Jean-Francois E. Hochedez

• PhD 1990, Ecole Centrale Paris 1987
• French National Centre for Scientific Research

Coronal rain is the most dramatic cooling phenomenon of the solar corona and an essential diagnostic tool for the coronal heating properties. A puzzling feature of the solar corona, besides the heating, is its EUV filamentary structure and variability. We aim to identify observable features of the TNE-TI scenario underlying coronal rain at small an...

Context. The Extreme Ultraviolet Imager (EUI), onboard Solar Orbiter consists of three telescopes: the two High Resolution Imagers in EUV (HRIEUV) and in Lyman-{\alpha} (HRILya), and the Full Sun Imager (FSI). Solar Orbiter/EUI started its Nominal Mission Phase on 2021 November 27. Aims. EUI images from the largest scales in the extended corona off...

Context. The magnetic field plays a dominant role in the solar irradiance variability. Determining the contribution of various magnetic features to this variability is important in the context of heliospheric studies and Sun-Earth connection. Aims. We studied the solar irradiance variability and its association with the underlying magnetic field fo...

PICARD is a mission devoted to solar variability observation, through imagery and radiometric measurements, with the goal to provide data for scientific investigation first in the area of solar physics, and second in the assessment of the influence of the solar variability on the Earth climate variability. PICARD contains a double program with in-s...

The PREcision Monitoring Sensor (PREMOS) is a solar radiometer on board the French PICARD mission that was launched in June 2010 and decommissioned in April 2014.Aims. The PREMOS radiometer obtains solar irradiance measurements in specific spectral windows in the UV, visible, and near- infrared. In this paper, the PREMOS data and calibration method...

The equator-to-pole radius difference (Δr=R eq−R pol) is a fundamental property of our star, and understanding it will enrich future solar and stellar dynamical models. The solar oblateness (Δ⊙) corresponds to the excess ratio of the equatorial solar radius (R eq) to the polar radius (R pol), which is of great interest for those working in relativi...

We present a long-term assessment of the radiometric calibration and degradation of the Large Yield Radiometer (LYRA), which has been on orbit since 2009. LYRA is an ultraviolet (UV) solar radiometer and is the first space experiment using aboard a pioneering diamond detector technology. We show that LYRA has degraded after the commissioning phase...

PICARD is an investigation dedicated to the simultaneous measurement of the absolute total and spectral solar irradiance, the diameter and solar shape, and to the Sun's interior probing by the helioseismology method. The spacecraft was successfully launched into a Sun-synchronous dawn-dusk orbit on 15 June 2010 by a DNEPR-1 launcher for a life expe...

On 5 to 6 June, 2012 the transit of Venus provided a rare opportunity to determine the radius of the Sun using solar imagers observing a well-defined object, namely the planet and its atmosphere, occulting partially the Sun. A new method has been developed to estimate the solar radius during a planetary transit. It is based on the estimation of the...

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...

Context. Astrophysical observations must be corrected for their imperfections of instrumental origin. When charge-coupled devices (CCDs) are used, their dark signal is one such hindrance. In their pristine state, most CCD pixels are cool, that is, they exhibit a low quasi-uniform dark current, which can be estimated and corrected for. In space, aft...

The Solar Diameter Imager and Surface Mapper (SODISM) onboard the Picard space mission provides wide-field images of the photosphere and chromosphere of the Sun in five narrow bandpasses centered at 215.0, 393.37, 535.7, 607.1, and 782.2 nm. The Picard spacecraft was successfully launched on 15 June 2010 into a Sun-synchronous dawn–dusk orbit. The...

The Project for On-Board Autonomy 2 (PROBA2) mission has been in orbit 3.5 years and has evolved from a successful technology demonstration platform to a solar-science observatory and will soon become a space-weather monitoring mission. Few satellites have been so versatile in use; this is all the more remarkable knowing that PROBA2 is only a cubic...

Knowledge of the Solar Diameter Imager and Surface Mapper (SODISM) plate scale is a fundamental parameter for obtaining the solar radius. We have determined the plate scale of the telescope on the ground and in flight onboard the Picard spacecraft. The results show significant differences; the main reason is that the conditions of observation are n...

PICARD is a spacecraft dedicated to the simultaneous measurement of the absolute total and spectral solar irradiance, the diameter, the solar shape, and to probing the Sun's interior by the helioseismology method. The mission has two scientific objectives, which are the study of the origin of the solar variability, and the study of the relations be...

The Large Yield Radiometer (LYRA) is an XUV-EUV-MUV (soft X-ray to mid-ultraviolet) solar radiometer onboard the European Space Agency PROBA2 mission that was launched in November 2009. LYRA acquires solar irradiance measurements at a high cadence (nominally 20 Hz) in four broad spectral channels, from soft X-ray to MUV, that have been chosen for t...

When Charge Coupled Devices are used for scientific observations, their dark signal is a hindrance. In their pristine state, most CCD pixels are `cool'; they exhibit low, quasi uniform dark current, which can be estimated and corrected for. In space, after having been hit by an energetic particle, pixels can turn `hot'. They start delivering excess...

PICARD is a CNES micro-satellite launched in June 2010 (Thuillier at al. 2006). Its main goal is to measure the solar shape, total and spectral irradiance during the ascending phase of the activity cycle. The SODISM telescope onboard PICARD also allows us to conduct a program for helioseismology in intensity at 535.7 nm (Corbard et al. 2008). One-m...

The PROBA2 Science Centre (P2SC) is a small-scale science operations centre supporting the Sun observation instruments onboard PROBA2: the EUV imager Sun Watcher using APS detectors and image Processing (SWAP) and Large-Yield Radiometer (LYRA). PROBA2 is one of ESA's small, low-cost Projects for Onboard Autonomy (PROBA) and part of ESA's In-Orbit T...

The Sun is the primary source of energy responsible for governing both the weather and climate of Earth. For that reason alone one would expect that changes in the amount and type of energy Earth received from the Sun could alter weather and climate on the Earth. The variations in the UV and EUV irradiance are produced by surface manifestation of s...

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 Alumin...

PROBA2 (http://proba2.sidc.be) is an ESA micro-satellite that was launched in November 2009. Two instruments on-board, SWAP and LYRA, are devoted to solar observations. SWAP (PI: D. Berghmans) is an EUV imager observing the corona with a bandpass centered on 174 Å at a cadence of 1-2 min. Its high contrast images, large FOV and flexible off-pointin...

The PICARD Spacecraft was launched on 15 June 2010. It carries four instruments. One of them, SODISM is an imaging telescope with a 2K x 2K CCD detector, dedicated to the measurement of the solar diameter and the limb shape. Although the data processing is still in a validation phase, we can already present some preliminary results concerning the s...

The mystery of the dynamics of the Sun is even deeper when it is quiet, i.e. when and where there are no coherent areas structured by strong magnetic field and called active regions. The corona that is part of the solar atmosphere is observed by extreme UV spatial telescopes for which higher resolutions are always desired: the best pixel resolution...

We present a new method of magnification for textured images featuring scale invariance properties. This work is originally motivated by an application to astronomical images. One goal is to propose a method to quantitatively predict statistical and visual properties of images taken by a forthcoming higher resolution telescope from older images at...

Context. The solar irradiance in the UV is a key ingredient in space weather applications; however, because of the lack of continuous and long-term observations, various indices are still used today as surrogates for the solar spectral irradiance. Aims: As an alternative to current spectrometers we use a few radiometers with properly chosen passban...

We present the first measurement results from hybrid AlGaN-on-Si-based Extreme Ultraviolet (EUV) imagers with 10 μm pixel-to-pixel pitch. The 256×256 backside illuminated Focal Plane Arrays (FPAs) were hybridized to dedicated Si-based CMOS Readouts (ROICs). The AlGaN active layer with 40% Al concentration provides an intrinsic rejection of waveleng...

In Fall 2008 NASA selected a large international consortium to produce a comprehensive automated feature-recognition system for the Solar Dynamics Observatory (SDO). The SDO data that we consider are all of the Atmospheric Imaging Assembly (AIA) images plus surface magnetic-field images from the Helioseismic and Magnetic Imager (HMI). We produce ro...

Inverse problems are of great importance in astrophysics for deriving information about the physical characteristics of hot optically thin plasma sources from their EUV and X-ray spectra. We describe and test an iterative method developed within the framework of a probabilistic approach to the spectral inverse problem for determining the thermal st...

LYRA is a solar radiometer, part of the PROBA-2 micro-satellite payload. The PROBA-2 mission has been launched on 02 November 2009 with a Rockot launcher to a Sun-synchronous orbit at an altitude of 725 km. Its nominal operation duration is two years with possible extension of 2 years. LYRA monitors the solar irradiance at a high cadence (> 20Hz) i...

Flares are powerful energy releases occurring in stellar atmospheres. Solar flares, the most intense energy bursts in the solar system, are however hardly noticeable in the total solar luminosity. Consequently, the total amount of energy they radiate 1) remains largely unknown and 2) has been overlooked as a potential contributor to variations in t...

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-alpha 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 sci...

The SDO Feature Finding Team produces robust and very efficient software modules that can keep up with the relentless SDO data stream, and detect, trace, and analyze a large number of phenomena including: flares, sigmoids, filaments, coronal dimmings, polarity inversion lines, sunspots, X-ray bright points, active regions, coronal holes, EIT waves,...

Solar images from space telescopes contain a wealth of information on solar variability, of great importance both in solar physics and in view of Space Weather applications. Obtaining this information, however, requires the ability to process large amounts of data over long periods in an objective fashion. In previous work, we have proposed a multi...

We report on the utilization of the two-photon induced free carrier generation in a diamond pin-type photodiode to record fringe-resolved second-order autocorrelations of femtosecond pulses in the UV. Measurements in photovoltaic mode are performed at the second and third harmonic of a Ti:sapphire laser ( λ 0 = 401 n m and λ 0 = 265 nm) with pulse...

In this letter, we report on the fabrication of near-ultraviolet 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...

On November 2, 2009, the PROBA2 space mission of ESA was launched into a sun-synchronous polar orbit allowing quasi-permanent solar observation. Onboard PROBA2, LYRA is the first radiometer in space that benefits from diamond ultraviolet detectors. LYRA consists of four large pass band channels. Each channel observes the irradiance of the Sun behin...

The Solar Dynamics Observatory (SDO) represents a new frontier in quantity and quality of solar data. At about 1.5 TB/day, the data will not be easily digestible by solar physicists using the same methods that have been employed for images from previous missions. In order for solar scientists to use the SDO data effectively they need meta-data that...

The ESA micro satellite PROBA2 was launched on November 2, 2009. It carries two solar instruments, the radiometer LYRA and the coronal imager SWAP whose commissioning ended in March 2010. LYRA (PI: J.-F. Hochedez) observes the solar irradiance in 4 wavelengths chosen for their relevance to space weather, solar physics and Earth aeronomy. LYRA is ab...

The SDO satellite, launched in February 2010, is on track to provide images of the Sun with unprecedented detail. For example, the SDO-AIA telescope can produce a 4k x 4k image every five seconds for each of its four telescopes (10 spectral bands). This mission increases the information flow available for solar observation and forecasting by severa...

The properties of the highly dynamic Sun will soon be revealed by the newly launched SDO, with data provided by its three instruments: AIA, HMI and EVE. This suite will produce, for the first time in solar physics, a large volume of data, equivalent to about 1.5 Tb/day, by observing the full disk Sun continuously at high cadence. A backbone network...

Inverse problems techniques allow deriving physical characteristics of hot optically thin so-lar and stellar plasma from their extreme ultraviolet and X-ray spectra. One of them, called Bayesian iterative method (BIM), relies on a probabilistic Bayesian framework for the spec-tral inverse problem, and reconstructs differential emission measure (DEM...

The Atmospheric Imaging Assembly (AIA) for the Solar Dynamics Observatory (SDO) mis-sion is designed to observe the Sun from the photosphere to the flaring corona. These data have to improve our understanding of processes in the solar atmosphere. The differential emis-sion measure (DEM) analysis is one of the main methods to derive information abou...

Solar images from the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Ob-servatory (SDO) will flood the solar physics community with a wealth of information on solar variability, of great importance both in solar physics and in view of Space Weather applica-tions. Obtaining this information, however, requires the ability to automatical...

Solid-state photon detectors based on semiconductors other than silicon are not yet considered mature technology but their current development opens new possibilities, also for space observations. Such devices are especially attractive for ultraviolet radiation detection, as semiconductor materials with band gaps larger than that of silicon can be...

Context: The study of the variability of the solar corona and the monitoring of coronal holes, quiet sun and active regions are of great importance in astrophysics as well as for space weather and space climate applications. Aims: In a previous work, we presented the spatial possibilistic clustering algorithm (SPoCA). This is a multi-channel unsupe...

Les images actuelles du Soleil calme issues du te?lescope spatial EIT sont telles que 1 pixel = (1800km)^2 alors que les e?chelles physiques les plus petites seraient de l'ordre de 100 m. La conception d'un te?lescope spatial haute re?solution a? 1 pixel=(80 km)^2 est envisage?e. Avec une re?solution environ 25 fois plus fine, les images risquent d...

Future missions for space astronomy and solar research require innovative vacuum ultraviolet (VUV) photodetectors. Present UV and VUV detectors exhibit serious limitations in performance, technology complexity and lifetime stability. New developments of metal-semiconductor-metal (MSM) solar-blind photodetectors based on diamond, cubic boron nitride...

With the multiplication of sensors and instruments, size, amount and quality of solar image data are constantly increasing, and analyzing this data requires defining and implementing accurate and reliable algorithms. In the context of solar features analysis, it is particularly important to accurately delineate their edges and track their motion, t...

PREMOS is a space experiment scheduled to fly on the French solar mission PICARD. The experiment comprises filter radiometers and absolute radiometers to measure the spectral and total solar irradiance. The aim of PREMOS is to contribute to the long term monitoring of the total solar irradiance, to use irradiance observations for 'nowcasting' the s...

LYRA is a solar EUV/VUV radiometer that will embark in early 2009 on-board the PROBA2 mission. Its heliosynchronous orbit generates brief eclipses, during which we intend to study the vertical distribution of the global extinction coefficient, using the solar occultation method. We also consider the potential of our approach in retrieving the therm...

We describe the fabrication and performance of diffractive filters designed for space-based x-ray and EUV solar observations. Unlike traditional thin film filters, diffractive filters can be made to have a high resistance against the destructive mechanical and acoustic loads of a satellite launch. The filters studied are made of plastic track-etche...

The DynaMICCS mission is designed to probe and understand the dynamics of crucial regions of the Sun that determine solar variability, including the previously unexplored inner core, the radiative/convective zone interface layers, the photosphere/chromosphere layers and the low corona. The mission delivers data and knowledge that no other known mis...

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 th...

SOHO EIT spectroheliograms showing the polar coronal holes during the present sunspot minimum are compared with National Solar Observatory (Kitt Peak) magnetograms taken in Fe I λ8688 and Ca II λ8542. The chromospheric λ8542 magnetograms, obtained on a routine, near-daily basis since 1996 June, reveal the Sun's strong polar fields with remarkable c...

The next ESA spatial mission planned to study the Sun, Solar Orbiter (SO), necessitates very innovative EUV detectors. The commonly used silicon detectors suffer important limitations mainly in terms of UV robustness and dark current level. An alternative comes from diamond or III-nitride materials. In these materials, the radiation hardness, solar...

Solar Orbiter will for the first time study the Sun with a full suite of in-situ and remote sensing instruments from inside 0.25 AU and will provide imaging and spectral observations of the Sun's polar regions, from out of the ecliptic. This proximity to the Sun will also have the significant advantage that the spacecraft will fly in near synchroni...

EIT waves are observed in EUV as bright fronts. Some of these bright fronts propagate across the solar disk. EIT waves are all associated with a flare and a CME and are commonly interpreted as fast-mode magnetosonic waves. Propagating EIT waves could also be the direct signature of the gradual opening of magnetic field lines during a CME. We quanti...

SECCHI-EUVI telescopes provide the first EUV images enabling a 3D reconstruction of solar coronal structures. We present a stereoscopic reconstruction method based on the Velociraptor algorithm, a multiscale optical-flow method that estimates displacement maps in sequences of EUV images. Following earlier calibration on sequences of SOHO-EIT data,...

Future missions such as Solar Orbiter (SO), InterHelioprobe, 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 eva...

Full-field full-resolution solar images obtained by the Extreme Ultraviolet Imaging Telescope on board the Solar and Heliospheric Observatory are used to analyse proper motions, velocity distributions, lifetimes, and diffusion coefficient of coronal bright points. The results obtained by the interactive method for three tracer subtypes (point-like...

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 multichannel unsupervised spatially constrained fuzzy clustering algorithm that...

Movies of the solar corona in Extreme UltraViolet (EUV) bandpasses exhibit complex patterns of magnetically structured plasma features surrounding the solar photosphere. Among the various phenomena to be observed in the EUV movies, coronal oscillations are an essential process for determining physical parameters of the plasma. In this paper we demo...

We report on the fabrication of Schottky-diode-based Extreme UltraViolet (EUV) photodetectors. The devices were processed on Gallium Nitride (GaN) layers epitaxially grown on 4 inch Silicon (111) substrates by Metal-Organic Chemical Vapor Deposition (MOCVD). Cutoff wavelength was determined together with the spectral responsivity measurements in th...

Solar telescopes will never be able to resolve the smallest events at their intrinsic physical scales. Pixel signals recorded by SOHO/(CDS, EIT, SUMER), STEREO/SECCHI/ EUVI, TRACE, SDO/AIA, and even by the future Solar Orbiter EUI/HRI contain an inherent “spatial noise” since they represent an average of the solar signal present at subpixel scales....

The knowledge of solar extreme and far ultraviolet (EUV) irradiance variations is essential for the characterization of the Earth’s upper atmosphere. For a long time, this knowledge has been based on empirical models, which are themselves based on proxies of the solar activity. However, the accurate modeling and prediction of the Earth’s upper atmo...

The LYRA instrument onboard ESA PROBA2 satellite will provide 6-hourly solar irradiance at the Lyman-alpha (121.6 nm) and the Herzberg continuum (~200–220 nm wavelength range). Because the nowcasting of the neutral and ionic state of the middle atmosphere requires the solar irradiance for the wide spectral range (120–680 nm) we have developed the s...

The LYRA instrument onboard ESA PROBA2 satellite will provide 6-hourly solar irradiance at the Lyman-alpha (121.6 nm) and the Herzberg continuum (~200–220 nm wavelength range). Because the nowcasting of the neutral and ionic state of the middle atmosphere requires the solar irradiance for the wide spectral area (120–680 nm) we have developed the st...

A new large-size metal–semiconductor–metal photoconductor device of 4.6 mm in diameter based on diamond material has been reprocessed and characterized in the vacuum-ultraviolet (VUV) wavelength range. The metal finger contacts have been processed to 2 µm in width with spacing between the contacts of 5 µm for a bias voltage of 5 V. The responsivity...

Deep-ultraviolet (DUV) solar-blind photodetectors based on high-quality cubic boron nitride (cBN) films with a metal/semiconductor/metal configuration were fabricated. The design of interdigitated circular electrodes enables high homogeneity of electric field between pads. The DUV photodetectors present a peak responsivity at 180 nm with a very sha...

The absolute responsivity of a metal-semiconductor-metal (MSM) photodiode based on high quality AlN material has been tested from the vacuum ultraviolet (vuv) to the near UV wavelength range (44–360 nm). The metal finger Schottky contacts have been processed to 2 μm in width with spacing between the contacts of 4 μm. In the vuv wavelength region, t...

The interaction between differential rotation and magnetic fields in the solar convection zone was recently modelled by Brun (2004). One consequence of that model is that the Maxwell stresses can oppose the Reynolds stresses, and thus contribute to the transport of the angular momentum towards the solar poles, leading to a reduced differential rota...

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. In this presentation, I will propose a multi-channel unsupervised spatially- constrained fuzzy cl...

We address the statistical modeling of solar images provided by the Extreme ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SoHO, a joint ESA/NASA mission). We focus in particular on the less structured regions, the "Quiet Sun". We first review on a brief historical viewpoint on multifractal processes for physica...

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 bee...

Accurate means of quantifying the respective contributions of different structures to the solar irradiance is now a key issue in Solar Physics, with implications to Sun-Earth relationships and space weather study. In this paper, we propose a three-step fusion scheme, that allows to aggregate (17.1 nm, 19.5 nm) data stemming from the solar EIT instr...

Metal-Semiconductor-Metal photodiodes were fabricated on epitaxially grown AlxGa1-xN on Si(111). The Aluminium content of the layers grown by means of molecular beam epitaxy (MBE) was 50, 80 and 100%, respectively. The processing was performed by standard microelectronic fabrication techniques like photolithography, wet and dry etching (RIE) and ph...

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 tha...