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| Titel |
Regularisation model study for the least-squares retrieval of aerosol extinction time series from UV/VIS MAX-DOAS observations for a ground layer profile parameterisation |
| VerfasserIn |
A. Hartl, M. O. Wenig |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 6, no. 8 ; Nr. 6, no. 8 (2013-08-12), S.1959-1980 |
| Datensatznummer |
250085032
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| Publikation (Nr.) |
 copernicus.org/amt-6-1959-2013.pdf |
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| Zusammenfassung |
The retrieval of tropospheric aerosol extinctions from MAX-DOAS observations
of O4 using a small number of three or four extinction profile parameters
suitable for boundary layer reconstruction is investigated with respect to
the following questions. First, to what extent does this nominally
over-constrained pure least-squares problem for the inversion of the
radiative transfer equation require regularisation and how should parameters
of the regularisation be chosen? Second, how can a lack of information in the
under-constrained case be best compensated by using the information contained
in a sequence of observations and by explicitly including intensities into
the fit?
The forward model parameterises the optical properties of the boundary layer
aerosol by its extinction profile, single-scattering albedo and a
Henyey–Greenstein phase function. Forward calculations are carried out
online, i.e. without look-up tables. The retrieval uses a Tikhonov
regularisation combined with an approximate L-curve criterion and empirical
a priori information from the retrieval sequence based on previous valid
solutions. The consistency of the approach is demonstrated in selected model
case studies assuming a polluted urban scenario and westward viewing
direction of the instrument. It is shown that a dynamic choice of the
regularisation parameter is crucial for high aerosol load and large diurnal
variations. The quality of the retrieval can be improved significantly if
the retrieval sequence and thus the a priori is chosen according to the
information content of the measurement series. Additional intensities improve
the solution for all solar angles if suitably weighted. This flexible
retrieval algorithm allows for reconstruction of aerosol profiles in the boundary
layer for a wide range of viewing directions and extinctions. It can thus be
applied to observational geometries scanning the sky in two angular
dimensions and to retrieve further aerosol optical parameters in the boundary
layer. |
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