Modeling errors in diffuse‐sky radiation: Vector <i>vs</i> scalar treatment

Lacis, Andrew A.; Chowdhary, Jacek; Mishchenko, Michael I.; Cairns, B.

doi:10.1029/97gl03613

Cited by 91 publications

(50 citation statements)

References 7 publications

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“…Neglecting polarization by scalar radiative transfer introduces errors in the modeled radiances, which can be as large as 10 % depending on the scattering geometry of the singly scattered light (Mishchenko et al, 1994;Stammes , 1994;Lacis et al, 1998). Consequently, one may argue that the use of the scalar radiative transfer solver in our LINTRAN forward model potentially causes retrieval biases depending on scattering geometry and subsequently on the solar zenith angles.…”

Section: The Scalar Radiative Transfer Approximationmentioning

confidence: 99%

The direct fitting approach for total ozone column retrievals: a sensitivity study on GOME-2/MetOp-A measurements

et al. 2015

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Abstract. We present a sensitivity study of the direct fitting approach to retrieve total ozone columns from the clear sky Global Ozone Monitoring Experiment 2/MetOp-A (GOME-2/MetOp-A) measurements between 325 and 335 nm in the period 2007-2010. The direct fitting of the measurement is based on adjusting the scaling of a reference ozone profile and requires accurate simulation of GOME-2 radiances. In this context, we study the effect of three aspects that introduce forward model errors if not addressed appropriately:(1) the use of a clear sky model atmosphere in the radiative transfer demanding cloud filtering, (2) different approximations of Earth's sphericity to address the influence of the solar zenith angle, and (3) the need of polarization in radiative transfer modeling. We conclude that cloud filtering using the operational GOME-2 FRESCO (Fast Retrieval Scheme for Clouds from the Oxygen A band) cloud product, which is part of level 1B data, and the use of pseudo-spherical scalar radiative transfer is fully sufficient for the purpose of this retrieval. A validation with ground-based measurements at 36 stations confirms this showing a global mean bias of −0.1 % with a standard deviation (SD) of 2.7 %. The regularization effect inherent to the profile scaling approach is thoroughly characterized by the total column averaging kernel for each individual retrieval. It characterizes the effect of the particular choice of the ozone profile to be scaled by the inversion and is part of the retrieval product. Two different interpretations of the data product are possible: first, regarding the retrieval product as an estimate of the true column, a direct comparison of the retrieved column with total ozone columns from ground-based measurements can be done. This requires accurate a priori knowledge of the reference ozone profile and the column averaging kernel is not needed. Alternatively, the retrieval product can be interpreted as an effective column defined by the total column averaging kernel. This interpretation relies much less on the a priori knowledge of the reference ozone profile; however, for its validation, measurements of the vertical ozone distribution are needed. The different manners of data interpretation are demonstrated for simulated and real measurements using on-ground ozone column and ozonesonde measurements for validation.

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Section: The Scalar Radiative Transfer Approximationmentioning

confidence: 99%

The direct fitting approach for total ozone column retrievals: a sensitivity study on GOME-2/MetOp-A measurements

et al. 2015

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“…1b), was run with a scalar radiative transfer solver, which did not take polarization into account. Lacis et al (1998) calculated that modelling errors for irradiance resulting from the omission of polarization in these calculations can be as large as 1.3 % for a Rayleigh atmosphere. However, errors for 310 and 337 nm (i.e.…”

Section: Discussionmentioning

confidence: 99%

Retrieving vertical ozone profiles from measurements of global spectral irradiance

2017

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Abstract.A new method is presented to determine vertical ozone profiles from measurements of spectral global (direct Sun plus upper hemisphere) irradiance in the ultraviolet. The method is similar to the widely used Umkehr technique, which inverts measurements of zenith sky radiance. The procedure was applied to measurements of a high-resolution spectroradiometer installed near the centre of the Greenland ice sheet. Retrieved profiles were validated with balloonsonde observations and ozone profiles from the space-borne Microwave Limb Sounder (MLS). Depending on altitude, the bias between retrieval results presented in this paper and MLS observations ranges between − 5 and +3 %. The magnitude of this bias is comparable, if not smaller, to values reported in the literature for the standard Dobson Umkehr method. Total ozone columns (TOCs) calculated from the retrieved profiles agree to within 0.7±2.0 % (±1σ ) with TOCs measured by the Ozone Monitoring Instrument on board the Aura satellite. The new method is called the "GlobalUmkehr" method.

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“…From a practical point of view, an important issue concerns the errors in the intensies of multiply scattered radiation when the incident light is unpolarized and the so-called scalar approximation is used, i.e., when polarization is completely ignored in the calculations. This has been investigated for a number of special cases Kattawar, 1970, 1993;Chandrasekhar, 1950;Hansen, 1971a,b;Van de Hulst, 1980;Adams, 1989, 1990;Mishchenko, Lacis, and Travis, 1994;Stammes, 1994Stammes, , 2001Lacis et al, 1998]. For light reflected by clouds of spherical particles with radii not smaller than the wavelength the errors in the intensities due to the scalar approximation were found to be smaller than about 1 %, but for atmospheres in which Rayleigh scattering plays an important role much larger errors may occur, since in that case the singly scattered light can be strongly polarized and this light is the input for multiply scattered light.…”

Section: Principle Of the Adding-doubling Methodsmentioning

confidence: 99%

Fast computation of two-level circulant preconditioners

2006

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In this paper we present an algorithm for the construction of the superoptimal circulant\ud preconditioner for a two-level Toeplitz linear system. The algorithm is fast, in the sense that it operates in FFT time. Numerical results are given to assess its performance when applied\ud to the solution of two-level Toeplitz systems by the conjugate gradient method, compared with the Strang and optimal circulant preconditioners

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Modeling errors in diffuse‐sky radiation: Vector vs scalar treatment

Cited by 91 publications

References 7 publications

The direct fitting approach for total ozone column retrievals: a sensitivity study on GOME-2/MetOp-A measurements

The direct fitting approach for total ozone column retrievals: a sensitivity study on GOME-2/MetOp-A measurements

Retrieving vertical ozone profiles from measurements of global spectral irradiance

Fast computation of two-level circulant preconditioners

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