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Papers by antoine llebaria
Proceedings IWISP '96, 1996
Publisher Summary A classical problem in image processing consists in determining the translation... more Publisher Summary A classical problem in image processing consists in determining the translation from one noisy image to a reference image. For the astronomical application that this chapter considers, the image detector is fastened to a shuttle whose motion blurs the observed images. To preserve the quality of this image, the exposure time of the detector is very small, and as a consequence, very few photons can be present in each observation. All the observed images S p are matched and added together in order to built a final image r . At low photon levels, the observed image S p is mainly corrupted by the discrete nature of the photon which is described by a Poisson statistics. The chapter considers the problem of matching astronomical images with a very low photon level. It also analyzes the performances of the optimal technique when the noise of the moved images is no longer Gaussian, and the classical linear intercorrelation method fails.
Astronomy and Astrophysics, 2010
We present the results of our photometric study of the Kreutz group of sungrazing comets observed... more We present the results of our photometric study of the Kreutz group of sungrazing comets observed by SOHO-LASCO from 1996-2005. We extend the work of Biesecker et al. (2002), expanding the sample from 141 to more than 900 comets. The Kreutz comets seen by SOHO are produced by fragmentation from the more massive members of the family which include Ikeya-Seki (C/1965 S1 = 1965f) and C/1882 R1. None of the SOHO observed Kreutz comets have survived perihelion due to both their small size (we infer sizes less than 50 meters in radius) and perihelion distances below 2 solar radii. Kreutz comets typically brighten at a rate near r-7.3 when first entering the SOHO field of view (at distances near 30 solar radii), then rapidly transition to brightening at a rate near r-3.8 from 16-24 solar radii. We find that they do not have a bimodal distance of peak brightness as previously reported by Biesecker et al. (2002), but instead peak between 10-14 solar radii, suggesting there is a continuum, perhaps due to compositional variations, rather than two distinct subpopulations. Inside of 10 solar radii but prior to perihelion, the comets fade rapidly and disappear by 6 solar radii. We derive nuclear sizes of up to 50 meters in radius, with a cumulative size distribution of N(>R) R-2.2 for comets larger than 5 meters in radius. This size distribution cannot explain the six largest members of the family seen from the ground, suggesting that either the family is not collisionally evolved or that the distribution is not uniform around the orbit. The total mass of the distribution up to the largest expected size ( 500 meters) is 4x1014 g, much less than the estimated mass of the largest ground observed members. This research was supported by NASA Planetary Atmospheres grants NAG513295 and NNG06GF29G.
International Conference on Space Optics — ICSO 1997, 2018
![Research paper thumbnail of Coronal Photopolarimetry with the LASCO-C3 Coronagraph over 24 Years [1996-2019] -- Application to the K/F Separation and to the Determination of the Electron Density](https://attachments.academia-assets.com/77946204/thumbnails/1.jpg)
](arXiv: Solar and Stellar Astrophysics, 2020
We present an in-depth characterization of the polarimetric channel of the Large-Angle Spectromet... more We present an in-depth characterization of the polarimetric channel of the Large-Angle Spectrometric COronagraph/LASCO-C3 onboard SOHO. The polarimetric analysis of the white-light images makes use of polarized sequences composed of three images obtained through three polarizers oriented at +60$^\circ$, 0$^\circ$, and -60$^\circ$, complemented by a neighboring unpolarized image. However, the degradation of the 0$^\circ$ polarizer noticed in 1999 compelled us to reconstruct the corresponding images from the other ones thereafter. The analysis closely follows the method developed for LASCO-C2 (Lamy, et al. Solar Physics 295, 89, 2020 and arXiv:2001.05925) and implements the formalism of Mueller, albeit with additional difficulties notably the presence of a non-axially symmetric component of stray light. Critical corrections were derived from a SOHO roll sequence and from consistency criteria (e.g., the tangential direction of polarization). The quasi-uninterrupted photopolarimetric an...
Knight, Michael F. A’Hearn, Doug A. Biesecker, Guillaume Faury, Doug P. Hamilton, Philippe Lamy, ... more Knight, Michael F. A’Hearn, Doug A. Biesecker, Guillaume Faury, Doug P. Hamilton, Philippe Lamy, and Antoine Llebaria, University of Maryland, College Park, MD, USA, NOAA, Boulder, CO, USA, Laboratoire d’Astronomie Spatiale, Marseille, France Unlike most comets seen at larger heliocentric distances, sungrazing comets seen near perihelion are often observed over a wide range of phase angles in a short time. The phase angle of the Marsden group comet C/1999 U2 changed by nearly 120◦ over ∼37 hours. Furthermore, many are seen at high phase angles where forward scattering is very important. The few comets that have been seen at large phase angles, including C/1976 V1 West, 96P/Machholz 1, and C/2006 P1 McNaught, have shown dramatic brightening. Studies by Kolokolova et al. [1] and Marcus [2] have quantified the phase dependence of brightness due to scattering off dust in the coma, showing a gentle increase due to backscattering (phase angle 100◦), and a relatively flat curve in between....
A sequence of 400 images obtained over three days with the C2-LASCO/SOHO coronagraph was used to ... more A sequence of 400 images obtained over three days with the C2-LASCO/SOHO coronagraph was used to disentangle the complex evolution of the structures observed on the corona of the Sun's North pole. Projective transforms were used to find and delimit the elusive linear structures on each image (< 1 : 1 of SNR). From frame to frame, these structures show strong brightness variations as well as lateral shifts which are linked to rotation of the Sun. Taking advantage of solar corona rotation as a rigid body (of ∼28 days period), we are able to extract short sinograms to obtain a 3-D reconstruction with few hypotheses. The whole procedure is described, emphasizing the role of the bilinear transform as a new tool in this process.
![Research paper thumbnail of Restoration of the K and F Components of the Solar Corona from LASCO-C2 Images over 24 Years [1996 – 2019]](https://attachments.academia-assets.com/77946207/thumbnails/1.jpg)
](arXiv: Solar and Stellar Astrophysics, 2020
We present a photometrically accurate restitution of the K and F coronae from white-light images ... more We present a photometrically accurate restitution of the K and F coronae from white-light images obtained over 24 Years [1996--2019] by the Large-Angle Spectrometric COronagraph "LASCO-C2" onboard the Solar and Heliospheric Observatory (SOHO). The procedure starts with the data set coming from the polarimetric separation of images of 512 x 512 pixels in which the F-corona and the instrumental stray light are entangled. Disentangling these components proceeds in three stages, each composed of several steps. Stage 1 establishes the distinct variations of the radiance of these components with the Sun--SOHO distance and generate a new data set of median images calculated for each Carrington rotation. Stage 2 achieves the restitution of a set of 36 stray light images reflecting its temporal variation and the periodic rolls of SOHO which started in 2003. Stage 3 achieves the restitution of the F-corona and a time series of daily images is generated. These results allowed us proc...
International Astronomical Union Colloquium
the large field Lallemand electronographic camera has proved to be an ideal receptor for bidimens... more the large field Lallemand electronographic camera has proved to be an ideal receptor for bidimensional photometry with the C.F.H. 3.6 m. Telescope. It permits to measure faint stars up to about B = 25. Plates of a large variety of objects have been obtained ; for example : crowded fields such as the nearby galaxy Messier 33 ; fields where one must recognize faint galaxies from stars; objects for which a high spatial resolution is needed, such as the optical jet of Messier 87 or gravitational lenses. It is possible to predict the limits of the receptor with a very large telescope.
Surface Measurement and Characterization, 1989
For many years we have developed a method to reconstruct the profiles of statistically rough surf... more For many years we have developed a method to reconstruct the profiles of statistically rough surfaces. This method is based on a microdensitometer analysis of electron micrographs of shadowed surface replicas. From the quantized profiles it is possible to compute the statistical moments -particularly the second order one called autocovariance function (ACF)- that characterize the surface. In general ACF's for pseudorandom surfaces are not decreasing monotonic functions and some complications arise when the definition of a auto-covariance length for those surfaces is considered. Solutions are proposed to overcome them; in particular, it seems preferable to deduce certain statistical parameters from the spectrum instead of the ACF. Moreover a new approach based on the minimal spanning tree (MST) -which is a graph constructed on the set of points representing the position of features on a surface- is proposed to study statistically order and disorder in the distribu-tion of these features.
Journal of the Optical Society of America A, 1993
It is shown that rough surfaces of thin silver films deposited on LiF underlayers may be accurate... more It is shown that rough surfaces of thin silver films deposited on LiF underlayers may be accurately described by a low-order autoregressive process. The autoregressive (AR) parameters are determined, and the advantages of describing statistically rough surfaces of thin deposits by linear models instead of with the traditional autocovariance function (ACF) or the profile power-spectral-density function (PPSDF) are discussed.
Advances in Space Research, 1985
Solar Physics, 1995
Abstract. The Large Angle Spectroscopic Coronagraph (LASCO) is a three coronagraph package which ... more Abstract. The Large Angle Spectroscopic Coronagraph (LASCO) is a three coronagraph package which has been jointly developed for the Solar and Heliospheric Observatory (SOHO) mission by the Naval Research Laboratory ...
![Research paper thumbnail of Coronal Photopolarimetry with the LASCO-C2 Coronagraph over 24 Years [1996 – 2019]](https://attachments.academia-assets.com/77945006/thumbnails/1.jpg)
](
Proceedings IWISP '96, 1996
Publisher Summary A classical problem in image processing consists in determining the translation... more Publisher Summary A classical problem in image processing consists in determining the translation from one noisy image to a reference image. For the astronomical application that this chapter considers, the image detector is fastened to a shuttle whose motion blurs the observed images. To preserve the quality of this image, the exposure time of the detector is very small, and as a consequence, very few photons can be present in each observation. All the observed images S p are matched and added together in order to built a final image r . At low photon levels, the observed image S p is mainly corrupted by the discrete nature of the photon which is described by a Poisson statistics. The chapter considers the problem of matching astronomical images with a very low photon level. It also analyzes the performances of the optimal technique when the noise of the moved images is no longer Gaussian, and the classical linear intercorrelation method fails.
Astronomy and Astrophysics, 2010
We present the results of our photometric study of the Kreutz group of sungrazing comets observed... more We present the results of our photometric study of the Kreutz group of sungrazing comets observed by SOHO-LASCO from 1996-2005. We extend the work of Biesecker et al. (2002), expanding the sample from 141 to more than 900 comets. The Kreutz comets seen by SOHO are produced by fragmentation from the more massive members of the family which include Ikeya-Seki (C/1965 S1 = 1965f) and C/1882 R1. None of the SOHO observed Kreutz comets have survived perihelion due to both their small size (we infer sizes less than 50 meters in radius) and perihelion distances below 2 solar radii. Kreutz comets typically brighten at a rate near r-7.3 when first entering the SOHO field of view (at distances near 30 solar radii), then rapidly transition to brightening at a rate near r-3.8 from 16-24 solar radii. We find that they do not have a bimodal distance of peak brightness as previously reported by Biesecker et al. (2002), but instead peak between 10-14 solar radii, suggesting there is a continuum, perhaps due to compositional variations, rather than two distinct subpopulations. Inside of 10 solar radii but prior to perihelion, the comets fade rapidly and disappear by 6 solar radii. We derive nuclear sizes of up to 50 meters in radius, with a cumulative size distribution of N(>R) R-2.2 for comets larger than 5 meters in radius. This size distribution cannot explain the six largest members of the family seen from the ground, suggesting that either the family is not collisionally evolved or that the distribution is not uniform around the orbit. The total mass of the distribution up to the largest expected size ( 500 meters) is 4x1014 g, much less than the estimated mass of the largest ground observed members. This research was supported by NASA Planetary Atmospheres grants NAG513295 and NNG06GF29G.
International Conference on Space Optics — ICSO 1997, 2018
arXiv: Solar and Stellar Astrophysics, 2020
We present an in-depth characterization of the polarimetric channel of the Large-Angle Spectromet... more We present an in-depth characterization of the polarimetric channel of the Large-Angle Spectrometric COronagraph/LASCO-C3 onboard SOHO. The polarimetric analysis of the white-light images makes use of polarized sequences composed of three images obtained through three polarizers oriented at +60$^\circ$, 0$^\circ$, and -60$^\circ$, complemented by a neighboring unpolarized image. However, the degradation of the 0$^\circ$ polarizer noticed in 1999 compelled us to reconstruct the corresponding images from the other ones thereafter. The analysis closely follows the method developed for LASCO-C2 (Lamy, et al. Solar Physics 295, 89, 2020 and arXiv:2001.05925) and implements the formalism of Mueller, albeit with additional difficulties notably the presence of a non-axially symmetric component of stray light. Critical corrections were derived from a SOHO roll sequence and from consistency criteria (e.g., the tangential direction of polarization). The quasi-uninterrupted photopolarimetric an...
Knight, Michael F. A’Hearn, Doug A. Biesecker, Guillaume Faury, Doug P. Hamilton, Philippe Lamy, ... more Knight, Michael F. A’Hearn, Doug A. Biesecker, Guillaume Faury, Doug P. Hamilton, Philippe Lamy, and Antoine Llebaria, University of Maryland, College Park, MD, USA, NOAA, Boulder, CO, USA, Laboratoire d’Astronomie Spatiale, Marseille, France Unlike most comets seen at larger heliocentric distances, sungrazing comets seen near perihelion are often observed over a wide range of phase angles in a short time. The phase angle of the Marsden group comet C/1999 U2 changed by nearly 120◦ over ∼37 hours. Furthermore, many are seen at high phase angles where forward scattering is very important. The few comets that have been seen at large phase angles, including C/1976 V1 West, 96P/Machholz 1, and C/2006 P1 McNaught, have shown dramatic brightening. Studies by Kolokolova et al. [1] and Marcus [2] have quantified the phase dependence of brightness due to scattering off dust in the coma, showing a gentle increase due to backscattering (phase angle 100◦), and a relatively flat curve in between....
A sequence of 400 images obtained over three days with the C2-LASCO/SOHO coronagraph was used to ... more A sequence of 400 images obtained over three days with the C2-LASCO/SOHO coronagraph was used to disentangle the complex evolution of the structures observed on the corona of the Sun's North pole. Projective transforms were used to find and delimit the elusive linear structures on each image (< 1 : 1 of SNR). From frame to frame, these structures show strong brightness variations as well as lateral shifts which are linked to rotation of the Sun. Taking advantage of solar corona rotation as a rigid body (of ∼28 days period), we are able to extract short sinograms to obtain a 3-D reconstruction with few hypotheses. The whole procedure is described, emphasizing the role of the bilinear transform as a new tool in this process.
arXiv: Solar and Stellar Astrophysics, 2020
We present a photometrically accurate restitution of the K and F coronae from white-light images ... more We present a photometrically accurate restitution of the K and F coronae from white-light images obtained over 24 Years [1996--2019] by the Large-Angle Spectrometric COronagraph "LASCO-C2" onboard the Solar and Heliospheric Observatory (SOHO). The procedure starts with the data set coming from the polarimetric separation of images of 512 x 512 pixels in which the F-corona and the instrumental stray light are entangled. Disentangling these components proceeds in three stages, each composed of several steps. Stage 1 establishes the distinct variations of the radiance of these components with the Sun--SOHO distance and generate a new data set of median images calculated for each Carrington rotation. Stage 2 achieves the restitution of a set of 36 stray light images reflecting its temporal variation and the periodic rolls of SOHO which started in 2003. Stage 3 achieves the restitution of the F-corona and a time series of daily images is generated. These results allowed us proc...
International Astronomical Union Colloquium
the large field Lallemand electronographic camera has proved to be an ideal receptor for bidimens... more the large field Lallemand electronographic camera has proved to be an ideal receptor for bidimensional photometry with the C.F.H. 3.6 m. Telescope. It permits to measure faint stars up to about B = 25. Plates of a large variety of objects have been obtained ; for example : crowded fields such as the nearby galaxy Messier 33 ; fields where one must recognize faint galaxies from stars; objects for which a high spatial resolution is needed, such as the optical jet of Messier 87 or gravitational lenses. It is possible to predict the limits of the receptor with a very large telescope.
Surface Measurement and Characterization, 1989
For many years we have developed a method to reconstruct the profiles of statistically rough surf... more For many years we have developed a method to reconstruct the profiles of statistically rough surfaces. This method is based on a microdensitometer analysis of electron micrographs of shadowed surface replicas. From the quantized profiles it is possible to compute the statistical moments -particularly the second order one called autocovariance function (ACF)- that characterize the surface. In general ACF's for pseudorandom surfaces are not decreasing monotonic functions and some complications arise when the definition of a auto-covariance length for those surfaces is considered. Solutions are proposed to overcome them; in particular, it seems preferable to deduce certain statistical parameters from the spectrum instead of the ACF. Moreover a new approach based on the minimal spanning tree (MST) -which is a graph constructed on the set of points representing the position of features on a surface- is proposed to study statistically order and disorder in the distribu-tion of these features.
Journal of the Optical Society of America A, 1993
It is shown that rough surfaces of thin silver films deposited on LiF underlayers may be accurate... more It is shown that rough surfaces of thin silver films deposited on LiF underlayers may be accurately described by a low-order autoregressive process. The autoregressive (AR) parameters are determined, and the advantages of describing statistically rough surfaces of thin deposits by linear models instead of with the traditional autocovariance function (ACF) or the profile power-spectral-density function (PPSDF) are discussed.
Advances in Space Research, 1985
Solar Physics, 1995
Abstract. The Large Angle Spectroscopic Coronagraph (LASCO) is a three coronagraph package which ... more Abstract. The Large Angle Spectroscopic Coronagraph (LASCO) is a three coronagraph package which has been jointly developed for the Solar and Heliospheric Observatory (SOHO) mission by the Naval Research Laboratory ...