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21.
The Preflight Photometric Calibration of the Extreme-Ultraviolet Imaging Telescope EIT 总被引:1,自引:0,他引:1
Dere K.P. Moses J.D. Delaboudinière J.-P. Brunaud J. Carabetian C. Hochedez J.-F. Song X.Y. Catura R.C. Clette F. Defise J.-M. 《Solar physics》2000,195(1):13-44
This paper presents the preflight photometric calibration of the Extreme-ultraviolet Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory (SOHO). The EIT consists of a Ritchey–Chrétien telescope with multilayer coatings applied to four quadrants of the primary and secondary mirrors, several filters and a backside-thinned CCD detector. The quadrants of the EIT optics were used to observe the Sun in 4 wavelength bands that peak near 171, 195, 284, and 304 Å. Before the launch of SOHO, the EIT mirror reflectivities, the filter transmissivities and the CCD quantum efficiency were measured and these values are described here. The instrumental throughput in terms of an effective area is presented for each of the various mirror quadrant and filter wheel combinations. The response to a coronal plasma as a function of temperature is also determined and the expected count rates are compared to the count rates observed in a coronal hole, the quiet Sun and an active region. 相似文献
22.
Solar telescopes will never be able to resolve the smallest events at their intrinsic physical scales. Pixel signals recorded
by SOHO/(CDS, EIT, SUMER), STEREO/SECCHI/ EUVI, TRACE, SDO/AIA, and even by the future Solar Orbiter EUI/HRI contain an inherent “spatial noise” since they represent an average of the solar signal present at subpixel scales.
In this paper, we aim at investigating this spatial noise, and hopefully at extracting information from subpixel scales. Two
paths are explored. We first combine a regularity analysis of a sequence of EIT images with an estimation of the relationship
between mean and standard deviation, and we formulate a scenario for the evolution of the local signal-to-noise ratio (SNR)
as the pixel size becomes smaller. Second, we use an elementary forward modeling to examine the relationship between nanoflare
characteristics (such as area, duration, and intensity) and the global mean and standard deviation. We use theoretical distributions
of nanoflare parameters as input to the forward model. A fine-grid image is generated as a random superposition of those pseudo-nanoflares.
Coarser resolution images (simulating images acquired by a telescope) are obtained by rebinning and are used to compute the
mean and standard deviation to be analyzed. Our results show that the local SNR decays more slowly in regions exhibiting irregularities
than in smooth regions. 相似文献
23.
Eit Observations of the Extreme Ultraviolet Sun 总被引:3,自引:0,他引:3
D. Moses F. Clette J.-P. Delaboudinière G. E. Artzner M. Bougnet J. Brunaud C. Carabetian A. H. Gabriel J. F. Hochedez F. Millier X. Y. Song B. Au K. P. Dere R. A. Howard R. Kreplin D. J. Michels J. M. Defise C. Jamar P. Rochus J. P. Chauvineau J. P. Marioge R. C. Catura J. R. Lemen L. Shing R. A. Stern J. B. Gurman W. M. Neupert J. Newmark B. Thompson A. Maucherat F. Portier-Fozzani D. Berghmans P. Cugnon E. L. Van Dessel J. R. Gabryl 《Solar physics》1997,175(2):571-599
The Extreme Ultraviolet Imaging Telescope (EIT) on board the SOHO spacecraft has been operational since 2 January 1996. EIT
observes the Sun over a 45 x 45 arc min field of view in four emission line groups: Feix, x, Fexii, Fexv, and Heii. A post-launch
determination of the instrument flatfield, the instrument scattering function, and the instrument aging were necessary for
the reduction and analysis of the data. The observed structures and their evolution in each of the four EUV bandpasses are
characteristic of the peak emission temperature of the line(s) chosen for that bandpass. Reports on the initial results of
a variety of analysis projects demonstrate the range of investigations now underway: EIT provides new observations of the
corona in the temperature range of 1 to 2 MK. Temperature studies of the large-scale coronal features extend previous coronagraph
work with low-noise temperature maps. Temperatures of radial, extended, plume-like structures in both the polar coronal hole
and in a low latitude decaying active region were found to be cooler than the surrounding material. Active region loops were
investigated in detail and found to be isothermal for the low loops but hottest at the loop tops for the large loops.
Variability of solar EUV structures, as observed in the EIT time sequences, is pervasive and leads to a re-evaluation of the
meaning of the term ‘quiet Sun’. Intensity fluctuations in a high cadence sequence of coronal and chromospheric images correspond
to a Kolmogorov turbulence spectrum. This can be interpreted in terms of a mixed stochastic or periodic driving of the transition
region and the base of the corona. No signature of the photospheric and chromospheric waves is found in spatially averaged
power spectra, indicating that these waves do not propagate to the upper atmosphere or are channeled through narrow local
magnetic structures covering a small fraction of the solar surface. Polar coronal hole observing campaigns have identified
an outflow process with the discovery of transient Fexii jets. Coronal mass ejection observing campaigns have identified the
beginning of a CME in an Fexii sequence with a near simultaneous filament eruption (seen in absorption), formation of a coronal
void and the initiation of a bright outward-moving shell as well as the coronal manifestation of a ‘Moreton wave’.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004902913117 相似文献