Sparse inversion of Stokes profiles

Ramos, A. Asensio; Rodríguez, J. de la Cruz

doi:10.1051/0004-6361/201425508

Cited by 32 publications

(4 citation statements)

References 49 publications

(52 reference statements)

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“…This attribute allowed the development of inversion codes that take into account the PSF self-consistently during the minimization process, with the result that maps having diffraction-limited resolution of the SOT may be obtained for the physical parameters in the solar atmosphere. Such techniques are described in van Noort (2012); Asensio Ramos and de la Cruz Rodríguez (2015) and also in this special issue (de la Cruz Rodriguez et al 2015). They have already resulted in numerous publications (e.g., Lagg et al 2014;Tiwari et al 2013;Buehler et al 2015).…”

Section: Hinode Sot/fg and Sot/spmentioning

confidence: 98%

“…This has been done successfully during the last years in terms of image reconstruction techniques based on phase-diversity, speckle, or MOMFBD techniques (Lofdahl and Scharmer 1994;von der Luehe 1993;van Noort et al 2005). The next evolutionary steps in this direction are novel inversion techniques, like the spatially-coupled inversions by van Noort (2012) or the sparse inversion of Stokes profiles by Asensio Ramos and de la Cruz Rodríguez (2015), which take into account the point-spread-function (PSF) of the telescope self-consistently during the inversion process. In a next development step, inversion programs must take into account the natural 2D-coupling between the single-column atmospheres.…”

Section: Technology and Data Analysis Challengesmentioning

confidence: 99%

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Measurements of Photospheric and Chromospheric Magnetic Fields

et al. 2015

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The Sun is replete with magnetic fields, with sunspots, pores and plage regions being their most prominent representatives on the solar surface. But even far away from these active regions, magnetic fields are ubiquitous. To a large extent, their importance for the thermodynamics in the solar photosphere is determined by the total magnetic flux. Whereas in low-flux quiet Sun regions, magnetic structures are shuffled around by the motion of granules, the high-flux areas like sunspots or pores effectively suppress convection, leading to a temperature decrease of up to 3000 K. The importance of magnetic fields to the conditions in higher atmospheric layers, the chromosphere and corona, is indisputable. Magnetic fields in both active and quiet regions are the main coupling agent between the outer layers of the solar atmosphere, and are therefore not only involved in the structuring of these layers, but also for the transport of energy from the solar surface through the corona to the interplanetary space. Consequently, inference of magnetic fields in the photosphere, and especially in the chromosphere, is crucial to deepen our understanding not only for solar phenomena such as chromospheric and coronal heating, flares or coronal mass ejections, but also for fundamental physical topics like dynamo theory or atomic physics. In this review, we present an overview of significant advances during the last decades in measurement techniques, analysis methods, and the availability of observatories, together with some selected results. We discuss the problems of determining magnetic fields at smallest spatial scales, connected with increasing demands on polarimetric sensitivity and temporal resolution, and highlight some promising future developments for their solution.Comment: Accepted for publication in "Space Science Reviews"; 42 pages, 16 figure

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Section: Hinode Sot/fg and Sot/spmentioning

confidence: 98%

Section: Technology and Data Analysis Challengesmentioning

confidence: 99%

Measurements of Photospheric and Chromospheric Magnetic Fields

et al. 2015

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“…A significant step forward has been adopted by three different techniques after acknowledging the spatial effects of non-ideal instruments (van Noort, 2012;Ruiz Cobo and Asensio Ramos, 2013;Asensio Ramos and de la Cruz Rodríguez, 2015). While the spectral PSF of the instruments was soon incorporated into the inversion codes, 21 the spatial blurring could not be satisfactorily dealt with until these works.…”

Section: Inversions Accounting For Spatial Degradationmentioning

confidence: 99%

Inversion of the radiative transfer equation for polarized light

Iniesta

Cobo

2016

Living Rev. Sol. Phys.

114

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Since the early 1970s, inversion techniques have become the most useful tool for inferring the magnetic, dynamic, and thermodynamic properties of the solar atmosphere. The intrinsic model dependence makes it necessary to formulate specific means that include the physics in a properly quantitative way. The core of this physics lies in the radiative transfer equation (RTE), where the properties of the atmosphere are assumed to be known while the unknowns are the four Stokes profiles. The solution of the (differential) RTE is known as the direct or forward problem. From an observational point of view, the problem is rather the opposite: the data are made up of the observed Stokes profiles and the unknowns are the solar physical quantities. Inverting the RTE is therefore mandatory. Indeed, the formal solution of this equation can be considered an integral equation. The solution of such an integral equation is called the inverse problem. Inversion techniques are automated codes aimed at solving the inverse problem. The foundations of inversion techniques are critically revisited with an emphasis on making explicit the many assumptions underlying each of them. An incremental complexity procedure is advised for the implementation in practice. Coarse details of the profiles or coarsely sam- pled profiles should be reproduced first with simple model atmospheres (with, for example, a few physical quantities that are constant with optical depth). If the Stokes profiles are well sampled and differences between synthetic and observed ones are greater than the noise, then the inversion should proceed by using more complex models (that is, models where physical quantities vary with depth or, eventually, with more than one component). Significant im- provements are expected as well from the use of new inversion techniques that take the spatial degradation by the instruments into account.Comment: Invited review accepted for publication in Living Reviews in Solar Physics. 84 pages, 30 figure

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“…Asensio Ramos et al (2007) proposed using a 'not-so-brute-force' procedure, a Markov chain Monte Carlo method, where marginal distributions of parameters can be obtained. An extremely interesting new generation of the inversion methods has been proposed by Asensio Ramos & de la Cruz Rodríguez (2015).…”

Section: Introductionmentioning

confidence: 99%

A Non-Linear Magnetic Field Calibration Method for Filter-Based Magnetographs by Multilayer Perceptron

et al. 2020

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For filter-based magnetographs, the linear calibration method under the weak-field assumption is usually adopted; this leads to magnetic saturation effect in the regions with strong magnetic field. This article explores a new method to overcome the above disadvantage using a multilayer perceptron network, which we call MagMLP, based on a back-propagation algorithm with one input layer, five hidden layers, and one output layer. We use the data from the Spectropolarimeter (SP) on board Hinode to simulate single-wavelength observations for the model training, and take into account the influence of the Doppler velocity field and the filling factor. The training results show that the linear fitting coefficient (LFC) of the transverse field reaches above 0.91, and that of the longitudinal field is above 0.98. The generalization of the models is good because the corresponding LFCs are above 0.9 for the test subsets. Compared with the linear calibration method, the MagMLP is much more effective on dealing with the magnetic saturation effect. Analyzing an active region, the results of the linear calibration present an evident magnetic saturation effect in the umbra regions; the corresponding systematic error reaches values greater than 1000 G in most areas, or even exceeds 2000 G at some pixels. However, the results of MagMLP at these locations are very close to the inversion results, and the systematic errors are basically within 300 G. In addition, we find that there are many "bright spots" and "dark spots" on the inclination angle images from the inversion results of Hinode/SP with values of 180 and 0 degrees, respectively, where the inversion is not reliable and does not produce a good result; the MagMLP handles these points well.

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Sparse inversion of Stokes profiles

Cited by 32 publications

References 49 publications

Measurements of Photospheric and Chromospheric Magnetic Fields

Measurements of Photospheric and Chromospheric Magnetic Fields

Inversion of the radiative transfer equation for polarized light

A Non-Linear Magnetic Field Calibration Method for Filter-Based Magnetographs by Multilayer Perceptron

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