523,734 research outputs found
A robust nonlinear scale space change detection approach for SAR images
In this paper, we propose a change detection approach based on nonlinear scale space analysis of change images for robust detection of various changes incurred by natural phenomena and/or human activities in Synthetic Aperture Radar (SAR) images using Maximally Stable Extremal Regions (MSERs). To achieve this, a variant of the log-ratio image of multitemporal images is calculated which is followed by Feature Preserving Despeckling (FPD) to generate nonlinear scale space images exhibiting different trade-offs in terms of speckle reduction and shape detail preservation. MSERs of each scale space image are found and then combined through a decision level fusion strategy, namely "selective scale fusion" (SSF), where contrast and boundary curvature of each MSER are considered. The performance of the proposed method is evaluated using real multitemporal high resolution TerraSAR-X images and synthetically generated multitemporal images composed of shapes with several orientations, sizes, and backscatter amplitude levels representing a variety of possible signatures of change. One of the main outcomes of this approach is that different objects having different sizes and levels of contrast with their surroundings appear as stable regions at different scale space images thus the fusion of results from scale space images yields a good overall performance
BAO Extractor: bias and redshift space effects
We study a new procedure to measure the sound horizon scale via Baryonic
Acoustic Oscillations (BAO). Instead of fitting the measured power spectrum
(PS) to a theoretical model containing the cosmological informations and all
the nonlinear effects, we define a procedure to project out (or to "extract")
the oscillating component from a given nonlinear PS. We show that the BAO scale
extracted in this way is extremely robust and, moreover, can be reproduced by
simple theoretical models at any redshift. By using N-body simulations, we
discuss the effect of the nonlinear evolution of the matter field, of redshift
space distortions and of scale-dependent halo bias, showing that all these
effects can be reproduced with sub-percent accuracy. We give a one-parameter
theoretical model based on a simple (IR) modification of 1-loop perturbation
theory, which reproduces the BAO scale from measurements of halo clustering in
redshift space at better than level and does not need any external UV
input, such as coefficients measured from N-body simulations.Comment: Published version. 32 pages, 15 figure
Nonlinear reconstruction
We present a direct approach to nonparametrically reconstruct the linear
density field from an observed nonlinear map. We solve for the unique
displacement potential consistent with the nonlinear density and positive
definite coordinate transformation using a multigrid algorithm. We show that we
recover the linear initial conditions up to the nonlinear scale
( for ) with minimal
computational cost. This reconstruction approach generalizes the linear
displacement theory to fully nonlinear fields, potentially substantially
expanding the baryon acoustic oscillations and redshift space distortions
information content of dense large scale structure surveys, including for
example SDSS main sample and 21cm intensity mapping initiatives.Comment: 7 pages, 7 figures, published versio
Primordial fractal density perturbations and structure formation in the Universe: 1-Dimensional collisionless sheet model
Two-point correlation function of galaxy distribution shows that the
structure in the present Universe is scale-free up to a certain scale (at least
several tens Mpc), which suggests that a fractal structure may exist. If small
primordial density fluctuations have a fractal structure, the present
fractal-like nonlinear structure below the horizon scale could be naturally
explained. We analyze the time evolution of fractal density perturbations in
Einstein-de Sitter universe, and study how the perturbation evolves and what
kind of nonlinear structure will come out. We assume a one-dimensional
collisionless sheet model with initial Cantor-type fractal perturbations. The
nonlinear structure seems to approach some attractor with a unique fractal
dimension, which is independent of the fractal dimensions of initial
perturbations. A discrete self-similarity in the phase space is also found when
the universal nonlinear fractal structure is reached.Comment: 17 pages, 19 jpeg figures. Accepted for publication in ApJ. Figures
are also available from
http://www.phys.waseda.ac.jp/gravity/~tatekawa/0003124/figs.tar.g
Anisotropic diffusion processes in early vision
Summary form only given. Images often contain information at a number of different scales of resolution, so that the definition and generation of a good scale space is a key step in early vision. A scale space in which object boundaries are respected and smoothing only takes place within these boundaries has been defined that avoids the inaccuracies introduced by the usual method of low-pass-filtering the image with Gaussian kernels. The new scale space is generated by solving a nonlinear diffusion differential equation forward in time (the scale parameter). The original image is used as the initial condition, and the conduction coefficient c(x, y, t) varies in space and scale as a function of the gradient of the variable of interest (e.g. the image brightness). The algorithms are based on comparing the local values of different diffusion processes running in parallel on the same image
- …