Joint estimation of object and aberrations by using phase diversity

Paxman, Richard G.; Schulz, Timothy J.; Fienup, James R.

doi:10.1364/josaa.9.001072

Cited by 461 publications

(349 citation statements)

References 18 publications

(20 reference statements)

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“…The arrow in the centre of the sunspot points to the solar disc centre. Paxman et al 1992;Löfdahl & Scharmer 1994;Paxman et al 1996). This technique allows a subtantial correction for the aberrations induced by both the telescope and the turbulent terrestrial atmosphere.…”

Section: Observations and Data Processingmentioning

confidence: 99%

Phase diversity restoration of sunspot images

Bonet¹,

Márquez

Müller

et al. 2005

A&A

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Abstract. Two time series, taken simultaneously in the G-band and in white-light, and corrected for telescope aberrations and turbulence perturbations using the method of phase diversity, are employed to study the motions of granules and G-band bright points (GBPs) in the moat of an old regular sunspot. Local correlation tracking and feature tracking have been utilized for this purpose. A large-scale radial outflow with a mean velocity of 0.51 km s −1 has been measured in the sunspot moat. Centres of diverging horizontal motions, identified with families of granules formed by repeatedly splitting granules, move away from the sunspot. Most of the GBPs in the moat also move outwards through radially orientated "channels" (confined between the borders of adjacent families) with velocities comparable to those of the adjacent granules. However, 6% of the GBPs move faster (>1.4 km s −1 ) than the neighbouring granules. GBPs in the moat are not regularly distributed but they are less frequent on its solar centre side.

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Section: Observations and Data Processingmentioning

confidence: 99%

Phase diversity restoration of sunspot images

Bonet¹,

Márquez

Müller

et al. 2005

A&A

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“…Our aim is to compare the asymmetries of Stokes V in the degraded profiles with those found in the original one and in the phase-diversity reconstructed data. Since we know the PSFs of the focused and defocused images exactly, we could apply a standard phase-diversity reconstruction algorithm (Gonsalves & Chidlaw 1979;Paxman et al 1992;Löfdahl & Scharmer 1994) and obtain a perfect reconstruction usinĝ…”

Section: Degradation and Phase-diversity Reconstructionmentioning

confidence: 99%

“…For this reason, the IMaX instrument onboard Sunrise was designed to use the phase-diversity, post-facto reconstruction algorithm (Paxman et al 1992;Vargas Domínguez 2009). In this paper, we focus on the interesting problem of testing how the spatial and spectral degradation produced by the Sunrise/IMaX combination affects circular polarization asymmetries and whether the post-reconstruction algorithms can help us extract reliable information (comparable to the unperturbed synthetic case) about them from degraded data.…”

Section: Introductionmentioning

confidence: 99%

Influence of phase-diversity image reconstruction techniques on circular polarization asymmetries

Ramos

González

Khomenko

et al. 2012

A&A

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Context. Full Stokes filter-polarimeters are key instruments for investigating the rapid evolution of magnetic structures on the solar surface. To this end, the image quality is routinely improved using a-posteriori image reconstruction methods. Aims. We analyze the robustness of circular polarization asymmetries to phase-diversity image reconstruction techniques. Methods. We used snapshots of magneto-hydrodynamical simulations carried out with different initial conditions to synthesize spectra of the magnetically sensitive Fe i line at 5250.2 Å. We degraded the synthetic profiles spatially and spectrally to simulate observations with the IMaX full Stokes filter-polarimeter. We also simulated the focused/defocused pairs of images used by the phase-diversity algorithm for reconstruction and the polarimetric modulation scheme. We assume that standard optimization methods are able to infer the projection of the wavefront on the Zernike polynomials with 10% precision. We also consider the less favorable case of 25% precision. We obtain reconstructed monochromatic modulated images that are later demodulated and compared with the original maps. Results. Although asymmetries are often difficult to define in the quiet Sun due to the complexity of the Stokes V profiles, we show how asymmetries are degraded with spatial and spectral smearing. The results indicate that, although image reconstruction techniques reduce the spatial smearing, they can modify the asymmetries of the profiles, which are mainly caused by the appearance of spatiallycorrelated noise.

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“…A few papers in the literature are complementary in the description of the PD technique for image reconstruction (e.g. Gonsalves & Childlaw 1979;Gonsalves 1982;Paxman et al 1992;Löfdahl & Scharmer 1994;Paxman et al 1996). However, we summarize the most relevant items of the method as an introduction to this powerful tool for high resolution solar imaging and to report on our particular setting of parameters and assumptions to run the computing code.…”

Section: Data Processingmentioning

confidence: 99%

Phase diversity restoration of sunspot images

Bonet

Márquez

Müller

et al. 2004

A&A

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Abstract. We investigate the dynamics of and the relations between small-scale penumbral and photospheric features near the outer penumbral boundary: penumbral grains (PGs), dark penumbral fibrils, granules, and photospheric G-band bright points. The analysis is based on a 2 h time sequence of a sunspot close to disc center, taken simultaneously in the G-band and in the blue continuum at 450.7 nm. Observations were performed at the Swedish Vacuum Solar Telescope (La Palma) in July 1999. A total of 2564 images (46 ×75 ) were corrected for telescope aberrations and turbulence perturbations by applying the inversion method of phase diversity. Our findings can by summarized as follows: (a) one third of the outward-moving PGs pass through the outer penumbral boundary and then either continue moving as small bright features or expand and develop into granules. (b) Former PGs and G-band bright points next to the spot reveal a different nature. The latter have not been identified as a continuation of PGs escaping from the penumbra. The G-band bright points are mostly born close to dark penumbral fibrils where the magnetic field is strong, whereas PGs stem from the less-magnetized penumbral component and evolve presumably to non-magnetic granules or small bright features.

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Joint estimation of object and aberrations by using phase diversity

Cited by 461 publications

References 18 publications

Phase diversity restoration of sunspot images

Phase diversity restoration of sunspot images

Influence of phase-diversity image reconstruction techniques on circular polarization asymmetries

Phase diversity restoration of sunspot images

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