Radiative transfer with reciprocal transactions: Numerical method and its implementation

Väisänen, Timo; Markkanen, Johannes; Penttilä, Antti; Muinonen, K.

doi:10.1371/journal.pone.0210155

Cited by 22 publications

(20 citation statements)

References 27 publications

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“…The recent works by, for example, Muinonen et al (2018) and Väisänen et al (2019) provide advanced multiple-scattering models for planetary regoliths. The disk-integrated brightness L equals the surface integral…”

Section: Asteroid Modelmentioning

confidence: 99%

Asteroid lightcurve inversion with Bayesian inference

Muinonen

Torppa

Wang

et al. 2020

A&A

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Context. We assess statistical inversion of asteroid rotation periods, pole orientations, shapes, and phase curve parameters from photometric lightcurve observations, here sparse data from the ESA Gaia space mission (Data Release 2) or dense and sparse data from ground-based observing programs. Aims. Assuming general convex shapes, we develop inverse methods for characterizing the Bayesian a posteriori probability density of the parameters (unknowns). We consider both random and systematic uncertainties (errors) in the observations, and assign weights to the observations with the help of Bayesian a priori probability densities. Methods. For general convex shapes comprising large numbers of parameters, we developed a Markov-chain Monte Carlo sampler (MCMC) with a novel proposal probability density function based on the simulation of virtual observations giving rise to virtual least-squares solutions. We utilized these least-squares solutions to construct a proposal probability density for MCMC sampling. For inverse methods involving triaxial ellipsoids, we update the uncertainty model for the observations. Results. We demonstrate the utilization of the inverse methods for three asteroids with Gaia photometry from Data Release 2: (21) Lutetia, (26) Proserpina, and (585) Bilkis. First, we validated the convex inverse methods using the combined ground-based and Gaia data for Lutetia, arriving at rotation and shape models in agreement with those derived with the help of Rosetta space mission data. Second, we applied the convex inverse methods to Proserpina and Bilkis, illustrating the potential of the Gaia photometry for setting constraints on asteroid light scattering as a function of the phase angle (the Sun-object-observer angle). Third, with the help of triaxial ellipsoid inversion as applied to Gaia photometry only, we provide additional proof that the absolute Gaia photometry alone can yield meaningful photometric slope parameters. Fourth, for (585) Bilkis, we report, with 1-σ uncertainties, a refined rotation period of (8.5750559 ± 0.0000026) h, pole longitude of 320.6° ± 1.2°, pole latitude of − 25.6° ± 1.7°, and the first shape model and its uncertainties from convex inversion. Conclusions. We conclude that the inverse methods provide realistic uncertainty estimators for the lightcurve inversion problem and that the Gaia photometry can provide an asteroid taxonomy based on the phase curves.

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Section: Asteroid Modelmentioning

confidence: 99%

Asteroid lightcurve inversion with Bayesian inference

Muinonen

Torppa

Wang

et al. 2020

A&A

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“…Nonetheless, the standard RTE is only applicable to sparse discrete random media where the grains are in each other's far zone. Recently, a numerical framework for electromagnetic scattering, absorption, and propagation in dense discrete random media was introduced which extends the applicability range of the standard RTE (Muinonen et al 2018;Markkanen et al 2018b;Väisänen et al 2019). Furthermore, Markkanen et al (2018a) augmented the method with the coherent field contribution to account for surface reflections and refractions allowing the scattering analysis of millimeter-A&A proofs: manuscript no.…”

Section: Introductionmentioning

confidence: 99%

Scattering, absorption, and thermal emission by large cometary dust particles: Synoptic numerical solution

Markkanen

Agarwal

2019

A&A

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Context. Remote light scattering and thermal infrared observations provide clues about the physical properties of cometary and interplanetary dust particles. Identifying these properties will lead to a better understanding of the formation and evolution of the Solar System. Aims. We present a numerical solution for the radiative and conductive heat transport in a random particulate medium enclosed by an arbitrarily shaped surface. The method will be applied to study thermal properties of cometary dust particles. Methods. The recently introduced incoherent Monte Carlo radiative transfer method developed for scattering, absorption, and propagation of electromagnetic waves in dense discrete random media is extended for radiative heat transfer and thermal emission. The solution is coupled with the conductive Fourier transport equation that is solved with the finite-element method.Results. The proposed method allows the synoptic analysis of light scattering and thermal emission by large cometary dust particles consisting of submicrometer-sized grains. In particular, we show that these particles can sustain significant temperature gradients resulting in the superheating factor phase function observed for the coma of comet 67P/Churyumov-Gerasimenko.

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“…We used the radiative transfer with reciprocal transactions method (R2T2) to calculate the scattering properties. R2T2 is an extension of the radiative transfer solution to the dense discrete random medium, including the coherent backscattering mechanism (Muinonen et al 2018;Väisänen et al 2019). For the sake of simplicity, we do not consider the hierarchical nature of dust agglomerates (i.e.…”

Section: Comparison With the Rosetta Observations And Estimation Of T...mentioning

confidence: 99%

VLT spectropolarimetry of comet 67P: Dust environment around the end of its intense Southern summer

Kwon,

Bagnulo,

Markkanen

et al. 2021

Preprint

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Context. A cornucopia of Rosetta and ground-based observational data sheds light on the evolution of the characteristics of dust particles from comet 67P/Churyumov-Gerasimenko (hereafter 67P) with seasons, implying the different dust environments in the source regions on the surface of the comet. Aims. We aim to constrain the properties of the dust particles of 67P and therefrom diagnose the dust environment of its coma and near-surface layer at around the end of the Southern summer of the comet. Methods. We performed spectropolarimetric observations for 67P dust over 4,000-9,000 Å using the ESO/Very Large Telescope in January-March 2016 (phase angle ranging ∼26 • -5 • ). We examined the optical behaviours of the dust, which, together with Rosetta colour data, were used to search for dust evolution with cometocentric distance. Modelling was also conducted to identify the dust attributes compatible with the results. Results. The spectral dependence of the polarisation degree of 67P dust is flatter than found in other dynamical groups of comets in similar observing geometry. The depth of its negative polarisation branch appears to be a bit shallower than in long-period comets and might be getting shallower as 67P repeats its apparitions. Its dust colour shows a change in slope around 5,500 Å, (17.3 ± 1.4) and (10.9 ± 0.6) % (1,000 Å) −1 for shortward and longward of the wavelength, respectively, which are slightly redder but broadly consistent with the average of Jupiter-Family comets. Conclusions. Observations of 67P dust in this study can be attributed to dust agglomerates of ∼100 µm in size detected by Rosetta in early 2016. A porosity of 60 % shows the best match with our polarimetric results, yielding a dust density of ∼770 kg m −3 . Compilation of Rosetta and our data indicates the dust's reddening with increasing nucleus distance, which may be driven by water-ice sublimation as the dust moves out of the nucleus. We estimate the possible volume fraction of water ice in the initially ejected dust as ∼6 % (i.e. the refractory-to-ice volume ratio of ∼14).

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Radiative transfer with reciprocal transactions: Numerical method and its implementation

Cited by 22 publications

References 27 publications

Asteroid lightcurve inversion with Bayesian inference

Asteroid lightcurve inversion with Bayesian inference

Scattering, absorption, and thermal emission by large cometary dust particles: Synoptic numerical solution

VLT spectropolarimetry of comet 67P: Dust environment around the end of its intense Southern summer

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