Validation of UV and Ozone EO based data used in PROMOTE/MEDSUN service,
by means of on ground measurements
Fabrizio Flore
(1),
Ronald van der A
(2)
, Gaetano Licitra
(3)
, Anna Fabozzi
(4)
, Emilio Simeone
(1)
and Vanni Nardino
(1)
(1) Flyby srl, via Puini 97 int.26, 57128 Livorno, Italy
(2) KNMI (Royal Netherlands Meteorological Institute), P.O.Box 201, 3730AE De Bilt, Netherlands
(3) ARPAT (Tuscany Agency for Environment Protection), via Porpora 22, 50144 Firenze, Italy
(4) University of Pisa, Largo Pontecorvo 3, 56127 Pisa, Italy
During Summer 2005 Flyby srl has delivered the MEDSUN public service
with the supervision of Regional Agency for Environmental Protection of Tuscany
(ARPAT). The MEDSUN service, funded by the GSE-PROMOTE ESA program,
provided a personalized safe sun exposure time by correlating the EO based UV
Index with the customized personal phototype. The UV-Index in the general
(cloudy) case is calculated as a function of both EO based cloud coverage and
UV-Index in clear-sky case. The clear-sky UV-Index is determined by RTM model
calculations, using EO based columnar ozone data and spatial and temporal
coordinates for each EO pixel. The Ozone is derived from SCIAMACHY by KNMI.
The cloud coverage is derived from MSG images by Flyby.
Here are presented the basic features of MEDSUN service and the results of two
validations based on on-ground measurements. The first validation regards the
EO based UV Index, the second validation regards the EO based total columnar
Ozone. Measurements were made with Flyby's spectroradiometer SpectrAIRTM.
The ground instrument
Ozone remote sensing
KNMI bases the ozone forecasts on a tracer-transport
and assimilation model called TM3DAM. Within TM3DAM
the three-dimensional advection of ozone is described by
the flux-based second order moments scheme. The model
is driven by 6-hourly meteorological fields (forecasts of
wind, surface pressure, and temperature) from ECMWF.
The total ozone data are assimilated in TM3DAM by
applying a parameterized Kalman filter technique.
SpectrAIRTM spectroradiometer
0.06
Spectral Irradiance [W/(m2nm)]
Characteristics:
• Resolution/spectral range: 0.5 nm /
290-850 nm
SpectrAIR
0.03
0.02
0.01
0
200
400
500
600
700
800
900
calibration (NIST)
• USB interface
0.025
Calibration Function
0.02
Spectral Irradiance/Counts
• Software SpectrAIR for Windows
• Lambertian diffuser with quartz
window
0.015
0.01
0.005
• Anti-solarization quartz optic fiber,
400 µm
south pole view
300
Lambda [nm]
• Integrated optical shutter for
automated subtraction of noise
diffuser
north pole view
0.04
• Accuracy UV: 8% (NIST)
Assimilated SCIAMACHY ozone field (KNMI)
global view
spectrAIR_50cm
NIST_50cm
0.05
0
200
300
400
500
600
700
800
900
Lambda [nm]
UV Index remote sensing
UV index validation
The clear sky UV Index is calculated at Flyby with a Radiative
Transfer Model as a function of the ozone (SCIAMACHY), the
altitude of the locality (DEM model, GTOPO30 version), the
aerosol (seasonal model in standard atmosphere) and the albedo
of the surrounding wide area (standard value). The UV Index for
the general case (cloudy sky) exploits a further model based on
MSG images at 1 km resolution and with 15 min. update rate.
The comparison between the UV Index calculated from satellite data and the UV
Index derived from on-ground measurements made by ARPAT in Livorno using the
SpectrAIRTM spectroradiometer shows an agreement better than 16% for Solar Zenith
Angle < 40°, also including the most critical cases of partially clouded sky
FBY-ASC-POS-001-10
The general case UV Index (compliant with WMO/WHO
standards) is then correlated with the user Minimum Erythemal
Dose and used by PROMOTE/MEDSUN service to calculate the
safe exposure time tailored to the user specific phototype.
Ozone validation
The spectral irradiance data have been measured on 14
March 2006 and 4 April 2006, in clear-sky conditions, in
Livorno, Italy (lat. 43.5092468 N; lon. 10.3249168 E).
180
160
140
120
100
80
5
25
45
55
60
65
70
SZA
400
60
375
40
20
0
200
250
300
350
400
O3 (DU)
R = exp{B(SZA) + (a(SZA)/cos(SZA))! O3}
450
350
325
Ozone from SpectrAir
300
04/4-12.30
04/4-12.15
04/4-12.00
04/4-11.45
04/4-11.30
04/4-11.15
14/3-13.59
14/3-13.32
14/3-13.02
14/3-12.31
14/3-12.01
14/3-11.31
14/3-11.01
14/3-10.28
14/3-09.59
UTC time
325
Ozone from SpectrAir
300
with a and B depending only on SZA:
14/3-09.32
350
14/3-08.32
Ozone (DU)
& cos(SZA) #
!!(ln(R) - B(SZA))
O3 = $$
% a(SZA) "
275
375
14/3-14.29
then by inverting we obtain:
04/4-11.00
Ozone from SCIAMACHY
400
04/4-10.39
Writing R as:
Ozone (DU)
R = Irr(323.5nm) / Irr(305.5nm)
The method has been developed using simulated
data calculated by FastRT program. The algorithm
uses the ratio R between the irradiance values in
323.0 nm and 305.0 nm bands, considering the
HWHM for each band equal to 2.0 nm and weighing
the shape function with a triangular function. Ground
albedo and quote have been set to 0.05 and 0 km.
Ozone from SCIAMACHY:
275
35
40
45
50
55
Solar Zenith Angle (degree)
60
65
The ozone measured by SpectrAIR shows a good agreement with
satellite data. In the above figure a relative error of 5% is
reported. The reported error on SCIAMACHY data is 5 DU.
Bibliography
• Sigrid Wuttke, Jean Verdebout and Gunther Seckmeyer (2003), “An Improved Algorithm for Satellite-derived UV Radiation”, Photochemistry and Photobiology, 77(1): 52–57
• A.Arola, S.Kalliskota, P.N. den Outer, K.Edwardsen, G.Hansen, T.Koskela, T.J.Martin, J. Matthijsen, R.Meerkötter, P.Peeters, G.Seckmeyer, P.Simon, H.Slaper, P.Taalas, J.Verdebout (2002), “Assessment of four methods to estimate surface UV radiation
using satellite data by comparison with ground measurements from four stations in Europe”, J. Geophys. Res., 107, D16, (10.1029/2001JD000462), ACL 11-1.
• Working Group 4 of the COST-713 Action (2000), “UV-Index for the Public - A guide for publication and interpretation of solar UV Index forecasts for the public”, European Communities, ISBN 92 828 81542 3.
• M. Houët, C. Brogniez, D. Bolsée, D. Gillotay, H. De Backer (2002), “Ozone column retrieval from UV spectral irradiance measurement”, Sixth European Symposium on Stratospheric Ozone, Göteborg, Sweden, 2-6 Sept. 2002.
• E.Simeone, F.Flore, V.Nardino, A.Masi, C.Lanzetta, G.Licitra, D.Palazzuoli, P.Gallo, S.Carpinello (2005), “Sistema di fotoprotezione solare mediante elaborazione di immagini ottiche satellitari”, Acta of 9th ASITA Conference, Catania, 15-18 Nov.2005