23,365 research outputs found
Logarithmic mathematical morphology: a new framework adaptive to illumination changes
A new set of mathematical morphology (MM) operators adaptive to illumination
changes caused by variation of exposure time or light intensity is defined
thanks to the Logarithmic Image Processing (LIP) model. This model based on the
physics of acquisition is consistent with human vision. The fundamental
operators, the logarithmic-dilation and the logarithmic-erosion, are defined
with the LIP-addition of a structuring function. The combination of these two
adjunct operators gives morphological filters, namely the logarithmic-opening
and closing, useful for pattern recognition. The mathematical relation existing
between ``classical'' dilation and erosion and their logarithmic-versions is
established facilitating their implementation. Results on simulated and real
images show that logarithmic-MM is more efficient on low-contrasted information
than ``classical'' MM
Ceres' opposition effect observed by the Dawn framing camera
The surface reflectance of planetary regoliths may increase dramatically
towards zero phase angle, a phenomenon known as the opposition effect (OE). Two
physical processes that are thought to be the dominant contributors to the
brightness surge are shadow hiding (SH) and coherent backscatter (CB). The
occurrence of shadow hiding in planetary regoliths is self-evident, but it has
proved difficult to unambiguously demonstrate CB from remote sensing
observations. One prediction of CB theory is the wavelength dependence of the
OE angular width. The Dawn spacecraft observed the OE on the surface of dwarf
planet Ceres. We characterize the OE over the resolved surface, including the
bright Cerealia Facula, and to find evidence for SH and/or CB. We analyze
images of the Dawn framing camera by means of photometric modeling of the phase
curve. We find that the OE of most of the investigated surface has very similar
characteristics, with an enhancement factor of 1.4 and a FWHM of 3{\deg} (broad
OE). A notable exception are the fresh ejecta of the Azacca crater, which
display a very narrow brightness enhancement that is restricted to phase angles
{\deg} (narrow OE); suggestively, this is in the range in which CB is
thought to dominate. We do not find a wavelength dependence for the width of
the broad OE, and lack the data to investigate the dependence for the narrow
OE. The prediction of a wavelength-dependent CB width is rather ambiguous. The
zero-phase observations allow us to determine Ceres' visible geometric albedo
as . A comparison with other asteroids suggests that
Ceres' broad OE is typical for an asteroid of its spectral type, with
characteristics that are primarily linked to surface albedo. Our analysis
suggests that CB may occur on the dark surface of Ceres in a highly localized
fashion.Comment: Credit: Schr\"oder et al, A&A in press, 2018, reproduced with
permission, \copyright ES
Logarithmic Image Processing for Color Images
43 pagesInternational audienceThe present paper is an extension to color images of the LIP (Logarithmic Image Processing) framework, initially dedicated to gray level image
Radio Observations of the January 20, 2005 X-Class Event
We present a multi-frequency and multi-instrument study of the 20 January
2005 event. We focus mainly on the complex radio signatures and their
association with the active phenomena taking place: flares, CMEs, particle
acceleration and magnetic restructuring. As a variety of energetic particle
accelerators and sources of radio bursts are present, in the flare-ejecta
combination, we investigate their relative importance in the progress of this
event. The dynamic spectra of {Artemis-IV-Wind/Waves-Hiras with 2000 MHz-20 kHz
frequency coverage, were used to track the evolution of the event from the low
corona to the interplanetary space; these were supplemented with SXR, HXR and
gamma-ray recordings. The observations were compared with the expected radio
signatures and energetic-particle populations envisaged by the {Standard
Flare--CME model and the reconnection outflow termination shock model. A proper
combination of these mechanisms seems to provide an adequate model for the
interpretation of the observational data.Comment: Accepted for publication in Solar Physic
Deep Learning for Audio Signal Processing
Given the recent surge in developments of deep learning, this article
provides a review of the state-of-the-art deep learning techniques for audio
signal processing. Speech, music, and environmental sound processing are
considered side-by-side, in order to point out similarities and differences
between the domains, highlighting general methods, problems, key references,
and potential for cross-fertilization between areas. The dominant feature
representations (in particular, log-mel spectra and raw waveform) and deep
learning models are reviewed, including convolutional neural networks, variants
of the long short-term memory architecture, as well as more audio-specific
neural network models. Subsequently, prominent deep learning application areas
are covered, i.e. audio recognition (automatic speech recognition, music
information retrieval, environmental sound detection, localization and
tracking) and synthesis and transformation (source separation, audio
enhancement, generative models for speech, sound, and music synthesis).
Finally, key issues and future questions regarding deep learning applied to
audio signal processing are identified.Comment: 15 pages, 2 pdf figure
Region-enhanced passive radar imaging
The authors adapt and apply a recently-developed region-enhanced synthetic aperture radar (SAR) image reconstruction technique to the problem of passive radar imaging. One goal in passive radar imaging is to form images of aircraft using signals transmitted by commercial radio and television stations that are reflected from the objects of interest. This involves reconstructing an image from sparse samples of its Fourier transform. Owing to the sparse nature of the aperture, a conventional image formation approach based on direct Fourier transformation results in quite dramatic artefacts in the image, as compared with the case of active SAR imaging. The regionenhanced image formation method considered is based on an explicit mathematical model of the observation process; hence, information about the nature of the aperture is explicitly taken into account in image formation. Furthermore, this framework allows the incorporation of prior information or constraints about the scene being imaged, which makes it possible to compensate for the limitations of the sparse apertures involved in passive radar imaging. As a result, conventional imaging artefacts, such as sidelobes, can be alleviated. Experimental results using data based on electromagnetic simulations demonstrate that this is a promising strategy for passive radar imaging, exhibiting significant suppression of artefacts, preservation of imaged object features, and robustness to measurement noise
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