CAOSP abstracts, Volume: 32, No.: 1, year: 2002
- Author(s): KOCIFAJ, M.
- Journal: Contributions of the Astronomical Observatory Skalnate Pleso, vol. 32, no. 1, p. 5-24.
- Date: 04/2002
- Title: On uncertainty of determination of particle optical thickness in atmospheric environment
- Keyword(s): PARTICLE OPTICAL THICKNESS, DIFFUSE RADIATION, EXTINCTION, OPTICAL AIR MASS
- Pages: 5 -- 24
Abstract:
The uncertainty of particle optical thickness retrieval in the Earth's
atmosphere is estimated. There are some specific factors, which are
notoriously not evaluated i) the intensity distribution on the solar disk,
ii) changes of the optical air mass along the solar disk, and iii) diffuse
radiation in the solar aureola, which represents an addition to the measured
intensity because of the finite instrument field-of-view. It is shown that
the first two factors, in general, reduce the final value of the aerosol
optical thickness tau_a, so that the corrected value tau_a^C looks to be
less than the approximate value tau_a^A obtained by a simple retrieval
mechanism. However, diffuse radiation in the aureola region causes an
increasing of tau_a^C by a factor Q. The corrected value of tau_a^C can
finally be about 2-3% larger than tau_a^A. This difference varies with modal
radius of the aerosol size distribution, due to sensitive dependence of the
scattering pattern (in the near-forward scattering region) on particle size.
An error level (2-3%) cannot be ignored, because it is comparable to the
standard systematic/random measurement error approx. 4-5%. It is shown that
such a small uncertainty in the aerosol optical thickness can produce large
changes in the solution of the inverse problem yielding the size
distribution of the aerosol particles f(r). This influences data processing
and it is, for instance, a source of new open questions when interpreting
the measured brightness of F-corona (to retrieve the number density of
interplanetary dust particles). The gained range of the possible solutions
of f(r) then has a direct impact on the calculation of radiation fluxes in
the atmosphere. The uncertainty in estimation of the radiative balance may
change the view of chemical and physical processes in the planetary
atmosphere, and may be a reason for partially inaccurate or inadequate
physical conclusions.
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