Time filter

Source Type

De Angelis S.,National institute for astrophysics | Carli C.,National institute for astrophysics | Tosi F.,National institute for astrophysics | Beck P.,Institute Of Planetologie Et Dastrophysique Of Grenoble Ipag | And 6 more authors.
Icarus | Year: 2017

We investigate two poly-hydrated magnesium sulfates, hexahydrite (MgSO4 · 6H2O) and epsomite (MgSO4 · 7H2O), in the visible and infrared (VNIR) spectral range 0.5/4.0 µm, as particulate for three different grain size ranges: 20–50 µm, 75–100 µm and 125–150 µm. All samples were measured in the 93–298 K temperature range. The spectra of these hydrated salts are characterized by strong OH absorption bands in the 1.0–1.5 µm region, and by H2O absorption bands near 2 and 3 µm. Other weak features show up at low temperatures near 1.75 µm (in both hexahydrite and epsomite) and 2.2 µm (only in hexahydrite). The spectral behavior of the absorption bands of these two minerals has been analyzed as a function of both grain size and temperature, deriving trends related to specific spectral parameters such as band center, band depth, band area, and band width. Hydrated minerals, in particular mono- and poly-hydrated sulfates, are present in planetary objects such as Mars and the icy Galilean satellites. Safe detection of these minerals shall rely on detailed laboratory investigation of these materials in different environmental conditions. Hence an accurate spectral analysis of such minerals as a function of temperature is key to better understand and constrain future observations. © 2016 Elsevier Inc.

Lilensten J.,Institute Of Planetologie Et Dastrophysique Of Grenoble Ipag | Coates A.J.,University College London | Dudok de Wit T.,LPC2E OSUC | Horne R.B.,British Antarctic Survey | And 4 more authors.
Astronomy and Astrophysics Review | Year: 2014

Space weather has become a mature discipline for the Earth space environment. With increasing efforts in space exploration, it is becoming more and more necessary to understand the space environments of bodies other than Earth. This is the background for an emerging aspect of the space weather discipline: planetary space weather. In this article, we explore what characterizes planetary space weather, using some examples throughout the solar system. We consider energy sources and timescales, the characteristics of solar system objects and interaction processes. We discuss several developments of space weather interactions including the effects on planetary radiation belts, atmospheric escape, habitability and effects on space systems. We discuss future considerations and conclude that planetary space weather will be of increasing importance for future planetary missions. © 2014, The Author(s).

Messerotti M.,National institute for astrophysics | Messerotti M.,University of Trieste | Lilensten J.,Institute Of Planetologie Et Dastrophysique Of Grenoble Ipag | Calders S.,Belgian Institute for Space Aeronomy | And 2 more authors.
Journal of Space Weather and Space Climate | Year: 2014

COST (European Cooperation in Science and Technology) is one of the longest-running European frameworks supporting cooperation among scientists and researchers across Europe. Its action ES0803 "Developing Space Weather Products and Services in Europe" involves the task "Exploitation, Dissemination, Education and Outreach". To meet the objectives of this task, we describe how we developed and maintained the Space Weather Portal, initiated the electronic Journal of Space Weather and Space Climate, took care of the scientific organization of the annual European Space Weather Week conference and of two schools for scientists and students from the space weather community. We also describe several dissemination projects supported by the action, which target the non-specialist in the field of space weather. © P. Vanlommel et al., Published by EDP Sciences 2014.

Anugu N.,University of Porto | Garcia P.,University of Porto | Amorim A.,SIM and FCUL Edificio C8 | Gordo P.,SIM and FCUL Edificio C8 | And 5 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

The GRAVITY acquisition camera has four 9x9 Shack-Hartmann sensors operating in the near-infrared. It measures the slow variations of a quasi-distorted wavefront of four telescope beams simultaneously, by imaging the Galactic Center field. The Shack-Hartmann lenslet images of the Galactic Center are generated. Since the lenslet array images are filled with the crowded Galactic Center stellar field, an extended object, the local shifts of the distorted wavefront have to be estimated with a correlation algorithm. In this paper we report on the accuracy of six existing centroid algorithms for the Galactic Center stellar field. We show the VLTI tunnel atmospheric turbulence phases are reconstructed back with a precision of 100 nm at 2 s integration. © 2014 SPIE.

Anugu N.,University of Porto | Garcia P.J.V.,University of Porto | Wieprecht E.,Max Planck Institute for Extraterrestrial Physics | Amorim A.,SIM Inc | And 8 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

The acquisition camera for the GRAVITY/VLTI instrument implements four functions: a) field imager: science field imaging, tip-tilt; b) pupil tracker: telescope pupil lateral and longitudinal positions; c) pupil imager: telescope pupil imaging and d) aberration sensor: The VLTI beam higher order aberrations measurement. We present the dedicated algorithms that simulate the GRAVITY acquisition camera detector measurements considering the realistic imaging conditions, complemented by the pipeline used to extract the data. The data reduction procedure was tested with real aberrations at the VLTI lab and reconstructed back accurately. The acquisition camera software undertakes the measurements simultaneously for all four AT/UTs in 1 s. The measured parameters are updated in the instrument online database. The data reduction software uses the ESO Common Library for Image Processing (CLIP), integrated in to the ESO VLT software environment. © 2014 SPIE.

Veganzones M.A.,CNRS GIPSA Laboratory | Cohen J.,CNRS GIPSA Laboratory | Farias R.C.,CNRS GIPSA Laboratory | Marrero R.,CNRS GIPSA Laboratory | And 4 more authors.
2015 23rd European Signal Processing Conference, EUSIPCO 2015 | Year: 2015

Spectral unmixing is one of the most important and studied topics in hyperspectral image analysis. By means of spectral unmixing it is possible to decompose a hyperspectral image in its spectral components, the so-called endmembers, and their respective fractional spatial distributions, so-called abundance maps. New hyperspectral missions will allow to acquire hyperspectral images in new ways, for instance, in temporal series or in multi-angular acquisitions. Working with these incoming huge databases of multi-way hyperspec-tral images will raise new challenges to the hyperspectral community. Here, we propose the use of compression-based non-negative tensor canonical polyadic (CP) decompositions to analyze this kind of datasets. Furthermore, we show that the non-negative CP decomposition could be understood as a multi-linear spectral unmixing technique. We evaluate the proposed approach by means of Mars synthetic datasets built upon multi-angular in-lab hyperspectral acquisitions. © 2015 EURASIP.

Paul B.,ONERA | Paul B.,Aix - Marseille University | Paul B.,University Paris Diderot | Sauvage J.-F.,ONERA | And 16 more authors.
Astronomy and Astrophysics | Year: 2014

Context. The second-generation instrument SPHERE, dedicated to high-contrast imaging, will soon be in operation on the European Very Large Telescope. Such an instrument relies on an extreme adaptive optics system coupled with a coronagraph that suppresses most of the diffracted stellar light. However, the coronagraph performance is strongly limited by quasi-static aberrations that create long-lived speckles in the scientific image plane, which can easily be mistaken for planets.Aims. The wavefront analysis performed by SPHERE's adaptive optics system uses a dedicated wavefront sensor. The ultimate performance is thus limited by the unavoidable differential aberrations between the wavefront sensor and the scientific camera, which have to be estimated and compensated for. In this paper, we use the COFFEE approach to measure and compensate for SPHERE's quasi-static aberrations.Methods. COronagraphic Focal-plane waveFront Estimation for Exoplanet detection (COFFEE), which consists in an extension of phase diversity to coronagraphic imaging, estimates the quasi-static aberrations, including the differential ones, using only two focal plane images recorded by the scientific camera. In this paper, we use coronagraphic images recorded from SPHERE's infrared detector IRDIS to estimate the aberrations upstream of the coronagraph, which are then compensated for using SPHERE's extreme adaptive optics loop SAXO.Results. We first validate the ability of COFFEE to estimate high-order aberrations by estimating a calibrated influence function pattern introduced upstream of the coronagraph. We then use COFFEE in an original iterative compensation process to compensate for the estimated aberrations, leading to a contrast improvement by a factor that varies from 1.4 to 4.7 between 2λ/D and 15λ/D on IRDIS. The performance of the compensation process is also evaluated through simulations. An excellent match between experimental results and these simulations is found. © ESO, 2014.

Ferrec Y.,ONERA | De la Barriere F.,ONERA | Le Coarer E.,Institute Of Planetologie Et Dastrophysique Of Grenoble Ipag | Diard T.,ONERA | And 6 more authors.
Fourier Transform Spectroscopy, FTS 2015 | Year: 2015

Microspoc is a family of miniaturized static Fourier transform spectrometers based on a wedge interferometer directly integrated on the focal plane array. Current status and perspective for visible and infrared instruments are presented. © OSA 2015.

Doute S.,Institute Of Planetologie Et Dastrophysique Of Grenoble Ipag | Ceamanos X.,Meteo - France | Appere T.,CEA Saclay Nuclear Research Center
Planetary and Space Science | Year: 2013

We propose a new method to retrieve the optical depth of Martian aerosols (AOD) from OMEGA and CRISM hyperspectral imagery at a reference wavelength of 1μm. Our method works even if the underlying surface is completely made of minerals, corresponding to a low contrast between surface and atmospheric dust, while being observed at a fixed geometry. Minimizing the effect of the surface reflectance properties on the AOD retrieval is the second principal asset of our method. The method is based on the parametrization of the radiative coupling between particles and gas determining, with local altimetry, acquisition geometry, and the meteorological situation, the absorption band depth of gaseous CO2. Because the last three factors can be predicted to some extent, we can define a new parameter β that expresses specifically the strength of the gas-aerosols coupling while directly depending on the AOD. Combining estimations of β and top of the atmosphere radiance values extracted from the observed spectra within the CO2 gas band at 2μm, we evaluate the AOD and the surface reflectance by radiative transfer inversion. One should note that practically β can be estimated for a large variety of mineral or icy surfaces with the exception of CO2 ice when its 2μm solid band is not sufficiently saturated. Validation of the proposed method shows that it is reliable if two conditions are fulfilled: (i) the observation conditions provide large incidence or/and emergence angles (ii) the aerosols are vertically well mixed in the atmosphere. Experiments conducted on OMEGA nadir looking observations as well as CRISM multi-angular acquisitions with incidence angles higher than 65 in the first case and 33 in the second case produce very satisfactory results. Finally in a companion paper the method is applied to monitoring atmospheric dust spring activity at high southern latitudes on Mars using OMEGA. © 2013 Elsevier Ltd.

Jacques J.,Lille University of Science and Technology | Fraix-Burnet D.,Institute Of Planetologie Et Dastrophysique Of Grenoble Ipag
EAS Publications Series | Year: 2015

Ordinary least square is the common way to estimate linear regression models. When inputs are correlated or when they are too numerous, regression methods using derived inputs directions or shrinkage methods can be efficient alternatives. Methods using derived inputs directions build new uncorrelated variables as linear combination of the initial inputs, whereas shrinkage methods introduce regularization and variable selection by penalizing the usual least square criterion. Both kinds of methods are presented and illustrated thanks to the R software on an astronomical dataset. © 2015 EAS, EDP Sciences.

Loading Institute Of Planetologie Et Dastrophysique Of Grenoble Ipag collaborators
Loading Institute Of Planetologie Et Dastrophysique Of Grenoble Ipag collaborators