High-order aberration compensation with multi-frame blind deconvolution and phase diversity image restoration techniques

Scharmer, G.; Löfdahl, Mats G.; Werkhoven, T. I. M. van; Rodríguez, J. de la Cruz

doi:10.1051/0004-6361/201014800

Cited by 37 publications

(45 citation statements)

References 23 publications

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“…This happens because the PD error metric does not optimize the WF, but the image quality. A similar phenomenon has been reported by [4,31]: PD can find better reconstructions compared to what is obtained when the deconvolution is done using a perfect modal WF representation being truncated to as many coefficients. Here, we observe a variation of the same effect.…”

Section: Performance On Realistic Ao Datasupporting

confidence: 84%

Joint optimization of phase diversity and adaptive optics: demonstration of potential

et al. 2011

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We study different possibilities to use adaptive optics (AO) and phase diversity (PD) together in a jointly optimized system. The potential of the joint system is demonstrated through numerical simulations. We find that the most significant benefits are obtained from the improved deconvolution of AO-corrected wavefronts and the additional wavefront sensor (WFS) information that reduces the computational demands of PD algorithms. When applied together, it is seen that the image error can be reduced by 20% compared to traditional PD, working with one focused and one defocused camera image, and the computational load is reduced by a factor of 20 compared to a more reliable PD algorithm requiring more camera images. In addition, we find that the system performance can be optimized by adjusting the magnitude of the applied diversity wavefronts.

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Section: Performance On Realistic Ao Datasupporting

confidence: 84%

Joint optimization of phase diversity and adaptive optics: demonstration of potential

et al. 2011

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“…This has now been resolved by measurements of the point spread function (PSF) in the Solar Optical Telescope (SOT) on the Hinode spacecraft (Wedemeyer-Böhm 2008) and comparison with artificial data (Wedemeyer-Böhm & Rouppe van der Voort 2009). Scharmer et al (2010, see their introduction for a full account of the problem) recently initiated a project to measure the straylight sources of the Swedish 1-meter Solar Telescope (SST; Scharmer et al 2003a) to also correct SST images for the missing contrast. Scharmer et al (2010) found that a significant part of the contrast reduction can be explained by high-order modes in the pupil wavefront phase that are not corrected by the Adaptive Optics (AO; Scharmer et al 2003b) or image restorations with multi-frame blind deconvolution (MFBD; Löfdahl 2002) techniques because of the finite number of modes used in those techniques.…”

Section: Introductionmentioning

confidence: 99%

“…Scharmer et al (2010, see their introduction for a full account of the problem) recently initiated a project to measure the straylight sources of the Swedish 1-meter Solar Telescope (SST; Scharmer et al 2003a) to also correct SST images for the missing contrast. Scharmer et al (2010) found that a significant part of the contrast reduction can be explained by high-order modes in the pupil wavefront phase that are not corrected by the Adaptive Optics (AO; Scharmer et al 2003b) or image restorations with multi-frame blind deconvolution (MFBD; Löfdahl 2002) techniques because of the finite number of modes used in those techniques. The authors also implemented a method for correcting the contrast by means of the known statistics of atmospheric turbulence and simultaneous measurements of Fried's parameter r 0 from a wide-field wavefront sensor.…”

Section: Introductionmentioning

confidence: 99%

Sources of straylight in the post-focus imaging instrumentation of the Swedish 1-m Solar Telescope

Löfdahl¹,

Scharmer²

2012

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Context. Recently measured straylight point spread functions (PSFs) in Hinode/SOT make granulation contrast in observed data and synthetic magnetohydrodynamic (MHD) data consistent. Data from earthbound telescopes also need accurate correction for straylight and fixed optical aberrations. Aims. We aim to develop a method for measuring straylight in the post-focus imaging optics of the Swedish 1-m Solar Telescope (SST). Methods. We removed any influence from atmospheric turbulence and scattering by using an artificial target. We measured integrated straylight from three different sources in the same data: ghost images caused by reflections in the near-detector optics, PSFs corresponding to wavefront aberrations in the optics by using phase diversity, and extended scattering PSF wings of unknown origin by fitting to a number of different kernels. We performed the analysis separately in the red beam and the blue beam. Results. Wavefront aberrations, which possibly originate in the bimorph mirror of the adaptive optics, are responsible for a wavelength-dependent straylight of 20-30% of the intensity in the form of PSFs with 90% of the energy contained within a radius of 0. 6. There are ghost images that contribute at the most a few percent of straylight. The fraction of other sources of scattered light from the post-focus instrumentation of the SST is only ∼10 −3 of the recorded intensity. This contribution has wide wings with a FWHM ∼ 16 in the blue and ∼34 in the red. Conclusions. The present method seems to work well for separately estimating wavefront aberrations and the scattering kernel shape and fraction. Ghost images can be expected to remain at the same level for solar observations. The high-order wavefront aberrations possibly caused by the AO bimorph mirror dominate the measured straylight but are likely to change when imaging the Sun. We can therefore make no firm statements about the origin of straylight in SST data, but strongly suspect wavefront aberrations to be the dominant source.

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“…The contrasts in Table 1 are much lower than those in Fig. 9 because of various sources of stray light, see discussion by Scharmer et al (2010). The contrasts show the expected increase in contrast with S tilt compensation, more for large θ than for small.…”

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confidence: 70%

A tilted interference filter in a converging beam

Löfdahl¹,

Henriques²,

Kiselman³

2011

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Context. Narrow-band interference filters can be tuned toward shorter wavelengths by tilting them from the perpendicular to the optical axis. This can be used as a cheap alternative to real tunable filters, such as Fabry-Pérot interferometers and Lyot filters. At the Swedish 1-meter Solar Telescope, such a setup is used to scan through the blue wing of the Ca ii H line. Because the filter is mounted in a converging beam, the incident angle varies over the pupil, which causes a variation of the transmission over the pupil, different for each wavelength within the passband. This causes broadening of the filter transmission profile and degradation of the image quality. Aims. We want to characterize the properties of our filter, at normal incidence as well as at different tilt angles. Knowing the broadened profile is important for the interpretation of the solar images. Compensating the images for the degrading effects will improve the resolution and remove one source of image contrast degradation. In particular, we need to solve the latter problem for images that are also compensated for blurring caused by atmospheric turbulence. Methods. We simulate the process of image formation through a tilted interference filter in order to understand the effects. We test the hypothesis that they are separable from the effects of wavefront aberrations for the purpose of image deconvolution. We measure the filter transmission profile and the degrading PSF from calibration data. Results. We find that the filter transmission profile differs significantly from the specifications. We demonstrate how to compensate for the image-degrading effects. Because the filter tilt effects indeed appear to be separable from wavefront aberrations in a useful way, this can be done in a final deconvolution, after standard image restoration with Multi-Frame Blind Deconvolution/Phase Diversity based methods. We illustrate the technique with real data.

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High-order aberration compensation with multi-frame blind deconvolution and phase diversity image restoration techniques

Cited by 37 publications

References 23 publications

Joint optimization of phase diversity and adaptive optics: demonstration of potential

Joint optimization of phase diversity and adaptive optics: demonstration of potential

Sources of straylight in the post-focus imaging instrumentation of the Swedish 1-m Solar Telescope

A tilted interference filter in a converging beam

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