Kipp&Zonen UVS-E-T UV Radiometers - Manual (Page 16)

16
4.1.2 CALIBRATION STEP B:
DETERMINATION OF THE CONVERSION
FACTOR TABLE
Without any measurement correction, a broad-band UV
radiometer can provide results that deviate by a factor
of 2 or more from the true values. The magnitude of the
deviation depends mainly on the extent of the spectral
mismatch and the measurement conditions.
The measurement conditions for which correction
factors are calculated are obtained by varying the solar
zenith angle,
Θ
0
, and the total Ozone column density,
[O
3
] in the radiative transfer model TUV [Ref. 3]. Other
atmospheric parameters affecting UV irradiances, such
as extinction due to aerosols, are not explicitly included
as they are assumed to be comparatively small.
The modelled UV spectra are used to determine the
conversion factors
,
γ (
Θ
0
,O
3
), which are defined as:
γ =T
UVS
/T
UVX
where T
UVS
and T
UVX
denote the normalized spectral
response function-weighted irradiance and the ‘true’
irradiance, respectively:
where e
TUV
(
λ
 Θ
0
,O
3
) denotes the TUV modelled
irradiance as a function of the variable input
parameters
Θ
0
and O
3
. Note, that the ‘true’ irradiance,
T
UVX
, represents the modelled irradiance weighted with
a theoretical spectral response function, s
UVX
(
λ
). Such
a theoretical spectral response function could be the
Erythemal weighting function CIE-1987 [Ref. 4]. The
conversion factors calculated with the Erythemal
weighting function provide the corrections for the UVS-
E-T and UVS-AE-T radiometers.