162 research outputs found
Remote Predictive Mapping 1. Remote Predictive Mapping (RPM): A Strategy for Geological Mapping of Canada’s North
Remote Predictive Mapping (RPM) techniques are being developed and refined by the Geological Survey of Canada for mapping Canada’s North. Remote Predictive Mapping should be considered an integral part of the geological mapping process designed to involve compilation, and re-compilation of data derived from existing geological maps, aerial photographs, satellite imagery, and airborne geophysical data. Predictive geological maps may be iteratively revised and upgraded to publishable geological maps by integrating remotely sensed data with newly acquired field and laboratory data, as RPM techniques are progressively tested and insight evolves. A predictive map, produced without collection of new, field-based data, may also serve as a first-order geologic map in areas where field-based studies cannot be accomplished due to expense of field access or remoteness. As a welcome consequence of adopting RPM into the normal work flow of any mapping or exploration project, there will, by necessity, be greater participation and integration of expertise of field geologists, geophysicists, Geographic Information System (GIS) and remote sensing specialists. Significantly, RPM also encourages geoscience organizations to make full use of all available geoscience data.
This paper outlines a strategy for RPM and provides processing and interpretation examples based on a variety of geoscience data and interpretation techniques to be employed for geologic mapping.
SOMMAIRE
La Commission géologique du Canada développe et raffine des techniques de télécartographique prédictive (TCP) pour cartographier du Nord canadien. La télécartographie prédictive doit être perçue comme une composante intégrée d’un processus de cartographie géologique de compilation et de recompilation de données extraites de cartes géologiques, de photographies aériennes, d’imageries satellitaires, et de géophysiques aéroportées existantes. Les cartes géologiques prédictives peu-vent ainsi être révisées, mises à jour et publiées selon une approche itérative intégrant les données de télédétection avec les données de terrain et de laboratoire nouvellement acquises, au gré de l’évolution et du raffinement des techniques de TCP. Dans les cas de régions trop éloignées, ou parce que les coûts d’établissement de cartes géologiques de base régulières seraient prohibitifs, la TCP peut aussi être utilisée pour produire une carte géologique de base. D’entrée de jeu, on réalise que l’adoption de la TCP dans la routine de production normale de tout projet de cartographie ou d’exploration permettra, en soi, une meilleure prise en compte et une meilleure intégration des savoirs-faires des géologues de terrain, des géophysiciens et des spécialistes de la télédétection et des systèmes d’information géographique (SIG). Par sa nature même, la TCP permet aux organisations géoscientifiques de faire plein usage de toutes les données géoscientifiques dont elles disposent.
Le présent article définit une stratégie de TCP et décrit des exemples de traitement et d’interprétation d’une variété de données géoscientifiques et de techniques d’interprétation utilisables pour la production de cartes géologiques
High-Resolution Mid-Infrared Morphology of Cygnus A
We present subarcsecond resolution mid-infrared images at 10.8 and 18.2
microns of Cygnus A. These images were obtained with the University of Florida
mid-IR camera/spectrometer OSCIR at the Keck II 10-m telescope. Our data show
extended mid-IR emission primarily to the east of the nucleus with a possible
western extension detected after image deconvolution. This extended emission is
closely aligned with the bi-conical structure observed at optical and near-IR
wavelengths by the HST. This emission is consistent with dust heated from the
central engine of Cygnus A. We also marginally detect large-scale low level
emission extending > 1.5 kpc from the nucleus which may be caused by in-situ
star formation, line emission, and/or PAH contamination within the bandpass of
our wide N-band filter.Comment: 20 pages, 8 figures, accepted for publication in the Astrophysical
Journa
MS 2053.7-0449: Confirmation of a bimodal mass distribution from strong gravitational lensing
We present the first strong lensing study of the mass distribution in the
cluster MS 2053-04 based on HST archive data. This massive, X-ray luminous
cluster has a redshift z=0.583, and it is composed of two structures that are
gravitationally bound to each other. The cluster has one multiply imaged system
constituted by a double gravitational arc.
We have performed a parametric strong lensing mass reconstruction using NFW
density profiles to model the cluster potential. We also included perturbations
from 23 galaxies, modeled like elliptical singular isothermal sphere, that are
approximately within 1'x1' around the cluster center. These galaxies were
constrained in both the geometric and dynamical parameters with observational
data. Our analysis predicts a third image which is slightly demagnified. We
found a candidate for this counter-image near the expected position and with
the same F702W-F814W colors as the gravitational arcs in the cluster. The
results from the strong lensing model shows the complex structure in this
cluster, the asymmetry and the elongation in the mass distribution, and are
consistent with previous spectrophotometric results that indicate that the
cluster has a bimodal mass distribution. Finally, the derived mass profile was
used to estimate the mass within the arcs and for comparison with X-ray
estimates.Comment: To be published in ApJ (accepted
Remote Predictive Mapping 3. Optical Remote Sensing – A Review for Remote Predictive Geological Mapping in Northern Canada
Optical remotely sensed data have broad application for geological mapping in Canada’s North. Diverse remote sensors and digital image processing techniques have specific mapping functions, as demonstrated by numerous examples and associated interpretations. Moderate resolution optical sensors are useful for discriminating rock types, whereas sensors that offer increased spectral resolution (i.e. hyperspectral sensors) allow the geologist to identify certain rock types (mainly different types of carbonates, Fe-bearing rocks, sulphates and hydroxyl-(clay-) bearing rocks) as opposed to merely discriminating between them. Increased spatial resolution and the ability to visualize the earth’s surface in stereo are now offered by a host of optical sensors. However, the usefulness of optical remote sensing for geological mapping is highly dependent on the geologic, surficial and biophysical environment, and bedrock predictive mapping is most successful in areas not obscured by thick drift and vegetation/lichen cover, which is typical of environments proximal to coasts. In general, predictive mapping of surficial materials has fewer restrictions. Optical imagery can be enhanced in a variety of ways and fused with other geo-science datasets to produce imagery that can be visually interpreted in a GIS environment. Computer processing techniques are useful for undertaking more quantitative analyses of imagery for mapping bedrock, surficial materials and geomorphic or glacial features.
SOMMAIRE
Les données recueillies par télédétection optique offrent beaucoup de possibilités pour la cartographie géologique des régions nordiques canadiennes. La diversité des télécapteurs et des techniques de traitement numérique des données permet la définition de fonctions de cartographie spécifique, tel que l’illustre de nombreux exemples et interprétations associées. Des capteurs optiques de moyenne résolution sont utiles pour différencier les types de roche, alors que les capteurs à plus fines résolutions (les capteurs hyperspectraux, par ex.) permettent au géologue de subdiviser certains types de roches (principalement différents types de carbonates, roches ferrugineuses, roches à sulfates et à hydroxyle (argile). Une meilleure résolution spatiale et la fonction de vision stéréoscopique sont maintenant offertes sur une gamme de capteurs optiques. Cela dit, l’utilité de la télédétection optique pour la cartographie géologique est fortement tributaire des conditions de la géologie de surface et de son environnement biophysique, le potentiel prédictif de la télécartographie étant maximal pour les régions exemptes d’une couverture épaisse de dépôts glaciaires ou d’une couverture végétale/lichen caractéristique typique des environnements longeant les côtes. Divers procédés permettent de rehausser l’imagerie optique et de réaliser des fusions avec d’autres jeux de données géoscientifiques et de produire une imagerie visuellement inter-prétable en environnement de SIG. Les techniques de traitement de données par ordinateur sont utiles pour d’autres types d’analyse quantitative d’imagerie pour la cartographie des matériaux de couverture du socle et pour répertorier des formes glaciaires et géomorphologiques
AKARI near-infrared spectroscopy of the aromatic and aliphatic hydrocarbon emission features in the galactic superwind of M 82
Aims. We investigate the properties of hydrocarbon grains in the galactic
superwind of M 82. Methods. With AKARI, we performed near-infrared (2.5 - 4.5
um) spectroscopic observations of 34 regions in M 82 including its northern and
southern halos. Results. Many of the spectra show strong emission at 3.3 um due
to polycyclic aromatic hydrocarbons (PAHs) and relatively weak features at 3.4
- 3.6 um due to aliphatic hydrocarbons. In particular, we clearly detect the
PAH 3.3 um emission and the 3.4 - 3.6 um features in halo regions, which are
located at a distance of 2 kpc away from the galactic center. We find that the
ratios of the 3.4 - 3.6 um features to the 3.3 um feature intensity
significantly increase with distance from the galactic center, while the ratios
of the 3.3 um feature to the AKARI 7 um band intensity do not. Conclusions. Our
results clearly confirm the presence of small PAHs even in a harsh environment
of the halo of M 82. The results also reveal that the aliphatic hydrocarbons
emitting the 3.4 - 3.6 um features are unusually abundant in the halo,
suggesting that small carbonaceous grains are produced by shattering of larger
grains in the galactic superwind.Comment: 5 pages, 3 figures, 1 table, accepted for publication in A&
Arc Statistics in Clusters: Galaxy Contribution
The frequency with which background galaxies appear as long arcs as a result
of gravitational lensing by foreground clusters of galaxies has recently been
found to be a very sensitive probe of cosmological models by Bartelmann et al.
(1998). They have found that such arcs would be expected far less frequently
than observed (by an order of magnitude) in the currently favored model for the
universe, with a large cosmological constant . Here we
analyze whether including the effect of cluster galaxies on the likelihood of
clusters to generate long-arc images of background galaxies can change the
statistics. Taking into account a variety of constraints on the properties of
cluster galaxies, we find that there are not enough sufficiently massive
galaxies in a cluster for them to significantly enhance the cross section of
clusters to generate long arcs. We find that cluster galaxies typically enhance
the cross section by only .Comment: 19 pages, 1 figure, uses aasms4.sty, submitted to Ap
Dust-temperature of an isolated star-forming cloud: Herschel observations of the Bok globule CB244
We present Herschel observations of the isolated, low-mass star-forming Bok
globule CB244. It contains two cold sources, a low-mass Class 0 protostar and a
starless core, which is likely to be prestellar in nature, separated by 90
arcsec (~ 18000 AU). The Herschel data sample the peak of the Planck spectrum
for these sources, and are therefore ideal for dust-temperature and column
density modeling. With these data and a near-IR extinction map, the MIPS 70
micron mosaic, the SCUBA 850 micron map, and the IRAM 1.3 mm map, we model the
dust-temperature and column density of CB244 and present the first measured
dust-temperature map of an entire star-forming molecular cloud. We find that
the column-averaged dust-temperature near the protostar is ~ 17.7 K, while for
the starless core it is ~ 10.6K, and that the effect of external heating causes
the cloud dust-temperature to rise to ~ 17 K where the hydrogen column density
drops below 10^21 cm^-2. The total hydrogen mass of CB244 (assuming a distance
of 200 pc) is 15 +/- 5 M_sun. The mass of the protostellar core is 1.6 +/- 0.1
M_sun and the mass of the starless core is 5 +/- 2 M_sun, indicating that ~ 45%
of the mass in the globule is participating in the star-formation process.Comment: Accepted for A&A Herschel Special Issue; 5 pages, 2 figure
ARCRAIDER II: Arc search in a sample of non-Abell clusters
We present a search for gravitational arcs in a sample of X-ray luminous,
medium redshift clusters of galaxies. The sample of clusters is called
ARCRAIDER, is based on the ROSAT Bright Survey (RBS) and fulfills the following
criteria: (a) X-ray luminosity Lx>=0.5x10^45erg/s (0.5-2keV band), (b) redshift
range 0.1<=z<=0.52, (c) classified as clusters in the RBS, (d) not a member of
the Abell catalogue and, finally, (e) visible from the ESO sites La
Silla/Paranal (declination \delta<=20deg). In total we found more than 35
(giant) arc/arclet candidates, including a possible radial arc, one
galaxy-galaxy lensing event and a possible quasar triple image in 14 of the 21
clusters of galaxies. Hence 66% of the sample members are possible lenses.Comment: Accepted for publication in Astronomy and Astrophysics; 8 pages
(excl. Appendix), 6 figures, 9 tables; Please download the high-res images of
the appendix from
http://astro-staff.uibk.ac.at/~w.kausch/ARCRAIDER_II_images.tar.g
Effects of Triaxiality on the Statistics of Large-Separation Gravitational Lenses
We study the statistics of large-separation gravitational lens systems
produced by non-spherical halos in the Cold Dark Matter (CDM) model.
Specifically, we examine how the triaxiality of CDM halos affects the overall
lensing probabilities and the relative numbers of different image
configurations (double, quadruple, and naked cusp lenses). We find that
triaxiality significantly enhances lensing probabilities by a factor of ~2-4,
so it cannot be ignored. If CDM halos have central density slopes alpha<~1.5,
we predict that a significant fraction (>~20%) of large-separation lenses
should have naked cusp image configurations; this contrasts with lensing by
isothermal (\alpha~2) galaxies where naked cusp configurations are rare. The
image multiplicities depend strongly on the inner density slope \alpha: for
\alpha=1, the naked cusp fraction is >~60%; while for \alpha=1.5, quadruple
lenses are actually the most probable. Thus, the image multiplicities in
large-separation lenses offer a simple new probe of the inner density profiles
of dark matter halos. We also compute the expected probabilities and image
multiplicities for lensed quasars in the Sloan Digital Sky Survey, and argue
that the recent discovery of the large-separation quadruple lens SDSS
J1004+4112 is consistent with expectations for CDM.Comment: 10 pages, 10 figures, using emulateapj.cls, accepted for publication
in Ap
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