Enhancing coronal structures with radial local multi-scale filter

Qiang, Zhenping; Bai, Xianyong; Ji, Kaifan; Liu, Hui; Shang, Zhaohui

doi:10.1016/j.newast.2020.101383

Cited by 3 publications

(1 citation statement)

References 24 publications

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“…An improvement on this algorithm was developed known as the Fourier normalising-radial-graded filter (FNRGF), based on finite Fourier series that takes a local average and standard deviation, and this was used to enhance the fine coronal structures in the low contrast regions (Druckmüllerová, Morgan, and Habbal, 2011). Recently, a new method called the radial local multi-scale filter (RLMF) was developed using multi-scale filtering on radial vectors extracted from coronagraph images followed by intensity normalisation leading to enhancement of coronal structures (Qiang et al, 2020). For the detection of inbound waves in the solar corona, DeForest, Howard, and McComas (2014) normalised the radial intensity of the COR-2 images by subtracting the average intensity across a column and time from each row, followed by dividing each row by its standard deviation across column and time.…”

Section: Introductionmentioning

confidence: 99%

A Simple Radial Gradient Filter for Batch-Processing of Coronagraph Images

Patel,

Majumdar,

Pant

et al. 2022

Preprint

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Images of the extended solar corona, as observed by white-light coronagraphs as observed by different white-light coronagraphs include the K-and F-corona and suffer from a radial variation in intensity. These images require separation of the two coronal components with some additional image-processing to reduce the intensity gradient and analyse the structures and processes occurring at different heights in the solar corona within the full field of view. Over the past few decades, coronagraphs have been producing enormous amounts of data, which will be continued with the launch of new telescopes. To process these bulk coronagraph images with steep radial-intensity gradients, we have developed an algorithm: Simple Radial Gradient Filter (SiRGraF). This algorithm is based on subtracting a minimum background (F-corona) created using long duration images and then dividing the resultant by a uniform intensity gradient image to enhance the K-corona. We demonstrate the utility of this algorithm to bring out the short time-scale transient structures of the corona. SiRGraF could be used to reveal and analyse such structures. It is not suitable for quantitative estimations based on intensity. We have successfully tested the algorithm on images of the Large Angle Spectroscopic COronagraph (LASCO)-C2 onboard the Solar and Heliospheric Observatory (SOHO), and COR-2A onboard the Solar TErrestrial D. Banerjee

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Section: Introductionmentioning

confidence: 99%

A Simple Radial Gradient Filter for Batch-Processing of Coronagraph Images

Patel,

Majumdar,

Pant

et al. 2022

Preprint

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show abstract

A Simple Radial Gradient Filter for Batch-Processing of Coronagraph Images

et al. 2022

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Derived Electron Densities from Linear Polarization Observations of the Visible-Light Corona During the 14 December 2020 Total Solar Eclipse

Edwards,

Bunting,

Ramsey

et al. 2023

Sol Phys

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A new instrument was designed to take visible-light (VL) polarized brightness ($\mathit{pB}$ pB ) observations of the solar corona during the 14 December 2020 total solar eclipse. The instrument, called the Coronal Imaging Polarizer (CIP), consisted of a 16 MP CMOS detector, a linear polarizer housed within a piezoelectric rotation mount, and an f-5.6, 200 mm DSLR lens. Observations were successfully obtained, despite poor weather conditions, for five different exposure times (0.001 s, 0.01 s, 0.1 s, 1 s, and 3 s) at six different orientation angles of the linear polarizer ($0^{\circ}$ 0 ∘ , $30^{\circ}$ 30 ∘ , $60^{\circ}$ 60 ∘ , $90^{\circ}$ 90 ∘ , $120^{\circ}$ 120 ∘ , and $150^{\circ}$ 150 ∘ ). The images were manually aligned using the drift of background stars in the sky and images of different exposure times were combined using a simple signal-to-noise ratio cut. The polarization and brightness of the local sky were also estimated and the observations were subsequently corrected. The $\mathit{pB}$ pB of the K-corona was determined using least-squares fitting and radiometric calibration was done relative to the Mauna Loa Solar Observatory (MLSO) K-Cor $\mathit{pB}$ pB observations from the day of the eclipse. The $\mathit{pB}$ pB data was then inverted to acquire the coronal electron density, $n_{e}$ n e , for an equatorial streamer and a polar coronal hole, which agreed very well with previous studies. The effect of changing the number of polarizer angles used to compute the $\mathit{pB}$ pB is also discussed and it is found that the results vary by up to $\approx 13\%$ ≈ 13 % when using all six polarizer angles versus only a select of three angles.

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Enhancing coronal structures with radial local multi-scale filter

Cited by 3 publications

References 24 publications

A Simple Radial Gradient Filter for Batch-Processing of Coronagraph Images

A Simple Radial Gradient Filter for Batch-Processing of Coronagraph Images

A Simple Radial Gradient Filter for Batch-Processing of Coronagraph Images

Derived Electron Densities from Linear Polarization Observations of the Visible-Light Corona During the 14 December 2020 Total Solar Eclipse

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