Geoscience Reference
In-Depth Information
λ
i
−
∆λ
λ
i
+
∆λ
(1999). According to this algorithm wavelength interval [
,
]is
λ
gets into
dividedintonarrowintervalsof1cm
−1
length. When wavelength
2 cm
−1
from
it only are considered with rigorous (2.18)-(2.19) and the yield of the farthest
lines to coefficient
the definite narrow interval the spectral lines within the distance
±
κ
m
is calculated with the approximated formula:
n
i
T
∗
T
l
(
i
)
M
4
=
κ
m
+
P
κ
m
:
ν
)
4−
k
R
ik
(
−
ν
P
∗
=
=
i
1
k
1
(5.6)
T
∗
T
m
ij
K
(
i
)
b
k
π
W
ij
(
T
)
W
ij
(
T
∗
)
d
ij
=
R
ik
S
ij
,
ν
i
)
6−
k
(
−
ν
=
j
1
|λ
,
ν
is the right boundary of the interval of the rigorous account-
ing of the spectral lines; the rest of the specifications are similar to (2.18)-(2.19).
According to Virolainen and Polyakov (1999) the magnitudes of the empirical
coefficients are:
b
1
ν
=
where
1
=
=
=
=
− 1.40276,
b
2
2.35451,
b
3
− 1.93698,
b
4
0.99854,
ν
.
As coefficients
R
ik
for every concrete gas depend only on temperature, they
are preliminarily tabulated and interpolated over the look-up tables during
the calculation process. This procedure decreases the computing time by an
order of magnitude. The uncertainty of approximation (5.6) is equal to about
the decimals of a percent as per the analysis of the study by Virolainen and
Polyakov (1999) and can be neglected in most cases.
All gases, about which the spectroscopic information (Sect. 1.2) is available,
shouldbe included in the computing codeof the etalonalgorithm.Nevertheless,
only the gases, which the processing results are sensitive to, are to be taken
into account by the applied algorithm. Thus, we are estimating the ratio of
the maximal irradiance variation caused by the variation of the concrete gas
content to the SD of the observations, i. e. the value called usually “
signal-to-
noise ratio (SNR)
”, and the necessity of the gas account in the applied algorithm
is considered according to this ratio. During this calculation, the contents of the
considered gases should be tripled to estimate the limit variation (excluding
O
2
). The condition of the relative humidity less than 95% should be tested
while tripling the H
2
O content otherwise, the content corresponding to 95%
relative humidity is used.
The results of the calculations are presented in Fig. 5.1. Only five absorbing
gases have been accounted for in the applied algorithm: H
2
O, O
3
,O
2
,NO
2
and
NO
3
.ConcerningtheabsenceofgasSO
2
and the presence of gas NO
3
in the
finallist,thefollowingshouldbepointedout.TheSO
2
absorption band is rather
strong in the UV region but it almost coincides with the strongest ozone band.
Spectral interval 340-380 nm,wherethesebandscouldbedivided,provides
too weak SO
2
absorption to be registered by the K-3 instrument (Rozanov et
al. 1995). As for NO
3
, it is characterized with a very strong absorption band
in the VD spectral region, but it is traditionally assumed to be decomposed
by solar light so its content is negligibly low in the atmosphere. Nevertheless,
according to the modern data some troposphere photochemical reactions (in
ν
;
b
1
=
=
=
=
for
<
10.6522,
b
2
1.2675,
b
3
2.14156,
b
4
0.99750, for
>
ν
ν
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