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...
EUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy VIII, 1997
The Extreme UV Imaging Telescope (EIT) on-board SOHO is performing a global survey of the extreme... more The Extreme UV Imaging Telescope (EIT) on-board SOHO is performing a global survey of the extreme ultraviolet (EUV) solar corona. Operating since January 96, EIT has been producing tens thousands of images of the Sun in four narrow channels (171, 195, 284 and 304 Å). Orbiting around the L1 Lagrangian point and oriented permanently towards the Sun, the EIT mission is a unique opportunity to study an instrument continuously exposed to solar EUV radiations. The backside thinned CCD detector is showing significant changes in its overall signal and in local "burn in" regions. Periodic bakeouts allowed to restore a good efficiency. However, a specific observation program has been set up to diagnose the origin of the signal decay. In this framework, photon transfer analyses are performed on solar EUV images, providing good indications on the local charge collection efficiency status. Calibration lamp images are also used to evaluate the signal recovery in the visible range. The signal degradation seems to be the result of two competing effects: periodic deposition of a contamination layer, and charge mobility change in the CCD Si layer as a function of the accumulated EUV dose. In this paper, the CCD quantum properties evolution is discussed, as well as the contamination issue. Preliminary diagnostics on the CCD aging under EUV radiations are exposed.
Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray, 2010
The Extreme Ultraviolet Imager (EUI) onboard Solar Orbiter consists of a suite of two high-resolu... more The Extreme Ultraviolet Imager (EUI) onboard Solar Orbiter consists of a suite of two high-resolution imagers (HRI) and one dual-band full Sun imager (FSI) that will provide EUV and Lyman-α images of the solar atmospheric layers above the photosphere. The EUI instrument is based on a set of challenging new technologies allowing to reach the scientific objectives and to cope with the hard space environment of the Solar Orbiter mission. The mechanical concept of the EUI instrument is based on a common structure supporting the HRI and FSI channels, and a separated electronic box. A heat rejection baffle system is used to reduce the Sun heat load and provide a first protection level against the solar disk straylight. The spectral bands are selected by thin filters and multilayer mirror coatings. The detectors are 10µm pitch back illuminated CMOS Active Pixel Sensors (APS), best suited for the EUI science requirements and radiation hardness. This paper presents the EUI instrument concept and its major subsystems. The current developments of the instrument technologies are also summarized.
Telescopes and Instrumentation for Solar Astrophysics, 2004
The Solar Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory will character... more The Solar Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory will characterize the dynamical evolution of the solar plasma from the chromosphere to the corona, and will follow the connection of plasma dynamics with magnetic activity throughout the solar atmosphere. The AIA consists of 7 high-resolution imaging telescopes in the following spectral bandpasses: 1215 Å /\D Å He II, 629 Å OV, 465 Å Ne VII, 195 Å Fe XII (includes Fe XXIV), 284 Å Fe XV, and 335 Å Fe XVI. The telescopes are grouped by instrumental approach: the MAGRITTE Filtergraphs (R. MAGRITTE, famous 20th Century Belgian Surrealistic Artist), five multilayer EUV channels and one VUV channel, with bandpasses ranging from 195 to 1216 Å, and the SPECTRE Spectroheliograph with one soft-EUV channel at OV 629 Å. They will be simultaneously operated with a 10-second imaging cadence. These two instruments, the electronic boxes and two redundant Guide Telescopes (GT) constitute the AIA suite. They will be mounted and coaligned on a dedicated common optical bench. The GTs will provide pointing jitter information to the whole SHARPP assembly. This paper presents the selected technologies, the different challenges, the trade-offs to be made in phase A, and the model philosophy. From a scientific viewpoint, the unique combination high temporal and spatial resolutions with the simultaneous multi-channel capability will allow MAGRITTE / SPECTRE to explore new domains in the dynamics of the solar atmosphere, in particular the fast small-scale phenomena. We show how the spectral channels of the different instruments were derived to fulfill the AIA scientific objectives, and we outline how this imager array will address key science issues, like the transition region and coronal waves or flare precursors, in coordination with other SDO experiments.
Telescopes and Instrumentation for Solar Astrophysics, 2004
3URFHVVLQJ is an instrument that has been selected to fly on the PROBA-II technology demonstratio... more 3URFHVVLQJ is an instrument that has been selected to fly on the PROBA-II technology demonstration platform, a program of the European Space Agency (ESA) to be launched in 2006. This paper presents the instrument concept and its scientific goals. SWAP uses an off-axis Ritchey Chretien telescope that will image the EUV solar corona at 19.5 nm on a specifically fabricated extreme ultraviolet (EUV) sensitivity enhanced CMOS APS detector. This type of detector has advantages that promise to be very profitable for solar EUV imaging. The SWAP design is built on a similar concept as the MAGRITTE instrument suite for the NASA Solar Dynamics Observatory (SDO)mission to be launched in 2007. The optics have been adapted to the detector size. The SWAP PROBA-2 program will be an opportunity to demonstrate and validate the optical concept of MAGRITTE, while it will also validate space remote sensing with APS detectors. On the science outcomes, SWAP will provide solar corona images in the Fe XII line on a baselined 1-min cadence. Observations with this specific wavelength allow detecting phenomena, such as solar flares or 'EIT-waves', associated with the early phase of coronal mass ejections. Image recognition software will be developed that automatically detects these phenomena and sends out space weather warnings. Different modules of this software will run both on the ground system as well as on the onboard computer of PROBA II. The SWAP data will complement the observations provided by SOHO-EIT, and STEREO-SECCHI. .H\ZRUGV Solar corona, EUV telescopes, PROBA ,1752'8&7,21 72 352%$ The PROBA-2 small satellite (> 120 kg), to be developed under an ESA General Support Technology Program (GSTP) contract by a consortium led by Verhaert Design & Development (Belgium) has two main mission objectives: (i) perform an in-flight demonstration of a series of new spacecraft technologies and (ii) support a scientific mission of a set of selected instruments. As a follow on of PROBA-1 successfully in orbit since October 2001, the performances and the autonomous functions previously demonstrated by PROBA-1 will also be met or exceeded. The technology demonstrations are in the field of avionics, spacecraft attitude control, power system and spacecraft propulsion. Two instruments are dedicated to the observation of the Sun, SWAP (imaging instrument) and LYRA (radiometer instrument), and two others are dedicated to plasma measurements. Possibly an Earth observation instrument will be included as well.
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
Solar Physics and Space Weather Instrumentation II, 2007
The SWAP telescope (Sun Watcher using Active Pixel System detector and Image Processing) is being... more The SWAP telescope (Sun Watcher using Active Pixel System detector and Image Processing) is being developed to be part of the PROBA2 payload, an ESA technological mission to be launched in early 2008. SWAP is directly derived from the concept of the EIT telescope that we developed in the '90s for the SOHO mission. Several major innovations have been introduced in the design of the instrument in order to be compliant with the requirements of the PROBA2 mini-satellite: compactness with a new off-axis optical design, radiation resistance with a new CMOS-APS detector, a very low power electronics, an athermal opto-mechanical system, optimized onboard compression schemes combined with prioritization of collected data, autonomy with automatic triggering of observation and off-pointing procedures in case of solar event occurrence, … All these new features result from the low resource requirements (power, mass, telemetry) of the mini-satellite, but also take advantage of the specificities of a modern technological platform, such as quick pointing agility, new powerful on-board processor, Packetwire interface and autonomous operations. These new enhancements will greatly improve the operations of SWAP as a space weather sentinel from a low Earth orbit while the downlink capabilities are limited. This paper summarizes the conceptual design, the development and the qualification of the instrument, the autonomous operations and the expected performances for science exploitation.
In this letter, we report on the fabrication of nearultraviolet photodetectors based on gallium n... more In this letter, we report on the fabrication of nearultraviolet photodetectors based on gallium nitride (GaN) layers grown on a Si(111) substrate. Optoelectronic characterization was performed using front-side and backside illumination, the latter possible by locally etching the Si substrate under the detectors using reactive ion etching. The dark current after removal of the Si substrate decreased by two orders of magnitude to around 20 fA at −1 V for a 300-μm-diameter Schottky photodiode. Responsivity at the cutoff wavelength (370 nm) was equal to 35 mA/W for the backside illumination. Detection at smaller wavelengths was not possible due to a nonoptimized layer stack. These first results do however illustrate the potential of backside-illuminated GaN-on-Si Schottky photodiodes in 2-D UV imagers.
Context. The study of solar irradiance variability is of great importance in heliophysics, the Ea... more Context. The study of solar irradiance variability is of great importance in heliophysics, the Earth's climate, and space weather applications. These studies require careful identifying, tracking and monitoring of active regions (ARs), coronal holes (CHs), and the quiet Sun (QS). Aims. We studied the variability of solar irradiance for a period of two years (January 2011-December 2012) using the Large Yield Radiometer (LYRA), the Sun Watcher using APS and image Processing (SWAP) on board PROBA2, and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). Methods. We used the spatial possibilistic clustering algorithm (SPoCA) to identify and segment coronal features from the EUV observations of AIA. The AIA segmentation maps were then applied on SWAP images, and parameters such as the intensity, fractional area, and contribution of ARs/CHs/QS features were computed and compared with the full-disk integrated intensity and LYRA irradiance measurements. Results. We report the results obtained from SDO/AIA and PROBA2/SWAP images taken from January 2011 to December 2012 and compare the resulting integrated full-disk intensity with PROBA2/LYRA irradiance. We determine the contributions of the segmented features to EUV and UV irradiance variations. The variations of the parameters resulting from the segmentation, namely the area, integrated intensity, and relative contribution to the solar irradiance, are compared with LYRA irradiance. We find that the active regions have a great impact on the irradiance fluctuations. In the EUV passbands considered in this study, the QS is the greatest contributor to the solar irradiance, with up to 63% of total intensity values. Active regions, on the other hand, contribute to about 10%, and off-limb structures to about 24%. We also find that the area of the features is highly variable suggesting that their area has to be taken into account in irradiance models, in addition to their intensity variations. Conclusions. We successfully show that the feature extraction allows us to use EUV telescopes to measure irradiance fluctuations and to quantify the contribution of each part to the EUV spectral solar irradiance observed with a calibrated radiometer. This study also shows that SPoCA is viable, and that the segmentation of images can be a useful tool. We also provide the measurement correlation between SWAP and AIA during this analysis.
Future missions such as Solar Orbiter (SO), Inter-Helioprobe, or Solar Probe aim at approaching t... more Future missions such as Solar Orbiter (SO), Inter-Helioprobe, 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 scaleinvariance continues to prevail at smaller scales, the conclu
Aims. LYRA, the Large Yield Radiometer, is a vacuum ultraviolet (VUV) solar radiometer, planned t... more Aims. LYRA, the Large Yield Radiometer, is a vacuum ultraviolet (VUV) solar radiometer, planned to be launched in November 2009 on the European Space Agency PROBA2, the Project for On-Board Autonomy spacecraft. Methods. The instrument was radiometrically calibrated in the radiometry laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the Berlin Electron Storage ring for SYnchroton radiation (BESSY II). The calibration was done using monochromatized synchrotron radiation at PTB's VUV and soft X-ray radiometry beamlines using reference detectors calibrated with the help of an electrical substitution radiometer as the primary detector standard. Results. A total relative uncertainty of the radiometric calibration of the LYRA instrument between 1% and 11% was achieved. LYRA will provide irradiance data of the Sun in four UV passbands and with high temporal resolution down to 10 ms. The present state of the LYRA pre-flight calibration is presented as well as the expected instrument performance.
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...
EUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy VIII, 1997
The Extreme UV Imaging Telescope (EIT) on-board SOHO is performing a global survey of the extreme... more The Extreme UV Imaging Telescope (EIT) on-board SOHO is performing a global survey of the extreme ultraviolet (EUV) solar corona. Operating since January 96, EIT has been producing tens thousands of images of the Sun in four narrow channels (171, 195, 284 and 304 Å). Orbiting around the L1 Lagrangian point and oriented permanently towards the Sun, the EIT mission is a unique opportunity to study an instrument continuously exposed to solar EUV radiations. The backside thinned CCD detector is showing significant changes in its overall signal and in local "burn in" regions. Periodic bakeouts allowed to restore a good efficiency. However, a specific observation program has been set up to diagnose the origin of the signal decay. In this framework, photon transfer analyses are performed on solar EUV images, providing good indications on the local charge collection efficiency status. Calibration lamp images are also used to evaluate the signal recovery in the visible range. The signal degradation seems to be the result of two competing effects: periodic deposition of a contamination layer, and charge mobility change in the CCD Si layer as a function of the accumulated EUV dose. In this paper, the CCD quantum properties evolution is discussed, as well as the contamination issue. Preliminary diagnostics on the CCD aging under EUV radiations are exposed.
Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray, 2010
The Extreme Ultraviolet Imager (EUI) onboard Solar Orbiter consists of a suite of two high-resolu... more The Extreme Ultraviolet Imager (EUI) onboard Solar Orbiter consists of a suite of two high-resolution imagers (HRI) and one dual-band full Sun imager (FSI) that will provide EUV and Lyman-α images of the solar atmospheric layers above the photosphere. The EUI instrument is based on a set of challenging new technologies allowing to reach the scientific objectives and to cope with the hard space environment of the Solar Orbiter mission. The mechanical concept of the EUI instrument is based on a common structure supporting the HRI and FSI channels, and a separated electronic box. A heat rejection baffle system is used to reduce the Sun heat load and provide a first protection level against the solar disk straylight. The spectral bands are selected by thin filters and multilayer mirror coatings. The detectors are 10µm pitch back illuminated CMOS Active Pixel Sensors (APS), best suited for the EUI science requirements and radiation hardness. This paper presents the EUI instrument concept and its major subsystems. The current developments of the instrument technologies are also summarized.
Telescopes and Instrumentation for Solar Astrophysics, 2004
The Solar Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory will character... more The Solar Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory will characterize the dynamical evolution of the solar plasma from the chromosphere to the corona, and will follow the connection of plasma dynamics with magnetic activity throughout the solar atmosphere. The AIA consists of 7 high-resolution imaging telescopes in the following spectral bandpasses: 1215 Å /\D Å He II, 629 Å OV, 465 Å Ne VII, 195 Å Fe XII (includes Fe XXIV), 284 Å Fe XV, and 335 Å Fe XVI. The telescopes are grouped by instrumental approach: the MAGRITTE Filtergraphs (R. MAGRITTE, famous 20th Century Belgian Surrealistic Artist), five multilayer EUV channels and one VUV channel, with bandpasses ranging from 195 to 1216 Å, and the SPECTRE Spectroheliograph with one soft-EUV channel at OV 629 Å. They will be simultaneously operated with a 10-second imaging cadence. These two instruments, the electronic boxes and two redundant Guide Telescopes (GT) constitute the AIA suite. They will be mounted and coaligned on a dedicated common optical bench. The GTs will provide pointing jitter information to the whole SHARPP assembly. This paper presents the selected technologies, the different challenges, the trade-offs to be made in phase A, and the model philosophy. From a scientific viewpoint, the unique combination high temporal and spatial resolutions with the simultaneous multi-channel capability will allow MAGRITTE / SPECTRE to explore new domains in the dynamics of the solar atmosphere, in particular the fast small-scale phenomena. We show how the spectral channels of the different instruments were derived to fulfill the AIA scientific objectives, and we outline how this imager array will address key science issues, like the transition region and coronal waves or flare precursors, in coordination with other SDO experiments.
Telescopes and Instrumentation for Solar Astrophysics, 2004
3URFHVVLQJ is an instrument that has been selected to fly on the PROBA-II technology demonstratio... more 3URFHVVLQJ is an instrument that has been selected to fly on the PROBA-II technology demonstration platform, a program of the European Space Agency (ESA) to be launched in 2006. This paper presents the instrument concept and its scientific goals. SWAP uses an off-axis Ritchey Chretien telescope that will image the EUV solar corona at 19.5 nm on a specifically fabricated extreme ultraviolet (EUV) sensitivity enhanced CMOS APS detector. This type of detector has advantages that promise to be very profitable for solar EUV imaging. The SWAP design is built on a similar concept as the MAGRITTE instrument suite for the NASA Solar Dynamics Observatory (SDO)mission to be launched in 2007. The optics have been adapted to the detector size. The SWAP PROBA-2 program will be an opportunity to demonstrate and validate the optical concept of MAGRITTE, while it will also validate space remote sensing with APS detectors. On the science outcomes, SWAP will provide solar corona images in the Fe XII line on a baselined 1-min cadence. Observations with this specific wavelength allow detecting phenomena, such as solar flares or 'EIT-waves', associated with the early phase of coronal mass ejections. Image recognition software will be developed that automatically detects these phenomena and sends out space weather warnings. Different modules of this software will run both on the ground system as well as on the onboard computer of PROBA II. The SWAP data will complement the observations provided by SOHO-EIT, and STEREO-SECCHI. .H\ZRUGV Solar corona, EUV telescopes, PROBA ,1752'8&7,21 72 352%$ The PROBA-2 small satellite (> 120 kg), to be developed under an ESA General Support Technology Program (GSTP) contract by a consortium led by Verhaert Design & Development (Belgium) has two main mission objectives: (i) perform an in-flight demonstration of a series of new spacecraft technologies and (ii) support a scientific mission of a set of selected instruments. As a follow on of PROBA-1 successfully in orbit since October 2001, the performances and the autonomous functions previously demonstrated by PROBA-1 will also be met or exceeded. The technology demonstrations are in the field of avionics, spacecraft attitude control, power system and spacecraft propulsion. Two instruments are dedicated to the observation of the Sun, SWAP (imaging instrument) and LYRA (radiometer instrument), and two others are dedicated to plasma measurements. Possibly an Earth observation instrument will be included as well.
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
Solar Physics and Space Weather Instrumentation II, 2007
The SWAP telescope (Sun Watcher using Active Pixel System detector and Image Processing) is being... more The SWAP telescope (Sun Watcher using Active Pixel System detector and Image Processing) is being developed to be part of the PROBA2 payload, an ESA technological mission to be launched in early 2008. SWAP is directly derived from the concept of the EIT telescope that we developed in the '90s for the SOHO mission. Several major innovations have been introduced in the design of the instrument in order to be compliant with the requirements of the PROBA2 mini-satellite: compactness with a new off-axis optical design, radiation resistance with a new CMOS-APS detector, a very low power electronics, an athermal opto-mechanical system, optimized onboard compression schemes combined with prioritization of collected data, autonomy with automatic triggering of observation and off-pointing procedures in case of solar event occurrence, … All these new features result from the low resource requirements (power, mass, telemetry) of the mini-satellite, but also take advantage of the specificities of a modern technological platform, such as quick pointing agility, new powerful on-board processor, Packetwire interface and autonomous operations. These new enhancements will greatly improve the operations of SWAP as a space weather sentinel from a low Earth orbit while the downlink capabilities are limited. This paper summarizes the conceptual design, the development and the qualification of the instrument, the autonomous operations and the expected performances for science exploitation.
In this letter, we report on the fabrication of nearultraviolet photodetectors based on gallium n... more In this letter, we report on the fabrication of nearultraviolet photodetectors based on gallium nitride (GaN) layers grown on a Si(111) substrate. Optoelectronic characterization was performed using front-side and backside illumination, the latter possible by locally etching the Si substrate under the detectors using reactive ion etching. The dark current after removal of the Si substrate decreased by two orders of magnitude to around 20 fA at −1 V for a 300-μm-diameter Schottky photodiode. Responsivity at the cutoff wavelength (370 nm) was equal to 35 mA/W for the backside illumination. Detection at smaller wavelengths was not possible due to a nonoptimized layer stack. These first results do however illustrate the potential of backside-illuminated GaN-on-Si Schottky photodiodes in 2-D UV imagers.
Context. The study of solar irradiance variability is of great importance in heliophysics, the Ea... more Context. The study of solar irradiance variability is of great importance in heliophysics, the Earth's climate, and space weather applications. These studies require careful identifying, tracking and monitoring of active regions (ARs), coronal holes (CHs), and the quiet Sun (QS). Aims. We studied the variability of solar irradiance for a period of two years (January 2011-December 2012) using the Large Yield Radiometer (LYRA), the Sun Watcher using APS and image Processing (SWAP) on board PROBA2, and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). Methods. We used the spatial possibilistic clustering algorithm (SPoCA) to identify and segment coronal features from the EUV observations of AIA. The AIA segmentation maps were then applied on SWAP images, and parameters such as the intensity, fractional area, and contribution of ARs/CHs/QS features were computed and compared with the full-disk integrated intensity and LYRA irradiance measurements. Results. We report the results obtained from SDO/AIA and PROBA2/SWAP images taken from January 2011 to December 2012 and compare the resulting integrated full-disk intensity with PROBA2/LYRA irradiance. We determine the contributions of the segmented features to EUV and UV irradiance variations. The variations of the parameters resulting from the segmentation, namely the area, integrated intensity, and relative contribution to the solar irradiance, are compared with LYRA irradiance. We find that the active regions have a great impact on the irradiance fluctuations. In the EUV passbands considered in this study, the QS is the greatest contributor to the solar irradiance, with up to 63% of total intensity values. Active regions, on the other hand, contribute to about 10%, and off-limb structures to about 24%. We also find that the area of the features is highly variable suggesting that their area has to be taken into account in irradiance models, in addition to their intensity variations. Conclusions. We successfully show that the feature extraction allows us to use EUV telescopes to measure irradiance fluctuations and to quantify the contribution of each part to the EUV spectral solar irradiance observed with a calibrated radiometer. This study also shows that SPoCA is viable, and that the segmentation of images can be a useful tool. We also provide the measurement correlation between SWAP and AIA during this analysis.
Future missions such as Solar Orbiter (SO), Inter-Helioprobe, or Solar Probe aim at approaching t... more Future missions such as Solar Orbiter (SO), Inter-Helioprobe, 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 scaleinvariance continues to prevail at smaller scales, the conclu
Aims. LYRA, the Large Yield Radiometer, is a vacuum ultraviolet (VUV) solar radiometer, planned t... more Aims. LYRA, the Large Yield Radiometer, is a vacuum ultraviolet (VUV) solar radiometer, planned to be launched in November 2009 on the European Space Agency PROBA2, the Project for On-Board Autonomy spacecraft. Methods. The instrument was radiometrically calibrated in the radiometry laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the Berlin Electron Storage ring for SYnchroton radiation (BESSY II). The calibration was done using monochromatized synchrotron radiation at PTB's VUV and soft X-ray radiometry beamlines using reference detectors calibrated with the help of an electrical substitution radiometer as the primary detector standard. Results. A total relative uncertainty of the radiometric calibration of the LYRA instrument between 1% and 11% was achieved. LYRA will provide irradiance data of the Sun in four UV passbands and with high temporal resolution down to 10 ms. The present state of the LYRA pre-flight calibration is presented as well as the expected instrument performance.
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