共查询到20条相似文献，搜索用时 328 毫秒
1.
Fernandez Borda Roberto A. Mininni Pablo D. Mandrini Cristina H. Gómez Daniel O. Bauer Otto H. Rovira Marta G. 《Solar physics》2002,206(2):347-357
We present a new method for automatic detection of flare events from images in the optical range. The method uses neural networks for pattern recognition and is conceived to be applied to full-disk Himages. Images are analyzed in real time, which allows for the design of automatic patrol processes able to detect and record flare events with the best time resolution available without human assistance. We use a neural network consisting of two layers, a hidden layer of nonlinear neurodes and an output layer of one linear neurode. The network was trained using a back-propagation algorithm and a set of full-disk solar images obtained by HASTA (HSolar Telescope for Argentina), which is located at the Estación de Altura Ulrico Cesco of OAFA (Observatorio Astronómico Félix Aguilar), El Leoncito, San Juan, Argentina. This method is appropriate for the detection of solar flares in the complete optical classification, being portable to any Hinstrument and providing unique criteria for flare detection independent of the observer. 相似文献
2.
Sylvain G. Korzennik 《Solar physics》2017,292(9):138
The Helioseismic and Magnetic Imager project recently started processing the continuum-intensity images following global helioseismology procedures similar to those used to process the velocity images. The spatial decomposition of these images has produced time series of spherical harmonic coefficients for degrees up to \(\ell=300\), using a different apodization than the one used for velocity observations. The first 360 days of observations were processed and are made available. I present initial results from fitting these time series using my fitting method and compare the derived mode characteristics to those estimated using coeval velocity observations. 相似文献
3.
This paper presents the techniques developed for the automated detection of filaments on Meudon H spectroheliograms, and, by extension, on any full-disk H Sun observations. Some cleaning processes are first applied to the images to correct them from defects characteristic of the instrument. Indeed, these defects may lead to spurious detections. From the cleaned images, filament areas are then segmented using a region growing method which efficiently returns the full extent of these dark areas. The filaments are finally described by means of their pruned skeleton. This representation allows one to compare the automatically segmented filaments with those manually recorded for Meudon Synoptic Maps. The very good agreement observed on a representative set of images confirms that this method can effectively be used in the frame of the EGSO (European Grid of Solar Observations) project in order to produce a reliable catalog dedicated to solar features. 相似文献
4.
A detailed study of the evolution and cooling process of post-flare loops is presented for a large X9.2 solar flare of 2 November 1992 by using H images obtained with Domeless Solar Telescope at Hida Observatory and soft X-ray images of Yohkoh Soft X-ray Telescope (SXT). The detailed analysis with a new method allows us to determine more precise values of the cooling times from 107 K to 104 K plasma in the post-flare loops than in previous works. The subtraction of sequential images shows that soft X-ray dimming regions are well correlated to the H brightening loop structure. The cooling times between 107 K and 104 K are defined as the time difference between the start of soft X-ray intensity decrease and the end of H intensity increase at a selected point, where the causal relation between H brightening and soft X-ray dimming loops is confirmed. The obtained cooling times change with time; about 10 min at the initial stage and about 40 min at the later stage. The combined conductive and radiative cooling times are also calculated by using the temperature and density obtained from SXT data. Calculated cooling times are close to observed cooling times at the beginning of the flare and longer in the later stage. 相似文献
5.
Erik R. Urbach 《Planetary and Space Science》2009,57(7):880-74
Impact craters are among the most studied geomorphic planetary features because they yield information about the past geological processes and provide a tool for measuring relative ages of observed geologic formations. Surveying impact craters is an important task which traditionally has been achieved by means of visual inspection of images. The shear number of smaller craters present in high resolution images makes visual counting of such craters impractical. In this paper we present a method that brings together a novel, efficient crater identification algorithm with a data processing pipeline; together they enable a fully automatic detection of sub-km craters in large panchromatic images. The technical details of the method are described and its performance is evaluated using a large, 12.5 m/pixel image centered on the Nanedi Valles on Mars. The detection percentage of the method is ∼70%. The system detects over 35,000 craters in this image; average crater density is , but localized spots of much higher crater density are present. The method is designed to produce “million craters” global catalogs of sub-km craters on Mars and other planets wherever high resolution images are available. Such catalogs could be utilized for deriving high spatial resolution and high temporal precision stratigraphy on regional or even planetary scale. 相似文献
6.
Klaus Jockers 《Experimental Astronomy》1997,7(4):305-318
The new Two-Channel Focal Reducer of the Max-Planck-Institut für Aeronomie is described. The instrument is primarily designed for astronomical imaging of solar system objects, where, because of changes in time scales of about 10-30 min not only the photon flux but also the total number of photons is limited. Colour dividers allow to split the light of the object into a "blue" and a "red" channel. Both channels are observed simultaneously with two separate CCD cameras. Besides wide-band imaging with filters derived from the Gunn photometric system, the instrument allows simultaneous determination of polarization and colour in a small field and imaging with interference filters and with a tunable Fabry-Perot interferometer. One Fabry-Perot system serves both channels. Proper selection of the interference order allows simultaneous observing in narrow bands of about 3 width for a large number of wavelength pairs. There is also a coronagraph mode with Lyot stops in both channels which allows observations of the torus associated with Jupiter's satellite Io. Long-slit two-channel spectroscopy will be possible as soon as the necessary grating prisms will have been acquired. 相似文献
7.
It is already known (Froeschlé, Lega and Gonczi, 1997) that the Fast Lyapunov Indicator (FLI), that is the computation on a relatively short time of the largest Lyapunov indicator, allows to discriminate between ordered and weak chaotic motion. We have found that, under certain conditions, the FLI also discriminates between resonant and non-resonant orbits, not only for two-dimensional symplectic mappings but also for higher dimensional ones. Using this indicator, we present an example of the Arnold web detection for four and six-dimensional symplectic maps. We show that this method allows to detect the global transition of the system from an exponentially stable Nekhoroshevs like regime to the diffusive Chirikovs one. 相似文献
8.
G. Herpe M. Chevreton J. C. Robin P. Prat B. Servan F. Gex 《Experimental Astronomy》1991,2(3):163-177
This paper deals with the study and the fabrication of an intensified C.C.D. camera for guiding telescopes or for searching fields containing faint stars. It describes the sensor of the camera (by connecting the Thomson C.C.D. and the RTC image intensifier) and its three working modes. The first is the direct exploitation of the video signal sent to the TV monitor, in conformity with the C.C.I.R. standard (the N.T.S.C. standard is also available). However, the study of stability and sensitivity of the intensifier lead us to create a second working mode necessary for the correct detection of faint objects (by an averaging filter improving the signal to noise ratio). The last mode is the integration by the C.C.D. itself: it allows a maximum of three-seconds integration time (therefore the detection of fainter objects), with the help of a thermoelectric cooling system. Moreover, the tests made on the 1.52 meter telescope of the O.A.N. (Calar-Alto, Spain) have been successful and confirm the capabilities of this camera to replace the intensified TV tube cameras, like the super-isocon camera. 相似文献
9.
This paper presents the development and testing of a new iterative reconstruction algorithm for astronomy. We propose a maximuma posteriori method of image reconstruction in the Bayesian statistical framework for the Poisson noise case. The method uses the entropy with an adjustable sharpness parameter to define the prior probability and the likelihood with data increment parameters to define the conditional probability. The method allows us to obtain reconstructions with neither the problem of the grey reconstructions associated with the pure Bayesian reconstructions nor the problem of image deterioration, typical of the maximum likelihood method. Our iterative algorithm is fast, stable, maintains positivity, and converges to feasible images.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain. 相似文献
10.
We present a new technique for the rapid, automatic identification of solar features on full-disk photometric images. The technique permits the detection of features whose contrasts are only slightly above the noise level. Contrast and contiguity criteria are used to identify pixels belonging to an individual feature. The criteria used are simple and objective, and do not require one to guess at the contrast distribution of the features. Comparison of Caii K images with magnetograms shows excellent agreement between the identified features and observed magnetic features. In addition, we can now reliably identify faculae on continuum images. Since this technique can be rapidly applied to a large set of images, it allows us to compile a database of the physical and photometric properties of individual solar features. 相似文献
11.
The degradation of astronomic images by optical inhomogeneities in the earth's atmosphere is generally called seeing. It represents the angular diameter of the stellar images as seen through a turbulent medium. Several techniques can be used to determine this parameter. The knowledge of the optical strength of atmospheric turbulence, namely, the integrated structure coefficient of the atmospheric refractive index Cn
2 allows to predict the atmospheric optical quality in terms of seeing. We tried in this study to assess an astronomical seeing using a model forecast using meteorological data collected in three stations in Latin America from 1958 to 1991. The efficiency of the model is tested by comparison with simultaneous seeing measurements, at Chiliean astronomical sites. 相似文献
12.
We present and compare energetic neutral atom (ENA) images that are calculated from plasma parameters given by three different simulation models of the interaction between the solar wind and Mars. The images are calculated by combining a model for the ion flow with a model of the neutral atmosphere using the cross-sections for the charge exchange collisions. The three ion models are: an empirical model that is based on Phobos 2 measurements; a three-dimensional hybrid simulation; and a three-dimensional MHD simulation. For the empirical and MHD models the images are obtained by integration of the ENA emission along lines of sight to a virtual ENA instrument. In the case of the hybrid model images are obtained by summing the contributions from all ions, whose positions, velocities, and weights are saved in files at regular intervals.Differences between the models can be detected in the images, for example the hybrid model produces ENA emissions from a larger region than the MHD model does. An asymmetry in the oxygen ion density develops in the hybrid model and can be seen in the oxygen ENA images. The images are influenced by finite gyro radius effects, which are included in the hybrid model but not in the other two. The total production rates of hydrogen ENAs are , , and for the empirical, hybrid and MHD models respectively.This study shows the importance of considering both the type of simulation model used and the proper inclusion of relevant physical phenomena and boundary conditions, when modelling the interaction between planets and the solar wind. Although the different models agree fairly well in terms of macroscopic plasma parameters they produce ENA images that differ substantially. 相似文献
13.
This paper presents an efficient and automatic method for detecting filament disappearances. This method was applied to the Big Bear Solar Observatory's (BBSO) full-disk H images. The initial step is to detect the filaments in the solar image, then determine if they are growing, stable or disappearing. If a disappearing filament is found, the solar community can be automatically alerted in near real time. This system is proven to be accurate and fast. In addition, three statistical studies of the appearance and disappearance of all filaments in 1999 are presented. 相似文献
14.
T. Kosugi K. Makishima T. Murakami T. Sakao T. Dotani M. Inda K. Kai S. Masuda H. Nakajima Y. Ogawara M. Sawa K. Shibasaki 《Solar physics》1991,136(1):17-36
The Hard X-ray Telescope (HXT) is a Fourier-synthesis imager; a set of spatially-modulated photon count data are taken from 64 independent subcollimators and are Fourier-transformed into an image by using procedures such as the maximum entropy method (MEM) or CLEAN. The HXT takes images of solar flares simultaneously in four energy bands, nominally 15 (or 19)–24, 24–35, 35–57, and 57–100 keV, with an ultimate angular resolution as fine as 5 arc sec and a time resolution 0.5 s. Each subcollimator has a field of view wider than the solar disk. The total effective area of the collimator/detector system reaches 70 cm2, about one order of magnitude larger than that of the HINOTORI hard X-ray imager. Thanks to these improvements, HXT will for the first time enable us to take images of flares at photon energies above 30 keV. These higher-energy images will be compared with lower-energy ones, giving clues to the understanding of nonthermal processes in solar flares, i.e., the acceleration and confinement of energetic electrons. It is of particular importance to specify the acceleration site with regard to the magnetic field figuration in a flaring region, which will be achieved by collaborative observations between HXT and the Soft X-ray Telescope on board the same mission.After the launch the name of SOLAR-A has been changed to YOHKOH. 相似文献
15.
Supergranule and Mesogranule Evolution 总被引：2，自引：0，他引：2
The MDI instrument on the SOHO satellite obtained a nearly continuous 45.5-hr run in high-resolution mode on 17–18 January 1997, collecting continuum, Dopplergram, and magnetogram images once per minute. This is one of the longest data sets yet obtained in this mode and shows significant evolution of the supergranulation pattern. After allowing for solar rotation within the fixed field of view, an area spanning 17° in latitude and 11° in longitude was extracted that covers the same area of the solar surface for the entire run. From the de-rotated continuum images, we computed flow maps of photospheric motions using local correlation techniques (LCT). Horizontal divergence maps constructed from the flow maps show local maxima of the size of mesogranules (5–10). We interpret these as mesogranules although the LCT flow map resolution (4.8 FWHM) may not completely resolve smaller mesogranules. Movies made from the divergence maps clearly show the outward convection (advection) of these mesogranules within each supergranule, and narrow boundaries of negative divergence outlining the supergranules. Several new supergranules are observed forming. These appear as areas of strong divergence that pop up between pre-existing supergranules and grow, pushing their neighbors apart. Others seem to perish between growing neighbors. We also computed the vertical component of vorticity from the flow maps. Movies of this vorticity do not show any obvious patterns. 相似文献
16.
We have developed an IDL procedure to analyze spatial and time evolution of loops observed in the outer solar atmosphere by EUV instruments. The use of this procedure, based on the assumption that loop portions have cylindrical symmetry, allows automatic processing of sequences of images. Our work mainly aims to describe spatial and temporal variations of brightness along the loop length and to determine the following physical parameters: emission measure EM, electron density N
e, pressure P, thermal energy E
th, radiative cooling time rad, and conductive cooling time cond. In this paper we describe an application of this procedure to a sequence of TRACE images at 171 Å, in order to study loop interaction during a flare that occurred in AR 8421 on 29 December 1998 at 09:41 UT. 相似文献
17.
G. Artzner 《Solar physics》1990,128(1):281-286
Observed temporal variations of shape and size of the solar disk as viewed from Earth may act as constraints for theories of the interior of the Sun. In addition to existing programs of solar diameter measurements we investigate a ground-based photographic method.The solar limb profile is recorded on a photoresist-coated substrate over a 20 radial length simultaneously all along the circonference as a three-dimensional 21 mm diameter, 0.0015mm thick permanent object available for inspection by interferometric methods. The exposure time is long enough for filtering much of the atmospheric turbulence, whereas the slope of the observed solar limb should help to locate a standard solar limb. The first results of February 1989 at large zenith distance and low altitude are a set of differential measurements of the position of a solar limb around a circle with, after taking into account the 3.7 atmospheric differential refraction, a 0.34r.m.s. dispersion of the residuals for a fit to a circular solar disk.We estimate that this method of accuracy comparable to other ground-based methods, with potentially more than 600 independent simultaneous measurements along the circonference, could help to discriminate between terrestrial and solar causes for variations of shape and size of the solar disk.We note that operation outside the Earth's atmosphere would provide access not only to undisturbed images but also to UV wavelengths, i.e., to a better definition of the solar limb. 相似文献
18.
S. Grzędzielski 《Solar physics》1971,21(1):225-236
The propagation of non-radial, small amplitude perturbations superposed on a zero-order, stationary, non-magnetic, polytropic, rotating stellar wind is studied in the limit of the local theory, i.e. for k r 1, k being the module of the wave vector and r the characteristic scale of the zero-order flow. The resulting dispersion equation is of the 3rd order in (complex) frequency and the possible modes correspond to two acoustic type waves, and to a gravity-shear wave with strongly anisotropic propagation properties, due to coupling between the internal gravity waves and shear motion. The gravity-shear mode allows velocity differences in the medium to exist with no corresponding density fluctuations and hence with no shock wave formation. It is suggested that this mode corresponds to some of the fast-slow velocity streams observed in the interplanetary medium and may provide means for wave energy being transported outwards with the zero-order flow, with little dissipation in the inner region of the solar wind. 相似文献
19.
目前,国际上诸多天文项目均遵循虚拟天文台（Virtual Observatory,VO）标准协议开发各天文数据检索发布系统,对外公开发布数据,并对数据资源进行VO注册,从而使用户通过虚拟天文台门户网站即可访问获取不同天文项目的数据集.硬X射线调制望远镜（HXMT）卫星项目也将虚拟天文台技术引入HXMT卫星数据检索发布系统的设计与实现过程中,既满足HXMT卫星数据发布需求,又将HXMT卫星数据融入虚拟天文台环境,实现国际天文数据的共享共用.系统提出了符合虚拟天文台规范的体系架构,并选取SCS锥形检索、VOTable数据格式等虚拟天文台标准协议加以实现,采用MVC模式、SSH框架以及各种J2EE技术进行软件研发,提供检索访问、浏览下载和可视化功能.实践和应用结果表明,系统在解决天文数据资源互操作、共享发布、检索访问及异构应用集成方面均具有可操作性,对我国空间天文卫星数据检索发布系统的研制具有参考意义. 相似文献
20.
The Montreal Infrared Camera (MONICA) consists of a LN2 cryostat enclosing a NICMOS3 array, re-imaging optics and a filter wheel mechanism containing broad-band and circular variable filters. A polarimetry mode with a warm half wave plate and a cold polarizer/filter combination is also supported. At the CFHT 0.5 (FWHM) images are routinely obtained with limiting magnitudes of 22.8 at J and 21.7 at K (S/N=3 in 1hr).The Spectrometre Infrarouge de Montréal (SIMON) is a versatile grating spectrometer with spectral resolutions ranging from 300 to 5000. Presently under construction, this spectrometer will initially contain a 512×512 HgCdTe array. Use of reflective optics will allow a future upgrade to a similar format InSb array, extending the wavelength coverage to 5m. SIMON will also have an imaging mode to facilitate the centering of objects within interchangeable slits. 相似文献