Spectral measurements of solar ultraviolet (UV) radiation have been made at several ground-based locations and for more than ten years at some sites. There are two main reasons why these measurements are important. Firstly, the measurements combined with results of radiative transfer models contribute toward our understanding of the many complicated radiative transfer processes in the atmosphere and at the Earth's surface. These processes include absorption of radiation by atmospheric gases such as ozone and sulfur dioxide, scattering by atmospheric aerosols and clouds, and scattering from the Earth's surface. Knowledge of these processes is required for operational applications such as the estimation of surface UV radiation from satellite data and the forecasting of the UV Index. Also, our ability to estimate UV climatology in the past, as well as the future, requires thorough knowledge of the UV radiative transfer processes. The second reason for making systematic ground-based measurements of UV radiation is to determine whether long-term changes are occurring as a result of ozone depletion or climate change and to identify specific causes. Examples of how long-term ground-based data records have contributed to our understanding of surface UV radiation will be presented.

Recent technology advances have made measurements of UV doses and ozone column amounts with multi-channel filter instruments not only possible, but also an attractive alternative to other more labor-intensive and weather dependent methods. Filter instruments can operate unattended for long periods of time, and it is possible to obtain accurate ozone column amounts even on cloudy days. We present results from extensive comparisons of the performance of several NILU-UV and GUV filter instruments against Dobson and Brewer instruments and the EP-TOMS instrument. The data used in the comparisons are from four different sites where we have had the opportunity to operate more than one type of UV instruments for extended periods of time. The sites include the University of Oslo, Norway, Ny-Alesund, Spitzbergen, Norway, the NASA Goddard Space Flight Center facilities at Wallops Island, VA, and Greenbelt, MD and the University of Alaska, Fairbanks. Our results show that ozone column amounts obtained with current filter-type instruments are just as good as those obtained with the Dobson instrument. The mean difference between NILU-UV and Dobson direct sun measurements were 0.4% ± 1.9% (1σ) in Oslo 2000-2003. The difference between a GUV and the same Dobson was 1.7% ± 1.4% for the same time period. The mean difference between GUV and TOMS in Ny-Alesund 79°N and Oslo 60°N in the period 1996-1999 was < 0.5% ± 3% for days with noon SZA < 80°.

Hourly UV Index values at 45 sites in Canada and 52 in the USA were estimated using a statistical relationship between UV irradiance and global solar radiation, total ozone, and dew point temperature. The estimation method also takes into account the enhancement of UV irradiance by snow using an empirical correction derived from Brewer UV measurements. Different characteristics of the UV Index distribution over North America were estimated from the derived UV irradiance for the period 1979-1987 and then presented in the form of monthly maps. Brewer UV measurements at 11 Canadian and 20 US sites and erythemal UV estimates from TOMS data were used for validation. Direct comparisons with Brewer measurements at 7 Canadian sites for the period in the 1990s when both pyranometer and spectral UV data were available demonstrated agreement within 2-3 percent except for periods of melting snow when variations in snow albedo yield higher errors in the derived UV irradiance.

Continuous measurements of solar ultraviolet spectral irradiance exist for four sites in the high latitude Southern Hemisphere, from 55° to 90° South, and span a time period in excess of a decade. This database allows comprehensive analyses of variability in ground-level radiation over a wide range of time scales. The behavior of irradiances within a single month reflects the combined influences of changing solar elevations, cloudiness and ozone amounts. Histograms assembled for corresponding months over the decadal time scale reveal maximum instantaneous irradiances that can vary by a factor of two or more among different years. An important portion of each year encompasses the months from October through December. The annual ozone loss develops during this period, and in some years this is sufficiently dramatic to distort the seasonal cycle in erythemal irradiance expected solely on the basis of solar elevation. Under unperturbed conditions, the largest monthly-integrated irradiances would occur in December at all wavelengths from 290 to 400 nm. However, in years of unusually low springtime ozone amounts the maximum monthly-integrated erythemal irradiances can appear in November.

As the art of forecasting the UV Index moves into its second decade, some issues affecting the creation of a valid UV Index forecast have been solved, yet others remain. The forecast of the UV Index is really the combination of multiple forecasts of ozone, clouds, and (in the future) aerosols. Ozone forecasts have improved significantly due to the assimilation of ozone into global numerical weather prediction models. The affects of aerosols on UV radiation are increasingly better understood. Parameterization of other factors affecting the UV radiation reaching the surface (albedo and elevation) have been increasingly studied and their affects better known. Clouds remain to be the primary source of error in UV Index forecasts. Each of these topics will be discussed with their impacts on the resulting UV Index forecast.

Compared to the visible spectral region very little is known about aerosol absorption in UV. Without such information it is impossible to quantify a cause to the observed discrepancy between modeled and measured UV irradiances and photolysis rates. We report preliminary results of an aerosol closure experiment where a UV-shadow-band radiometer (UVMFRSR, USDA UVB Monitoring and Research Network) and well-calibrated sun-sky radiometer (CIMEL, NASA AERONET network) were run side-by-side for several months at NASA/GSFC site in Greenbelt, MD. The aerosol optical thickness, τ, was measured at 340nm and 380nm by the CIMEL direct-sun technique. These results compared well with independent MFRSR τ measurements at 368nm (using total minus diffuse irradiance technique). Such comparisons provide an independent check of both instrument’s radiometric and MFRSR’s angular calibration and allow precise tracking of the UV filter degradation by repeating the comparisons made at somewhat regular time intervals. The τ measurements were used as input to a radiative transfer model along with AERONET retrievals of the column-integrated particle size distribution (PSD) to infer an effective imaginary part of the UV aerosol refractive index (k). This was done by fitting the MFRSR diffuse fraction measurements to the calculated values for each UV spectral channel. Inferred values of refractive index and PSD allow calculation of the single scattering albedo, ω, in the UV and comparisons with AERONET ω retrievals. The advantage of utilizing diffuse fraction measurements is that radiometric calibration is not needed for the MFRSR since the same detector measures both the total and diffuse flux. The additional advantage is that surface albedo is much smaller in the UV than in the visible spectral range and has much less effect on aerosol measurements.

Seasonal variability of solar UV radiation in ocean waters is estimated on a global scale by combining satellite measurements of scene reflectivity (TOMS), column ozone (TOMS) and chlorophyll concentration (SeaWiFS) with radiative transfer calculations for an ocean-atmosphere system. The new features are an extension of underwater radiative transfer (scattering and absorption) into the UV, inclusion of polarization in the above water diffuse radiances, the proper treatment of Fresnel reflection, and first order atmospheric backscatter of water-leaving radiance to the oceans. Maps of downwelling diffuse irradiances (E_d) at ocean surface and at different depths in the ocean, diffuse attenuation coefficient (K_d), and ten percent penetration depth (Z₁₀) of solar irradiation are computed for open ocean waters. Results on spectral irradiances at 310 nm in UV-B and at 380 nm in UV-A part of the spectrum are presented with particular emphasis on the role of aerosols, clouds, and ozone in the atmosphere and chlorophyll concentrations in the ocean.

Broadband shortwave diffuse horizontal irradiance models overestimate measurements by between 7 and 14% using the most reliable input data for the models and the best available broadband measurements of diffuse irradiance. This paper uses spectral irradiance measurements and models as opposed to broadband measurements and models to investigate the contributions to this difference from various regions of the spectrum. The data are from the first Atmospheric Radiation Measurement (ARM) diffuse irradiance intensive observation period (IOP) held in September and October of 2001 at the Oklahoma ARM site near Ponca City. Visible and ultraviolet (UV) rotating shadowband spectroradiometers (RSS) acquired data during the IOP. Diffuse measurements with conventional broadband diffuse pyranometers and direct irradiance measurements using an absolute cavity radiometer are also available for analysis. Integrated spectral measurements are consistent with broadband measurements and, therefore, confirm the earlier results that models over predict diffuse. The wavelength dependent differences in models and measurements are illustrated and discussed.

Several ground based ultraviolet (UV) monitoring networks exist in the United States, each of which is unique in the instrumentation employed for measurements. Two of these UV networks are the US EPA’s Brewer Spectrophotometer network and the USDA’s UVB Monitoring network, with a combined instrument total of 52 sites throughout the mainland USA, US territories and some overseas locations. The Brewer records full sky spectra from 287-363nm with 0.5nm resolution whereas the USDA instrument is a broadband device that measures broadband erythemally weighted UV data over a number of bands in the UV. To date, limited comparisons of data collected from these networks have been analyzed for comparative and quality assurance (QA) purposes. The data used in this paper is taken from sites where instruments from each program are co-located, namely, BigBend National Park, Texas and Everglades National Park, Florida. In order to reduce the contribution of errors in the Brewer-based instruments, the raw data has been corrected for stray light rejection, the angular response of the full sky diffuser, the temperature dependence of the instruments and the temporal variation. This reduces the estimated errors of the absolute irradiance values of each Brewer spectral measurement to approximately ±5%. The estimated uncertainty of the USDA instruments is also ±5%. Uncertainty is comprised of (1) standard lamp measurement errors, (2) spectral response determination and (3) the angular response of the diffuser. In this paper, we perform spectrally resolved comparisons between the Brewer UV irradiance measurements and the data collected by the broadband erythemal UV meters at co-located sites between 1997 through to 2002.

This is a continuation of work begun by Dave Bigelow and James Slusser in their study of the same name published in 2000 in J. Geophys. Res., 105, 4833-4840. This continuation study began in January 2002, when the entire database for the UV Multifilter Rotating Shadowband Radiometers (UV-MFRSR) was analyzed using the Langley regression technique, as described in "Langley Method of Calibrating UV Filter Radiometers," Slusser et. al., 2000, J. Geophys. Res., 105, 4841-4849. In conjunction with scientists at ASRC, SUNY, Albany (New York), the UVMRP has refined the air mass range versus wavelength that is used in the Langley analysis methodology to conform to the greater optical depths in the UV (290)-380 nm) compared with the visible (400-965 nm). A time series of direct Sun voltage intercepts (V_o's) from Langley plots is an indication of stability, which augments the traditional periodic standard lamp calibrations. Overall, 129 cases representing 28 sites and 39 instruments, with 21 sites and 30 instruments having multiple cases, were studied. The results presented herein show the mean annual drift in sensitivity for the seven nominal wavelengths of the UV-MFRSR instrument are: 300 nm - 1.2%, 305 nm - 4.8%, 311 nm - 2.6%, 317 nm - 3.0%, 325 nm - 4.8%, 332 nm - 4.9%, 368 nm - 3.7%.

A weatherproof spectroradiometer has been developed for spectral measurements of direct, global and radiance ultraviolet radiation. The core of the instrument is a Bentham D150 double monochromator with two input entrances with a swing away mirror. Two 4.0 m quarts fibers connect the optical input to the monochromator. Global irradiance was measured with an ideal cosine diffusor. Direct irradiance and radiance measurements were performed with a telescope having a field of view 1.5° mounted on a weatherproof sun tracker. The whole system is operated by an integrated software, running the tracker and the spectroradiometer at the same time. Calibration of the direct unit and the global irradiance were done with a 1000 W FEL lamp. Langley calibration was found more difficult due to changing atmospheric conditions and difficulties having proper clear sky days. Radiance distribution was measured two days in May 2003, showing similar pattern as for other places with a low aerosol content.

At the Swedish Meteorological and Hydrological Institute (SMHI) an operational radiation model system has been set up. It produces hourly fields of global-, photosynthetically active- and CIE weighted UV-radiation with a resolution of about 22 x 22 km for a geographic area covering Scandinavia and the run off region of the Baltic sea. This paper presents the model system and its data sources together with some validation results. The model output is available on the Internet page http://www.smhi.se/strang.

Two recently developed different types of fast spectroradiometers measuring solar UV irradiance have been compared in a field campaign: i) the UV spectroradiometer on filter model basis (UV-SPRAFIMO) and ii) the modified version of the spectroradiometer SPECTRO 320D by Instrument Systems. The all-weather UV-SPRAFIMO instrument combines a UV filter radiometer with 5 narrow-band (FBHM ≈ 2.0 to 2.5 nm) filters centered within ± 0.01 nm at 303.5, 309.0, 314.5, 327.0 and 387.0 nm, and an advanced neural network-based model. It allows up to 5 measurements per second to be taken that are averaged within time intervals between 5 and 30 s. The neural networks model that is embedded in the PC-based processing software converts the 5 measured irradiances into a full spectrum from 280 to 450 nm at small wavelength steps (≥ 0.05 nm). These spectra can be convoluted with user-defined slit function and integrated to broad-band and action-spectra-weighted irradiance values. Users can access the data stored in the internal data logger by a serial RS232 interface or by a modem and display them on a PC-based Graphical User Interface. The spectroradiometer SPECTRO320D consists of a grating double monochromator with a cooled (-20°C) PMT receiver. The modified instrument version run by DWD uses a Schreder type cosine diffuser that directs the solar global irradiance via quartz fiber optics onto the spectroradiometer's entrance slit. The spectroradiometer used at the campaign was installed in a thermostatted (22 ± 0.02)°C aluminum box. The modified instrument version performs a spectral scan over the whole UV region in two subsequent parts, with a lower speed in the UV-B than in the UV-A to account for the exponential changes of solar irradiance with increasing wavelengths in the UV-B and for the almost linear change in the UV-A region. In the configuration applied in the comparison, i.e. wavelength steps of 0.2 nm within the scan range from 290 nm to 450 nm, the resulting scan time of the SPECTRO 320D was 23 s. The two spectroradiometers, which both have been absolutely calibrated in the DWD lab using FEL 1000 W halogen lamps traceable to the German Physikalisch-Technische Bundesanstalt (PTB), were used in a field campaign at Izana (Tenerife Island) at a height of 2409 m to compare measured spectral and integral values of solar irradiance. Results of that comparison and the instruments’ characteristics revealed under those special field conditions will be discussed.

At present the United States Department of Agriculture (USDA) Reference Spectroradiometric Network consists of 4 sites: Table Mt. CO, Ft. Collins CO, Lamont OK (The ARM program SGP site), and Beltsville MD. At each site we operate a 1-meter cascaded additive-double Czerny-Turner scanning monochromator with a bi-alkali Photomultiplier and photon-counting detection. Irradiance calibrations are provided for the instrument at Table Mt CO by NOAA's Central Ultraviolet Calibration Facility (CUCF) from NIST-traceable standards. Calibrations are transferred from this instrument to others in the network (and additional stability monitoring of the primary instrument conducted) using shippable transfer calibrators we have designed. Here we describe these transfer calibrators, and our operational experience seen at the Table Mt. Site in 2002 and 2003 to date.

Since 1995 GOME-1 is measuring ozone (total column and profile), nitrogen dioxide and other minor trace gases on-board of ERS-2. An advanced GOME-2 instrument will fly on the METOP satellites. The GOME-2 measurements will provide the input for the ozone data record in the timeframe 2005 to 2020 provided by the EUMETSAT Polar System. The on-ground calibration of the instrument encompasses spectral, absolute radiance and irradiance calibrations as well as polarization, straylight, and slit function characerization. Main results of the first flight model are discussed.

Measurements of UV radiation at the earth’s surface may be highly impacted by the presence of clouds. In order to provide support for UV research, a Daylight Visible/NIR Whole Sky Imager was developed to provide cloud fraction assessment over the whole sky, as well as measurements of the radiance distribution over the full sky in several spectral bands. Radiances are determined in approximately 700,000 directions simultaneously with a given optical filter. Data may be acquired in seven spectral bands that may be selected for the application. The current instrument uses filters near 450 and 650 nm, open-hole, filters in the blue-green broadband and NIR long-pass, and two polarizers. Opaque and thin cloud fraction is determined from images acquired in the blue and red wavelengths. A more sophisticated version of the algorithm to detect thinner clouds and enable aerosol assessment is in development, and will be based on use of the NIR data in conjunction with the blue and red data. This paper will provide an overview of the instrument design and calibration, and sample sky radiance results. The cloud algorithms for determination of cloud fraction will be discussed, and the cloud imager results will also be presented.

Multi-channel moderate-bandwidth GUV filter radiometers have recently been added to the suite of instruments deployed in the US National Science Foundation Office of Polar Programs' UV monitoring network. The GUV instruments complement the stations' SUV-100 high-resolution scanning spectroradiometers, which have been monitoring UV levels in Antarctica, South America, and Alaska for more than a decade. The GUV instruments are used to help quality control SUV measurements, and to calculate total column ozone and a variety of biologically relevant UV integrals and dose-rates in real time. The results are updated every minute on web pages, and can be accessed via the website www.biospherical.com/nsf, or the stations' intranets. Online data may guide researchers on station in planning experiments, or for "first-look" analysis. The instruments underwent a detailed characterization. Their spectral response functions were measured with an apparatus that was specifically designed for this purpose. The apparatus and the data analysis method are described in detail with special attention given to a deconvolution method to correct measured data for the finite spectral resolution of the apparatus. The impact of uncertainties in measuring the spectral response of GUV channels on solar measurements is discussed. The GUV instruments are calibrated by comparison with a SUV-150B spectroradiometer, and dose-rates for 15 different biological action spectra are calculated based on an algorithm suggested by Dahlback. A comparison of calibrated GUV and SUV data indicates that erythemal (CIE) irradiance can be derived from GUV measurements to within 3% relative to the SUV up to a solar zenith angle (SZA) of 80°. A similar level of agreement can also be reached for other action spectra. Ozone values derived from GUV measurements at San Diego agree to within 3 Dobson Units (DU) with SUV ozone data and within a few DU with Earth Probe TOMS satellite observations.

At Stevens Institute of Technology, Hoboken, NJ we have operated a site with NILU-UV instruments for nearly two years. For most of this time only one instrument has been in operation, but we also have data for extended periods of time when up to three instruments have been working in parallel. The site is in close proximity to New York City and it is equipped with basic radiation sensors in addition to the NILU-UV sensors. In a companion paper we present results from intercomparisons between filter-based instruments, such as the NILU-UV, and the Dobson and Brewer instruments. Here we describe our experience operating filter-based radiation instruments. In particular, we discuss data quality issues and describe how one can detect and correct for drift in filter-based instruments. We also investigate the effect of elevated detector temperatures due to over-heating of the instrument by solar radiation on very warm days. Our experience with the newer versions of the filter instruments is that most of them have only minor problems with filter drift over time, and that this drift (if any) is easily detectable and can be corrected for. A potential problem is that varying detector temperature can degrade the instrument performance. Since filter UV instruments are normally set to operate with detector temperatures much higher than ambient temperatures this is a minor issue for most locations, and one that can easily be prevented.

Polysulphone has been widely used as a dosimeter to quantify personal solar UV exposures to humans during normal daily activities. In summer at sub-tropical and tropical latitudes, the dynamic range for UV exposures allows the use of the polysulphone to measure solar UV over periods of approximately three to six hours. The use of mesh as a filter over the polysulphone has been previously reported to extend the dynamic range. In this paper the use of a simple filter that is incorporated as part of the dosimeter is reported. The dynamic range of the polysulphone was significantly extended with the incorporation of the filter by a factor of approximately four to five.

The assessment of human UV exposure is an important part of any public health research program investigating potential positive and negative health effects from exposure to artificial and environmental levels of UV. Human UV exposure depends on a variety of factors such as location, activity, UV protective devices used, and body posture. This paper will provide an overview of techniques that may be used for assessing UV exposures, such as UV dosimetry and UV exposure modelling. Results presented in this paper highlight the need for further research into human UV exposure assessments, in particular for population groups considered not at risk, such as homeworkers.

Studies into the biological effects of acute exposures requires understanding of the probability of an event of a given intensity and duration. The occurrence of high hourly biologically-effective UVB (UVB_BE) exposures were evaluated for the 1997-2001 summer growing seasons (May-August) at five locations between 38° and 41° longitude across the continental United States. In general, the frequency of extreme hourly exposures decreased from west to east. The daily UVB_BE exposures resulting from the extreme hourly UVB_BE exposures were inversely correlated with TOC for that day. Hourly exposures in the upper 10% of all exposures occurred most frequently during June and July. There was a 30% probability of having a day with 2h of exposure in the upper 5% of UVB_BE values across the entire USA. The probability of having two sequential days with 2h of high exposure was approximately 10% most locations. The probability of having six sequential days of 2h extreme exposure was approximately equivalent to two to three days of 4h extreme exposure. Based on this analysis, a reasonable exposure regime for acute UVB effects on plants is the insertion of a 1 kJm^-2 h^-1 UVB_BE exposure for two to four hours into the ambient conditions for three sequential days.

UV plays a key roll in several biological functions. As consequence of the ozone depletion investigations to study the effects of UV radiation on human health and terrestrial and aquatic ecosystems have been carried out in laboratories and in the field. Experiments performed in laboratories, irradiating samples with lamps often present the inconvenience that light sources do not reproduce properly the solar spectrum. Field experiments are usually carried out comparing samples exposed to ambient irradiance (normal or increased) against 100% UV-B screened samples. This scenario also differs from the real situation of normal irradiance against UV-B increased irradiance. Some authors have solved this problem performing studies under ambient conditions, simulating the ozone depletion by supplementation of the UV-B radiation with lamps. As part of the IAI CNR-26, "Enhanced Ultraviolet-B Radiation in Natural Ecosystems as an added Perturbation due to Ozone Depletion," mesocosms experiments were performed at Rimouski (Canada), Ubatuba (Brasil) and Ushuaia (Argentina) using the supplementing methodology. In this paper we introduce the design of the measurements and lamps setting and the methodology used to calculate the attenuation constant and the irradiance at the water column at the mesocosms during the experiment, emphasizing on the Ubatuba campaign.

Evaluating the impact of ultraviolet-B radiation (UVB) on urban populations would be enhanced by improved predictions of the UVB radiation at the level of human activity. This paper reports the status of plans for incorporating a UVB prediction module into an existing Urban Forest Effects (UFORE) model. UFORE currently has modules to quantify urban forest structure, urban tree volatile organic compound emissions, carbon storage and sequestration in urban vegetation, dry deposition of air pollutants on trees, tree influences on energy use for heating and cooling buildings, tree pollen allergenicity index, and replacement cost of trees. These modeled effects are based upon field sampling to characterize land use, vegetation cover, and building features. The field sampling includes recording of tree species, total height, height to base of live crown, and crown width on randomly selected 0.04-ha (0.1 acre) plots. Distance and direction from sampled trees to buildings are also measured. The input for UFORE modeling of effects includes hourly meteorological data and pollution-concentration data. UFORE has already been used in assessing the urban forest functionof 13 cities in the United States and 5 cities in other countries. The objective of the present work is to enable UFORE to predict the effect of different urban tree densities on potential average human exposure to UVB. The current version of UFORE is written using the Statistical Analysis System (SAS); a new version will be a user-friendly Windows application and will be available for wide distribution. Progress to date on the UVB module consists primarily of examining available modeling and data collection tools. Two methods are proposed for the UVB module. In Method 1, we will derive predicted UVB irradiance <I_b> at person height, that is, below the urban tree and building canopy, using gap fractions (sky view portions) measured from digitized fisheye photos taken from each of the UFORE plot centers during a UFORE field survey. A promising method for analyzing the photos is the use of Gap Light Analyzer (GLA). A human thermal comfort model will be used to determine the times when people would be comfortable outdoors in light attire, and UVB <I_b> will be determined for those times. Method 2 will be applied in cases where hemispherical photos cannot be made available, and for making predictions for cities where surveys have already been done. Method 2 will use a 3D canopy UV radiation transfer model to derive <I_b> based on tree canopy cover maps from GIS analysis of aerial color IR photographs or Landsat TM images. The UV module addition to UFORE will make it useful in epidemiology of UV-related human disease and assessment of UV benefits, such as in vitamin D production, and it will also facilitate consideration of UV exposure in urban forest management.

Sorghum bicolor is grown in equatorial regions that have naturally high ultraviolet-B (UVB) exposures. To determine whether the increased wax production on the sorghum leaves and sheaths protects the plant by increased scattered radiation from the plant surface, the effects of wax amount on UVB reflectances were examined in greenhouse and field experiments involving three isolines of sorghum -- wild-type and two wax mutants. Reflectance of the wild-type sheath was found to be a result of the wax present while that on the mutant sheaths was not dependent on wax amount. Overhead UVB exposure corresponded with reduced sheath and increased leaf UVB reflectance for wild-type but negligible changes in both sheath and leaf reflectance for the two mutants. Although the sheath reflectances of wild-type were twice that of the two mutants, the negligible difference in leaf reflectance between isolines resulted in negligible differences in the canopy bi-directional reflectance, even at high view angles. The UVA canopy reflectance factors of the three sorghum isolines were measured at 0.03 at viewing angles near nadir on clear sky days. Predicted reflectance factors were calculated using the SAIL model then compared with the measured reflectance factors to evaluate the effect of sky diffuse fraction on the measured differences.

We have developed a satellite-based numerical simulation for determining the extent to which enhanced solar ultraviolet radiation (UVR) under the springtime Antarctic ozone decrese affects primary production throughout the Southern Ocean. This satellite approach using NASA Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data for chlorophyll and phytoplankton biomass, passive microwave data for sea ice concentration, and Total Ozone Mapping Spectrometer (TOMS) data for total column ozone and cloud reflectivity, circumvents many of the limitations involved with extrapolating point field measurements to larger geographical areas. The satellite data are used to force a physiology-based model of phytoplankton growth in response to UV-B, UV-A, and photosynthetically active radiation(PAR). Comparison with field measurements in the Western Antarctic Peninsula region shows excellent agreement. UVR-induced losses of surface phytoplankton production were substantial under all ozone conditions, due mostly to UV-A. However, when integrated to the 0.1% light depth, the loss of primary production resulting from enhanced fluxes of UV-B due to ozone depletion was less than 0.25%. The loss of primary production is minimized by the strong attenuation of UVR in the water column and by the spatial and temporal mismatch between the maximum extent of the Antarctic ozone hole and the maximum abundance of phytoplankton in the open water.

This paper shows the results of measurements carried out in November 2002 in the Italian Antarctic Base of Baia Terranova (74.07°S, 164.08°E) to test polysulphone film badges as possible UV personal dosimeters in such extreme environmental conditions. In the Italian Antarctic Base a multichannel radiometer GUV 511 (Biospherical Inc.) is routinely used by the Italian National Research Council (CNR) for UV irradiance at sea level. This instrument measures the intensity of the solar UV spectrum at four different wavelengths: 305, 320, 340, 380 nm, respectively. Data obtained from polysulphone badges exposed in the horizontal and the vertical configurations during diverse time lapses of the day, and from polysulphone badges worn by three volunteers of the base staff during several outdoors activities, have been compared with the irradiance data calculated from the measured values of GUV 511. A preliminary analysis of the whole data, also in the light of other recorded atmospheric and climatic parameters, shows a reasonable consistency. As also shown by previous measurements, carried out in June 2002 in the locality of Ny Alesund (Svalbard -- Artic Region), the calibration of the above mentioned personal dosimeters by means of another instrument operating in the same locality is a crucial step. Further work is required to demonstrate this approach is suitable for an acceptable evaluation of personal radiant exposures.

Increasing surface UV-B radiation (UV-B) and atmospheric carbon dioxide concentration [(CO₂)] are two major issues of climate change and agriculture. Although numerous studies have evaluated elevated UV-B or (CO₂) effects on crop growth, development and yield, little is known about the interactive effects of these two factors on cotton. The objective of this study was to determine the combined effects of elevated (CO₂) and UV-B radiation on cotton growth and physiology under controlled environmental conditions. The four treatments imposed were control [360 μmol (CO₂) mol^-1 and 8 kJ m^-2 d^-1 UV-B], +CO₂ [720 μmol (CO₂) mol^-1 and 8 kJ m^-2 d^-1 UV-B], +UV-B [360 μmol (CO₂) mol^-1 and 16 kJ m^-2 d^-1 UV-B] and +CO₂+UV-B [720 μmol (CO₂) mol^-1 and 16 kJ m^-2 d^-1 UV-B]. Treatments were imposed from emergence through three weeks after the first flower stage. Plants grown in +CO₂ showed greater plant height, leaf thickness, leaf area, leaf and canopy photosynthesis (P_N) and total biomass compared to the control, and fruit biomass was not affected by +CO₂ conditions. On the other hand, plants grown in +UV-B treatment exhibited slower growth as reflected by reduced plant height, shorter internodes and branch lengths, and total biomass due to smaller leaf areas and less lower leaf P_N. The +UV-B treatment also altered the leaf morphology and significantly reduced flower and petal lengths and petal area. Reduction in fruit production under both +UV-B and +CO₂+UV-B treatments was due to reduced photosynthesis and alterations in reproductive development. The results also showed interactive effects of UV-B on cotton leaf P_N, phenolics, wax content and some physiological parameters measured. Thus, a failure to increase cotton fruit production with +CO₂ and +CO₂+UV-B suggests that breeding UV-B radiation-tolerant cultivars is important in both the present and future solar UV-B radiation environments.

Since the 1970's stratospheric zone attenuation liable for surface UV radiation enhancement has been among the ever-increasing concerns of global climatologists. In recent years, numerous efforts have been undertaken at home and abroad to investigate the effect of enhanced surface UV-B on crops' growth, development and yield formation, achieving a lot of significant fruits and concurrently on field ecosystems. As we know, most of the experiments in the past were conducted in laboratories, including a short-term response on an individual-plant basis. This condition differs consipicuously from yield experiments at the level of an ecosystem with regard to its long-range response. Specifically the degree to which the UV radiation influences non-crop species, which leads to the distortion of the response to UV-B enhancement of crop's population and its ecosystem. As a result, it is necessary to carry out long-range field experiments at an ecosystem's level. This paper aims at the impacts of intensified UV-B upon weeds and large soil worms (i.e., microanimals) in an ecosystem of growing wheat, corn (maize) and spinach together with preliminary investigation of the mechanisms.

The depth of light penetration from the adaxial surfaces of the mature leaves of pecan (Carya illinoensis) was measured using a fiber optic microprobe system at four wavelengths: UV-B (310nm), UV-A (360 nm), blue light (430nm), and red light (680nm). The average thickness of the leaf adaxial epidermal layer was 15um and the total leaf thickness was 219um. The patterns of the light attenuation by the leaf tissues exhibited strong wavelength dependence. The leaf adaxial epidermal layer was chiefly responsible for absorbing the UV-A UV-B radiation. About 98% of 310 nm light was steeply attenuated within the first 5 um of the adaxial epidermis; thus, very little UV-B radiation was transmitted to the mesophyll tissues where contain photosynthetically sensitive sites. The adaxial epidermis also attenuated 96% of the UV-A radiation. In contrast, the blue and red light penetrated much deeper and was gradually attenutated by the leaves. The mesophyll tissues attenuated 17% of the blue light and 42% of the red light, which were available for photosynthesis use. Since the epidermal layer absorbed nearly all UV-B light, it acted as an effective filter screening out the harmful radiation and protecting photosynthetically sensitive tissues from the UV-B damage. Therefore, the epidermal function of the UV-B screening effectiveness can be regarded as one of the UV-B protection mechanisms in pecan.

Global atmospheric trends in ozone column amount has focused attention on the environmental risk of exposure to ultraviolet (UV) radiation. Monitoring UV irradiance in diverse and remote locations is necessary to understand the variability of exposure, dose rates and resultant vulnerability of ecological systems. The USDA UV-B Monitoring Program maintains a wide network for ground-based continuous measurement of solar radiation in several wavelengths of interest for photosynthesis, plant growth and UV exposure to humans. This network provides data for analysis of UV climatology and trends at those sites. A satellite-based technique for producing mesoscale-resolution mapped distributions of UV spectral irradiance has been developed for extending this information into a region surrouding the network sites. The methodology combines radiative transfer modeling, multispectral image pixel classification, cloud optical depth retrievals and auxiliary remote sensing data. The results of the method are compared with ground-based measurements and utilized to examine the role of cloud distribution and surface albedo in determining mesoscale variability of UV exposure in high-latitude and high-altitude environments.

Seasonal variation of global solar radiation: ultraviolet-B (UV-B: 290 - 320 nm), ultraviolet-A (UV-A: 320 - 400 nm) and Total (Total: 300 - 3000 nm) has been measured at the Shonan Campus of Tokai University (35°21’N, 139°16’E, in central Japan) since October 1990. To clarify regional difference of solar radiation in East Asia, the same type of radiometers were installed at Wakkanai (October 2000: 141°48’N, 145°21’E, in Hokkaido, at the northern end of Japan), Mashiki (June 1996: 32°50'N, 130°52'E, in Kumamoto, at the mid-west Japan) and Taketomi (July 1998: 24°20’N, 123°41'E, on Iriomote Island, in Okinawa, at the south western end of Japan). Observation data are transferred to the Shonan Campus every day via Internet, and the data were posted on our web site. Comparison of sensitivity among all radiometers used in this network was carried out from August 2002 to September 2002. Observed data were corrected based on the comparison results. Solar radiation showed clear regional differences depending on the season. Global solar radiation in summer was almost the same among stations, but in winter, global radiation showed very significantly among the stations. The ratio of UV-B in winter to summer was 14 times at Wakkanai, 6 times at Shonan and Mashiki, and 2 times at Taketomi. The ratio of Total in winter to summer was 2 times at Shonan, Mashiki and Taketomi, and 6 times at Wakkanai. The seasonal variation of the ozone level corresponded the latitude with Taketomi registering the least amplitude.

During the period August 2001 to February 2003 global solar UV measurements were performed with a high resolution spectroradiometer at Melbourne Australia (37.7°S, 144.9°E). From these measurements total column ozone amounts were derived and compared with those of a nearby Dobson spectrophotometer. The effects of cloud cover, solar zenith angle and the choice of various parameters used for the total ozone retrieval were examined. The comparison showed that mean difference between the two instruments was either -0.3% or +1.8% depending on the choice of parameters used in the total ozone retrieval. The standard deviation of the differences was 2.7% in both cases. It was observed that the presence of smoke haze increased the difference between the instruments and some preliminary work on reducing this effect is presented.

Increased levels of biologically harmful Uv radiatonhave beenshown to affec aquatic ecosystems, marine photocynmetiry, and their imapct on carbon cycling. A quantiative assessment of UV effectw requires an estimate of the in-water raiationfield. An esitmate of underwater UV radiatonis porosed based on satellit meausrments fromthe TOMS and SeaWiFS and modesl fo radiatve transfer (RT). The Hydrolight code, modified toe xtnd it to the 290 - 400 nm wavleength range, is used for REt calucaitons in theocean. Solar direc tandidffuse radiances at the ocean surfce are calculated using a fulll RT code for clear-sky coditions, whicha re then modified for clouds and aerosols.Teh TOMS total column ozone and reflectivity productsa reinputs for RT calcuaitons in the atmosphere. An essential component of the in-water RT model is a model of seawater inherent optical properties (IOP). The IOP model is an extension of the Case-1 water model to the UV spectral region. Pure water absorption is interpolated between experimental datasets available in the literature. A new element of the IOP model is parameterization of particulate matter absorption in the UV based on recent in situ data. The SeaWiFS chlorophyll product is input for the IOP model. The in-water computational scheme is verified by comparing the calculated diffuse attenuation coefficient K_d, with one measured for a variety of seawater IOP. The calculated K_d is in a good agreement with the measured K_d. The relative RMS error for all of the cruise stations is about 20%. The error may be partially attributed to variability of solar illumination conditions not accounted for in calculations. The conclusion is that we are now able to model ocean UV irradiances and IOP properties with accuracies approaching those visible region, and in agreement with experimental in situ data.

A Brewer MKIII double spectrophotometer has been modified to measure direct sun and sky radiance from 303nm to 363nm for the purpose of measuring aerosol optical depth, Angstrom parameter, and single scattering albedo. Results from a detailed instrument calibration showed that there is a temperature dependence of -0.3% per degree Celsius, the field of view was 2.6° full width half maximum, and the wavelength calibration was accurately determined using a dye-LASER. Using both integrating sphere and lamp-diffuser plate combinations, absolute diffuse radiometric calibration was performed and converted into direct calibration using the measured field of view. Aerosol optical depth and Angstrom parameter were measured on 4 clear sky days in June 2003 at Greenbelt, Maryland and compared to AERONET-data at the same location. The average difference in the aerosol optical depth at 340nm was smaller than 0.02. A depolarizing element was inserted in the Brewer's optical path to reduce the very pronounced polarization sensitivity, and additional polarized filters were added to explore the possibility to obtain additional aerosol information. Because of a defect in the depolarizer, the current residual polarization is 5%, which has to be reduced to less than 1% to derive additional aerosol parameters from sky radiance measurements.

Ground-based visible and UV irradiances at 11 wavelengths were measured in order to characterize the wavelength dependence of aerosol optical depth during the biomass burning period (October~November 2002) with a visible/ultraviolet multifilter rotating shadowband radiometer (vis-MFRSR, UV-MFRSR) at Gwangju (35.13°N, 126.53°E), South Korea. UVMFR has 7 wavelengths of 2 nm FWHM centered on, 299, 305, 310, 317, 323, 331, and 367 nm, and vis-MFRSR has 6 channels of 10 nm FWHM on 415, 500, 615, 673, 870 and 930 nm. Measurement outputs from the MFRSRs were sampled at 20 seconds interval and saved every minute as a mean value into a YESDAS data logger. In order to calculate aerosol optical depth at the visible and UV range, total column ozone should be considered because the surface UV radiation, especially UV-B radiation, is highly absorbed by atmospheric ozone. Ozone optical depths were calculated using TOMS (Total ozone mapping spectrometer) daily total column ozone (DU) and WMO (1985) ozone absorption coefficients. Exceptionally, UV radiation at 367.4 nm is free from ozone absorption. Rayleigh optical depth was highly dependent on the wavelength and was calculated using surface pressure information provided by the KMA (Korea Meteorological Administration). This study shows the results on October and November 2002 when both ground-based spectral AOD at visible/UV range and aerosol measurements and chemical analysis were executed simultaneously. AOD varied 0.16 ~ 0.64 dependent on the wavelengths during the measurement period and the AOD values had an anticorrelation with wavelength. On November 12, 2002 both biomass burning and Asian dust were observed simultaneously. The AOD analysis results showed that AOD increased 100~200% dependent on the wavelength when Asian dust and biomass burning were observed compared to the days when no events occurred. Aerosol measurement confirmed this from the increase of mass concentration of aerosol on this date. Aerosol optical parameters were compared with aerosol chemical composition.

In general measurements of UV-radiation are related to horizontal surfaces, as e.g. also done for the internationally standardized and applied UV-index. In order to get more information on biologically relevant UV-exposure, there is a need for quantitative data of radiation fluxes on tilted surfaces. UV exposure of the human skin is one of the most essential issues in UV research, and therefore UV-irradiance for surface orientations typical for the human body should be known for all kinds of meteorological conditions. To measure these fluxes the new automatic system ASCARATIS (Angle SCAnning RAdiometer for determination of erythemally weighted irradiance on TIlted Surfaces) was developed and built. With three units of ASCARATIS hundreds of thousands of sets of UV-index measurements (each set consisting of measurements in 27 directions) have been made at different sites (urban, rural, mountain) during the last three years. The measurements cover the whole variability of weather conditions for all seasons. The results show large differences between UV-irradiation of horizontal surfaces (measuring standard) and inclined surfaces especially during the time of the year with lower sun elevations. The measuring data are used to fit a radiation model for inclined surfaces and to model the UV-irradiance of the human body.

UV-SPRAFIMO is a completely new developed UV instrument for very fast measurements of solar spectral irradiance with high spectral resolution and arbitrary step width. It combines sophisticated filter radiometer technique with a new model based on neural networks. UV-SPRAFIMO has the following specifications: (1) Spectral region 280 - 400 nm. (2) Arbitrary spectral resolution and step width of the UV spectra (≥ 0.05 nm). (3) Simultaneous measurement of all spectral channels. (4) Up to 5 measurements per second with arbitrary averaging interval of 5 to 30 seconds. (5) Weatherproofed, air conditioned housing and fully automatic measurement system. (6) No moving parts. (7) Data logger up to 64 Mbytes memory for long-term measurements at remote sites. (8) GPS to automatically set up time and geographical position data. (9) PC based, graphical user interface for measurement set up and monitoring and processing of data. (10) Online calculation and visualization of integrated irradiances like UV-A, UV-B and UV-Index as well as erythemal or user defined weighted irradiance. (11) Simultaneous total ozone column retrieval from spectral measurements. UV-SPRAFIMO is a standalone and easy to use UV spectral radiometer; it was tested in different climate regions during field measurement campaigns in order to compare measurement performance and accuracy to high quality scanning spectral radiometers. Details of functional principles and results of the measurement campaigns are presented.

Decreasing trends of total ozone affect mainly solar ultraviolet (UV) levels at ground level with adverse effects on the biosphere. Highly accurate measurements of solar UV irradiance have become an important issue to assess UV trends. To detect these trends stations with well calibrated instruments, with long-term stability and Quality Assurance (QA)/ Quality Control (QC) carefully followed procedures, are necessary. The Solar Radiometry Observatory of Rome, University “La Sapienza” (city center) is one of the stations regularly measuring UV irradiance in Italy. Measurements of UV spectral (290-325 nm) irradiance started in 1992, using Brewer MKIV 067. Measurements of total irradiance contained in the 280 - 320 nm waveband begun in 2000 with the YES UVB-1 broad-band radiometer. An investigation of the internal temperature dependence of the spectral responsivity to improve the quality of the Brewer UV data was carried out. The study was based on the analysis of responsivity files recorded during the years 2000-2002. Responsivities are provided by specific tests through a set of five 50 W quartz tungsten-halogen lamps, traceable to the standards of the National Institute of Standards and Technology (NIST). The lamp tests allow to measure any changes in the instrument response over time. It was observed that a decrease in the instrument's responsivity resulted from an increase of the internal temperature. A methodology based on a family of responsivity files at different temperature intervals is proposed to allow correction of UV irradiances using the responsivity file at the corresponding temperatures. The mean percentage differnce between temperature corrected and non-corrected Brewer data varies from 0.8% to 1.5% over an internal temperature of 8°C-42°C. In addition the results of a field evaluation in Rome between Brewer 067 and two temperature stabilized instruments, a broad-band radiometer (YES UVB-1) and a moderate bandwidth multichannel radiometer (Biospherical GUV-511C) were analyzed using temperature corrected spectral measurements.

NILU has developed an accurate, reliable and robust filter instrument for measuring irradiances at ultraviolet (UV) and visible wavelengths. The NILU-UV instrument has been thoroughly tested through comparisons with well calibrated spectral radiometers over extended time periods with significant variations in ozone and cloud cover. The objective of this work is to present the instrument and to derive UV doses, total ozone abundances and cloud effects from the NILU-UV instrument, and compare the results with similar results from a double monochromator Bentham spectroradiometer and a Brewer ozone spectrophotometer.

Solar UV irradiance measurements in Antarctica are often carried out by automatic or semiautomatic equipment. The unattended way of managing instruments needs accurate knowledge of the parameters affecting experimental data, among which cloudiness plays a fundamental role. A moderate-band multifilter radiometer and a total sky camera were installed for a test in the Italian Antarctic base (Terra Nova Bay, 74.07°S, 164.08°E) during the summer campaign 2002 - 2003. This paper shows preliminary results on the radiometer spectral data and a comparison with modelled spectral irradiances. Moreover, the radiometer integrated irradiance, computed by means of a new model, was compared with the updated Green model integrated irradiance, corrected by a cloud factor obtained from the sky camera images. Results showed good agreement on the integrated irradiances but poor results, except for 305 nm, when spectral values were analyzed.

We initiated a study in winter 2000 in a Colorado shortgrass steppe to investigate effects of altered ultraviolet-B (UVB) radiation and altered precipitation on plant growth, plant tissue decomposition, and litter faunal activity. In the field, open-air structures were constructed of solid plastic sheet material that either passed all wavelengths of solar radiation or passed only wavelengths greater than 400 nm (UVB =280-315 nm). Preliminary results indicate decreases in warm-season grass production under UVB radiation and drought conditions. Analysis of fiber constituents shows some significant seasonal and UVB treatment effects. The results of in vitro digestible dry matter analyses show significantly higher digestibility with UVB. Simulated grazing increased plant production, but there were no UVB by grazing interactions. Litter decomposition was affected by UVB exposure, the CO₂ growing conditions, and precipitation level. Under dry conditions, UVB radiation tended to increase litter decomposition, as measured by mass loss. There were no clear initial effects of UVB treatment on soluble and fiber constituents of litter. Exclusion of UVB resulted in reduced fungal hyphae counts in ambient CO₂-grown litter collected in fall 2002. Preliminary results indicate that litter arthropod density was lower with exposure to UVB and also lower under drought conditions.

Stratospheric ozone depletion and enhanced solar ultraviolet-B (UV-B) irradiance may have adverse impacts on the productivity of agricultural crops. Though only a small portion of the total solar electromagnetic spectrum, UV-B irradiance has a disproportionately large photobiological effect, largely because it is readily absorbed by important macromolecules such as proteins and nucleic acids. Numerous investigations have demonstrated that the effect of UV-B enhancements on plants includes a reduction in grain yield, alteration in species competition, susceptibility to disease, and changes in plant structure and pigmentation. Many experiments examining UV-B radiation effects on plants were conducted in growth chambers or greenhouses. It has been questioned if the effect of UV-B radiation on plants can be extrapolated to field responses from indoor studies because of the unnaturally high ratios of UV-B/UV-A and UV-B/PAR in many indoor studies. Field studies on UV-B radiation effect on plants have been recommended in order to use the UV and PAR irradiance provided by natural light. This study found the maize yield formation and yield structural elements responded to enhanced UV-B radiation under field conditions. Enhanced UV-B radiation caused a significant reduction of the dry matter accumulation and the maize grain yield in turn was affected. Analysis of yield structure indicates that the maize yield decreased with increased UV-B radiation and was evidently related to the decreased kernel weight and kernel number per ear.

Converting discreet narrowband filter radiometer irradiance measurements into continuous allows the construction of weighted doses such as an erythemal and plant action spectra. Synthetic spectra were retrieved from 7 UV narrowband channels using a fast 5 parameter fit. The synthetic spectra are compared with measurements from a collocated spectroradiometer and the erythemally weighted doses from the synthetic spectra are compared with daily erythemal doses from a collocated broadband radiometer. The agreement in spectral data ranges generally from 0.75 to 1.25 depending upon wavelength and solar zenith angle. Agreement between daily erythemal doses are generally between 0.70 and 0.90.

FastRT is a fast, yet accurate UV simulation tool which computes downward surface UV doses, indices and irradiances in the spectral range 290 - 400 nanometers. It takes the main radiative input parameters into account, i.e. instrumental characteristics, solar zenith angle, ozone column, aerosol loading, clouds, surface albedo and topography. CheckUVSpec is a quality assurance program to check incoming UV spectra for an EU-funded European UV database. The algorithm is based on comparisons of measured UV spectra with FastRT simulations. The QA program can also be run by users to check measured UV spectra for obvious errors and to report the most likely type of atmospheric and surface scenario which was present during the measurements. An interactive URL WWW site: http://zardoz.nilu.no/~olaeng/fastrt/fastrt.html allows the public to run the FastRT program with most input options. This page also contains updated information about the FastRT and CheckUVSpec and links to freely downloadable source codes and binaries.