340 research outputs found
Effects of additive noise on the stability of glacial cycles
It is well acknowledged that the sequence of glacial-interglacial cycles is
paced by the astronomical forcing. However, how much is the sequence robust
against natural fluctuations associated, for example, with the chaotic motions
of atmosphere and oceans? In this article, the stability of the
glacial-interglacial cycles is investigated on the basis of simple conceptual
models. Specifically, we study the influence of additive white Gaussian noise
on the sequence of the glacial cycles generated by stochastic versions of
several low-order dynamical system models proposed in the literature. In the
original deterministic case, the models exhibit different types of attractors:
a quasiperiodic attractor, a piecewise continuous attractor, strange nonchaotic
attractors, and a chaotic attractor. We show that the combination of the
quasiperiodic astronomical forcing and additive fluctuations induce a form of
temporarily quantised instability. More precisely, climate trajectories
corresponding to different noise realizations generally cluster around a small
number of stable or transiently stable trajectories present in the
deterministic system. Furthermore, these stochastic trajectories may show
sensitive dependence on very small amounts of perturbations at key times.
Consistently with the complexity of each attractor, the number of trajectories
leaking from the clusters may range from almost zero (the model with a
quasiperiodic attractor) to a significant fraction of the total (the model with
a chaotic attractor), the models with strange nonchaotic attractors being
intermediate. Finally, we discuss the implications of this investigation for
research programmes based on numerical simulators. }Comment: Parlty based on a lecture given by M. Crucifix at workshop held in
Rome in 2013 as a part of Mathematics of Planet Earth 201
Results on Discrete-Time, Decision-Directed Integrated Detection, Estimation, and Identification
©1977 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.New results are presented for symbol-by-symbol detection with decision-directed tracking of colored channel disturbances. Recursive sampled-data algorithms are shown for Maximum A Posteriori Probability of detection under colored additive and multiplicative Gaussian noises along with white Gaussian noise. Preliminary evaluation of the algorithms via Monte Carlo simulation shows good performance compared to standard white-noise only algorithms.IEEE Communications Societ
Image Restoration for Remote Sensing: Overview and Toolbox
Remote sensing provides valuable information about objects or areas from a
distance in either active (e.g., RADAR and LiDAR) or passive (e.g.,
multispectral and hyperspectral) modes. The quality of data acquired by
remotely sensed imaging sensors (both active and passive) is often degraded by
a variety of noise types and artifacts. Image restoration, which is a vibrant
field of research in the remote sensing community, is the task of recovering
the true unknown image from the degraded observed image. Each imaging sensor
induces unique noise types and artifacts into the observed image. This fact has
led to the expansion of restoration techniques in different paths according to
each sensor type. This review paper brings together the advances of image
restoration techniques with particular focuses on synthetic aperture radar and
hyperspectral images as the most active sub-fields of image restoration in the
remote sensing community. We, therefore, provide a comprehensive,
discipline-specific starting point for researchers at different levels (i.e.,
students, researchers, and senior researchers) willing to investigate the
vibrant topic of data restoration by supplying sufficient detail and
references. Additionally, this review paper accompanies a toolbox to provide a
platform to encourage interested students and researchers in the field to
further explore the restoration techniques and fast-forward the community. The
toolboxes are provided in https://github.com/ImageRestorationToolbox.Comment: This paper is under review in GRS
Super-resolution time delay estimation in multipath environments
The problem of super-resolution time delay estimation in multipath environments is addressed in this paper. Two cases, active and passive systems, are considered. The time delay estimation is first converted into a sinusoidal parameter estimation problem. Then the sinusoidal parameters are estimated by generalizing the Multiple Signal Classification (MUSIC) algorithm for single-experiment data. The proposed method, referred to as the MUSIC-type algorithm, approximates the Cramer-Rao bound (CRB) in terms of the mean square errors (MSEs) for different signal-to-noise ratios (SNRs) and separations of muitipath components. Simulation results show that the MUSIC-type algorithm performs better than the classical correlation approach and the conventional MUSIC method for the closely spaced components in muitipath environments.published_or_final_versio
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