411 research outputs found
Independent Component analysis of the Cosmic Microwave Background
This paper presents an application of ICA to astronomical imaging. A first section describes the astrophysical context and motivates the use of source separation ideas. A second section describes our approach to the problem: the use of a noisy Gaussian stationary model. This technique uses spectral diversity and take explicitly into account contamination by additive noise. Preliminary and extremely encouraging results on realistic synthetic signals and on real data will be presented at the conferenc
Adaptive Langevin Sampler for Separation of t-Distribution Modelled Astrophysical Maps
We propose to model the image differentials of astrophysical source maps by
Student's t-distribution and to use them in the Bayesian source separation
method as priors. We introduce an efficient Markov Chain Monte Carlo (MCMC)
sampling scheme to unmix the astrophysical sources and describe the derivation
details. In this scheme, we use the Langevin stochastic equation for
transitions, which enables parallel drawing of random samples from the
posterior, and reduces the computation time significantly (by two orders of
magnitude). In addition, Student's t-distribution parameters are updated
throughout the iterations. The results on astrophysical source separation are
assessed with two performance criteria defined in the pixel and the frequency
domains.Comment: 12 pages, 6 figure
Independent Component Separation from incomplete spherical data using wavelets. Application to CMB data analysis
Spectral matching ICA (SMICA) is a source separation method based on covariance matching in Fourier space that was designed to address in a flexible way some of the general problems raised by Cosmic Microwave Background data analysis. However, a common issue in astronomical data analysis is that the observations are unevenly sampled or incomplete maps with missing patches or intentionally masked parts. In addition, many astrophysical emissions are not well modeled as stationary processes over the sky. These effects impair data processing techniques in the spherical harmonics representation. This paper describes a new wavelet transform for spherical maps and proposes an extension of SMICA in this space-scale representation
Multi-Detector Multi-Component spectral matching and applications for CMB data analysis
We present a new method for analyzing multi--detector maps containing
contributions from several components. Our method, based on matching the data
to a model in the spectral domain, permits to estimate jointly the spatial
power spectra of the components and of the noise, as well as the mixing
coefficients. It is of particular relevance for the analysis of
millimeter--wave maps containing a contribution from CMB anisotropies.Comment: 15 pages, 7 Postscript figures, submitted to MNRA
Cosmic Microwave Background Images
We aim to present a tutorial on the detection, parameter estimation and
statistical analysis of compact sources (far galaxies, galaxy clusters and
Galactic dense emission regions) in cosmic microwave background observations.
The topic is of great relevance for current and future cosmic microwave
background missions because the presence of compact sources in the data
introduces very significant biases in the determination of the cosmological
parameters that determine the energy contain, origin and evolution of the
universe and because compact sources themselves provide us with important
information about the large scale structure of the universe.Comment: 10 pages, 2 figures. This preprint replaces a previous one posted in
arXiv under the title 'An introduction to compact source detection in cosmic
microwave background images'. The change of title was forced by the
publishing journa
A harmonic excitation state-space approach to blind separation of speech
We discuss an identification framework for noisy speech mixtures. A block-based generative model is formulated that explicitly incorporates the time-varying harmonic plus noise (H+N) model for a number of latent sources observed through noisy convolutive mixtures. All parameters including the pitches of the source signals, the amplitudes and phases of the sources, the mixing filters and the noise statistics are estimated by maximum likelihood, using an EM-algorithm. Exact averaging over the hidden sources is obtained using the Kalman smoother. We show that pitch estimation and source separation can be performed simultaneously. The pitch estimates are compared to laryngograph (EGG) measurements. Artificial and real room mixtures are used to demonstrate the viability of the approach. Intelligible speech signals are re-synthesized from the estimated H+N models
MULTI-CHANNEL IMAGE SOURCE SEPARATION BY DICTIONARY UPDATE METHOD
In real world, a large set of mixed signals are available from which each source signal need to be recovered and this problem can be addressed with adaptive dictionary method. In the case of multichannel observations sparsity found to be very useful for source separation. The problem exist is that in most cases the sources are not sparsified in their domain and it will become necessary to sparsify the source by using some known dictionaries. In order to recover the sources successfully a prior knowledge of the sparse domain is required, if not available this problem can be solved by using dictionary learning technique into source separation. The proposed method, a local dictionary is adaptively learned for each source separately along with separation. This approach improves the quality of source separation both in noiseless and different noisy situations. The advantage of this method is that it denoise the sources during separation
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