Antarctic network of lamp-calibrated multichannel radiometers for continuous ozone and uv radiation data

Abstract

Three NILU-UV multichannel radiometers have been installed in 1999 at the Argentinian sites of Ushuaia (54S), Marambio (64S) and Belgrano-II (77S) in order to continuously monitor UV radiation, photosynthetically active radiation and total ozone. The measurements were established by INM, Spain in collaboration with FMI, Finland, DNA-IAA, Argentina and CADIC, Argentina to observe and characterize the spatial and temporal evolution of ozone and ultraviolet radiation in the Antarctic region. Special attention has been given to the quality control and quality assurance of the measurements under harsh climatological conditions. The ozone and UV time series of 2000–2006 were calibrated using a polynomial fit for lamp measurements performed every second week all year round. The gaps in these data are minimal, with almost no data missing, and the data products are available from http://www.polarvortex.org in near real time. The data products include the erythemally-weighted UV, UVB and UVA radiation, photosynthetically active radiation (PAR), total ozone (O3) and a cloud parameter (CLT). For UV data, dose rates as well as daily doses are available; from these the maximum measured UV indices (UVI), during 2000–2006, were 12.0, 9.7 and 8.1 at Ushuaia, Marambio and Belgrano-II, respectively.

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Atmos. Chem. Phys. Discuss., 8, 3383–3404, 2008
www.atmos-chem-phys-discuss.net/8/3383/2008/
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmospheric
Chemistry
and Physics
Discussions
Antarctic network of lamp-calibrated
multichannel radiometers for continuous
ozone and uv radiation data
A. Redondas1, C. Torres1, O. Meinander2, K. Lakkala2, R. Garc´ ıa1, E. Cuevas1,
H. Ochoa3, G. Deferrari4, and S. D´ ıaz4
1Instituto Nacional de Meteorolog´ ıa, Iza˜ na Atmospheric Research Center, Spain
2Finnish Meteorological Institute, Helsinki, Finland
3Direcci´ on Nacional del Ant´ artico, Instituto Ant´ artico Argentino, Buenos Aires, Argentina
4Centro Austral de Investigaciones Cient´ ıficas, Ushuaia, Argentina
Received: 3 January 2008 – Accepted: 9 January 2008 – Published: 18 February 2008
Correspondence to: A. Redondas (aredondas@inm.es)
Published by Copernicus Publications on behalf of the European Geosciences Union.
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Abstract
Three NILU-UV multichannel radiometers have been installed in 1999 at the Argen-
tinian sites of Ushuaia (54S), Marambio (64S) and Belgrano-II (77S) in order to contin-
uously monitor UV radiation, photosynthetically active radiation and total ozone. The
measurements were established by INM, Spain in collaboration with FMI, Finland,
DNA-IAA, Argentina and CADIC, Argentina to observe and characterize the spatial
and temporal evolution of ozone and ultraviolet radiation in the Antarctic region. Spe-
cial attention has been given to the quality control and quality assurance of the mea-
surements under harsh climatological conditions. The ozone and UV time series of
2000–2006 were calibrated using a polynomial fit for lamp measurements performed
every second week all year round. The gaps in these data are minimal, with almost
no data missing, and the data products are available from http://www.polarvortex.org
in near real time. The data products include the erythemally-weighted UV, UVB and
UVA radiation, photosynthetically active radiation (PAR), total ozone (O3) and a cloud
parameter (CLT). For UV data, dose rates as well as daily doses are available; from
these the maximum measured UV indices (UVI), during 2000–2006, were 12.0, 9.7
and 8.1 at Ushuaia, Marambio and Belgrano-II, respectively.
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1Introduction
Due to climate change, the expected recovery of the stratospheric ozone layer (Had-
jinicolaou et al., 2005; Weatherhead and Andersen, 2006) may be endangered, as
changes in the climate may serve to cool the stratosphere to temperatures favourable
for ozone depletion (Butchart et al., 2000). All the factors that affect UV radiation, i.e.,
ozone, clouds, albedo (especially the effect of snow cover) and aerosols are related to
climate change. Continuous quality- controlled Antarctic measurements of total ozone
and UV radiation are therefore of great importance. It is evident that the ozone de-
pletion area is variable and changes from year to year (WMO (World Meteorological
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Organization), 2007).
The Spanish contribution to Antarctic research began with the installation of three
UV-VIS spectrometers at the Argentinian bases of Belgrano-II, Marambio and Ushuaia
in 1994; in 1999 ozone soundings for the INTA (Instituto Nacional de T´ ecnica Aeroes-
pacial, Spain) were started at Belgrano-II, as well as the installation of three radiome-
ters for the INM (Instituto Nacional de Meteorolog´ ıa, Spain), at the above-mentioned
stations thanks to the existing agreements on scientific collaboration between the
DNA/IAA (Direcci´ on Nacional del Ant´ artico/Instituto Ant´ artico Argentino, Argentina)
and INTA and INM, respectively. These complementary and coordinated networks
of instruments are intended to observe and characterise the spacial and temporal evo-
lution of the O3, NO2, OClO and ultraviolet radiation in these regions during coming
years. This project will provide and unique information to other Spanish and interna-
tional groups involved in Antarctic biology research (Parrondo et al., 2007; Steck et al.,
2007; Yela et al., 2003). The observation data are accessible to researcher at the web
http://www.spain.oracle-o3.org.
In order to monitor the ozone profiles of the Antarctic, an Argentinian-Finnish co-
operation project initiated regular ozone soundings at Marambio in November 1988.
Nowadays they make a significant contribution to the regular ozone depletion re-
ports, ozone bulletins, compiled by the WMO (http://www.wmo.ch/pages/prog/arep/
gaw/ozone/), and have been used in scientific research (Taalas et al., 1997). The
sounding data are available to all researchers from the data bases of WOUDC (World
Ozone and UV radiation Data Center) and NILU (Norwegian Institute for Air Research).
Since 1999, the ozone-hole-related activities at Marambio have been enlarged into
Spanish-Argentinian-Finnish co-operative project, as it became one of the three year-
around Antarctic region stations to measure simultaneously total ozone and UV radia-
tion with NILU-UV multichannel filter radiometers.
Previously, in 1988, NSF (U.S. National Science Foundation) had established a mea-
surement network comprising six high-latitude sites from the South Pole to Alaska
(Bernhard et al., 2005). The NSF network in the Antarctic region includes Ushuaia
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(54◦49?S, 68◦19?W), McMurdo (77◦50?S, 166◦40?E), Palmer (64◦46?S, 64◦03?W), and
the South Pole (90◦00?S). NSF sites are equipped with scanning spectroradiome-
ters (type SUV-100 or SUV-150B) and multichannel filter instruments (type GUV-
511 or GUV-541).The NSF observations are freely available via the internet at
http://www.biospherical.com/NSF/.
The Antarctic NILU-UV network by the Spanish-Finnish-Argentinian co-operative
project is unique in the sense that no earlier UV network has linked the Antarctic and
the European Arctic. The NILU-UV network travelling reference of FMI, described fur-
ther in Sect. 2.2, can be used to compare and transfer the UV irradiance scale from
one hemisphere to another. In addition to this, the station of Ushuaia belongs to both
the NSF and our network. This makes solar comparisons possible, and all the stations
of both of networks can be used for any study with knowledge of the irradiance scales.
According to Lakkala et al. (2005), the irradiance scales of NSF and our network are
within 5%.
The ozone and UV data from the NILU-UV network, documented here for the first
time, are quality-controlled, continuous and have the potential for wide use among
scientists. Recently, the results of the network were also used for the WMO ozone
bulletin for the first time. The quality assurance of the network has been published
earlier in Lakkala et al. (2005).
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2NILU-UV antarctic network
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In 1999, an Antarctic network of multichannel NILU-UV instruments was established
in order to measure real-time ground-based UV radiation and total ozone columns.
The network was established by INM in collaboration with FMI, DNA-IAA and CADIC
(Centre for Scientific Research, Argentina). The main objectives of the network are to
observe and to characterise the spatial and temporal evolution of both the ozone and
the ultraviolet radiation in the Antarctic region and to carry out dynamics studies of the
Antarctic polar vortex. At the present time, the network has been consolidated, and
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this makes it possible to analyse how the daily evolution of the vortex affects the ozone
and UV radiation. Great effort has been put into the quality control of the network data
so that they can also be used for studies that require high accuracy in the data, e.g.,
climatological studies.
2.1 Stations
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NILU-UV multichannel filter radiometers have been set up at three Argentinian Antarctic
stations. The location of the stations with respect to the stratospheric polar vortex, and
to the ozone depletion area, is the underlying motive for selecting the sites: Belgrano-II
(77◦52?29??S, 34◦37?37??W, 50ma.s.l.) is mostly located inside the vortex; Marambio
(64o14?S, 56o38?W, 200m a.s.l.) is at various times inside, on the edge of, or outside
the vortex; while Ushuaia (54◦49?S, 68◦19?W, 50ma.s.l.) is mostly outside the vortex.
All these bases are permanent and manned all the year round. At all the stations,
the NILU-UV radiometers are installed on the roofs of the permanent buildings of the
bases.
The Argentinian city of Ushuaia is the southernmost city in the world, and is located
on Grande Island of the Land of the Fire. Ushuaia is affected by the Antarctic ozone
loss, especially during an event in which it is beneath the vortex, and for this reason it
is one of the most populated towns affected by the yearly ozone loss. Ushuaia is the
capital of the Land of the Fire, and it extends over the slopes of the Martial Mounts. The
measurement instruments are in the facilities of the CADIC. This Center was created
on the 9 of April, 1969, and belongs to the National Council of Scientific and Technical
Research (CONICET). In Ushuaia, the weather is variable all year round, with the
lowest daily mean temperature of 1◦C occurring at the end of July and beginning of
August.
Marambio and Belgrano-II are two of the six Argentinian bases that remain open all
year long, and belong to IAA-DNA. They were set up in 1969 and 1979, respectively.
Marambio is located on the Island of Seymour, approximately 1.6km to the NE of the
Island of Cerro Nevado on the southern margin of the gulfs of Erebus and Terror in
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the Sea of Weddell. This base is located on a plateau 14 km in length and 8km wide,
200ma.s.l., and hosts many other scientific instruments, e.g., for carrying out regular
ozone soundings and aerosol measurements. Sometimes the air masses there orig-
inate in midlatitudes and have high total ozone column values, while at other times
polar air masses with only little ozone affect the area. Belgrano-II is located in Nunatak
Bertrab, on the Confin Coast (Land of Coast), Sea of Weddell. Because of its location,
this base is one of the most important observatories for the study of the ozone destruc-
tion during the austral spring, but it is only accessible once a year, during the austral
summer, and then only with the aid of the “Icebreakers Almirante Irizar”. The weather
at Belgrano-II is harsh. The wind may reach 200km/h, and the measured maximum
and minimum temperatures range from −2◦C to −4◦C. Due to the high latitude, the sun
does not rise at all for 4 months of the year.
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2.2 Instrument
The NILU-UV 6T radiometer is a filter instrument with five UV channels, with central
wavelengths at around 305, 312, 320, 340 and 380nm, and bandwidths of around
10nm at full-width half-maximum (FWHM). A sixth channel measures the photosyn-
thetic active radiation (PAR) in the 400–700nm wavelength region. The radiometer
has a Teflon diffuser, silicon detectors, high-quality bandpass filters and is temperature-
stabilized to 40◦C. One-min averages of measured irradiances and detector tempera-
tures are recorded. The measurements can be used to retrieve UV-B, UV-A, erythe-
mally -weighted UV radiation and the total ozone column, as well as to provide cloudi-
ness information, using the method described by Dahlback (1996). The characteristics
of the instrument are described in more detail in H¨ oiskar et al. (2003).
During the period 2000–2006, the NILU-UV #012 and NILU-UV #011 radiometers
have been measuring continuously at Ushuaia and Marambio, respectively, while at
the Belgrano-II base, three different instruments have been used for measurements:
NILU-UV #009, NILU-UV #010 and NILU-UV #023 (Table 1). Due to technical prob-
lems during the exchange of instruments in Belgrano-II, the NILU-UV#023 has been
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measuring in this site since 2004 until now.
2.3Quality control (QC) and Quality assurance (QA)
The quality control and quality assurance of the network is based on regular lamp mea-
surements and, for UV radiation measurements, on a travelling reference (Lakkala et
al., 2005). An important part of the quality control has been to train the station opera-
tors; this training is repeated every second year. The operators perform daily checks
that include timing control and cleaning of the diffuser. The levelling of the instrument
is also regularly checked. The operators perform lamp tests and dark current measure-
ments, as well as solar comparisons between the station instrument and the travelling
reference NILU-UV radiometer.
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2.3.1Lamp measurements: QC
The quality control for the site instruments consists of 100W OSRAM Radium lamp
measurements and dark current measurements. Two lamps are measured every two
weeks and a third lamp is measured on every third calibration to exclude possible lamp
drift. During the calibration, the power supply of the lamp is controlled with software
that keeps the lamp intensity constant. Lamp tests are also made before and after
each solar comparison to determinate the stability of the reference NILU.
In order to study the stability of the NILU-UV, the lamp measurement time series for
each instrument was calculated. The normalized averages of lamp measurements at
Ushuaia, Marambio and Belgrano (2000–2006) are shown in Fig. 1. The results of all
the six channels of the radiometer are shown. In each case, the lamp averages were
normalized with the first calibration, in order to observe any changes in the sensitivity
of the channels.
When we have four successive instruments at one station, as at Belgrano-II, it is
not always is possible to perform a direct comparison of the two instruments being
interchanged. In this case, the last lamp calibration of the leaving instrument and the
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first lamp calibration of the replacing instrument are used to adjust the calibration scales
of the instruments. As the instruments are manufactured using the same filter batch,
we convert the measurements of the lamps for each instrument to that of the other one
before it. In this way, all calibrations are referenced to the first instrument NILU-UV
#009 and a unique lamp series is used for all the NILU-UV radiometers at Belgrano-II.
Changes of more than 50% in the sensitivity of some of the channels have been
observed in all the instruments. The channels with the largest drift are #3 and #4 in
all the radiometers. To obtain the UV dose rates and ozone, the observed values have
been corrected for the drift of the channels. The procedure used is shown in Sect. 3
and its validation using ozone measurements from different sources was described in
Torres et al. (2002).
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2.3.2Travelling reference: QA
The quality assurance of the UV measurements of the whole network is based on a
travelling reference NILU-UV which makes it possible to maintain the absolute irradi-
ance scale of the different stations. The irradiance scale can be transferred using the
results of solar comparisons between the reference NILU-UV and the NILU-UV of the
station (Lakkala et al., 2005). The travelling reference visits Ushuaia three times and
Marambio twice during the spring-summer-autumn season. Visits of the travelling ref-
erence to Belgrano-II are impossible, due to the inaccessibility of the site for most of the
year. Access is possible, using an icebreaker, only during the summer, when the NILU-
UV at Belgrano is replaced each year by another, well-calibrated, NILU-UV, of which
the calibration is traceable to the irradiance scale used at Marambio and Ushuaia.
The travelling reference is calibrated every year or every second year. During the
winter period of the Antarctic, the reference NILU-UV measures in the Arctic, and may
attend intercomparison campaigns. This makes possible the comparison of UV mea-
surements performed in both hemispheres using the same irradiance scale. Table 2
shows the ratios between the erythemally-weighted UV dose rates retrieved from the
reference NILU-UV, network NILU#012 and those measured by the NSF-network SUV-
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spectroradiometer at Ushuaia. The results are shown for the lowest SZA in almost
clear-sky conditions. A cosine correction of 5% has been assumed for the SUV-data
(Bernhard, G., personal communication, 2004). The results show compatibility within
the measurement uncertainties. The reference instrument for the calibration of the
reference NILU-UV is the Bentham spectroradiometer of the NRPA, whose irradiance
scale is traceable to the National Institute of Standards and Technology (NIST) via the
laboratory of SP, the Swedish National Testing and Research Institute (Johnsen et al.,
2002). The irradiance scale of the SUV-spectroradiometer is also traceable to the NIST
via 200W lamps (Bernhard et al., 2006).
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The total ozone column and the biologically-effective UV rates are determinate using
the method described by Dahlback (1996).
The total ozone column (Ω) is determined by comparing a calculated irradiance ratio,
(N?), with the corresponding measured ratio (N), Eq. (1),
N(θ,Ω)=Vi(θ,Ω)/Vj(θ,Ω)
where Vi and Vj are the irradiances in two channels with a different sensitivity to ozone
absorption. We have used the ratio between the irradiances at 320nm (Vi) and 312nm
(Vj), low and high ozone absorption, respectively. A radiative-transfer model (Mayer
and Kylling, 2005) is used to determine a look-up table of ratio N?as a function of solar
zenith angle (θ) and ozone (Ω). The look-up table also depends on the atmosphere,
ozone profile, aerosols, clouds and surface albedo.
The UV dose rates (D), Eq. (2), are determined as a linear combination of the irradi-
ances, represented by the NILU-UV raw data (Vi) obtained from the five UV channels
(i).
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D =
i=1
aiVi
(2)
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In order to obtain the coefficients of the linear combination (ai), spectroradiometer-
based calibration and radiative-transfer calculations are needed (Dahlback, 1996).
To apply this method, it is necessary to correct the drift shown by the quality control.
A polynomial fit is calculated with the normalized average of lamp measurements to ob-
tain a daily correction coefficient for each channel and instrument (Fig. 1). With these
coefficients, all the raw data are referenced to the first absolute calibration. This first
calibration of all the network instruments was performed by the manufacturer at the
Iza˜ na Atmospheric Observatory, Iza˜ na (Tenerife, Spain), in 1999. Following that, NILU-
UV #012, NILU-UV #011 and NILU-UV #009 were set up at Ushuaia, Marambio and
Belgrano-II, respectively. All measurements are referenced to the first instrument NILU-
UV #009 at Belgrano-II and all the other instruments are converted to this standard.
The drift is corrected using its normalized lamp average, as at the other stations. With
this correction method all the three stations maintain the scale of the manufacturer cal-
ibration; this absolute scale can be changed using the travelling reference in Ushuaia
and Marambio and in Belgrano we can use the NILU#023 compared with QASUME unit
(Gr¨ obner et al., 2005) just before its setup at Belgrano as is described by Meinander et
al. (2004).
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4Results and discussion
4.1Ozone and UV time series
As the NILU-UV instrument gives a reading every min, it is perfect for monitoring rapid
changes in the atmosphere. The total ozone changes during a day can be followed, as
well as the exact UV daily doses, even during days with rapidly-changing cloudiness.
The time series of 2000–2006 covers almost all the days of the year, with a minimal
amount of missing data.
The total ozone and maximum daily UV index time series are shown in Fig. 2 for
Ushuaia, Marambio and Belgrano-II. The connection between the total ozone and UV
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radiation is clearly seen in the time series. Maximum spring-time UV values are mostly
connected with low ozone values. The daily evolution of the stratospheric polar vortex
can also be studied from our measurements. The location of the polar vortex and its
associated low ozone values can move from day to day and have an effect even at
the latitudes of Ushuaia. This event is usually recorded as high UV values at Ushuaia.
During 2000–2006, the highest UV index value measured at Ushuaia was 12.0 on 27
Nov 2003. For the same period the highest UV index at Marambio was 8.1 on 04 Dec
2001 and 9.7 in Marambio on 22 Oct 2000.
The UV daily doses at three stations are shown in Fig. 3 during spring-time the
daily doses are similar, even though the latitude of Marambio and Belgrano would sug-
gest significantly lower UV daily doses comparing with Ushuaia. High daily doses are
strongly connected to low ozone values at Marambio and low cloudiness at Belgrano.
The monthly means of erythemally-weighted UV daily doses are shown in Table 3.
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4.2Web site implementation
The NILU-UVs at the bases are controlled by individual workstations, in which the raw
data are stored. The raw data are remotely harvested from the logging computers, and
all data products are calculated and presented on the webpage http://www.polarvortex.
org as soon as they are available. These data available from the web are thus real-
time data and are considered to be provisional. Any user of the data is kindly asked
to contact the web-master to get the latest QC/QA information. Two types of data are
available for downloading: daily course data (of ozone, UVI, CIE, UVA, UVB, UVA/UVB
CLT, PAR ) and summary files with the solar noon data. For both, two data versions,
V1.1 and V1.2 exist, depending on the last available lamp test. V1.1 contains data
extending up to the last-available stability check, while V1.2 is produced when the
data has been processed using both the previous and the following lamp test. V1.1 is
updated daily and V1.2 every two weeks after the lamp test has been performed.
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5Conclusions
In this paper we have presented the Antarctic NILU-UV network established in 1999
as a joint Spanish-Finnish-Argentinian co-operation. Three NILU-UV multichannel ra-
diometers have been installed at the sites of Ushuaia, Marambio and Belgrano-II. Spe-
cial attention has been given to the quality control and quality assurance of the data.
Initial and refresher training is provided for the operators, and regular lamp tests are
performed in order to monitor the stability of the instruments. Severe drift of the chan-
nels of the multifilter radiometers has been detected and corrected in order to produce
homogenized time series. The time series contain daily UV and ozone data since 2006
and are available online at http://www.polarvortex.org. The data contain UVB, UVA,
erythemally-weighted UV dose rates, PAR and cloud information, and ozone data.
Daily summaries of UV data are also available.
It is of major importance to continue long-term measurements of ozone and UV in the
Antarctic region; extension of the existing valuable data series will enable monitoring
of future changes of all the relevant environmental factors, and ensure the availability
of these data to the research community representing various fields of science. We
have found the NILU-UV radiometer to be a good instrument for operation in harsh
environments, but that QA/QC are essential to monitor the drift in the sensitivity of the
channels. In the future, we plan to include the Norwegian Troll station (72◦0?S, 2◦32?E)
in the network and its data in the web pages.
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Acknowledgements. The MAR Project is financed by the National R&D Plan of the Span-
ish Ministry of Science and Technology (National Research Program in the Antarctic) under
contract REN2000-0245-C02-01.The Academy of Finland has given financial support for this
work (FARPOCC -project). The SUV-spectroradiometer UV data from Ushuaia were provided
by the NSF UV Monitoring Network, operated by Biospherical Instruments Inc. under a con-
tract from the United States National Science Foundation’s Office of Polar Programs via the
Raytheon Polar Services Company. We are grateful to B. Johnsen of the Norwegian Radiation
Protection Authority for relative response measurements and fruitful discussions. We thank the
operators of the NILU-UV Antarctic Network.
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References
Bernhard, G., Booth, C. R., and Ehramjian, J. C.: Real-time ultraviolet and column ozone from
multichannel ultraviolet radiometers deployed in the national science foundation’s ultraviolet
monitoring network, Opt. Eng., 44, 1011–1012, 2005.
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Table 1. NILU-UV radiometers set up in the Base Belgrano-II.
Instruments DateDate
NILU-UV #009
NILU-UV #010
NILU-UV #009
NILU-UV #010
NILU-UV #023
02/03/2000
27/02/2001
24/02/2002
25/02/2003
04/02/2004
26/02/2001
23/02/2002
25/02/2003
03/02/2004
To present
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