IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING, VOL. 2, NO. 3, SEPTEMBER 2009 207

The PROMOTE UV Record: Toward aGlobal Satellite-Based Climatology

of Surface Ultraviolet IrradianceAnders Lindfors, Aapo Tanskanen, Antti Arola, Ronald van der A, Alkiviadis Bais, Uwe Feister, Michal Janouch,Weine Josefsson, Tapani Koskela, Kaisa Lakkala, Peter N. den Outer, Andrew R. D. Smedley, Harry Slaper, and

Ann R. Webb

Abstract—This paper describes the PROMOTE UV Record,which aims to provide a global long-term record of the surfaceUV radiation. The algorithm developed takes as input cloudinformation from the International Satellite Cloud ClimatologyProject (ISCCP) and a recently developed multisensor assim-ilated record of the total ozone column. Aerosols and surfacealbedo are based on climatologies. Here, first validation resultsof the PROMOTE UV Record are presented through comparisonagainst ground-based measurements of daily erythemal UV dosesat eight European stations. The validation shows that the methodis working reasonably, although there is a clear tendency towardoverestimation. Typically, the median bias as compared to mea-surements is 3%–10% and 56%–68% of the daily doses are within

20% from the ground-based reference. The prototype versionof the PROMOTE UV Record included in this paper covers theperiod from July 2002 to June 2005. The time series will later beextended to start in 1983.

Index Terms—Aerosols, albedo, clouds, International SatelliteCloud Climatology Project (ISCCP), long-term, satellite, UV.

Manuscript received February 26, 2009; revised May 29, 2009; accepted Au-gust 02, 2009. First published October 13, 2009; current version published Oc-tober 28, 2009. This work was supported by ESA through PROMOTE project.

A. Lindfors and T. Koskela are with the Climate Change Research, FinnishMeteorological Institute, Helsinki, Finland (e-mail: anders.lindfors@fmi.fi;tapani.koskela@fmi.fi).

A. Tanskanen is with Nuclear Services, Fortum, Espoo, Finland (e-mail: aapo.tanskanen@netsonic.fi).

A. Arola is with the Kuopio Research Unit, Finnish Meteorological Institute,Kuopio, Finland (e-mail: antti.arola@fmi.fi).

R. van der A is with the Atmospheric Composition Research Division,Royal Netherlands Meteorological Institute, De Bilt, The Netherlands (e-mail:avander@knmi.nl).

A. Bais is with the Physics Department, Aristotle University of Thessaloniki,Thessaloniki, Greece (e-mail: abais@auth.gr).

U. Feister is with the Lindenberg Observatory, Deutscher Wetterdienst, Lin-denberg, Germany (e-mail: uwe.feister@dwd.de).

M. Janouch is with the Solar and Ozone Observatory, Czech Hydrometeoro-logical Institute, Hradec Kralove, Czech Republic (e-mail: janouch@chmi.cz).

W. Josefsson is with the Core Service, Swedish Meteorological and Hydro-logical Institute, Norrköping, Sweden (e-mail: weine.josefsson@smhi.se).

K. Lakkala is with the Arctic Research Centre, Finnish Meteorological Insti-tute, Sodankylä, Finland (e-mail: kaisa.lakkala@fmi.fi).

P. N. den Outer and H. Slaper are with the Laboratory for Radiation Re-search, National Institute for Public Health and the Environment, Bilthoven,The Netherlands (e-mail: peter.den.outer@rivm.nl; harry.slaper@rivm.nl).

A. R. D. Smedley and A. R. Webb are with the School of Earth Atmosphericand Environmental Sciences, University of Manchester, Manchester, U.K.(e-mail: andrew.smedley@manchester.ac.uk; ann.webb@manchester.ac.uk).

Digital Object Identifier 10.1109/JSTARS.2009.2030876

I. INTRODUCTION

P ROMOTE, or protocol monitoring for the Global Mon-itoring for Environment and Security (GMES) Service

Element Atmosphere, is an initiative of the European SpaceAgency, with the mission to “deliver a sustainable and re-liable operational service to support informed decisions onthe atmospheric policy issues of stratospheric ozone deple-tion, surface UV exposure, air quality and climate change”(http://www.gse-promote.org). This paper presents the PRO-MOTE UV Record, which aims to provide a global, long-termsatellite-retrieved record of surface UV radiation. The algo-rithm is described, and first validation results are presented.

Earlier work on satellite-retrieved surface UV radiation in-clude methods based on the Total Ozone Mapping Spectrometer(TOMS) and its successor, the Ozone Monitoring Instrument(OMI) [1]–[3], which have the advantage that much of the infor-mation necessary for retrieving the surface UV (clouds, ozone,even aerosol to some extent) are available from measurementsby a single satellite instrument. Concerning daily UV doses, adisadvantage of these TOMS-type of satellite UV-retrievals isthat they typically include only one satellite overpass per day.This means that the algorithm cannot account for variations inthe cloudiness during the day. Instead the cloud situation ofthe overpass is assumed to be valid the whole day and, there-fore, days with varying cloud conditions cause a larger uncer-tainty in the retrieved daily UV doses [4]. To some extent, theTOMS/OMI UV record also suffers from gaps in the time series.

Another approach for retrieving the surface UV from satellitedata is to use cloud information from geostationary satellites incombination with total ozone column from polar orbiting plat-forms. This approach has been successfully applied to the Eu-ropean region [5], and recently also to North America [6].

The aim of the PROMOTE UV Record is to provide globaland long-term information on the surface UV radiation. A majorchallenge for this task is to ensure homogeneity when com-bining data from multiple satellite sensors. In order to meet thisaim, we have chosen to use cloud data of the International Satel-lite Cloud Climatology Project (ISCCP) in combination with amultisensor, assimilated record of the total ozone column. Thus,our study will complement earlier work on ISCCP-based UV es-timates [7], [8].

It should be noted that the present paper includes only a pro-totype of the PROMOTE UV Record, covering the period fromJuly 2002 to June 2005, whereas in its final version, the PRO-MOTE UV Record will cover the whole ISCCP period startingin 1983.

II. INPUT DATA

In order to be able to retrieve the surface UV irradiance, in-formation is needed both on atmospheric conditions, such as

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208 IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING, VOL. 2, NO. 3, SEPTEMBER 2009

clouds and total ozone column, and on geophysical quantities,such as the altitude of the location considered. The followingsubsections describe the input data used for the PROMOTE UVRecord.

A. Total Ozone Column

The source of the total column ozone data is the PROMOTETotal Ozone Record, which is developed by the Royal Nether-lands Meteorological Institute (KNMI). This data set includesmeasurements from a number of satellite instruments of the past30 years: TOMS (Nimbus7 and EarthProbe), SBUV (Nimbus7,NOAA-9, 11 and 16), GOME (ERS-2), SCIAMACHY (EN-VISAT), OMI (Aura), and GOME-2 (METOP). The measure-ments from the individual satellite instruments will be correctedfor biases as function of solar zenith angle and temperature, andthe corrected data will be assimilated with a chemistry-transportmodel in order to provide a homogeneous, global and long-termrecord on the total ozone column. The modelling of the trans-port, chemistry and the aspects of the ozone data assimilationare described in more detail in Eskes et al. [9].

Work is, however, still on-going (January 2009) to producethe complete long-term ozone record (which is expected tobecome available during spring 2009). Therefore, we useda shorter data record, covering the period from July 2002 toJune 2005, based on assimilated SCIAMACHY total ozonecolumn for developing the first PROMOTE UV Record resultspresented in this paper.

B. Clouds

The International Satellite Cloud Climatology Project(ISCCP) was established in 1982 as part of the World ClimateResearch Programme to collect and analyze satellite radiancemeasurements to infer the global distribution of clouds, theirproperties, and their diurnal, seasonal, and interannual varia-tions. The resulting datasets and analysis products are beingused to improve our understanding of the role of clouds inclimate, with the primary focus being on the elucidation of theeffects of clouds on the radiation balance.

The ISCCP data have been described elsewhere [10], [11],including also discussion on the efforts to make the data homo-geneous. The PROMOTE UV Record uses ISCCP version D1cloud data as input. This data set contains merged spatial av-erages of satellite-derived cloud properties in a global 280 kmequal-area grid with a time resolution of 3 h. The cloud frac-tion and the cloud optical depth of the cloudy part of the gridare the quantities used as input for the PROMOTE UV Recordalgorithm.

C. Aerosols

The Global Aerosol Data Set (GADS; [12]) is a global aerosolclimatology. In GADS, atmospheric aerosol particles are de-scribed by different aerosol components, such as water-soluble,water-insoluble, soot, sea-salts and minerals. Each componentis characterized through size distribution and refractive indexdepending on wavelength. For the PROMOTE UV Record, weused GADS version 2.2 available with a 5 5 resolution. Theaerosol optical depth and single scattering albedo were extractedfor the wavelength 300 nm, separately for winter and summer,assuming a relative humidity of 70%.

D. Surface Albedo

The moving time-window (MTW) method is based on the as-sumption that the satellite reflectivity values within a certaintime-window around the day of interest form a sample of thereflectivity distribution. The lower tail of this distribution cor-responds to cloudless skies, that is, situations when the reflec-tivity measured by the satellite represents the surface albedo.The MTW algorithm has been applied to the TOMS 360 nmLambertian Equivalent Reflectivity (LER) time series to con-struct a daily surface albedo climatology for the Nimbus-7 pe-riod 1979–1992 [13]. This surface UV albedo climatology wasused as input for the PROMOTE UV Record algorithm.

E. Altitude

GTOPO30 is a digital elevation model (DEM) for the world,developed by the United States Geological Survey (USGS). Ele-vations in GTOPO30 are regularly spaced at 30-arc seconds. Forthe PROMOTE UV Record, however, a version of GTOPO30converted to a 1 1 resolution, available at the TEMIS web-site (http://www.temis.nl/data/topo/dem2grid.html), was used.

III. PROMOTE UV ALGORITHM

Daily erythemal UV doses constitute the main product of thePROMOTE UV Record. These are provided as both global andEuropean maps, and as local time series for more than one hun-dred selected locations. Before performing the actual UV calcu-lations, all input data were converted to a 1 1 resolution (ifnecessary), which is also the resolution of the PROMOTE UVRecord.

The applied UV algorithm is based on radiative transfer cal-culations with appropriate input data to describe the factors af-fecting the surface UV irradiance. Using the sdisort (pseudo-spherical) solver of the radiative transfer equation, included inthe libRadtran package [14], look-up-tables were produced thatgive the erythemally weighted UV irradiance as

(1)

where is the clear-sky irradiance, is thecontribution of the cloud-free part of the satellite grid cell, and

is the contribution of the cloudy part of the grid.is the cloud fraction, which is defined as the fraction of

the grid cell covered by clouds, is the aerosol correc-tion factor accounting for the effect of aerosols, andis a correction factor taking into account the combined effectof clouds and aerosols on UV radiation (see also [15]). ,

, and are retrieved from the look-up-tables men-tioned above, using as input the following parameters: altitude(z), total column ozone , surface albedo , solar zenithangle , aerosol optical depth and single scattering albedo

, and cloud optical depth . Note that external mixingof aerosols and cloud droplets was assumed when calculating

. More details on the look-up-tables, including verifica-tion of the outcome, are available on the PROMOTE UV Recordweb pages.

The erythemal irradiance is calculated for each hour, and ad-justed for the variations in the Earth-Sun distance depending on

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LINDFORS et al.: PROMOTE UV RECORD: TOWARD A GLOBAL SATELLITE-BASED CLIMATOLOGY OF SURFACE ULTRAVIOLET IRRADIANCE 209

TABLE IOVERVIEW OF THE DATA USED IN THIS STUDY AND VALIDATION RESULTS

the time of year. The daily erythemal UV dose is then deter-mined from the hourly irradiances using the trapezoid integra-tion method. Since cloud data are available only for every threehour, it was assumed that the cloud properties remain constantover a three-hour time window, from one hour before the timestamp of the observation to one hour after.

IV. VALIDATION

A. Reference Data

The PROMOTE UV Record was validated using daily ery-themal UV doses from ground-based measurements at eight Eu-ropean stations from Sodankylä (Finland) in the north to Thes-saloniki (Greece) in the south. These ground-based data includemeasurements done both by spectroradiometers and broadbandUV radiometers. Table I lists the stations included in this studytogether with instrument type, and provides references (whenavailable) to more details on the data. Based on earlier studieson measurement uncertainty and instrument comparisons [17],[19], [20], we expect that the daily erythemal UV doses inferredfrom these measurements are accurate within roughly 10%.

B. Results

The satellite-retrieved daily erythemal UV doses over theperiod July 2002 to June 2005 were compared to ground-basedmeasurements at the above-mentioned eight European sites.Following the paper by Tanskanen et al. [22], we applied athreshold filter of 200 J/m2 to the daily doses, so that only dosesexceeding that value were included in the validation analysispresented beneath.

As an example of the validation results, Fig. 1 shows thescatter plots of satellite-retrieved UV versus measurements forBilthoven, the Netherlands, and Thessaloniki, Greece. Althoughthese stations are located in different climatic regions, both ofthem show quite typical performance compared to the other sta-tions included in this study: the daily UV doses show a rea-sonable general agreement, although a fair amount of scatter ispresent. There is a clear tendency toward overestimation of thedaily UV doses. For the monthly values, the random-like errorsare partly averaged out, and the agreement with measurementsis better.

Table I lists more in detail the performance of the PROMOTEUV Record as compared to the ground-based measurements,showing for each station the following quantities:

• number of days included in the analysis;• mean bias mean value of the percentage deviation of the

satellite-retrieved UV (sat) as compared the the ground-based refernce (ref), i.e., mean ([sat ref]/ref %);

• median bias median value of the percentage de-viation as compared to the reference, i.e., median([sat ref]/ref %);

• std standard deviation of the ratio of satellite-retrievedto ground-based UV, i.e., std(sat/ref);

• W amount (relative frequency in %) of values foundwithin % from the reference.

The values in parentheses are for cloud-free or almost cloud-free days, selected based on the ISCCP cloud data as the 5th per-centile with the weakest cloud attenuation at each station [i.e.,days with highest ratios of ; see (1)].

The results detailed in Table I show that the PROMOTEUV Record algorithm is working reasonably. The performanceis similar to that of the OMI-retrieved daily UV doses [22],with quite a clear tendency toward overestimation. Excludingthe station showing the highest and the lowest value for eachquantity yields a range of 3%–10% for the median bias, and56%–68% for the amount of satellite-retrieved daily dosesthat are within 20% from the ground-based reference (W20).Lindenberg constitutes an exception from the general pattern,as the satellite-retrieved UV doses there are systematically toolow (median bias 15%). For Reading, on the other hand, astronger overestimation is seen (median bias 15%).

The reasons for the observed behavior of the PROMOTEUV Record in comparison with ground-based measurementsare most probably related to the input used for the UV calcu-lations. At some stations the GADS aerosol climatology maynot be representative, while the data from high latitude stationsto some extent may suffer from problems connected to the sur-face albedo. At Thessaloniki (Fig. 1) it is, for instance, seenthat the overestimation prevails also during the summer daysshowing the highest measured UV doses. As these days are,in practice, cloud free, this overestimation can be attributed toaerosols (see also, e.g., [23]). For Bilthoven, on the other hand,the high summer values are in good agreement, indicating thataerosols is not a significant problem there. A similar conclusioncan be reached also by looking at the selected cloud-free or al-most cloud-free days (the values in parentheses in Table I). Weemphasize, however, that that the selection itself suffers fromuncertainty and that some of the selected days may have hadclouds present in reality although the ISCCP data did not showthat. Thus, the results shown for these cloud-free days shouldnot be interpreted too strictly.

Still, comparing the performance of the PROMOTE UVRecord for the selected cloud-free days with that for all daysindicates that clouds are responsible for a considerable partof the typical overestimation; the mean bias, for instance, issmaller for the cloud-free days at most stations. A more detailedanalysis (not shown) indicates that days with a strong cloud

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210 IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING, VOL. 2, NO. 3, SEPTEMBER 2009

Fig. 1. Measured versus satellite-retrieved daily and monthly mean erythemal UV doses at Bilthoven and Thessaloniki.

attenuation according to ground-based measurements show astronger tendency toward overestimation by the PROMOTEUV Record. This agrees with earlier work [8], [24] usingISCCP clouds for estimating the surface UV irradiance, wherethis behavior was found to prevail also when comparing theISCCP-based data against the mean value of several stationswithin the ISCCP grid. Thus, it seems that the overestima-tion cannot be attributed to different fields-of-view of theground-based measurements and the satellite grid cell (280 kmequal area grid). On the other hand, underestimation of the UVdoses during some days, seen more commonly under conditionsof weak cloud attenuation, may well arise because of differentfields-of-view.

V. DISCUSSION

This paper presents the PROMOTE UV Record algorithm,where surface UV irradiances are retrieved using appropriateinput data concerning total ozone column, clouds, aerosols, sur-face albedo, and altitude. Furthermore, first validation results ofthe algorithm are presented through comparison against ground-based measurements of daily erythemal UV doses at eight Eu-ropean stations.

The validation shows that the method is working reasonably.There is a general agreement with measurements, although thePROMOTE UV Record tends to overestimate the daily UVdoses. The median bias is typically 3%–10%, which translatesinto a mean bias of 11%–19%, and 56%–68% of the daily

doses are typically within 20% from the ground-based ref-erence. Since a considerable part of the overestimation seemsto be connected to the cloud data, it would be interesting toinvestigate whether using the ISCCP version DX data, whichhas a much higher spatial resolution (30 km), would make animprovement to the performance of the algorithm.

The prototype of the PROMOTE UV Record presented in thispaper covers the period from July 2002 to June 2005. As the aimof the PROMOTE UV Record is to provide a long-term recordon the surface UV, the time series will be extended as soon asmore ozone data become available (see Section II-A).

The final PROMOTE UV Record, covering the period startingin 1983, is expected to become available in autumn 2009, andit will provide important information on past variations in thesurface UV on a global scale. The project includes also planson validating the UV Record with a long-term perspective byinvestigating how well the PROMOTE UV Record manages toreproduce the year-to-year variablity in the surface UV irradi-ance at different locations, and whether the observed biases arestable over time.

It is emphasized that the data is available on the PROMOTEUV Record web pages, both as maps and as time series overselected locations. Specific locations of interest can be addedon request. Furthermore, it is worth mentioning, that the service,currently providing erythemally weighted UV doses, is plannedto be broadened to include also vitamin-D weighted doses anddaily maximum UV Indices in the near future.

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LINDFORS et al.: PROMOTE UV RECORD: TOWARD A GLOBAL SATELLITE-BASED CLIMATOLOGY OF SURFACE ULTRAVIOLET IRRADIANCE 211

ACKNOWLEDGMENT

The authors would like to thank the SCOUT-O3 EU-fundedproject for making UV data available and the ISCCP team fortheir long-term efforts on the cloud data.

REFERENCES

[1] T. F. Eck, P. K. Bhartia, and J. B. Kerr, “Satellite estimation of spectralUVB irradiance using TOMS derived total ozone and UV reflectivity,”Geophys. Res. Lett., vol. 22, no. 5, pp. 611–614, 1995.

[2] J. R. Herman, N. Krotkov, E. Celarier, D. Larko, and G. Labow, “Dis-tribution of UV radiation at the earth’s surface from TOMS-measuredUV-backscattered radiances,” J. Geophys. Res., vol. 104, no. D10, pp.12 059–12 076, 1999.

[3] A. Tanskanen, N. A. Krotkov, J. R. Herman, and A. Arola, “Surfaceultraviolet irradiance from OMI,” IEEE Trans. Geosci. Remote Sens.,vol. 44, pp. 1267–1271, 2006.

[4] L. Bugliaro, B. Mayer, R. Meerkötter, and J. Verdebout, “Potential andlimitations of space-based methods for the retrieval of surface UV-Bdaily doses: A numerical study,” J. Geophys. Res., vol. 111, no. D10,2006.

[5] J. Verdebout, “A method to generate surface UV radiation maps overEurope using GOME, Meteosat, and ancillary geophysical data,” J.Geophys. Res., vol. 105, pp. 5049–5058, 2000.

[6] H. Gadhavi, R. T. Pinker, and I. Laszlo, “Estimates of surface ultra-violet radiation over north America using Geostationary OperationalEnvironmental Satellites observations,” J. Geophys. Res., vol. 113, no.D12, p. 21 205, 2008.

[7] P. Ciren and Z. Li, “Long-term global earth surface ultraviolet radia-tion exposure derived from {ISCCP} and {TOMS} satellite measure-ments,” Agricult. Forest Meteorol., vol. 120, pp. 51–68, 2003.

[8] J. Matthijsen, H. Slaper, H. A. J. M. Reinen, and G. J. M. Velders, “Re-duction of solar UV by clouds: A comparison between satellite-derivedcloud effects and ground-based radiation measurements,” J. Geophys.Res., vol. 105, pp. 5069–5080, 2000.

[9] H. J. Eskes, P. F. J. V. Velthoven, P. J. M. Valks, and H. M. Kelder,“Assimilation of GOME total-ozone satellite observations in a three-dimensional tracer-transport model,” Quart. J. Roy. Meteorol. Soc., vol.129, pp. 1663–1681, 2003.

[10] W. B. Rossow and R. A. Schiffer, “ISCCP cloud data products,” Bull.Amer. Meteorol. Soc., vol. 72, pp. 2–20, 1991.

[11] W. B. Rossow and R. A. Schiffer, “Advances in understanding cloudsfrom ISCCP,” Bull. Amer. Meteorol. Soc., vol. 80, pp. 2261–2288,1999.

[12] P. Koepke, M. Hess, I. Schult, and E. P. Shettle, Global Aerosol DataSet, Tech. Rep. No. 243, Max-Planck-Institut für Meteorologie, Ham-burg, Germany, 1997.

[13] A. Tanskanen, “Lambertian surface albedo climatology at 360 nm fromTOMS data using moving time-window technique,” in Proc. Quadren-nial Ozone Symp., Athens, Greece, 2004, vol. II, pp. 1159–1160.

[14] B. Mayer and A. Kylling, “Technical note: The libRadtran softwarepackage for radiative transfer calculations—Description and examplesof use,” Atmos. Chem. Phys., vol. 5, pp. 1855–1877, 2005.

[15] N. A. Krotkov, J. R. Herman, P. K. Bhartia, V. Fioletov, and Z. Ahmad,“Satellite estimation of spectral surface UV irradiance 2. Effects of ho-mogeneous clouds and snow,” J. Geophys. Res., vol. 106, pp. 11 743–11760, 2001.

[16] K. Lakkala, A. Arola, A. Heikkilä, J. Kaurola, T. Koskela, E. Kyrö,A. Lindfors, O. Meinander, A. Tanskanen, J. Gröbne, and G. Hülsen,“Quality assurance of the Brewer UV measurements in Finland,”Atmos. Chem. Phys., vol. 8, pp. 3369–3383, 2008.

[17] W. Josefsson, “UV-radiation 1983–2003 measured at Norrköping,Sweden,” Theoret. Appl. Climatol., vol. 83, 2006.

[18] U. Feister, J. Junk, M. Woldt, A. Bais, A. Helbig, M. Janouch, W.Josefsson, A. Kazantzidis, A. Lindfors, P. N. den Outer, and H. Slaper,“Long-term solar UV radiation reconstructed by ANN modelling withemphasis on spatial characteristics of input data,” Atmos. Chem. Phys.,vol. 8, pp. 3107–3118, 2008.

[19] P. N. den Outer, H. Slaper, and R. B. Tax, “UV radiation in the Nether-lands: Assessing long-term variability and trends in relation to ozoneand clouds,” J. Geophys. Res., vol. 110, 2005.

[20] J. Gröbner, M. Blumthaler, S. Kazadzis, A. Bais, A. Webb, J. Schreder,G. Seckmeyer, and D. Rembges, “Quality assurance of spectral solarUV measurements: Results from 25 UV monitoring sites in Europe,2002 to 2004,” Metrologia, vol. 43, 2006.

[21] A. Kazantzidis, A. Bais, K. Garane, S. Kazadzis, and C. Meleti, “Es-timation of UV irradiance from ancillary data and comparison withmeasurements at Thessaloniki, Greece (40.5 N, 23 E,” in Proc. SPIERemote Sensing of Clouds and the Atmosphere XI, J. R. Slusser, K.Schäfer, and A. Comeron, Eds., 2006, vol. 6362.

[22] A. Tanskanen, A. Lindfors, A. Määttä, N. Krotkov, J. Herman, J. Kau-rola, T. Koskela, K. Lakkala, V. Fioletov, G. Bernhard, R. McKenzie,Y. Kondo, M. O’Neill, H. Slaper, P. den Outer, A. F. Bais, and J.Tamminen, “Validation of daily erythemal doses from Ozone Moni-toring Instrument with ground-based UV measurement data,” J. Geo-phys. Res. (Atmos.), vol. 112, p. 24, 2007.

[23] A. Arola, S. Kazadzis, N. Krotkov, A. Bais, J. Grbner, and J. R.Herman, “Assessment of TOMS UV bias due to absorbing aerosols,”J. Geophys. Res., vol. 110, 2005.

[24] J. E. Williams, P. N. den Outer, H. Slaper, J. Matthijsen, and G.Kelfkens, “Cloud induced reduction of solar UV-radiation: A compar-ison of ground-based and satellite based approaches,” Geophys. Res.Lett., vol. 31, 2004.

Anders Lindfors received the M.Sc. and Ph.D. de-grees in meteorology from the University of Helsinki,Finland, in 2002 and 2008, respectively, conductingpart of his postgraduate studies at the Chalmers Uni-versity of Technology in Gothenburg, Sweden.

He joined the Finnish Meteorological Institute in2001, and has since then conducted research on UVradiation and climate. He has, for instance, made pi-oneering work in utilizing sunshine duration data forestimating past UV radiation. Since June 2009, he hasbeen with the University of Edinburgh, U.K.

Aapo Tanskanen received the M.Sc. and Lic.Tech. degrees in nuclear engi-neering from the Helsinki University of Technology, Espoo, Finland, in 1997and 2002, respectively, and the Ph.D. degree in physics from the University ofHelsinki in 2008.

He was with the Finnish Meteorological Institute from 2002 to 2008 and wasresponsible for the UV Record service of GMES PROMOTE. He is currentlywith Fortum Nuclear Services.

Antti Arola received the M.Sc. degree in engineeringfrom the Helsinki University of Technology, Espoo,Finland, in 1991, the Phil.Lic. degree in meteorologyfrom the University of Helsinki, Helsinki, Finland, in1999, and the Ph.D. degree in applied physics fromthe University of Kuopio, Kuopio, Finland, in 2006.

His research work has been focused on several as-pects of solar UV radiation, mainly on the area ofsatellite-based UV and analysis of ground-based UVmeasurements. He is a member of the Kuopio Re-search Unit at the Finnish Meteorological Institute.

Ronald van der A received the Ph.D. degree in1997 from the University of Leiden and the SpaceResearch Organisation Netherlands with the subjectozone profile retrieval for SCIAMACHY on boardENVISAT.

He joined the Royal Netherlands MeteorologicalInstitute in 1997, where he worked on the retrievalof data products from satellite observations. He is in-volved in the development and validation of retrievalalgorithms for SCIAMACHY, GOME-2, and OMI.Within the GMES project PROMOTE, he is part of

the management team. He is currently also project manager of the EU-projectAMFIC (FP-6) and the ESA-project TEMIS.

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212 IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING, VOL. 2, NO. 3, SEPTEMBER 2009

Alkiviadis Bais is a Professor in the Physics De-partment at the Aristotle University of Thessaloniki,Greece, where he is teaching various courses relatedto atmospheric physics. He has been involved inscientific research for more than 25 years, with aparticular focus on solar UV radiation, stratosphericozone, and global change. His favored field isatmospheric measurements using ground-basedinstruments.

Uwe Feister received the Ph.D. degree in 1982 witha dissertation on satellite-based remote sensing of at-mospheric ozone.

He is a senior scientist at the Richard AmannObservatory Lindenberg of Deutscher Wetterdienst,Germany. He has been involved in atmosphericresearch for 35 years. In recent years, his main topicsof research have been ground-based measurementsof solar spectral UV radiation and clouds.

Michal Janouch is with the Solar and Ozone Observatory of the Czech Hy-drometeorological Institute, located at Hradec Kralove.

Weine Josefsson received the M.Sc. degree in mete-orology and physics from the University of Uppsala,Sweden, in 1979.

Since then, he has been with the Swedish Meteo-rological and Hydrological Institute (SMHI) mainlyworking with solar radiation, total ozone, and ultravi-olet radiation. From late 1999 to 2005, he was Headof the Atmospheric Research Unit in the ResearchDepartment, SMHI. This unit is active in a wide fieldof remote sensing. In March 2005, he changed his po-sition to the Core Service Department of SMHI and

since 2009, he has been the Head of the Climate information Group within thisdepartment. Currently, his work also includes traditional climatology, climatechange, and public information.

Tapani Koskela received the M.Sc. degree in mete-orology from the University of Helsinki, Finland, in1987.

He worked in both modeling and measuring tasksat the Finnish Meteorological Institute (FMI) inbioclimatological research from 1988–1992 andin ozone and UV research since then. His currentduties include optical measurements in general,public information, and national and internationalcooperation. He is currently a member of the ClimateChange Research Unit of FMI.

Kaisa Lakkala received the M.Sc and Phil.Lic. de-grees in meteorology from the University of Helsinki,Finland, in 1998 and 2001, respectively.

She is a member of both the Climate ChangeResearch Unit and the Arctic Research Unit atthe Finnish Meteorological Institute. Her researchfocuses on the quality assurance of ground basedUV radiation measurement time series.

Peter N. den Outer studied physics at the Universityof Utrecht, The Netherlands, in 1984, and receivedthe Ph.D. degree from the University of Amsterdam,The Netherlands, in 1995, where he studied appliedas well as fundamental aspects of multiple light scat-tering in random discrete media.

He worked for one year in the industrial researchon applied physics and joined the Laboratory for Ra-diation Research at RIVM in 1997 where he is in-volved in UV-data-analysis and UV-transfer modeldevelopment.

Andrew R. D. Smedley received the M.Sc.degree in natural sciences fromCambridge University, Cambridge, U.K., and the Ph.D. degree in atmosphericphysics from the University of Manchester Institute of Science and Technology(UMIST), U.K. (now the University of Manchester).

Since graduating, he has remained with the Centre for Atmospheric Scienceand has primarily been employed within the U.K.’s ozone and spectral UV mon-itoring program. In addition to this, he has been involved in a number of otherprojects connected to UV instrumentation and measurements such as SUNalland INSPECTRO, and more recently, has had the main responsibility for twomodelling studies. He presently holds the position of CIE Division 6 Secretary.

Harry Slaper received the M.S. degree in experi-mental physics in 1982 and the Ph.D. degree in 1987from the Utrecht University, The Netherlands, with adissertation entitled “Skin Cancer and UV Exposure:Investigations on the Estimation of Risks.”

He is a Senior Scientist and Head of the unitRisk-Analysis and Modelling within the Laboratoryfor Radiation Research at RIVM. He has over 20years of research experience in the area of UVradiation and UV risk-assessments. He is, as ProjectLeader/PI, responsible for the development of the

RIVM UV monitoring system, the development of UV maps using satelliteremote sensing data, and the integrative source-effect chain model for theeffects of ozone depletion.

Ann R. Webb received the B.Sc. degree in physics and meteorology from theUniversity of Reading, U.K., the Ph.D. degree in environmental physics fromUniversity of Nottingham, U.K., and the D.Sc. degree in atmospheric physicsfrom University of Manchester Institute of Science and Technology (UMIST),U.K.

She is Chair of WMO Scientific Advisory Group for UV Measurementsand Director of Division 6 (Photobiology and Photochemistry) of the Inter-national Lighting Commission (CIE). Her current position is Reader in theSchool of Earth Atmospheric and Environmental Sciences at the University ofManchester.

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