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| Titel |
Quantifying and containing the curse of high resolution coronal imaging |
| VerfasserIn |
V. Delouille, P. Chainais, J.-F. Hochedez |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 26, no. 10 ; Nr. 26, no. 10 (2008-10-15), S.3169-3184 |
| Datensatznummer |
250016263
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| Publikation (Nr.) |
 copernicus.org/angeo-26-3169-2008.pdf |
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| Zusammenfassung |
Future missions such as Solar Orbiter (SO), InterHelioprobe, or Solar Probe
aim at approaching the Sun closer than ever before, with on board some high
resolution imagers (HRI) having a subsecond cadence and a pixel area of about
(80 km)2 at the Sun during perihelion. In order to guarantee their
scientific success, it is necessary to evaluate if the photon counts
available at these resolution and cadence will provide a sufficient
signal-to-noise ratio (SNR).
For example, if the inhomogeneities in the Quiet Sun emission prevail at
higher resolution, one may hope to locally have more photon counts than in
the case of a uniform source. It is relevant to quantify how inhomogeneous
the quiet corona will be for a pixel pitch that is about 20 times smaller
than in the case of SoHO/EIT, and 5 times smaller than TRACE.
We perform a first step in this direction by analyzing and characterizing the
spatial intermittency of Quiet Sun images thanks to a multifractal analysis.
We identify the parameters that specify the scale-invariance behavior. This
identification allows next to select a family of multifractal processes,
namely the Compound Poisson Cascades, that can synthesize artificial images
having some of the scale-invariance properties observed on the recorded
images.
The prevalence of self-similarity in Quiet Sun coronal images makes it
relevant to study the ratio between the SNR present at SoHO/EIT images and in
coarsened images. SoHO/EIT images thus play the role of "high resolution"
images, whereas the "low-resolution" coarsened images are rebinned so as to
simulate a smaller angular resolution and/or a larger distance to the Sun.
For a fixed difference in angular resolution and in Spacecraft-Sun distance,
we determine the proportion of pixels having a SNR preserved at high
resolution given a particular increase in effective area. If scale-invariance
continues to prevail at smaller scales, the conclusion reached with SoHO/EIT
images can be transposed to the situation where the resolution is increased
from SoHO/EIT to SO/HRI resolution at perihelion. |
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