith angle smaller than 75deg. Moreover, a hybrid photon detection system enables continuous tracking of the instrument's responsivity changes. For both spectroradiometer systems an uncertainty budget was calculated. The improvements have reduced the measurement uncertainties of solar spectral UV irradiance measurements from 4.8% in 2005 to 2.0% (k=2) in the spectral region above 310nm. The largest sources of uncertainty were the absolute spectral irradiance responsivity calibration, the angular response uncertainty, and the instrument stability using the hybrid detector, which were reduced from 3.6% to 1.1%, from 1.2% to 0.6%, and from 0.65% to 0.4%, with respect to the situation prior to the project. The new instrument was validated during a four month intercomparison relative to the Qasume reference. The mean ratio of the solar irradiance scans between the two reference spectroradiometers has an offset of +0.7% and a standard deviation of ±1.5% for a wavelength greater than 305nm, which is well within the combined uncertainty of 3.7% calculated from the uncertainties of the two systems.

Quality assessment of solar UV irradiance measured with array spectroradiometers

Abstract. The reliable quantification of ultraviolet (UV) radiation at the earth's surface requires accurate measurements of spectral global solar UV irradiance in order to determine the UV exposure to human skin and to understand long-term trends in this parameter. Array spectroradiometers (ASRMs) are small, light, robust and cost-effective instruments, and are increasingly used for spectral irradiance measurements. Within the European EMRP ENV03 project “Solar UV”, new devices, guidelines and characterization methods have been developed to improve solar UV measurements with ASRMs, and support to the end user community has been provided. In order to assess the quality of 14 end user ASRMs, a solar UV intercomparison was held on the measurement platform of the World Radiation Center (PMOD/WRC) in Davos, Switzerland, from 10 to 17 July 2014. The results of the blind intercomparison revealed that ASRMs, currently used for solar UV measurements, show a large variation in the quality of their solar UV measurements. Most of the instruments overestimate the erythema-weighted UV index – in particular at large solar zenith angles – due to stray light contribution in the UV-B range. The spectral analysis of global solar UV irradiance further supported the finding that the uncertainties in the UV-B range are very large due to stray light contribution in this wavelength range. In summary, the UV index may be detected by some commercially available ASRMs within 5 % compared to the world reference spectroradiometer, if well characterized and calibrated, but only for a limited range of solar zenith angles. Generally, the tested instruments are not yet suitable for solar UV measurements for the entire range between 290 and 400 nm under all atmospheric conditions.

Ten-year monitoring of an ultraviolet disinfection plant for drinking water

Information about the capability and performance of ultraviolet (UV) disinfection plants for drinking water is mainly available from lab-scale evaluations or prototype testing. Information about these during operation is rare. In this paper, controlled onsite measurements over a period of 10 years are presented. Measurements were taken in a UV disinfection plant equipped with amalgam low-pressure, high-output lamps every 2 months over the whole period. From these, information about lamp ageing, emittance in dependence on water temperature and differences of emittance within one type of lamp was gained. The decrease of emittance follows an exponential decay. After 700 h of operation, the UV emission is reduced by 10% compared to a new lamp, after 1800 h by 20% and by 30% after 3200 h. Emittance of new lamps may differ by 10%. Further, the influence of water temperature on the UV emission of the lamps was estimated as 0·5%/°C. Our results (not statistically significant) suggest that on-off switches and low water temperature may shorten the lifetime of lamps. A comparison onsite has shown that measurements of UV irradiance by all types of certified reference radiometers according to ÖNORM M5873-1 agree within ±2·0%.

Comparison of measured and modelled spectral UV irradiance at Izaña high mountain station: estimation of the underlying effective albedo

In this work, we have carried out a comparison study between measured and modelled direct and global ultraviolet (UV) (300–400 nm) spectral irradiances and the determination of the surface effective albedo at the high altitude Izana Observatory [IZO; 2400 m above sea level (a.s.l.)] located in Tenerife (Canary Islands, Spain). The spectral measurements were performed with a Bentham spectroradiometer during the Quality Assurance of Solar Ultraviolet Spectral Irradiance Measurements (QASUME) comparison campaign in June 2005. The simulations were obtained with the LibRadtran radiative transfer model. The model input parameters, such as total ozone and aerosol optical depth (AOD), were measured at IZO. The comparison between measured and modelled direct solar radiation component was made at 0.5 nm spectral resolution, showing excellent agreement, with differences below 5% for solar zenith angle (SZA) < 60°. These differences were attributed to the effect of the underlying surface albedo due to the frequent existence of a sea of clouds below the station altitude. The underlying surface albedo was determined using different methods. In spite of the variability of this parameter through the day due to the strong influence and variable structure of these underlying clouds, the mean of this effective surface albedo in the UV region gives a value between 0.2 and 0.5 in the UV range, 10 times higher than the local surface albedo (0.02–0.05).

Extreme ultraviolet spectral irradiance measurements since 1946

Abstract. In the physics of the upper atmosphere the solar extreme ultraviolet (EUV) radiation plays a dominant role controlling most of the thermospheric/ionospheric (T/I) processes. Since this part of the solar spectrum is absorbed in the thermosphere, platforms to measure the EUV fluxes became only available with the development of rockets reaching altitude levels exceeding 80 km. With the availability of V2 rockets used in space research, recording of EUV spectra started in 1946 using photographic films. The development of pointing devices to accurately orient the spectrographs toward the sun initiated intense activities in solar–terrestrial research. The application of photoelectric recording technology enabled the scientists placing EUV spectrometers aboard satellites observing qualitatively strong variability of the solar EUV irradiance on short-, medium-, and long-term scales. However, as more measurements were performed more radiometric EUV data diverged due to the inherent degradation of the EUV instruments with time. Also, continuous recording of the EUV energy input to the T/I system was not achieved. It is only at the end of the last century that there was progress made in solving the serious problem of degradation enabling to monitore solar EUV fluxes with sufficient radiometric accuracy. The data sets available allow composing the data available to the first set of EUV data covering a period of 11 years for the first time. Based on the sophisticated instrumentation verified in space, future EUV measurements of the solar spectral irradiance (SSI) are promising accuracy levels of about 5% and less. With added low-cost equipment, real-time measurements will allow providing data needed in ionospheric modeling, e.g., for correcting propagation delays of navigation signals from space to earth. Adding EUV airglow and auroral emission monitoring by airglow cameras, the impact of space weather on the terrestrial T/I system can be studied with a spectral terrestrial irradiance camera (STI-Cam) and also be used investigating real-time space weather effects and deriving more detailed correction procedures for the evaluation of Global Navigation Satellite System (GNSS) signals. Progress in physics goes with achieving higher accuracy in measurements. This review historically guides the reader on the ways of exploring the impact of the variable solar radiation in the extreme ultraviolet spectral region on our upper atmosphere in the altitude regime from 80 to 1000 km.

Effective ultraviolet irradiance measurements from artificial tanning devices in Greece.

Artificial tanning remains very popular worldwide, despite the International Agency for Research on Cancer classification of ultraviolet (UV) radiation from sunbeds as 'carcinogenic to humans'. Greek Atomic Energy Commission has initiated a surveillance action of the artificial tanning devices in Greece in order to record the effective irradiance levels from the sunbeds and to inform and synchronise the domestic artificial tanning business sector with the requirements of the European Standard EN 60335-2-27:2010. In this direction, in situ measurements of UV emissions from sunbeds in solaria businesses all over Greece were performed from October 2013 until July 2014, with a radiometer and a portable single-monochromator spectrophotometer. Analysis of the measurements' results revealed that effective irradiance in ∼60 % of the measured sunbeds exceeded the 0.3 W m(-2) limit value set by EN 60335-2-27:2010 and only 20 % of the devices could be categorised as UV type 3.

Usability of a Fourier transform spectroradiometer for absolute surface spectral solar UV irradiance measurements.

The suitability of a commercially available Fourier transform spectrometer equipped with a fiber-coupled global entrance optic as a reference spectroradiometer for the measurement of spectral solar ultraviolet irradiance at ground level has been investigated. The instrument has been characterized with respect to the wavelength uncertainty, and a calibration of the spectral irradiance responsivity has been performed by using the calculable irradiance of a high temperature black-body radiator and by using a secondary irradiance standard lamp. The relative standard uncertainty of solar irradiance measurements in the wavelength range from 310 nm to 400 nm with this spectroradiometer, based on the described methodology, is 1.6% for solar zenith angles of less than 60°.

Spectral attenuation of global and diffuse UV irradiance and actinic flux by clouds

Measurements of spectral global and diffuse ultraviolet (UV) irradiance, and of spectral actinic flux were made jointly with determinations of cloud properties during a two‐ month experimental campaign that took place in southern Italy in May–June 2010. The cloud modification factor (CMF) which is the ratio between the incoming radiation under cloudy and in cloud‐free conditions, was obtained for the global (direct plus diffuse) and diffuse components of the irradiance, and for the actinic flux in the UV spectral range for overcast conditions. Measurements of the diffuse irradiance and actinic flux CMFs are very scarce, and are particularly important to characterize the radiation field and verify the behaviour of radiative transfer models in cloudy conditions. In addition to measurements, one‐dimensional radiative transfer simulations are used to investigate the cloud influence on the spectral solar UV radiation. The analysis shows that the wavelength dependence of CMF for the global irradiance is mainly due to the normalization for cloud‐free conditions. The CMF for the diffuse irradiance and for the actinic flux displays a strong dependence on the solar zenith angle. This dependence appears to be mainly driven by the large role played by the zenith radiation in overcast conditions. Radiative transfer model determinations of CMF satisfactorily reproduce observations.

UV Irradiance and Albedo at Union Glacier Camp (Antarctica): A Case Study

We report on the first spectral measurements of ultraviolet (UV) irradiance and the albedo at a Camp located in the southern Ellsworth Mountains on the broad expanse of Union Glacier (700 m altitude, 79° 46′ S; 82° 52′W); about 1,000 km from the South Pole. The measurements were carried out by using a double monochromator-based spectroradiometer during a campaign (in December 2012) meant to weight up the effect of the local albedo on the UV irradiance. We found that the albedo measured at noon was about 0.95 in the UV and the visible part of the spectrum. This high surface reflectivity led to enhancements in the UV index under cloudless conditions of about 50% in comparison with snow free surfaces. Spectral measurements carried out elsewhere as well as estimates retrieved from the Ozone Monitoring Instrument (OMI) were used for further comparisons.

Selection of cloudless sky conditions by applying solar global ultraviolet irradiance measurements

Taking advantage of UV (295–385nm) irradiance measurements is one of the objectives of this paper. A new index termed kt″ is established for this band. This new index works as a ‘zenith angle independent clearness index’ for band measurements and has similar applications to those of kt′ for broadband measurements. The new index may be applied to identify cloudless instants from UV band measurements. Both indexes were correlated throughout the period 1998–2004 with a R2 of 0.85. A selection criterion of kt″UV >1.1 classified cloudless sky conditions with a probability of 95% in comparison with a selection that two criteria-applying broadband measurements would make. This index may be of interest for classifying cloudless sky conditions when only UV band measurements are available. An estimation method from the literature was applied to the period 1998–2004. This method was previously validated for the UV band with a measurement campaign made in Valencia (Spain) in the summer season.

Validation of Environment Canada and NOAA UV Index Forecasts with Brewer Measurements from Canada

AbstractGround-based ultraviolet (UV) irradiance measurements by Brewer spectrophotometers at 10 sites across Canada are compared with UV index forecasts for the same locations from Environment Canada (EC) and NOAA. For the EC forecast validation, summertime (May–August) data for the period from 1996 to 2009 are used. Comparison with NOAA forecasts is made for the more limited period of May–August 2006 and 2007. Several statistical measures are used, including the mean and the standard deviation of differences, correlation coefficients, and the probability of detection and false-alarm rate for prediction of high (UV index of 6 or above) values. For most conditions, only modest differences are found between the two forecasting systems; that is, UV index forecasts reported in the United States and Canada for Canadian sites are compatible. In general, the physically based NOAA system, which started operation in 2005, performs better than the semiempirical EC model, developed in the mid-1990s. The difference in model performance is not large under clear-sky and light-cloud conditions, but the EC model underperforms relative to the NOAA model under heavy-cloud and rainy conditions. Both the EC and the NOAA forecast models tend to overestimate UV under clear-sky and light-cloud conditions. Under heavy-cloud and rainy conditions, the EC model underestimates UV values, with about 30% of all forecasts under these conditions being 2 or more units below observations. NOAA forecasts tend to overestimate UV index values under these conditions.