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of all parameters of the direct problem to the solution of the inverse problem.
Further we can divide vector
X
=
U
into two parts:
X
(1)
are the retrieved
parameters (their analysis has the meaning) and
X
(2)
are the parameters for
which the uncertainty of the initial values setting is taken into account cor-
rectly.
However, in practice this path is unrealizable, it is enough to weigh up the
number of the parameters describing the molecular absorption lines. Thus,
only the set of parameters, whose magnitudes are not initially defined, are
included to vector
X
, and other parameters
U
X
are assumed as the exactly
known ones. The influence of the uncertainty of the
U
\
X
assignment is es-
timated from the dependence of the exactness of the direct problem solution
upon this uncertainty, and it is to be considered as a part of systematic un-
certainty
\
Y
. This estimation is usually accomplished either from the physical
reasons (in this case there is a possibility to neglect the inaccurate assignment
of the parameters) or from the results of the numerical experiments, i. e. the
direct problem solving with varying values
U
∆
X
in limits of the fixed accuracy
(Mironenkov et al. 1996). Note, that the possibilities of the modern computers
open large perspectives for the pointed numerical experiments. For example,
it is possible to obtain the reliable assessment of the complex effect of the
indeterminacy of the assignment of all vector
U
\
X
components to the direct
problem solution, after varying all components of vector
U
\
X
at once with the
method of statistical modeling and accumulating the representative sample.
Concerning the dividing of the retrieved parameters
X
\
=
U
to the analyzed
X
(1)
and non-analyzed
X
(2)
ones, it should be noted that this dividing is to be
accomplished based on the reasons of the retrieval accuracy only. Namely, the
retrieved parameters
X
(2)
could be meaningless if their posterior dispersion
is close to the a priori one. However, the latter recommendation is rather
relative either, because even small preciseness of some physical parameters
mightbetheratheractualone.Quiteoftenthevector
X
(1)
components are
selected based on the problem stated while accomplishing the observations,
and as a result the precise data are thrown out to “a tray” - to vector
X
(2)
.
Therefore, for example in the study by Mironenkov et al. (1996), only the
possibility and accuracy of the total content of the gases absorbing radiation is
analyzed while processing the data of the ground observations of atmospheric
transparence within IR spectral region. At the same time the product of the
solar constant, instrument sensitivity, and aerosol extinction is accepted as
a retrieved parameter in this method, that could give useful information about
the aerosol extinction spectrum within the IR range while taking into account
thesmoothspectraldependenceofthetwofirstfactors.
According to the physical meaning, the part of the retrieved parameters
presents the vertical profiles (of the temperature or gases content). The problem
arises of describing these profiles with the finite set of parameters. Then two
approaches are used: the approximation of the profile by the discrete altitude
grid and approximation of the profile by a certain function. In fact, both
approaches are equivalent, because anydiscrete grid supposes the interpolation
to the intermediate altitudes that the definite function accomplishes. However,
it is desirable to distinguish these approaches in the aspect of the application.
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