14,619 research outputs found
A novel satellite mission concept for upper air water vapour, aerosol and cloud observations using integrated path differential absorption LiDAR limb sounding
We propose a new satellite mission to deliver high quality measurements of upper air water vapour. The concept centres around a LiDAR in limb sounding by occultation geometry, designed to operate as a very long path system for differential absorption measurements. We present a preliminary performance analysis with a system sized to send 75 mJ pulses at 25 Hz at four wavelengths close to 935 nm, to up to 5 microsatellites in a counter-rotating orbit, carrying retroreflectors characterized by a reflected beam divergence of roughly twice the emitted laser beam divergence of 15 µrad. This provides water vapour profiles with a vertical sampling of 110 m; preliminary calculations suggest that the system could detect concentrations of less than 5 ppm. A secondary payload of a fairly conventional medium resolution multispectral radiometer allows wide-swath cloud and aerosol imaging. The total weight and power of the system are estimated at 3 tons and 2,700 W respectively. This novel concept presents significant challenges, including the performance of the lasers in space, the tracking between the main spacecraft and the retroreflectors, the refractive effects of turbulence, and the design of the telescopes to achieve a high signal-to-noise ratio for the high precision measurements. The mission concept was conceived at the Alpbach Summer School 2010
Innovative Techniques for the Retrieval of Earth’s Surface and Atmosphere Geophysical Parameters: Spaceborne Infrared/Microwave Combined Analyses
With the advent of the first satellites for Earth Observation: Landsat-1 in July 1972 and ERS-1 in May 1991, the discipline of environmental remote sensing has become, over time, increasingly fundamental for the study of phenomena characterizing the planet Earth. The goal of environmental remote sensing is to perform detailed analyses and to monitor the temporal evolution of different physical phenomena, exploiting the mechanisms of interaction between the objects that are present in an observed scene and the electromagnetic radiation detected by sensors, placed at a distance from the scene, operating at different frequencies. The analyzed physical phenomena are those related to climate change, weather forecasts, global ocean circulation, greenhouse gas profiling, earthquakes, volcanic eruptions, soil subsidence, and the effects of rapid urbanization processes. Generally, remote sensing sensors are of two primary types: active and passive. Active sensors use their own source of electromagnetic radiation to illuminate and analyze an area of interest. An active sensor emits radiation in the direction of the area to be investigated and then detects and measures the radiation that is backscattered from the objects contained in that area. Passive sensors, on the other hand, detect natural electromagnetic radiation (e.g., from the Sun in the visible band and the Earth in the infrared and microwave bands) emitted or reflected by the object contained in the observed scene. The scientific community has dedicated many resources to developing techniques to estimate, study and analyze Earth’s geophysical parameters. These techniques differ for active and passive sensors because they depend strictly on the type of the measured physical quantity. In my P.h.D. work, inversion techniques for estimating Earth’s surface and atmosphere geophysical parameters will be addressed, emphasizing methods based on machine learning (ML). In particular, the study of cloud microphysics and the characterization of Earth’s surface changes phenomenon are the critical points of this work
A Data Cube Extraction Pipeline for a Coronagraphic Integral Field Spectrograph
Project 1640 is a high contrast near-infrared instrument probing the
vicinities of nearby stars through the unique combination of an integral field
spectrograph with a Lyot coronagraph and a high-order adaptive optics system.
The extraordinary data reduction demands, similar those which several new
exoplanet imaging instruments will face in the near future, have been met by
the novel software algorithms described herein. The Project 1640 Data Cube
Extraction Pipeline (PCXP) automates the translation of 3.8*10^4 closely
packed, coarsely sampled spectra to a data cube. We implement a robust
empirical model of the spectrograph focal plane geometry to register the
detector image at sub-pixel precision, and map the cube extraction. We
demonstrate our ability to accurately retrieve source spectra based on an
observation of Saturn's moon Titan.Comment: 35 pages, 15 figures; accepted for publication in PAS
Observing planet-disk interaction in debris disks
Context. Structures in debris disks induced by planetdisk interaction are
promising to provide valuable constraints on the existence and properties of
embedded planets. Aims. We investigate the observability of structures in
debris disks induced by planet-disk interaction. Methods. The observability of
debris disks with the Atacama Large Millimeter/submillimeter Array (ALMA) is
studied on the basis of a simple analytical disk model. Furthermore, N-body
simulations are used to model the spatial dust distribution in debris disks
under the influence of planet-disk interaction. Images at optical scattered
light to millimeter thermal re-emission are computed. Available information
about the expected capabilities of ALMA and the James Webb Space Telescope
(JWST) are used to investigate the observability of characteristic disk
structures through spatially resolved imaging. Results. Planet-disk interaction
can result in prominent structures. This provides the opportunity of detecting
and characterizing extrasolar planets in a range of masses and radial distances
from the star that is not accessible to other techniques. Facilities that will
be available in the near future are shown to provide the capabilities to
spatially resolve and characterize structures in debris disks. Limitations are
revealed and suggestions for possible instrument setups and observing
strategies are given. In particular, ALMA is limited by its sensitivity to
surface brightness, which requires a trade-off between sensitivity and spatial
resolution. Space-based midinfrared observations will be able to detect and
spatially resolve regions in debris disks even at a distance of several tens of
AU from the star, where the emission from debris disks in this wavelength range
is expected to be low. [Abridged]Comment: 16 pages, 10 figures, accepted by A&
SPHERE: the exoplanet imager for the Very Large Telescope
Observations of circumstellar environments to look for the direct signal of
exoplanets and the scattered light from disks has significant instrumental
implications. In the past 15 years, major developments in adaptive optics,
coronagraphy, optical manufacturing, wavefront sensing and data processing,
together with a consistent global system analysis have enabled a new generation
of high-contrast imagers and spectrographs on large ground-based telescopes
with much better performance. One of the most productive is the
Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE)
designed and built for the ESO Very Large Telescope (VLT) in Chile. SPHERE
includes an extreme adaptive optics system, a highly stable common path
interface, several types of coronagraphs and three science instruments. Two of
them, the Integral Field Spectrograph (IFS) and the Infra-Red Dual-band Imager
and Spectrograph (IRDIS), are designed to efficiently cover the near-infrared
(NIR) range in a single observation for efficient young planet search. The
third one, ZIMPOL, is designed for visible (VIR) polarimetric observation to
look for the reflected light of exoplanets and the light scattered by debris
disks. This suite of three science instruments enables to study circumstellar
environments at unprecedented angular resolution both in the visible and the
near-infrared. In this work, we present the complete instrument and its on-sky
performance after 4 years of operations at the VLT.Comment: Final version accepted for publication in A&
Neptune at Summer Solstice: Zonal Mean Temperatures from Ground-Based Observations 2003-2007
Imaging and spectroscopy of Neptune's thermal infrared emission is used to
assess seasonal changes in Neptune's zonal mean temperatures between Voyager-2
observations (1989, heliocentric longitude Ls=236) and southern summer solstice
(2005, Ls=270). Our aim was to analyse imaging and spectroscopy from multiple
different sources using a single self-consistent radiative-transfer model to
assess the magnitude of seasonal variability. Globally-averaged stratospheric
temperatures measured from methane emission tend towards a quasi-isothermal
structure (158-164 K) above the 0.1-mbar level, and are found to be consistent
with spacecraft observations of AKARI. This remarkable consistency, despite
very different observing conditions, suggests that stratospheric temporal
variability, if present, is 5 K at 1 mbar and 3 K at 0.1 mbar during
this solstice period. Conversely, ethane emission is highly variable, with
abundance determinations varying by more than a factor of two. The retrieved
C2H6 abundances are extremely sensitive to the details of the T(p) derivation.
Stratospheric temperatures and ethane are found to be latitudinally uniform
away from the south pole (assuming a latitudinally-uniform distribution of
stratospheric methane). At low and midlatitudes, comparisons of synthetic
Voyager-era images with solstice-era observations suggest that tropospheric
zonal temperatures are unchanged since the Voyager 2 encounter, with cool
mid-latitudes and a warm equator and pole. A re-analysis of Voyager/IRIS 25-50
{\mu}m mapping of tropospheric temperatures and para-hydrogen disequilibrium
suggests a symmetric meridional circulation with cold air rising at
mid-latitudes (sub-equilibrium para-H2 conditions) and warm air sinking at the
equator and poles (super-equilibrium para-H2 conditions). The most significant
atmospheric changes are associated with the polar vortex (absent in 1989).Comment: 35 pages, 19 figures. Accepted for publication in Icaru
Imaging of X-Ray-Excited Emissions from Quantum Dots and Biological Tissue in Whole Mouse
© The Author(s) 2019. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.Optical imaging in clinical and preclinical settings can provide a wealth of biological information, particularly when coupled with targetted nanoparticles, but optical scattering and absorption limit the depth and resolution in both animal and human subjects. Two new hybrid approaches are presented, using the penetrating power of X-rays to increase the depth of optical imaging. Foremost, we demonstrate the excitation by X-rays of quantum-dots (QD) emitting in the near-infrared (NIR), using a clinical X-ray system to map the distribution of QDs at depth in whole mouse. We elicit a clear, spatially-resolved NIR signal from deep organs (brain, liver and kidney) with short (1 second) exposures and tolerable radiation doses that will permit future in vivo applications. Furthermore, X-ray-excited endogenous emission is also detected from whole mouse. The use of keV X-rays to excite emission from QDs and tissue represent novel biomedical imaging technologies, and exploit emerging QDs as optical probes for spatial-temporal molecular imaging at greater depth than previously possible.Peer reviewe
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