Geoscience Reference
In-Depth Information
r
n
ðkÞ
is the absorption cross-section of the nth atmospheric absorber; N is the
number of absorbers;
are reference spectra of rotational
Raman scattering (RRS), VRS and CDOM fluorescence, respectively;
P
m¼0
a
m
k
r
R
ðkÞ
,
r
V
ðkÞ
, and
r
f
ðkÞ
m
is the low order polynomial, typically of the order M
4.
The minimization is carried out with Sf
n
, S
R
, S
V
, S
f
and polynomial coef
cients
as the
tted parameters. The parameter S
n
is the integrated number density of the
nth atmospheric absorber along the slant optical path, which is generally related to
the concentration of a given absorber. Parameters Sf
R
, S
V
, and S
f
are called scaling
or
fit factors and carry information about the strength of the corresponding inelastic
process.
2.2 CDOM Fluorescence Modeling
In order to perform the CDOM
fl
fluorescence retrieval with the DOAS method, an
adequate
fluorescence spectrum has to be used as a priori information, which is then
scaled in the
fl
fluorescence is
calculated as the difference between the optical density modeled without and with
CDOM
fitting procedure. The reference spectrum for CDOM
fl
fl
fluorescence (after Vountas et al.
1998
):
ln
I
þ
ðkÞ
r
f
ðkÞ
¼
ð
2
Þ
I
ðkÞ
;
where I
þ
ðkÞ
and I
ðkÞ
are modeled radiances calculated including and excluding
inelastic processes, respectively.
The radiances I
þ
ðkÞ
and I
ðkÞ
at the top of the atmosphere have been calculated
by using the coupled ocean-atmosphere radiative transfer model SCIATRAN
(Rozanov et al.
2014
; Blum et al.
2012
). Atmospheric conditions, namely the
pressure, temperature, and water vapor pro
les were set as default in the model for
April and latitude of 45
, according to a climatological database obtained using a 2D
chemical transport model developed at the University of Bremen (Sinnhuber et al.
2009
). The solar zenith angle was set to 45
°
°
. Fluorescence was implemented using
bð
z
; n
0
! n; k
0
! kÞ
the spectral volume inelastic function
, after Mobley (
1994
):
bð
z
; n
0
! n; k
0
! kÞ
¼a
ð
z
; k
0
Þ
R
ðk
0
! kÞbðn
0
! nÞ
½m
1
sr
1
nm
1
;
ð
3
Þ
where a
ð
z
; k
0
Þ
k
0
, usually
is an absorption coef
cient at the depth z and wavelength
cient a
ðk
0
Þ
expressed as a product of a speci
c absorption coef
and concentration
. R
ðk
0
! kÞ
C
ð
z
Þ
is a wavelength redistribution function from excitation wavelength
k
0
to emission wavelength
.
bðn
0
! nÞ
k
is a phase function for the radiance emitted
n
0
to a direction
from a direction
n
, which is assumed to be isotropic. The CDOM
fl
fluorescence was implemented into the SCIATRAN radiative transfer model on the
base of two different approaches as described below.
Search WWH ::
Custom Search