Solar Image Restoration By Use Of Multi-frame Blind De-convolution With Multiple Objects And Phase Diversity

Noort, M. van; Voort, L. Rouppe van der; Löfdahl, Mats G.

doi:10.1007/s11207-005-5782-z

Cited by 411 publications

(281 citation statements)

References 28 publications

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“…From the ground the situation becomes more complicated, as the time-varying seeing imposes strong limits as to how fast the observations must be carried out in order to be corrected. In this case P (x, y) must be determined empirically via reconstruction techniques such a Speckle-reconstruction (Keller & von der Luehe 1992), Multi-Object Multi-Frame Blind Deconvolution (Löfdahl 2002;van Noort et al 2005) or Phase Diversity (Paxman et al 1996). For these reasons, in ground-based observations, the aforementioned procedure has been limited to high-throughput filter-based spectropolarimeters (Scharmer et al 2008a;Bello González & Kneer 2008;Del Moro et al 2010;Martínez Pillet et al 2011).…”

Section: Spatial Point Spread Functionmentioning

confidence: 99%

Deep probing of the photospheric sunspot penumbra: no evidence of field-free gaps

Borrero

Ramos

Collados

et al. 2016

A&A

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Context. Some models for the topology of the magnetic field in sunspot penumbrae predict the existence of field-free or dynamically weak-field regions in the deep Photosphere. Aims. To confirm or rule out the existence of weak-field regions in the deepest photospheric layers of the penumbra. Methods. The magnetic field at log τ5 = 0 is investigated by means of inversions of spectropolarimetric data of two different sunspots located very close to disk center with a spatial resolution of approximately 0.4-0.45 ′′ . The data have been recorded using the GRIS instrument attached to the 1.5-meters GREGOR solar telescope at El Teide observatory. It includes three Fe i lines around 1565 nm, whose sensitivity to the magnetic field peaks at half a pressure-scale-height deeper than the sensitivity of the widely used Fe i spectral line pair at 630 nm. Prior to the inversion, the data is corrected for the effects of scattered light using a deconvolution method with several point spread functions. Results. At log τ5 = 0 we find no evidence for the existence of regions with dynamically weak (B < 500 Gauss) magnetic fields in sunspot penumbrae. This result is much more reliable than previous investigations done with Fe i lines at 630 nm. Moreover, the result is independent of the number of nodes employed in the inversion, and also independent of the point spread function used to deconvolve the data, and does not depend on the amount of straylight (i.e. wide-angle scattered light) considered.

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Section: Spatial Point Spread Functionmentioning

confidence: 99%

Deep probing of the photospheric sunspot penumbra: no evidence of field-free gaps

Borrero

Ramos

Collados

et al. 2016

A&A

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“…54 and a sampling of 0.034 /px. Image post-processing included the Multi-Object Multi-Frame Blind-Deconvolution (MOMFBD, Van Noort et al 2005) restoration technique to correct for atmospheric and instrumental aberrations. The final products were two time series of images (s1: 08:47−09:07 UT and s2: 09:14−09:46 UT) with a cadence of 15 s. Additional data postprocessing steps were: compensation for diurnal field rotation, rigid alignment of the images, correction for distortion, and subsonic filtering to eliminate residual jittering (Title et al 1986).…”

Section: Ground-based Observationsmentioning

confidence: 99%

Evidence of small-scale magnetic concentrations dragged by vortex motion of solar photospheric plasma

Balmaceda

Domínguez

Palacios³

et al. 2010

A&A

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Vortex-type motions have been measured by tracking bright points in high-resolution observations of the solar photosphere. These small-scale motions are thought to be determinant in the evolution of magnetic footpoints and their interaction with plasma and therefore likely to play a role in heating the upper solar atmosphere by twisting magnetic flux tubes. We report the observation of magnetic concentrations being dragged towards the center of a convective vortex motion in the solar photosphere from highresolution ground-based and space-borne data. We describe this event by analyzing a series of images at different solar atmospheric layers. By computing horizontal proper motions, we detect a vortex whose center appears to be the draining point for the magnetic concentrations detected in magnetograms and well-correlated with the locations of bright points seen in G-band and CN images.

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“…Bello González & Kneer 2008) at the VTT on 07 June 2009, are described in detail in Puschmann & Beck (2011, PuB11). We use the same spectral scan as those authors, with data reduced on the one hand with the multi-object multi-frame blind deconvolution (MOMFBD; van Noort et al 2005) method, and on the other hand only destretched to a reference image that was speckle-reconstructed with the method of Puschmann & Sailer (2006). The spectral line was sampled on 28 wavelength steps.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations

Beck

Fabbian

Moreno‐Insertis

et al. 2013

A&A

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Context. Numerical three-dimensional (3D) radiative (magneto-)hydrodynamical [(M)HD] simulations of solar convection are nowadays used to understand the physical properties of the solar photosphere and convective envelope, and, in particular, to determine the Sun's photospheric chemical abundances. To validate this approach, it is important to check that no excessive thermodynamic fluctuations arise as a consequence of the partially incomplete treatment of radiative transfer causing radiative damping that is too modest. Aims. We investigate the realism of the thermodynamics in recent state-of-the-art 3D convection simulations of the solar atmosphere carried out with the Stagger code.Methods. We compared the characteristic properties of several Fe i lines (557.6 nm, 630 nm, 1565 nm) and one Si i line at 1082.7 nm in solar disc-centre observations of different spatial resolution with spectra synthesized from 3D convection simulations. The observations were taken with ground-based (Echelle spectrograph, Göttingen Fabry-Pérot Interferometer (GFPI), POlarimetric LIttrow Spectrograph, Tenerife Infrared Polarimeter, all at the Vacuum Tower Telescope on Tenerife) and space-based instruments (Hinode/Spectropolarimeter). We degraded the synthetic spectra to the spatial resolution of the observations, based on the distribution of the continuum intensity I c . We estimated the spectral degradation to be applied to the simulation results by comparing atlas spectra with averaged observed spectra. In addition to deriving a set of line parameters directly from the intensity profiles, we used the SIR (Stokes Inversion based on Response functions) code to invert the spectra. Results. The spatial degradation kernels yield a similar generic spatial stray-light contamination of about 30% for all instruments. The spectral stray light inside the different spectrometers is found to be between 2% and 20%. Most of the line parameters from the observational data are matched by the degraded HD simulation spectra. The inversions predict a macroturbulent velocity v mac below 10 m s −1 for the HD simulation spectra at full spatial resolution, whereas they yield v mac 1000 m s −1 at a spatial resolution of 0. 3. The temperature fluctuations in the inversion of the degraded HD simulation spectra do not exceed those from the observational data (of the order of 100−200 K rms for −2 log τ 500 nm −0.5). The comparison of line parameters in spatially averaged profiles with the averaged values of line parameters in spatially resolved profiles indicates a significant change in (average) line properties on a spatial scale between 0. 13 and 0. 3. Conclusions. Up to a spatial resolution of 0. 3 (GFPI spectra), we find no indications of excessive thermodynamic fluctuations in the 3D HD simulation. To definitely confirm that simulations without spatial degradation contain fully realistic thermodynamic fluctuations requires observations at even higher spatial resolution (i.e. <0. 13).

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Solar Image Restoration By Use Of Multi-frame Blind De-convolution With Multiple Objects And Phase Diversity

Cited by 411 publications

References 28 publications

Deep probing of the photospheric sunspot penumbra: no evidence of field-free gaps

Deep probing of the photospheric sunspot penumbra: no evidence of field-free gaps

Evidence of small-scale magnetic concentrations dragged by vortex motion of solar photospheric plasma

Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations

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