134,428 research outputs found
Discrimination of rock classes and alteration products in southwestern Saudi Arabia with computer-enhanced LANDSAT data
Digital LANDSAT MSS data for an area in the southwestern Arabian Shield were computer-enhanced to improve discrimination of rock classes, and recognition of gossans associated with massive sulphide deposits. The test area is underlain by metamorphic rocks that are locally intruded by granites; these are partly overlain by sandstones. The test area further includes the Wadi Wassat and Wadi Qatan massive sulphide deposits, which are commonly capped by gossans of ferric oxides, silica, and carbonates. Color patterns and boundaries on contrast-stretched ratio color composite imagery, and on complementary images constructed using principal component and canonical analyses transformations, correspond exceptionally well to 1:100,000 scale field maps. A qualitative visual comparison of information content showed that the ratio enhancement provided the best overall image for identification of rock type and alteration products
Spatial deconvolution of spectropolarimetric data: an application to quiet Sun magnetic elements
Observations of the Sun from the Earth are always limited by the presence of
the atmosphere, which strongly disturbs the images. A solution to this problem
is to place the telescopes in space satellites, which produce observations
without any (or limited) atmospheric aberrations. However, even though the
images from space are not affected by atmospheric seeing, the optical
properties of the instruments still limit the observations. In the case of
diffraction limited observations, the PSF establishes the maximum allowed
spatial resolution, defined as the distance between two nearby structures that
can be properly distinguished. In addition, the shape of the PSF induce a
dispersion of the light from different parts of the image, leading to what is
commonly termed as stray light or dispersed light. This effect produces that
light observed in a spatial location at the focal plane is a combination of the
light emitted in the object at relatively distant spatial locations. We aim to
correct the effect produced by the telescope's PSF using a deconvolution
method, and we decided to apply the code on Hinode/SP quiet Sun observations.
We analyze the validity of the deconvolution process with noisy data and we
infer the physical properties of quiet Sun magnetic elements after the
deconvolution process.Comment: 14 pages, 9 figure
Signatures of galactic magnetic lensing upon ultra high energy cosmic rays
We analyse several implications of lensing by the regular component of the
galactic magnetic field upon the observed properties of ultra high energy
cosmic rays. Magnetic fields deflect cosmic ray trajectories, causing flux
(de)magnification, formation of multiple images of a single source, and time
delays. We derive the energy dependence of these effects near the caustics at
which the flux amplification of a point source diverges. We show that the large
magnification of images around caustics leads to an amplification bias, which
can make them dominate the flux in some energy ranges. We argue that clustering
in the arrival directions of UHECRs of comparable energy may be due to magnetic
lensing around caustics. We show that magnetic lensing can also significantly
alter the observed composition of cosmic rays at the highest energies. We also
show that the time delay between events from a single image may monotonically
decrease with decreasing energy in the neighborhood of a caustic, opposite to
its behaviour in normal regions.Comment: 18 pages, 7 figures, uses JHEP.cl
Multiseasonal variables in digital image enhancements for geological applications
Examples of enhanced multiseasonal orbital imagery illustrate the influence of multiseasonal changes in their spatial and spectral attributes, and consequently in their application to structural geology and lithological discrimination. Shadow effects associated with appropriate solar elevation and azimuth effects enhance the spatial attributes but not the spectral. In this case, variations in illumination conditions should be minimized by selecting images with high solar elevation and by the use of techniques that minimize illumination conditions. Multiseasonal imagery should be used in the identification of spectral contrast changes of rock-soil-vegetation associations which can provide evidences of related lithological units and structural features. The extraction of maximum geological information requires, at least, a fall/winter and a spring/summer scene from which spatial, spectral and multiseasonal attributes can be adequately explored
Color enhancement of landsat agricultural imagery: JPL LACIE image processing support task
Color enhancement techniques were applied to LACIE LANDSAT segments to determine if such enhancement can assist analysis in crop identification. The procedure involved increasing the color range by removing correlation between components. First, a principal component transformation was performed, followed by contrast enhancement to equalize component variances, followed by an inverse transformation to restore familiar color relationships. Filtering was applied to lower order components to reduce color speckle in the enhanced products. Use of single acquisition and multiple acquisition statistics to control the enhancement were compared, and the effects of normalization investigated. Evaluation is left to LACIE personnel
Probing for Exoplanets Hiding in Dusty Debris Disks: Disk Imaging, Characterization, and Exploration with HST/STIS Multi-Roll Coronagraphy
Spatially resolved scattered-light images of circumstellar (CS) debris in
exoplanetary systems constrain the physical properties and orbits of the dust
particles in these systems. They also inform on co-orbiting (but unseen)
planets, systemic architectures, and forces perturbing starlight-scattering CS
material. Using HST/STIS optical coronagraphy, we have completed the
observational phase of a program to study the spatial distribution of dust in
ten CS debris systems, and one "mature" protoplanetrary disk all with HST
pedigree, using PSF-subtracted multi-roll coronagraphy. These observations
probe stellocentric distances > 5 AU for the nearest stars, and simultaneously
resolve disk substructures well beyond, corresponding to the giant planet and
Kuiper belt regions in our Solar System. They also disclose diffuse very
low-surface brightness dust at larger stellocentric distances. We present new
results inclusive of fainter disks such as HD92945 confirming, and better
revealing, the existence of a narrow inner debris ring within a larger diffuse
dust disk. Other disks with ring-like sub-structures, significant asymmetries
and complex morphologies include: HD181327 with a posited spray of ejecta from
a recent massive collision in an exo-Kuiper belt; HD61005 suggested interacting
with the local ISM; HD15115 & HD32297, discussed also in the context of
environmental interactions. These disks, and HD15745, suggest debris system
evolution cannot be treated in isolation. For AU Mic's edge-on disk,
out-of-plane surface brightness asymmetries at > 5 AU may implicate one or more
planetary perturbers. Time resolved images of the MP Mus proto-planetary disk
provide spatially resolved temporal variability in the disk illumination. These
and other new images from our program enable direct inter-comparison of the
architectures of these exoplanetary debris systems in the context of our own
Solar System.Comment: 109 pages, 43 figures, accepted for publication in the Astronomical
Journa
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