12,569 research outputs found
Astrometry.net: Blind astrometric calibration of arbitrary astronomical images
We have built a reliable and robust system that takes as input an
astronomical image, and returns as output the pointing, scale, and orientation
of that image (the astrometric calibration or WCS information). The system
requires no first guess, and works with the information in the image pixels
alone; that is, the problem is a generalization of the "lost in space" problem
in which nothing--not even the image scale--is known. After robust source
detection is performed in the input image, asterisms (sets of four or five
stars) are geometrically hashed and compared to pre-indexed hashes to generate
hypotheses about the astrometric calibration. A hypothesis is only accepted as
true if it passes a Bayesian decision theory test against a background
hypothesis. With indices built from the USNO-B Catalog and designed for
uniformity of coverage and redundancy, the success rate is 99.9% for
contemporary near-ultraviolet and visual imaging survey data, with no false
positives. The failure rate is consistent with the incompleteness of the USNO-B
Catalog; augmentation with indices built from the 2MASS Catalog brings the
completeness to 100% with no false positives. We are using this system to
generate consistent and standards-compliant meta-data for digital and digitized
imaging from plate repositories, automated observatories, individual scientific
investigators, and hobbyists. This is the first step in a program of making it
possible to trust calibration meta-data for astronomical data of arbitrary
provenance.Comment: submitted to A
Seismotectonic, structural, volcanologic, and geomorphic study of New Zealand; indigenous forest assessment in New Zealand; mapping, land use, and environmental studies in New Zealand, volume 2
The author has identified the following significant results. Ship detection via LANDSAT MSS data was demonstrated. In addition, information on ship size, orientation, and movement was obtained. Band 7 was used for the initial detection followed by confirmation on other MSS bands. Under low turbidity, as experienced in open seas, the detection of ships 100 m long was verified and detection of ships down to 30 m length theorized. High turbidity and sea state inhibit ship detection by decreasing S/N ratios. The radiance effect from snow of local slope angles and orientation was also studied. Higher radiance values and even overloading in three bands were recorded for the sun-facing slope. Local hot spots from solar reflection appear at several locations along transect D-C in Six Mile Creek Basin during September 1976
Digital Color Imaging
This paper surveys current technology and research in the area of digital
color imaging. In order to establish the background and lay down terminology,
fundamental concepts of color perception and measurement are first presented
us-ing vector-space notation and terminology. Present-day color recording and
reproduction systems are reviewed along with the common mathematical models
used for representing these devices. Algorithms for processing color images for
display and communication are surveyed, and a forecast of research trends is
attempted. An extensive bibliography is provided
The Orbital and Absolute Magnitude Distributions of Main Belt Asteroids
We have developed a model-independent analytical method for debiasing the
four-dimensional (a,e,i,H) distribution obtained in any asteroid observation
program and have applied the technique to results obtained with the 0.9m
Spacewatch Telescope. From 1992 to 1995 Spacewatch observed ~3740 deg^2 near
the ecliptic and made observations of more than 60,000 asteroids to a limiting
magnitude of V~21. The debiased semi-major axis and inclination distributions
of Main Belt asteroids in this sample with 11.5<= H <16 match the distributions
of the known asteroids with H <11.5. The absolute magnitude distribution was
studied in the range 8< H <17.5. We have found that the set of known asteroids
is complete to about absolute magnitudes 12.75, 12.25 and 11.25 in the inner,
middle and outer regions of the belt respectively. The number distribution as a
function of absolute magnitude cannot be represented by a single power-law
(10^{alpha H}) in any region. We were able to define broad ranges in H in each
part of the belt where alpha was nearly constant. Within these ranges of H the
slope does not correspond to the value of 0.5 expected for an equilibrium
cascade in self-similar collisions (Dohnanyi, 1971). The value of alpha varies
with absolute magnitude and shows a `kink' in all regions of the belt for H~13.
This absolute magnitude corresponds to a diameter ranging from about 8.5 to
12.5 km depending on the albedo or region of the belt.Comment: 33 pages, 6 figures, 6 tables. published in Icaru
Digital Image Access & Retrieval
The 33th Annual Clinic on Library Applications of Data Processing, held at the University of Illinois at Urbana-Champaign in March of 1996, addressed the theme of "Digital Image Access & Retrieval." The papers from this conference cover a wide range of topics concerning digital imaging technology for visual resource collections. Papers covered three general areas: (1) systems, planning, and implementation; (2) automatic and semi-automatic indexing; and (3) preservation with the bulk of the conference focusing on indexing and retrieval.published or submitted for publicatio
Galaxy alignments: An overview
The alignments between galaxies, their underlying matter structures, and the
cosmic web constitute vital ingredients for a comprehensive understanding of
gravity, the nature of matter, and structure formation in the Universe. We
provide an overview on the state of the art in the study of these alignment
processes and their observational signatures, aimed at a non-specialist
audience. The development of the field over the past one hundred years is
briefly reviewed. We also discuss the impact of galaxy alignments on
measurements of weak gravitational lensing, and discuss avenues for making
theoretical and observational progress over the coming decade.Comment: 43 pages excl. references, 16 figures; minor changes to match version
published in Space Science Reviews; part of a topical volume on galaxy
alignments, with companion papers at arXiv:1504.05546 and arXiv:1504.0546
The tidal tails of NGC 2298
We present an implementation of the matched-filter technique to detect tidal
tails of globular clusters. The method was tested using SDSS data for the
globular cluster Palomar 5 revealing its well known tidal tails. We also ran a
simulation of a globular cluster with a tidal tail where we successfully
recover the tails for a cluster at the same position and with the same
characteristics of NGC 2298. Based on the simulation we estimate that the
matched-filter increases the contrast of the tail relative to the background of
stars by a factor of 2.5 for the case of NGC 2298. We also present the
photometry of the globular cluster NGC 2298 using the MOSAIC2 camera installed
on the CTIO 4m telescope. The photometry covers ~ 3deg2 reaching V ~ 23. A fit
of a King profile to the radial density profile of NGC 2298 shows that this
cluster has a tidal radius of 15.91' \pm 1.07' which is twice as in the
literature. The application of the matched-filter to NGC 2298 reveals several
extra-tidal structures, including a leading and trailing tail. We also find
that NGC 2298 has extra-tidal structures stretching towards and against the
Galactic disk, suggesting strong tidal interaction. Finally, we assess how the
matched-filter performs when applied to a globular cluster with and without
mass segregation taken into account. We find that disregarding the effects of
mass segregation may significantly reduce the detection limit of the
matched-filter.Comment: 11 pages, 9 figures, 1 table. Accepted for publication on MNRAS main
journa
Overview of Hydrological Dynamics and Geomorphological Aspects of the Amazon Region Rivers to Characterize Fluvial Sensitivity to Oil Spills
This chapter presents a collection of studies performed in the Amazon region that includes thematic products portraying its fluvial sensitivity to oil spills. The research addresses the intense Amazonian seasonal dynamics, as well as the environmental peculiarities of this singular ecosystem. Periodic changes caused by natural phenomena have a significant impact on not only flooded alluvial plains and riverine habitats but also on petroleum exploration, production, and transportation activities. Therefore, the implementation of tools to assess the potential impact of oil spills in the Amazonian rivers must be adjusted to the local conditions. The main deliverables of the research are (1) fluvial oil spill sensitivity index maps contemplating each phase of the hydrological cycle (low water, high water, receding water, and rising water), (2) a computational method to represent fluctuations of the seasonal inundation, and (3) a risk analysis method using linguistic rules for the construction of a risk matrix
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