Jean-François Hochedez

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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 lower(More)
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, we apply(More)
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 (lambda(0)=401 nm and lambda(0)=265 nm) with pulse(More)
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 passbands and(More)
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 spectral(More)
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 20Hz) in four broad spectral channels, from soft X-ray to MUV, that have been chosen for their(More)
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 the(More)