738 research outputs found
Polarization of the WMAP Point Sources
The detection of polarized sources in the WMAP 5-year data is a very
difficult task. The maps are dominated by instrumental noise and only a handful
of sources show up as clear peaks in the Q and U maps. Optimal linear filters
applied at the position of known bright sources detect with a high level of
significance a polarized flux P from many more sources, but estimates of P are
liable to biases. Using a new technique, named the "filtered fusion technique",
we have detected in polarization, with a significance level greater than 99.99%
in at least one WMAP channel, 22 objects, 5 of which, however, do not have a
plausible low radio frequency counterpart and are therefore doubtful. Estimated
polarized fluxes P < 400 mJy at 23 GHz were found to be severely affected by
the Eddington bias. The corresponding polarized flux limit for Planck/LFI at 30
GHz, obtained via realistic simulations, is 300 mJy. We have also obtained
statistical estimates of, or upper limits to the mean polarization degrees of
bright WMAP sources at 23, 33, 41, and 61 GHz, finding that they are of a few
percent.Comment: 10 pages, 6 figures. Accepted for publication in Ap
Detection/estimation of the modulus of a vector. Application to point source detection in polarization data
Given a set of images, whose pixel values can be considered as the components
of a vector, it is interesting to estimate the modulus of such a vector in some
localised areas corresponding to a compact signal. For instance, the
detection/estimation of a polarized signal in compact sources immersed in a
background is relevant in some fields like astrophysics. We develop two
different techniques, one based on the Neyman-Pearson lemma, the Neyman-Pearson
filter (NPF), and another based on prefiltering-before-fusion, the filtered
fusion (FF), to deal with the problem of detection of the source and estimation
of the polarization given two or three images corresponding to the different
components of polarization (two for linear polarization, three including
circular polarization). For the case of linear polarization, we have performed
numerical simulations on two-dimensional patches to test these filters
following two different approaches (a blind and a non-blind detection),
considering extragalactic point sources immersed in cosmic microwave background
(CMB) and non-stationary noise with the conditions of the 70 GHz \emph{Planck}
channel. The FF outperforms the NPF, especially for low fluxes. We can detect
with the FF extragalactic sources in a high noise zone with fluxes >=
(0.42,0.36) Jy for (blind/non-blind) detection and in a low noise zone with
fluxes >= (0.22,0.18) Jy for (blind/non-blind) detection with low errors in the
estimated flux and position.Comment: 11 pages, 5 figure
Filter design for the detection of compact sources based on the Neyman-Pearson detector
This paper considers the problem of compact source detection on a Gaussian
background in 1D. Two aspects of this problem are considered: the design of the
detector and the filtering of the data. Our detection scheme is based on local
maxima and it takes into account not only the amplitude but also the curvature
of the maxima. A Neyman-Pearson test is used to define the region of
acceptance, that is given by a sufficient linear detector that is independent
on the amplitude distribution of the sources. We study how detection can be
enhanced by means of linear filters with a scaling parameter and compare some
of them (the Mexican Hat wavelet, the matched and the scale-adaptive filters).
We introduce a new filter, that depends on two free parameters (biparametric
scale-adaptive filter). The value of these two parameters can be determined,
given the a priori pdf of the amplitudes of the sources, such that the filter
optimizes the performance of the detector in the sense that it gives the
maximum number of real detections once fixed the number density of spurious
sources. The combination of a detection scheme that includes information on the
curvature and a flexible filter that incorporates two free parameters (one of
them a scaling) improves significantly the number of detections in some
interesting cases. In particular, for the case of weak sources embedded in
white noise the improvement with respect to the standard matched filter is of
the order of 40%. Finally, an estimation of the amplitude of the source is
introduced and it is proven that such an estimator is unbiased and it has
maximum efficiency. We perform numerical simulations to test these theoretical
ideas and conclude that the results of the simulations agree with the
analytical ones.Comment: 15 pages, 13 figures, version accepted for publication in MNRAS.
Corrected typos in Tab.
A multifrequency method based on the Matched Multifilter for the detection of point sources in CMB maps
In this work we deal with the problem of simultaneous multifrequency
detection of extragalactic point sources in maps of the Cosmic Microwave
Background. We apply a linear filtering technique that uses spatial information
and the cross-power spectrum. To make this, we simulate realistic and
non-realistic flat patches of the sky at two frequencies of Planck: 44 and 100
GHz. We filter to detect and estimate the point sources and compare this
technique with the monofrequency matched filter in terms of completeness,
reliability, flux and spectral index accuracy. The multifrequency method
outperforms the matched filter at the two frequencies and in all the studied
cases in the work.Comment: 14 pages, 6 figures, 1 tabl
Evaluating seawater quality objectives: Application to the Andalusian littoral
The University of Cadiz (southern Spain) and the Andalusian Environmental Agency (AMA) have signed an agreement to draw up a proposal of quality objectives for Andalusian littoral waters in accordance with the classification of zones approved in the Andalusian Littoral Waters Quality Objectives Regulations (Decree 14/1996, 01-16-1996, BOJA no. 19, 02-08-1996). The present paper reviews different regulations (European Union, Spain and the United States) concerning seawater quality criteria and presents the quality criteria proposed by the University of Cadiz.La Universidad de Cádiz y la Agencia de Medio Ambiente Andaluza (AMA) han desarrollado un convenio cuya finalidad es la realización de una propuesta de objetivos de calidad para las aguas litorales andaluzas según la clasificación de zonas establecida en el Decreto 14/1996, por el que se aprueba el Reglamento de Calidad de las Aguas Litorales Andaluzas (BOJA n.° 19 de 8 de febrero de 1996). En este trabajo se hace una revisión de la normativa referente a los objetivos de calidad de las aguas marinas en la Unión Europea, España y Estados Unidos. Además, se recoge la propuesta de objetivos de calidad de aguas litorales realizada por la Universidad de Cádiz.Instituto Español de Oceanografí
Comparison of micrometeorological techinques for estimating ammonia emission from covered slurry storage and land spreading of cattle slurry
The micrometeorological mass-balance integrated horizontal flux (IHF) technique has been commonly employed for measuring ammonia (NH3) emissions inon-field experiments. However, the inverse-dispersion modeling technique, such as the backward Lagrangian stochastic (bLS) modeling approach, is currently highlighted as offering flexibility in plot design and requiring a minimum number of samplers (Ro et
al., 2013). The objective of this study was to make a comparison between the bLS technique with the IHF technique for estimating NH3 emission from flexible bag storage and following landspreading of dairy cattle slurry. Moreover, considering that NH3 emission in storage could have been non uniform, the effect on bLS estimates of a single point and multiple downwind concentration measurements was tested, as proposed by Sanz et al. (2010)
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