Marco Matricardi and Roger Saunders, "Fast radiative transfer model for simulation of infrared atmospheric sounding interferometer radiances," Appl. Opt. 38, 5679-5691 (1999)
A fast radiative transfer model has been developed for prelaunch
simulation studies of Infrared Atmospheric Sounding Interferometer
(IASI) data and for the exploitation of IASI radiances within the
framework of a numerical weather prediction variational analysis
scheme. The model uses profile-dependent predictors to parameterize
the atmospheric optical depths and is fast enough to cope with the
processing of observations in near real time and with the several
thousands of transmittance calculations required to simulate radiances
from a full range of atmospheric conditions. The development of the
model has involved the selection of a training set of atmospheric
profiles, the production of a line-by-line transmittance database, the
selection of optimal predictors for the gases considered in the study,
and the production of regression coefficients for the fast
transmittance scheme. The model fit to the line-by-line radiances
shows that it can reproduce the line-by-line radiances to a degree of
accuracy that is at or below the instrumental noise.
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Definition of Profile Variables Used in Predictors Defined
in Table 3a
T(l) = [Tprofile(l + 1) + Tprofile(l)]/2
T*(l) = [Treference(l + 1) + Treference(l)]/2
W(l) = [Wprofile(l + 1) + Wprofile(l)]/2
W*(l) = [Wreference(l + 1) + Wreference(l)]/2
O(l) = [Oprofile(l + 1) + Oprofile(l)]/2
O*(l) = [Oreference(l + 1) + Oreference(l)]/2
P(l) = [pres(l + 1) + pres(l)]/2
Tr(l) = T(l)/T*(l)
δT(l) = T(l) - T*(l)
Wr(l) = W(l)/W*(l)
Or(l) = O(l)/O*(l)
The pres(l)’s are the
values of the pressure at each
level. Tprofile(l),
Wprofile(l), and
Oprofile(l) are the temperature,
water vapor mixing ratio, and ozone mixing ratio
profiles. Treference(l),
Wreference(l), and
Oreference(l) are the
corresponding reference profiles. For these variables l
refers to the lth level; otherwise l is the
lth layer, i.e., the layer above the lth
level. Note that we take P(0) = 2P(1) -
P(2). Also Tw(1) = 0 and
OTw(1) = 0.
Table 3
Regression Predictors Used by the RTIASI for Fixed Gases,
Water Vapor, and Ozone
Predictor
Fixed Gases
Water Vapor
Ozone
Xj,1
sec(θ)
sec(θ)Wr
2
(j)
sec(θ)Or(j)
Xj,2
sec2(θ)
sec2(θ)Wr
2
(j)
Xj,3
sec(θ)Tr(j)
[sec(θ)Ww(j)]
2
sec(θ)Or(j)δT(j)
Xj,4
sec(θ)Tr
2
(j)
[sec(θ)Ww(j)]
4
[sec(θ)Or(j)]
2
Xj,5
Tr(j)
sec(θ)Wr(j)δT(j)
δT(j)
Xj,6
Tr
2
(j)
sec(θ)Or(j)
2
Ouw(j)
Xj,7
sec(θ)Tw(j)
4
Xj,8
sec(θ)Wr(j)
Xj,9
[sec(θ)Wr(j)]
3
Or(j)sec(θ)
Xj,10
4
Wr(j)
sec2(θ)Or(j) OTw(j)
Xj,11
0.0
sec(θ)Wr(j)δT(j)|δT(j)|
0.0
Xj,12
0.0
[]δT(j)
0.0
Xj,13
0.0
0.0
Xj,14
0.0
0.0
Tables (3)
Table 1
Minimum and Maximum Values of the Temperature, Water
Vapor, and Ozone Values Used in the Regression at Each Point of the
Pressure Layer Grid
Definition of Profile Variables Used in Predictors Defined
in Table 3a
T(l) = [Tprofile(l + 1) + Tprofile(l)]/2
T*(l) = [Treference(l + 1) + Treference(l)]/2
W(l) = [Wprofile(l + 1) + Wprofile(l)]/2
W*(l) = [Wreference(l + 1) + Wreference(l)]/2
O(l) = [Oprofile(l + 1) + Oprofile(l)]/2
O*(l) = [Oreference(l + 1) + Oreference(l)]/2
P(l) = [pres(l + 1) + pres(l)]/2
Tr(l) = T(l)/T*(l)
δT(l) = T(l) - T*(l)
Wr(l) = W(l)/W*(l)
Or(l) = O(l)/O*(l)
The pres(l)’s are the
values of the pressure at each
level. Tprofile(l),
Wprofile(l), and
Oprofile(l) are the temperature,
water vapor mixing ratio, and ozone mixing ratio
profiles. Treference(l),
Wreference(l), and
Oreference(l) are the
corresponding reference profiles. For these variables l
refers to the lth level; otherwise l is the
lth layer, i.e., the layer above the lth
level. Note that we take P(0) = 2P(1) -
P(2). Also Tw(1) = 0 and
OTw(1) = 0.
Table 3
Regression Predictors Used by the RTIASI for Fixed Gases,
Water Vapor, and Ozone
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