158 research outputs found
Mobile target detection on SAR images
The synthesis of multiple look SAR images allows for speckle noise reduction through non-coherent summing . We present here
a method for detection and localisation of moving targets derived from multiple look imaging . Its basis is to compute severa l
single-look pushbroom images, then to search for pointwise reflections whose location and/or intensity vary from look to look .
The approach is validated with several examples . Raw signals were acquired with the RAMSES airborne experimental radar o f
the ONERA, during a MTI test-flight .
Theoretical limitation studies show the strong Zink between the multi-look method and more conventional MTI technics such a s
Doppler filtering (for radially moving targets) and time-frequency transforms (for detecting cross-range motions through thei r
difference in Doppler frequency slope )La synthèse de plusieurs vues en imagerie SAR permet une diminution du bruit de speckle par sommation incohérente. Nous exposons dans ce document une méthode pour la détection des cibles mobiles fondée sur l'imagerie SAR multi-vues. Le principe est de calculer un ensemble de vues panoramiques pour des valeurs différentes du Doppler et de détecter par des techniques de traitement d'image classiques, des échos dont la position et/ou l'intensité varient d'une vue à l'autre. La méthode est illustrée par de nombreux exemples. Les signaux bruts ont été obtenus au cours d'une campagne de mesure de la station RAMSÈS réalisée à l'ONERA. L'étude des limitations théoriques montre que les méthodes de MTI plus classiques comme le filtrage Doppler (détection des cibles à vitesse radiale) ou les transformées temps-fréquence (détection des échos de pente Doppler atypique pour la mise en évidence de mouvements transversaux) ont un lien avec la méthode multi-vues proposée ici
A novel modified Omega-K algorithm for circular trajectory scanning SAR imaging using series reversion
The SHARDDS survey: limits on planet occurrence rates based on point sources analysis via the Auto-RSM framework
In the past decade, HCI surveys provided new insights about the frequency and
properties of substellar companions at separation larger than 5 au. In this
context, our study aims to detect and characterise potential exoplanets and
brown dwarfs within debris disks, by considering the SHARDDS survey, which
gathers 55 Main Sequence stars with known bright debris disk. We rely on the
AutoRSM framework to perform an in-depth analysis of the targets, via the
computation of detection maps and contrast curves. A clustering approach is
used to divide the set of targets in multiple subsets, in order to reduce the
computation time by estimating a single optimal parametrisation for each
considered subset. The use of Auto-RSM allows to reach high contrast at short
separations, with a median contrast of 10-5 at 300 mas, for a completeness
level of 95%. Detection maps generated with different approaches are used along
with contrast curves, to identify potential planetary companions. A new
planetary characterisation algorithm, based on the RSM framework, is developed
and tested successfully, showing a higher astrometric and photometric precision
for faint sources compared to standard approaches. Apart from the already known
companion of HD206893 and two point-like sources around HD114082 which are most
likely background stars, we did not detect any new companion around other
stars. A correlation study between achievable contrasts and parameters
characterising HCI sequences highlights the importance of the strehl, wind
speed and wind driven halo to define the quality of high contrast images.
Finally, planet detection and occurrence frequency maps are generated and show,
for the SHARDDS survey, a high detection rate between 10 and 100 au for
substellar companions with mass >10MJ
The adaptive optics simulation analysis tool(kit) (AOSAT)
AOSAT is a python package for the analysis of single-conjugate adaptive optics (SCAO) simulation results. Python is widely used in the astronomical community these days, and AOSAT may be used stand-alone, integrated into a simulation environment, or can easily be extended according to a user's needs. Standalone operation requires the user to provide the residual wavefront frames provided by the SCAO simulation package used, the aperture mask (pupil) used for the simulation, and a custom setup file describing the simulation/analysis configuration. In its standard form, AOSAT's "tearsheet" functionality will then run all standard analyzers, providing an informative plot collection on properties such as the point-spread function (PSF) and its quality, residual tip-tilt, the impact of pupil fragmentation, residual optical aberration modes both static and dynamic, the expected high-contrast performance of suitable instrumentation with and without coronagraphs, and the power spectral density of residual wavefront errors. AOSAT fills the gap between the simple numerical outputs provided by most simulation packages, and the full-scale deployment of instrument simulators and data reduction suites operating on SCAO residual wavefronts. It enables instrument designers and end-users to quickly judge the impact of design or configuration decisions on the final performance of down-stream instrumentation.EPI
RPBS: a web resource for structural bioinformatics
RPBS (Ressource Parisienne en Bioinformatique Structurale) is a resource dedicated primarily to structural bioinformatics. It is the result of a joint effort by several teams to set up an interface that offers original and powerful methods in the field. As an illustration, we focus here on three such methods uniquely available at RPBS: AUTOMAT for sequence databank scanning, YAKUSA for structure databank scanning and WLOOP for homology loop modelling. The RPBS server can be accessed at and the specific services at
Post conjunction detection of Pictoris b with VLT/SPHERE
With an orbital distance comparable to that of Saturn in the solar system,
\bpic b is the closest (semi-major axis \,9\,au) exoplanet that has
been imaged to orbit a star. Thus it offers unique opportunities for detailed
studies of its orbital, physical, and atmospheric properties, and of
disk-planet interactions. With the exception of the discovery observations in
2003 with NaCo at the Very Large Telescope (VLT), all following astrometric
measurements relative to \bpic have been obtained in the southwestern part of
the orbit, which severely limits the determination of the planet's orbital
parameters. We aimed at further constraining \bpic b orbital properties using
more data, and, in particular, data taken in the northeastern part of the
orbit.
We used SPHERE at the VLT to precisely monitor the orbital motion of beta
\bpic b since first light of the instrument in 2014. We were able to monitor
the planet until November 2016, when its angular separation became too small
(125 mas, i.e., 1.6\,au) and prevented further detection. We redetected \bpic b
on the northeast side of the disk at a separation of 139\,mas and a PA of
30 in September 2018. The planetary orbit is now well constrained.
With a semi-major axis (sma) of au (1 ), it
definitely excludes previously reported possible long orbital periods, and
excludes \bpic b as the origin of photometric variations that took place in
1981. We also refine the eccentricity and inclination of the planet. From an
instrumental point of view, these data demonstrate that it is possible to
detect, if they exist, young massive Jupiters that orbit at less than 2 au from
a star that is 20 pc away.Comment: accepted by A&
The beta Pictoris system: Setting constraints on the planet and the disk structures at mid-IR wavelengths with NEAR
[abridged] We analyzed mid-infrared high-contrast coronagraphic images of the
beta Pictoris system, taking advantage of the NEAR experiment using the
VLT/VISIR instrument. The goal of our analysis is to investigate both the
detection of the planet beta Pictoris b and of the disk features at mid-IR
wavelengths. In addition, by combining several epochs of observation, we expect
to constrain the position of the known clumps and improve our knowledge on the
dynamics of the disk. To evaluate the planet b flux contribution, we extracted
the photometry and compared it to the flux published in the literature. In
addition, we used previous data from T-ReCS and VISIR, to study the evolution
of the position of the southwest clump that was initially observed in the
planetary disk back in 2003. While we did not detect the planet b, we were able
to put constraints on the presence of circumplanetary material, ruling out the
equivalent of a Saturn-like planetary ring around the planet. The disk presents
several noticeable structures, including the known southwest clump. Using a
16-year baseline, sampled with five epochs of observations, we were able to
examine the evolution of the clump: the clump orbits in a Keplerian motion with
an sma of 56.1+-0.4 au. In addition to the known clump, the images clearly show
the presence of a second clump on the northeast side of the disk and fainter
and closer structures that are yet to be confirmed. We found correlations
between the CO clumps detected with ALMA and the mid-IR images. If the
circumplanetary material were located at the Roche radius, the maximum amount
of dust determined from the flux upper limit around beta Pictoris b would
correspond to the mass of an asteroid of 5 km in diameter. Finally, the
Keplerian motion of the southwestern clump is possibly indicative of a
yet-to-be-detected planet or signals the presence of a vortex.Comment: Accepted in Astronomy and Astrophysic
Performance of the extreme-AO instrument VLT/SPHERE and dependence on the atmospheric conditions
SPHERE is the high-contrast exoplanet imager and spectrograph installed at the Unit Telescope 3 of the Very Large Telescope. After more than two years of regular operations, we analyse statistically the performance of the adaptive optics system and its dependence on the atmospheric conditions above the Paranal observatory, as measured by the suite of dedicated instruments which are part of the Astronomical Site Monitor and as estimated by the SPHERE real-time calculator. We also explain how this information can be used to schedule the observations in order to yield the best data quality and to guide the astronomer when processing his/her data
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