Images Of Corona Research Articles

Exploring the Sun

NASA has selected five science investigations for its Solar Probe Plus, a spacecraft slated to launch by 2018 and explore the Sun's corona as it extends into space. The selected science proposals include an investigation to count electrons, protons, and helium ions in the solar wind and measure their properties; a wide‐field imager telescope to make three‐dimensional images of the Sun's corona; and a fields experiment to make direct measurements of electric and magnetic fields, radio emissions, and shock waves moving through the Sun's atmospheric plasma. Other selected proposals include an integrated science investigation of the Sun to monitor electrons, protons, and ions accelerated to high energies in the Sun's atmosphere and an investigation of heliospheric origins.“The experiments selected for Solar Probe Plus are specifically designed to solve two key questions of solar physics—why is the Sun's outer atmosphere so much hotter than the Sun's visible surface and what propels the solar wind that affects Earth and our solar system? We've been struggling with these questions for decades and this mission should finally provide those answers,” said Richard Fisher, director of NASA's Heliophysics Division.

Design of a Novel Corona Plasma Reactor for Decomposition of VOCs

The configuration of discharge electrode is closely related to the uniformity and the strength of corona plasma, which has big effect on the efficiency of plasma in destructing pollutants, treating materials and so on. A novel sheet electrode was devised to enhance the input energy and the uniformity of plasma’s distribution, and its production performance of plasma was compared with other discharge electrodes including wire, needle and multi-needles. Corona images and I-V characteristic curves of discharge electrodes indicate that ultra-thin sheet electrode could produce more uniform and stronger corona plasma zone than other electrodes in this paper, which is advantageous for decomposing pollutants, treating material surface and so on. Primary VOCs decomposition experiments were conducted, and the results indicated that the highest energy yield of VOCs decomposition reached 1.8 g (benzene) • (kWh)-1 /3.5 g (toluene) • (kWh)-1.

Coronal structure at the total solar eclipse 2009-07-22

Solar corona is the outermost part of the solar atmosphere, from which strong UV and X-ray radiation are emitted. Coronal high temperature plasma outflows and forms the solar wind. Coronal activities influence seriously the space environment between the Sun and the Earth. Coronal structures are closely related with the solar activities. The total solar eclipse at the July 22, 2009, is the best magnificent sight in the 21st century and the best opportunity to observe the corona on ground. However, due to bad weather, most observations in the total eclipse areas were baffled. Fortu-nately, some images of high quality were taken in a few places with good weather. In this work, a series of images are selected and digital processing is made with the computer. Studying them together with the images of outer corona by SOHO satellite/LASCO C2 at that day, some coronal structures are revealed and radial brightness profiles of the corona in directions of pole and equator of the Sun are measured. The solar cycle 24 began in 2009 and a few sunspots ap-peared. At this eclipse, coronal structures show more extents in equatorial regions than in polar regions, with differ-ences between east and west and between south and north of the solar disk. Coronal streamers on east of the disk, par-ticularly the largest one in north of the equator are very obvious. Polar rays are more in south polar region than in north polar region. The radial brightness profiles of the corona in directions of pole and equator are rather similar to those at the total eclipse in 2008 and those of the Van de Hulst model in solar minimum. Some features are also shown in the isophote map of the corona.

Automated Detection of Coronal Loops Using a Wavelet Transform Modulus Maxima Method

We propose and test a wavelet transform modulus maxima method for the automated detection and extraction of coronal loops in extreme ultraviolet images of the solar corona. This method decomposes an image into a number of size scales and tracks enhanced power along each ridge corresponding to a coronal loop at each scale. We compare the results across scales and suggest the optimum set of parameters to maximize completeness, while minimizing detection of noise. For a test coronal image, we compare the global statistics (e.g. number of loops at each length) to previous automated coronal-loop detection algorithms.

The TESIS Solar imaging spectroscopy experiment on board the CORONAS-Photon satellite

The CORONAS-Photon spacecraft was successfully launched in January 2009. Its scientific payload included the TESIS complex of telescopes and spectrometers, designed to obtain high spectral, temporal and spatial resolution solar corona images in soft X-ray to far UV spectral range.

New method for separating K- and F-corona brightness based on LASCO/SOHO data

A relatively simple (in technology) method for separating K- and F-corona brightness based on LASCO data, which makes it possible to obtain the latitude distribution of this brightness in the field of view of the LASCO C2 and C3 coronographs at any instant for which white light corona images are available, has been proposed. It has been estimated that the error in determining K-corona brightness varies from 20 to 50% at distances of R ≤ 6R⊙ (R⊙ is the solar radius). At distances of R > (5–6)R⊙, the accuracy of the K-corona brightness determination decreases and is of an estimative character. Nevertheless, it is often possible to trace the brightest coronal rays and the K-corona regions of decreased brightness (including such regions in coronal holes) to distances of R ≈ 15R⊙ and 25–30R⊙ for some events. This makes it possible to estimate and compare electron densities in different coronal structures to large distances. Examples of method testing are presented. For the first time, we have managed to obtain continuous (in latitude) distributions of K- and F-corona brightness, using this method.

Patterns and dynamics of land-cover changes since the 1960s over three experimental areas in Mali

This paper addresses a critical need to provide a better quantitative understanding of how the Sudano-Sahelian environments actually been changing under the combined impacts of climate variability and the increasing pressure of human activity. Using Corona, Landsat and SPOT satellite images of three areas (90–250km2) along the climatic gradient of a large catchment in Mali, significant land-cover changes since the 1960s were identified through visual interpretation of images following a common classification scheme. The pattern and trajectory of changes differed markedly between the three areas studied. Overall, the 40-year trends indicate: (i) in the Sahelian area, a steady increase in croplands and erosional surfaces with sparse vegetation and a corresponding drastic reduction in woody covers; (ii) in the Sudano-Sahelian area, a large increase in croplands and a moderate reduction in woody covers; (iii) in the Sudanian area, agricultural extension, deforestation, but also reforestation and land rehabilitation, due to alternating periods of exploitation and recolonization by natural vegetation. These patterns and dynamics can be partially explained by the differences in demographic pressure between the three areas. They also highlight differences in response to anthropogenic and climate forcings depending on the areas’ respective climatic and environmental endowments. This study is a first step towards an in-depth analysis of the various forces and processes driving these changes and the formulation of prospective environmental scenarios for the catchment in line with hydrological studies.

Metrical use of declassified satellite imagery for an area of archaeological interest in Turkey

Abstract The adoption of satellite imagery in archaeology is well recognized today, and is rapidly increasing with the greater availability of high resolution sensors, in the past limited solely to military applications. The metrical use of declassified satellite images from the intelligence CORONA project, the first US operational space photo reconnaissance project operating in the period 1960–1972, has been verified within the framework of a multidisciplinary research project carried out by the University of Bologna, in collaboration with Istanbul University and Gaziantep archaeological museum, at the archaeological site of Tilmen Hoyuk (south-eastern Turkey) and its surrounding landscape. These images, characterized by a panoramic geometry, indeed represent an important historical resource for photointerpretation in archaeology, but their metrical use is difficult, owing to the severe distortions affecting the acquisition together with the problems of finding technical data related to the missions. In order to produce metric products of sufficient quality for mapping purposes, a high resolution scanned copy of a CORONA image of the relevant area was processed using commercial digital photogrammetric workstations operating with different approaches, whose aim was to evaluate the potential and specific problems connected to these kinds of data. A full orientation and digital triangulation of these images is possible if all the technical data on the sensor and the acquisition are well-known, and in any case the existence of well-distributed and reliable ground control points in the study area is crucial. The results obtained are interesting as they allow for integration, on a common cartographic reference base, with current aerial and satellite imagery (medium to very high geometric resolution) to perform automatic or visual change analysis procedures.

A satellite based assessment of the impact of urban expansion around a lagoon

This paper examines the coastal regional trends in urbanization processes using remotely sensed images around the Kucukcekmece Lagoon as a case study, located in the western part of Istanbul, Turkey. Throughout the examination process, the coastline changes are determined for a long-term period. To achieve this goal, post-classification comparison method is applied to the CORONA and LANDSAT TM satellite images of 1963, 1987 and 2005. In order to identify the land use changes, common landscape structures in the region were distinguished as water, green and open land, urban and industrial areas. Due to the mix up of land-cover types between urban and industrial areas, the classified images are integrated with geographic information system data obtained from visual interpretation of the enhanced images and auxiliary data sets. The results of the change analyses in coastal region showed that important alterations are taking place in the area due to the unplanned urban and industrial expansions that has irreversibly changed the physical features of the Kucukcekmece Lagoon. According to image classification results, the urban land use area increased from 2 % oftotal area in 1963 to 38 % in 1987 and 46 % in 2005, most of which converted from agricultural and greenlands. At the same time, the ecological impact of the loss of specific land covers is highlighted based on the results of the land use changes and the previous scientific applications. Furthermore, some recommendations are given to planners, decision makers and politicians to maintain the sustainable coastal ecosystem management.

FIRST DETERMINATION OF THE TRUE MASS OF CORONAL MASS EJECTIONS: A NOVEL APPROACH TO USING THE TWOSTEREOVIEWPOINTS

The twin Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) COR2 coronagraphs of the Solar Terrestrial Relations Observatory (STEREO) provide images of the solar corona from two view points in the solar system. Since their launch in late 2006, the STEREO Ahead (A) and Behind (B) spacecrafts have been slowly separating from Earth at a rate of 22.5 degrees per year. By the end of 2007, the two spacecraft were separated by more than 40 degrees from each other. At this time, we began to see large-scale differences in the morphology and total intensity between coronal mass ejections (CMEs) observed with SECCHI-COR2 on STEREO-A and B. Due to the effects of the Thomson scattering geometry, the intensity of an observed CME is dependent on the angle it makes with the observed plane of the sky. From the intensity images, we can calculate the integrated line of sight electron density and mass. We demonstrate that is is possible to simultaneously derive the direction and true total mass of the CME if we make the simple assumption that the same mass should be observed in COR2-A and B.

The plasma filling factor of coronal bright points

Aims. In a previous paper, the volumetric plasma filling factor of coronal bright points was determined from spectra obtained with the Extreme ultraviolet Imaging Spectrometer (EIS). The analysis of these data showed that the median plasma filling factor was 0.015. One interpretation of this result was that the small filling factor was consistent with a single coronal loop with a width of 1–2 �� , somewhat below the apparent width. In this paper, higher spatial resolution observations with the Transition Region and Corona Explorer (TRACE) are used to test this interpretation. Methods. Rastered spectra of regions of the quiet Sun were recorded by the EIS during operations with the Hinode satellite. Many of these regions were simultaneously observed with TRACE. Calibrated intensities of Fe xii lines were obtained and images of the quiet corona were constructed from the EIS measurements. Emission measures were determined from the EIS spectra and geometrical widths of coronal bright points were obtained from the TRACE images. Electron densities were determined from density-sensitive line ratios measured with EIS. A comparison of the emission measure and bright point widths with the electron densities yielded the plasma filling factor. Results. The median electron density of coronal bright points is 3 × 10 9 cm −3 at a temperature of 1.6 × 10 6 K. The volumetric plasma filling factor of coronal bright points was found to vary from 3 × 10 −3 to 0.3 with a median value of 0.04. Conclusions. The current set of EIS and TRACE coronal bright-point observations indicate the median value of their plasma filling factor is 0.04. This can be interpreted as evidence of a considerable subresolution structure in coronal bright points or as the result of a single completely filled plasma loop with widths on the order of 0.2–1.5 �� that has not been spatially resolved in these measurements.

The SOHO/LASCO CME Catalog

Coronal mass ejections (CMEs) are routinely identified in the images of the solar corona obtained by the Solar and Heliospheric Observatory (SOHO) mission’s Large Angle and Spectrometric Coronagraph (LASCO) since 1996. The identified CMEs are measured and their basic attributes are cataloged in a data base known as the SOHO/LASCO CME Catalog. The Catalog also contains digital data, movies, and plots for each CME, so detailed scientific investigations can be performed on CMEs and the related phenomena such as flares, radio bursts, solar energetic particle events, and geomagnetic storms. This paper provides a brief description of the Catalog and summarizes the statistical properties of CMEs obtained using the Catalog. Data products relevant to space weather research and some CME issues that can be addressed using the Catalog are discussed. The URL of the Catalog is: http://cdaw.gsfc.nasa.gov/CME_list.

The plasma filling factor of coronal bright points

Aims. We determine the volumetric plasma filling factor of coronal bright points. Methods. Rastered spectra of the regions of the quiet Sun were recorded by the Extreme ultraviolet Imaging Spectrometer (EIS) during operations with the Hinode satellite. Calibrated intensities of Fe xii lines were obtained and images of the quiet corona were constructed. From the imaged spectra, the emission measures and geometrical widths of coronal bright points were obtained. Electron densities were determined from density-sensitive line ratios. A comparison of the emission measure and bright point widths with the electron densities yielded the plasma-filling factor. Results. The median electron density of coronal bright points is 4 × 10 9 cm −3 at a temperature of 1.6 × 10 6 K. The volumetric plasmafilling factor of coronal bright points was found to vary from 4 × 10 −5 to 0.2 with a median value of 0.015. Conclusions. The current set of EIS coronal bright point observations indicates that the median value of their plasma filling-factor is 0.015. This can be interpreted as evidence of a considerable subresolution structure in coronal bright points or as the result of a single completely-filled plasma loop with a width on the order of 1–2 arcsec that has not been spatially resolved in these measurements.

A Novel Algorithm for Coastline Fitting through a Case Study over the Bosphorus

Decrease of habitat, coastal erosion, and shoreline changes are recent issues for coastal management. In this study, an algorithm which extracts coastlines efficiently and automatically by processing low- or medium-resolution satellite images has been developed. The junction of sea and land is a common result yielded by the automatic coastline extraction method.In this study, CORONA (1963), IRS-1D (2000), and LANDSAT-7 (2001) satellite images for the same region in Istanbul, Turkey were used. A novel algorithm was developed for automatic coastline extraction. The algorithm is encoded in a C environment. The results of automatic coastline extraction obtained from different images were compared to the results derived from manual digitizing. Random control points which are seen on every image were used.The average differences of selected points were calculated. Obtained results from selected points were rendered as 3 pixels on the CORONA and IRS-1D images and as 2 pixels on the LANDSAT-7 image. These show that the differences are similar, although different images were used. On the other hand, the results are acceptable compared to manual digitizing.

Change Detection with GRASS GIS – Comparison of images taken by different sensors

Images of American military reconnaissance satellites of the Sixties (CORONA) in combination with modern sensors (SPOT, QuickBird) were used for detection of changes in land use. The pilot area was located about 40 km northwest of Yemen’s capital Sana’a and covered approximately 100 km2 . To produce comparable layers from images of distinctly different sources, the moving window technique was applied, using the diversity parameter. The resulting difference layers reveal plausible and interpretable change patterns, particularly in areas where urban sprawl occurs.<br />The comparison of CORONA images with images taken by modern sensors proved to be an additional tool to visualize and quantify major changes in land use. The results should serve as additional basic data eg. in regional planning.<br />The computation sequence was executed in GRASS GIS.

Extraction of digital surface models from CORONA satellite stereo images

Satellite images can be utilised for observing surficial changes, especially efficient in the monitoring of larger areas. The comparative analysis of high resolution images from earlier periods with recent data can provide insight in the scale of changes in topography, and with meteorological, hydrological and other historic records, can lead to better understanding and more reliable modelling of the predominant processes causing mass movement. More accurate morphometric and visual analysis of the topographic changes is possible using digital surface model (DSM), which can be obtained from satellite stereo images. In this paper, the authors evaluated methods of creation digital surface models obtained from satellite images from the CORONA program in monitoring surficial mass movement processes in the Fruška Gora mountain area, in the southern part of the Vojvodina province in Serbia. This area is of particular interest because of its favourable geographic location, rich geo- and cultural heritage and increasing demand for exploitation, which results in greater impact of natural hazards. The CORONA images were chosen because of good availability of high resolution coverage for the whole area from the period of past four decades.

A Streamer Ejection with Reconnection Close to the Sun

We previously described coronal events that expand gradually outward over an interval of 1-2 days and then suddenly tear apart in the coronagraph's 2-6 R☉ field of view to form an outgoing flux rope and an inward system of collapsing loops. Now, we combine LASCO white-light images of the outer corona with spectrally resolved EIT images of the inner corona to describe a similar event for which the separation occurs closer to the Sun. The evolution of this 2006 July 1-2 event had four phases: (1) an expansion phase in which magnetic loops rise slowly upward and increase the amount of open flux in the adjacent polar coronal hole and in the low-latitude hole of opposite polarity; (2) a stretching phase in which the legs of the rising loops pinch together to form a current sheet; (3) a transition phase in which field line reconnection produces an outgoing flux rope and a hot cusp of new loops; and (4) an end phase in which the reconnected loops become visible at lower temperatures, and the outgoing flux rope plows through the slow material ahead of it to form a traveling bow wave. During this time, the photospheric field was relatively weak and unchanging, as if the eruption had a nonmagnetic origin. We suppose that coronal heating gradually overpowers magnetic tension and causes the streamer to separate into a system of collapsing loops and a flux rope that is carried outward in the solar wind.

Fine Thermal Structure of a Coronal Active Region

The determination of the fine thermal structure of the solar corona is fundamental to constraining the coronal heating mechanisms. The Hinode X-ray Telescope collected images of the solar corona in different passbands, thus providing temperature diagnostics through energy ratios. By combining different filters to optimize the signal-to-noise ratio, we observed a coronal active region in five filters, revealing a highly thermally structured corona: very fine structures in the core of the region and on a larger scale further away. We observed continuous thermal distribution along the coronal loops, as well as entangled structures, and variations of thermal structuring along the line of sight.

Intricacies of the fine structure of the eclipse corona

The inner white-light corona (up to 2 solar radii) can only be observed during total solar eclipses. New mathematical methods of the corona image processing and digital photo cameras or CCD cameras allow us to detect very faint structures (of a few arcseconds) in this part of the corona, even from images taken with relatively small telescopes (1–2 meters in the focal length). In the present paper we will discuss such structures as observed during the last few solar eclipses, mainly those of 2001 and 2006. Obtained results show that the white-light corona is highly structured not only in the sense of a variety of different types of its classical “objects”, e.g., polar plumes, helmet streamers, threadlike streamers, etc, but also within these objects themselves. Voids, loops, radial and non-radial threads, and other yet-undefined dark structures (“empty space”?) are well visible especially inside helmet streamers. This strongly indicates that the classical picture of the corona characterized by a hydrostatic distribution of density and temperature is no longer a sufficient assumption. It is magnetic forces that play a dominant role in shaping and structuring this part the corona. Given a remarkable similarity between the EUV corona as observed by SOHO and the white-light corona observed by us during the above-mentioned eclipses up to two solar radii. We suggest that the “missing” observations of the white-light corona should be replaced by those of the EUV one. Moreover, the last eclipse’s observations also indicate that the knots of some prominences extend well into the white-light corona. So, the next total eclipses of the Sun, of 1 August 2008 and 22 July 2009, offer an excellent opportunity for preparing joint observations for space-borne and ground-based eclipse teams.

Coexistence of Self-Organized Criticality and Intermittent Turbulence in the Solar Corona

An extended data set of extreme ultraviolet images of the solar corona provided by the SOHO spacecraft is analyzed using statistical methods common to studies of self-organized criticality (SOC) and intermittent turbulence (IT). The data exhibit simultaneous hallmarks of both regimes: namely, power-law avalanche statistics as well as multiscaling of structure functions for spatial activity. This implies that both SOC and IT may be manifestations of a single complex dynamical process entangling avalanches of magnetic energy dissipation with turbulent particle flows.