UV measurements in the centre of East Antarctic Plateau - GEWEX

Eleventh BSRN Scientific Review and Workshop, Queenstown, New Zealand
13-16 April 2010
Measurements of the surface UV irradiance at the
central part of East Antarctic Plateau
B. Petkov, V. Vitale, C. Lanconelli, M. Mazzola, M. Busetto, A. Lupi
Institute of Atmospheric Sciences and Climate (ISAC) of the
Italian National Research Council (CNR), Bologna, Italy

The results, presented below are obtained by
UltraViolet narrow-band filter RADiometer (UV-RAD),
designed at the Institute of Atmospheric Sciences
and Climate (ISAC) of the Italian National Research
Council (CNR) to measure the surface solar UV
irradiance in harsh Antarctic conditions.

On the left, diagram of the UV-RAD radiometer, with its main components: 1 –
hemispherical diffuser; 2 – entrance optics with field stopper and collimating system
(consisting of two lenses); 3 – UV-VIS pass-band with the pair of colored glass filters
(see also Fig. 3); 4 – filter-wheel; 5 – synchronous motor rotating the filter-wheel; 6 –
photomultiplier; 7 – thermoelectric (Peltier) heat pump; 8 – recording and controlling
electronics. On the right, photograph of the instrument during a measurement test in
Antarctica. The radiometer sizes are 310x300x370 mm, with an overall weight of 12 kg.

COMPONENT TRANSMITTANCE (%)
OVERALL
TRANSMITTANCE (%)
100
75
50
25
0
100
75
50
25
0
100
75
50
25
0
100
75
50
25
0
30
20
10
0
UV-VIS Pass-band
UV short-pass
Narrow-band Filter
314.25 nm channel
WAVELENGTH (nm)
(a)
(b)
Colored Filter
ORIEL 51 124
(c)
(d)
(e)
200 300 400 500 600 700 800
The channel
structure
Photomultiplier Entranse optics
UV-VIS Pass band
Colored filter
Colored filter
UV short-pass
F i l t e r
N
1
2
3
4
5
6
7
UV
Shortpass
UV-
VIS
Passband
1
1
1
1
1
1
1
Characteristics of the UV-RAD channels
Number of the optical elements employed
to define each UV-RAD channel
Colored
glass
filter
2
2
2
2
2
2
2
2
2
2
1
1
1
1
Narrowband
filter
1
1
1
1
1
1
1
Peak
transmittance
wavelength
(nm)
299.60
305.80
309.60
314.25
325.50
338.30
364.05
FWHM
(nm)
0.67
0.71
0.67
0.73
0.80
0.86
0.98
Peak
transmittance
0.14
0.15
0.20
0.26
0.24
0.27
0.12
From the left (i) spectral transmittance
curves of the various components used to
give form to the 314.25 nm UV-RAD channel
(ii) sequence of the optical components
used to define the overall UV-RAD channel
structure following the incoming radiation
direction (from the top to the bottom) and
(iii) the characteristics of the UV-RAD
channels

C o s i n e e r r o r
1.08
C O S I N E E R R O R
1.06
1.04
1.02
1.00
CEg (299.60 nm)
CEg (325.50 nm)
CEg (364.05 nm) Angular dependence
0.98
0° 30° 60° 90°
S O L A R Z E N I T H A N G L E
curves of the cosine
error CE g of UV-RAD
entrance optics, as a
function of solar zenith
angle for three different
channels.

The performed by UV-RAD measurements allow:
Retrieval of the total ozone amount using the Stamnes method (The
ratio of irradiance at two wavelengths is compared with the
corresponding one evaluated by radiative transfer model for different
solar zenith angles and ozone amounts).
Reconstruction of the surface solar UV spectrum
Evaluation of the weighted dose rates and corresponding daily doses

Reconstruction of the solar spectrum using the UV-RAD data
IRRADIANCE (mW m -2 nm -1 )
140
120
100
80
60
40
20
model (TUV)
measured (Brewer)
0
290 300 310 320 330 340 350 360 370
WAVELENGTH (nm)
The nowadays radiative transfer
models are able to represent
realistically the features of the
surface solar irradiance. The figure
shows a comparison between
measured by Brewer UV spectrum at
ALOMAR, Norway and
corresponding one, evaluated
through TUV model
IRRADIANCE (mW m -2 nm -1 )
200
150
100
50
0
3
290 300 310 320 330 340 350 360 370 380 390 400 410
WAVELENGTH (nm)
Bearing in mind this and the spectral characteristics of the
UV-RAD channels, the solar spectrum is reconstructed
through the following steps:
1. Measurements
2
2. Model evaluation (using TUV) with 1 nm resolution
and FWHM = 0.8 nm, taking the retrieved total
ozone as input
3. Fitting the evaluated spectrum to measured values
1

Evaluation of the erythemal dose rate
200
10 1
dD
dt
=
∫ ∞
0
F( λ)
A(
λ)
dλ
IRRADIANCE (mW m -2 nm -1 )
150
100
50
Solar spectrum at the ground
CIE Erythemal action spectrum
10 0
10 -1
10 -2
10 -3
10 -4
ERITHEMA ACTION SPECTRUM
0
290 300 310 320 330 340 350 360 370 380 390 400 410
WAVELENGTH (nm)
10 -5
F(λ) is measured solar spectrum
A(λ) is the erythemal action spectrum

UV-RAD was calibrated through a comparison with
the Bentam spectroradiometer operating at
ALOMAR (Arctic Lidar Observatory for Middle
Atmosphere Research), Andenes, Norway. After
that, UV-RAD was participated in several
intercomparison campaigns which help to control
the quality of the instrument and to make the
necessary corrections.

Intercomparison campaign at ALOMAR, Norway
September-November, 2004
Brewer
Bentham
UV-RAD
GUV

ERYTHEMAL
DOSE RATE (mW m -2 )
10
8
6
4
2
0
1.2
UV-RAD
GUV
Brewer
Daily time-patterns of the UV erythemal dose
rates measured at the ALOMAR
Observatory, on 17 October, 2004, for
predominant clear-sky conditions, with the
UV-RAD radiometer, GUV radiometer, and
Brewer spectroradiometer.
BREWER / UV-RAD
GUV / UV-RAD
1.1
1.0
0.9
0.8
1.4
1.2
1.0
0.8
0.6
7 8 9 10 11 12 13 14 15 16 17
LOCAL TIME
Values of the difference between the UV dose rates
determined from the Brewer
spectroradiometer and the UV-RAD
radiometer measurements, carried out at
different hours of the day during the
ALOMAR campaign, giving overall mean
value equal to 0.9%, together with standard
deviations of 2.4%.
Scatter diagram of the UV dose rates determined
by GUV and UV-RAD at ALOMAR on the
different days of the October 2004 fieldcampaign,
giving a mean value of 5% with
standard deviation equal to 6%.

Intercomparison campaign at Aosta, Italy
September, 2006
IRRADIANCE (W m -2 )
UV-RAD / BENTHAM
0.4
0.3
0.2
0.1
325 nm 338 nm
UV-RAD
Bentham
0.0
1.3
1.2
1.1
1.0
0.9
0.8
0.7
4 6 8 10 12 14 16 18 20 6 8 10 12 14 16 18 20
TIME (hours UTC)
Comparison between UV
irradiance, measured by UV-
RAD at 325 and 338 nm
channels, respectively at Aosta,
Italy on 20 Sep 2006 and
corresponding ones given by
Bentham spectroradiometer
routinely operating at ARPA
Aosta station. The lower panels
show the ratio between two
instruments.

Intercomparison campaign at Ny-Ålesund, Norway
May-June, 2009

Solar UV-Index measurements from the AWI
spectroradiometer, Brewer #050, the multifilter
radiometer UVRAD, the multifilter radiometer
GUV7275 and the QASUME reference
spectroradiometer. The measurement period lasted
from 27 May to 6 June 2009 and was located at Ny-
Ålesund, Svalbard, Norway.
Ratio between the UV-Indices
determined by UVRAD to the ones from
the QASUME spectroradiometer.
Gröbner et al., Photochem. Photobiol. Sci., 2009, DOI: 10.1039/B9PP00170K

Three radiometers UV-RAD has
been operating

at ISAC-CNR Bologna, Italy station from 2005

at Dome Concordia Antarctic station from 2007

at Ny-Ålesund Arctic station from 2008

TOTAL OZONE AMOUNT, MEASURED AT NY-ÅLESUND AND
DOME CONCORDIA
R A T I O
TOTAL OZONE (DU)
500
450
400
350
300
250
200
1.2
1.1
1.0
0.9
0.8
0.7
Ny-Ålesund
MAY JUN JUL AUG
UV-RAD/OMI
UV-RAD/SAOZ
JUN JUL AUG SEP OCT
2008 2009
UV-RAD
SAOZ
OMI
RATIO
TOTAL OZONE (DU)
400
360
320
280
240
200
160
120
Nov Dec
1.6
1.4
1.2
1.0
0.8
0.6
0.4
Nov Dec
2007
Dome Concordia
Jan Feb
Jan Feb
SAOZ
OMI
UV-RAD
Oct Nov Dec Jan Feb Oct Nov
Oct Nov Dec
2008
UV-RAD/OMI
UV-RAD/SAOZ
Jan Feb Oct Nov
2009
The figures present the total ozone amount measured by UV-RAD (in blue) at Ny-Ålesund
(2008 and 2009) and Dome Concordia (2007-2009). For comparison the data taken from the
satellite instrument OMI (in green) and spectrophotometer SAOZ (in red) based at both
stations are also given. The SAOZ data obtained as a result of observations performed in the
period, when the solar elevation exceeded 5° during all the day are not considered. The lower
panels show the ratio between UV-RAD and two other instruments.

DAILY ERYTHEMAL DOSE
AT NY-ÅLESUND AND
DOME CONCORDIA
The daily erythemal dose, defined by
UV-RAD at two stations during the 2007-
2009 period. The clear sky values are
determined trough model evaluations
taking the total ozone, retrieved from the
UV-RAD data as input parameter.
The figures demonstrate
that the daily erythemal
dose at Ny-Ålesund is
mainly affected by the
cloud cover conditions
while the total ozone
variations predominantly
cause the corresponding
erythemal dose variations
at Concordia station.
ERYTHEMAL DOSE (kJ m -2 )
8
6
4
2
0
Nov
Dec
2007
ERYTHEMAL DOSE (kJ m -2 )
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Dome Concordia
Jan Feb
MAY JUN JUL AUG
2008
2008
Aug Sep Oct Nov Dec
Clear sky Dose
Measured Dose
Ny-Ålesund
JUN JUL AUG SEP
Jan Feb Mar
2009
Clear sky Dose
Measured Dose
2009
AugSepOctNov

TOTAL OZONE (DU)
450
400
350
300
250
200
150
100
(a)
SAOZ
OMI
UV-RAD
VARIATION OF THE
SURFACE UV IRRADIANCE
DURING THE 2008 AND
2009 AUSTRAL SPRINGS AT
DOME CONCORDIA
I R R A D I A N C E ( W m -2 nm -1 )
CLOUD TRANSMITTANCE
T cloud
6.0 10 -4
5.0
4.0
3.0
2.0
1.0
(b)
0.0
8.0 10 -2
7.0
6.0
5.0
4.0
3.0
1.0
0.9
0.8
0.7
0.6
0.5
0.4
AUG
306 nm
364 nm
(c)
(d)
SEP OCT NOV AUG SEP OCT NOV
2008 2009
180
160
140
120
100
80
60
40
LONGWAVE
IRRADIANCE (W m -2 )
Comparison between (a) variations of the
total ozone amount determined at
Concordia station by different instruments,
(b) time-patterns of the solar irradiance at
306 nm and (c) 364 nm wavelengths
respectively, measured by UV-RAD at z o
= 85°. The yellow curve in (c) presents the
running average of the measurements
performed over five days. Panel (d) shows
variations of the cloud transmittance T cloud
(green dots) as obtained following the
Long and Ackerman methodology. The
dark green curves represent the five-days
running averaged time-patterns of T cloud .
In the same panel, the mean daily values
of LWI down-welling irradiation are also
given (yellow triangles) together with fivedays
running averaged time-patterns
(dark yellow curves).
Vitale et al., submitted to Antarctic Science

DEPENDENCE OF UV-B IRRADIANCE ON THE TOTAL OZONE
AMOUNT DURING THE 2008 AND 2009 SPRINGS
IRRADIANCE I(306 nm) (W m -2 )
6.0 10 -4 I 306
−4
= 10.37 10
−
e
R = - 0.75
5.0
4.0
−3
8.0 10 Q
( )
3.0
2.0
1.0
0.0
100 150 200 250 300
TOTAL OZONE AMOUNT Q (DU)
Irradiance I(306) measured by
UV-RAD versus total ozone
amount determined by SAOZ
and OMI instruments. The
irradiance values presented
refer to the case in which the
solar zenith angle was equal to
85°. The best curve (solid) is
presented together with its
analytical expression and two
dashed curves showing the
standard error of estimation.
The corresponding regression
coefficient R is also indicated.
Vitale et al., submitted to Antarctic Science

Thank you for the attention!