32,034 research outputs found
Automated detection of extended sources in radio maps: progress from the SCORPIO survey
Automated source extraction and parameterization represents a crucial
challenge for the next-generation radio interferometer surveys, such as those
performed with the Square Kilometre Array (SKA) and its precursors. In this
paper we present a new algorithm, dubbed CAESAR (Compact And Extended Source
Automated Recognition), to detect and parametrize extended sources in radio
interferometric maps. It is based on a pre-filtering stage, allowing image
denoising, compact source suppression and enhancement of diffuse emission,
followed by an adaptive superpixel clustering stage for final source
segmentation. A parameterization stage provides source flux information and a
wide range of morphology estimators for post-processing analysis. We developed
CAESAR in a modular software library, including also different methods for
local background estimation and image filtering, along with alternative
algorithms for both compact and diffuse source extraction. The method was
applied to real radio continuum data collected at the Australian Telescope
Compact Array (ATCA) within the SCORPIO project, a pathfinder of the ASKAP-EMU
survey. The source reconstruction capabilities were studied over different test
fields in the presence of compact sources, imaging artefacts and diffuse
emission from the Galactic plane and compared with existing algorithms. When
compared to a human-driven analysis, the designed algorithm was found capable
of detecting known target sources and regions of diffuse emission,
outperforming alternative approaches over the considered fields.Comment: 15 pages, 9 figure
SPIRE Point Source Catalog Explanatory Supplement
The Spectral and Photometric Imaging Receiver (SPIRE) was launched as one of
the scientific instruments on board of the space observatory Herschel. The
SPIRE photometer opened up an entirely new window in the Submillimeter domain
for large scale mapping, that up to then was very difficult to observe. There
are already several catalogs that were produced by individual Herschel science
projects. Yet, we estimate that the objects of only a fraction of these maps
will ever be systematically extracted and published by the science teams that
originally proposed the observations. The SPIRE instrument performed its
standard photometric observations in an optically very stable configuration,
only moving the telescope across the sky, with variations in its configuration
parameters limited to scan speed and sampling rate. This and the scarcity of
features in the data that require special processing steps made this dataset
very attractive for producing an expert reduced catalog of point sources that
is being described in this document. The Catalog was extracted from a total of
6878 unmodified SPIRE scan map observations. The photometry was obtained by a
systematic and homogeneous source extraction procedure, followed by a rigorous
quality check that emphasized reliability over completeness. Having to exclude
regions affected by strong Galactic emission, that pushed the limits of the
four source extraction methods that were used, this catalog is aimed primarily
at the extragalactic community. The result can serve as a pathfinder for ALMA
and other Submillimeter and Far-Infrared facilities. 1,693,718 sources are
included in the final catalog, splitting into 950688, 524734, 218296 objects
for the 250\mu m, 350\mu m, and 500\mu m bands, respectively. The catalog comes
with well characterized environments, reliability, completeness, and
accuracies, that single programs typically cannot provide
Radio-optically selected clusters of galaxies. I. The radiogalaxy sample
In order to study the status and the possible evolution of clusters of
galaxies at intermediate redshifts (z ~ 0.1 - 0.3), as well as their spatial
correlation and relationship with the local environment, we built a sample of
candidate groups and clusters of galaxies using radiogalaxies as tracers of
dense environments. This technique - complementary to purely optical or X-ray
cluster selection methods - represents an interesting tool for the selection of
clusters in a wide range of richness, so to make it possible to study the
global properties of groups and clusters of galaxies, such as their
morphological content, dynamical status and number density, as well as the
effect of the environment on the radio emission phenomena. In this paper we
describe the compilation of a catalogue of 16000 radio sources in the region of
the South Galactic Pole extracted from the publicly available NRAO VLA Sky
Survey maps, and the optical identification procedure with galaxies brighter
than b_J=20.0 in the EDSGC Catalogue. The radiogalaxy sample, valuable for the
study of radio source populations down to low flux levels, consists of 1288
identifications and has been used to detect candidate groups and clusters
associated to NVSS radio sources. In a companion paper we will discuss the
cluster detection method, the cluster sample as well as first spectroscopic
results.Comment: 15 pages, 6 Postscript and 1 GIF figures. Accepted for publication in
A&
A Fast Radio Burst Search Method for VLBI Observation
We introduce the cross spectrum based FRB (Fast Radio Burst) search method
for VLBI observation. This method optimizes the fringe fitting scheme in
geodetic VLBI data post processing, which fully utilizes the cross spectrum
fringe phase information and therefore maximizes the power of single pulse
signals. Working with cross spectrum greatly reduces the effect of radio
frequency interference (RFI) compared with using auto spectrum. Single pulse
detection confidence increases by cross identifying detections from multiple
baselines. By combining the power of multiple baselines, we may improve the
detection sensitivity. Our method is similar to that of coherent beam forming,
but without the computational expense to form a great number of beams to cover
the whole field of view of our telescopes. The data processing pipeline
designed for this method is easy to implement and parallelize, which can be
deployed in various kinds of VLBI observations. In particular, we point out
that VGOS observations are very suitable for FRB search.Comment: Accepted for publication in A
GLR-Parsing of Word Lattices Using a Beam Search Method
This paper presents an approach that allows the efficient integration of
speech recognition and language understanding using Tomita's generalized
LR-parsing algorithm. For this purpose the GLRP-algorithm is revised so that an
agenda mechanism can be used to control the flow of computation of the parsing
process. This new approach is used to integrate speech recognition and speech
understanding incrementally with a beam search method. These considerations
have been implemented and tested on ten word lattices.Comment: 4 pages, 61K postscript, compressed, uuencoded, Eurospeech 9/95,
Madri
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