The first and preliminary results of the photometry of Large Yield Radiometer (LYRA) and Sun Watc... more The first and preliminary results of the photometry of Large Yield Radiometer (LYRA) and Sun Watcher using Active Pixel system detector and Image Processing (SWAP) onboard PROBA2 are presented in this paper. To study the day-to-day variations of LYRA irradiance, we have compared the LYRA irradiance values (observed Sun as a star) measured in Aluminum filter channel (171 Å–500 Å) with spatially resolved full-disk integrated intensity values measured with SWAP (174 Å) and Ca II K 1 Å index values (ground-based observations from NSO/Sac Peak) for the period from 01 April 2010 to 15 Mar 2011. We found that there is a good correlation between these parameters. This indicates that the spatial resolution of SWAP complements the high temporal resolution of LYRA. Hence SWAP can be considered as an additional radiometric channel. Also the K emission index is the integrated intensity (or flux) over a 1 Å band centered on the K line and is proportional to the total emission from the chromospher...
Instrumentation for UV/EUV Astronomy and Solar Missions, 2000
The ability to derive physical parameters of the Sun from observations by the Solar and Heliosphe... more The ability to derive physical parameters of the Sun from observations by the Solar and Heliospheric Observatory (SOHO) Extreme Ultraviolet Imaging Telescope (EIT) greatly increases the scientific return of the mission. The absolute and time variable calibration of EIT therefore is of extreme interest. The NRL EIT Calibration Sounding Rocket (CalRoc) program was initiated to provide well calibrated, contemporaneous observations
Multilayer and Grazing Incidence X-Ray/EUV Optics for Astronomy and Projection Lithography, 1993
ABSTRACT Very efficient mirrors designed for rejection of the 30.4 nm HeII line while transmittin... more ABSTRACT Very efficient mirrors designed for rejection of the 30.4 nm HeII line while transmitting the 28.4 nm FeXV line are needed for observations of the solar corona. Light traps, based on multilayered structures, using moderately absorbing diffractor layers of SiO2 and aluminum as spacer material, have been successfully fabricated providing dramatically high rejection ratios. However, accurate tuning at the desired wavelength has proven to be extremely difficult to achieve in combination with high nominal reflectivity. Very slight deviations of thicknesses or optical constants can easily destroy the desired antiresonance effect. Classical Mo/Si structures, although somewhat less selective, can also be specially designed for this application and they prove more amenable to proper adjustment.
The European Space Agency’s PROBA2 mission, due for launch in February 2007, will carry onboard t... more The European Space Agency’s PROBA2 mission, due for launch in February 2007, will carry onboard two instruments which will enhance greatly ESA's space weather capabilities. The Sun Watcher with APS Detector and Processing - SWAP - is a full disk imager to monitor the Sun at high temporal cadence and spatial resolution in a single extreme UV passband, while the Large Yield Radiometer - LYRA - will measure irradiance in four carefully selected UV passbands: all five were selected for their relevance to aeronomy, space weather and solar physics. SWAP can be viewed as ESA's replacement for the ageing EIT [1] instrument onboard the joint ESA/NASA SOHO [2] mission, while LYRA's higher-energy channels will augment the soft X-ray time series observed by NOAA's GOES [3] satellites. Together they will monitor solar output, eruptive events and atmospheric response in real-time.
The study of the variability of the solar corona and the monitoring of its traditional regions (C... more The study of the variability of the solar corona and the monitoring of its traditional regions (Coronal Holes, Quiet Sun and Active Regions) are of great importance in astrophysics as well as in view of the Space Weather and Space Climate applications. Here we propose a multi-channel unsupervised spatially-constrained fuzzy clustering algorithm that automatically segments EUV solar images into Coronal Holes, Quiet Sun and Active Regions. Fuzzy logic allows to manage the various noises present in the images and the im-precision in the definition of the above regions. The process is fast and automatic. It is applied to SoHO-EIT images taken from January 1997 till May 2005, i.e. along almost a full solar cycle. Results in terms of areas and intensity estimations are consistent with previous knowledge. The method reveal the rotational and other mid-term periodicities in the extracted time series across solar cycle 23. Further, such an approach paves the way to bridg-ing observations bet...
BOLD (Blind to the Optical Light Detectors) is an international initiative dedicated to the devel... more BOLD (Blind to the Optical Light Detectors) is an international initiative dedicated to the development of novel imaging detectors for UV solar observations. It relies on the properties of wide-bandgap semiconductor materials (in particular diamond and Al-Ganitrides). This investigation is proposed in view of the Solar Orbiter UV instruments, for which the expected benefits of the new sensors, visible blindness and radiation hardness, will be highly valuable. Despite various advances in the technology of imaging detectors over the last few decades, the present UV imagers based on silicon CCDs or microchannel plates exhibit limitations which are inherent to their actual material and technology. Yet the utmost spatial resolution, fast temporal cadence, sensitivity, and photometric accuracy will all be decisive for forthcoming solar space missions. The advent of imagers made of large wide-bandgap semiconductors would surmount many present weaknesses. This would open up new scientific p...
Nous nous intéressons à la modélisation d'images du Soleil acquises dans l'extrême ultrav... more Nous nous intéressons à la modélisation d'images du Soleil acquises dans l'extrême ultraviolet par le télescope Extreme ultraviolet Imaging Telescope (EIT) de la mission Solar and Heliospheric Observatory (SoHO, ESA/NASA). Nous nous intéressons aux régions les moins structurées en apparence, le "Soleil calme". Nous présentons d'abord une analyse multifractale des images de Soleil calme. Au-delà de l'analyse des données, il s'agit d'identifier un modèle stochastique des images étudiées à partir duquel il sera possible de simuler des images similaires mais de résolution arbitrairement fine en exploitant la propriété d'invariance d'échelle. Nous comparons deux familles de modèles (cascades infiniment divisibles et draps stables fractionnaires) permettant de simuler numériquement des images statistiquement similaires aux images de Soleil calme. Cette modélisation permettra la préparation des prochaines observations à haute résolution et d'ét...
The first and preliminary results of the photometry of Large Yield Radiometer (LYRA) and Sun Watc... more The first and preliminary results of the photometry of Large Yield Radiometer (LYRA) and Sun Watcher using Active Pixel system detector and Image Processing (SWAP) onboard PROBA2 are presented in this paper. To study the day-to-day variations of LYRA irradiance, we have compared the LYRA irradiance values (observed Sun as a star) measured in Aluminum filter channel (171 Å–500 Å) with spatially resolved full-disk integrated intensity values measured with SWAP (174 Å) and Ca II K 1 Å index values (ground-based observations from NSO/Sac Peak) for the period from 01 April 2010 to 15 Mar 2011. We found that there is a good correlation between these parameters. This indicates that the spatial resolution of SWAP complements the high temporal resolution of LYRA. Hence SWAP can be considered as an additional radiometric channel. Also the K emission index is the integrated intensity (or flux) over a 1 Å band centered on the K line and is proportional to the total emission from the chromospher...
Instrumentation for UV/EUV Astronomy and Solar Missions, 2000
The ability to derive physical parameters of the Sun from observations by the Solar and Heliosphe... more The ability to derive physical parameters of the Sun from observations by the Solar and Heliospheric Observatory (SOHO) Extreme Ultraviolet Imaging Telescope (EIT) greatly increases the scientific return of the mission. The absolute and time variable calibration of EIT therefore is of extreme interest. The NRL EIT Calibration Sounding Rocket (CalRoc) program was initiated to provide well calibrated, contemporaneous observations
Multilayer and Grazing Incidence X-Ray/EUV Optics for Astronomy and Projection Lithography, 1993
ABSTRACT Very efficient mirrors designed for rejection of the 30.4 nm HeII line while transmittin... more ABSTRACT Very efficient mirrors designed for rejection of the 30.4 nm HeII line while transmitting the 28.4 nm FeXV line are needed for observations of the solar corona. Light traps, based on multilayered structures, using moderately absorbing diffractor layers of SiO2 and aluminum as spacer material, have been successfully fabricated providing dramatically high rejection ratios. However, accurate tuning at the desired wavelength has proven to be extremely difficult to achieve in combination with high nominal reflectivity. Very slight deviations of thicknesses or optical constants can easily destroy the desired antiresonance effect. Classical Mo/Si structures, although somewhat less selective, can also be specially designed for this application and they prove more amenable to proper adjustment.
The European Space Agency’s PROBA2 mission, due for launch in February 2007, will carry onboard t... more The European Space Agency’s PROBA2 mission, due for launch in February 2007, will carry onboard two instruments which will enhance greatly ESA's space weather capabilities. The Sun Watcher with APS Detector and Processing - SWAP - is a full disk imager to monitor the Sun at high temporal cadence and spatial resolution in a single extreme UV passband, while the Large Yield Radiometer - LYRA - will measure irradiance in four carefully selected UV passbands: all five were selected for their relevance to aeronomy, space weather and solar physics. SWAP can be viewed as ESA's replacement for the ageing EIT [1] instrument onboard the joint ESA/NASA SOHO [2] mission, while LYRA's higher-energy channels will augment the soft X-ray time series observed by NOAA's GOES [3] satellites. Together they will monitor solar output, eruptive events and atmospheric response in real-time.
The study of the variability of the solar corona and the monitoring of its traditional regions (C... more The study of the variability of the solar corona and the monitoring of its traditional regions (Coronal Holes, Quiet Sun and Active Regions) are of great importance in astrophysics as well as in view of the Space Weather and Space Climate applications. Here we propose a multi-channel unsupervised spatially-constrained fuzzy clustering algorithm that automatically segments EUV solar images into Coronal Holes, Quiet Sun and Active Regions. Fuzzy logic allows to manage the various noises present in the images and the im-precision in the definition of the above regions. The process is fast and automatic. It is applied to SoHO-EIT images taken from January 1997 till May 2005, i.e. along almost a full solar cycle. Results in terms of areas and intensity estimations are consistent with previous knowledge. The method reveal the rotational and other mid-term periodicities in the extracted time series across solar cycle 23. Further, such an approach paves the way to bridg-ing observations bet...
BOLD (Blind to the Optical Light Detectors) is an international initiative dedicated to the devel... more BOLD (Blind to the Optical Light Detectors) is an international initiative dedicated to the development of novel imaging detectors for UV solar observations. It relies on the properties of wide-bandgap semiconductor materials (in particular diamond and Al-Ganitrides). This investigation is proposed in view of the Solar Orbiter UV instruments, for which the expected benefits of the new sensors, visible blindness and radiation hardness, will be highly valuable. Despite various advances in the technology of imaging detectors over the last few decades, the present UV imagers based on silicon CCDs or microchannel plates exhibit limitations which are inherent to their actual material and technology. Yet the utmost spatial resolution, fast temporal cadence, sensitivity, and photometric accuracy will all be decisive for forthcoming solar space missions. The advent of imagers made of large wide-bandgap semiconductors would surmount many present weaknesses. This would open up new scientific p...
Nous nous intéressons à la modélisation d'images du Soleil acquises dans l'extrême ultrav... more Nous nous intéressons à la modélisation d'images du Soleil acquises dans l'extrême ultraviolet par le télescope Extreme ultraviolet Imaging Telescope (EIT) de la mission Solar and Heliospheric Observatory (SoHO, ESA/NASA). Nous nous intéressons aux régions les moins structurées en apparence, le "Soleil calme". Nous présentons d'abord une analyse multifractale des images de Soleil calme. Au-delà de l'analyse des données, il s'agit d'identifier un modèle stochastique des images étudiées à partir duquel il sera possible de simuler des images similaires mais de résolution arbitrairement fine en exploitant la propriété d'invariance d'échelle. Nous comparons deux familles de modèles (cascades infiniment divisibles et draps stables fractionnaires) permettant de simuler numériquement des images statistiquement similaires aux images de Soleil calme. Cette modélisation permettra la préparation des prochaines observations à haute résolution et d'ét...
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Papers by Jean-Francois E Hochedez