495 research outputs found
Modifying the Yamaguchi Four-Component Decomposition Scattering Powers Using a Stochastic Distance
Model-based decompositions have gained considerable attention after the
initial work of Freeman and Durden. This decomposition which assumes the target
to be reflection symmetric was later relaxed in the Yamaguchi et al.
decomposition with the addition of the helix parameter. Since then many
decomposition have been proposed where either the scattering model was modified
to fit the data or the coherency matrix representing the second order
statistics of the full polarimetric data is rotated to fit the scattering
model. In this paper we propose to modify the Yamaguchi four-component
decomposition (Y4O) scattering powers using the concept of statistical
information theory for matrices. In order to achieve this modification we
propose a method to estimate the polarization orientation angle (OA) from
full-polarimetric SAR images using the Hellinger distance. In this method, the
OA is estimated by maximizing the Hellinger distance between the un-rotated and
the rotated and the components of the coherency matrix
. Then, the powers of the Yamaguchi four-component model-based
decomposition (Y4O) are modified using the maximum relative stochastic distance
between the and the components of the coherency matrix at the
estimated OA. The results show that the overall double-bounce powers over
rotated urban areas have significantly improved with the reduction of volume
powers. The percentage of pixels with negative powers have also decreased from
the Y4O decomposition. The proposed method is both qualitatively and
quantitatively compared with the results obtained from the Y4O and the Y4R
decompositions for a Radarsat-2 C-band San-Francisco dataset and an UAVSAR
L-band Hayward dataset.Comment: Accepted for publication in IEEE J-STARS (IEEE Journal of Selected
Topics in Applied Earth Observations and Remote Sensing
Improvement of PolSAR Decomposition Scattering Powers Using a Relative Decorrelation Measure
In this letter, a methodology is proposed to improve the scattering powers
obtained from model-based decomposition using Polarimetric Synthetic Aperture
Radar (PolSAR) data. The novelty of this approach lies in utilizing the
intrinsic information in the off-diagonal elements of the 33 coherency
matrix represented in the form of complex correlation
coefficients. Two complex correlation coefficients are computed between
co-polarization and cross-polarization components of the Pauli scattering
vector. The difference between modulus of complex correlation coefficients
corresponding to (i.e. the degree of polarization
(DOP) optimized coherency matrix), and (original) matrices is
obtained. Then a suitable scaling is performed using fractions \emph{i.e.,}
obtained
from the diagonal elements of the matrix.
Thereafter, these new quantities are used in modifying the Yamaguchi
4-component scattering powers obtained from . To
corroborate the fact that these quantities have physical relevance, a
quantitative analysis of these for the L-band AIRSAR San Francisco and the
L-band Kyoto images is illustrated. Finally, the scattering powers obtained
from the proposed methodology are compared with the corresponding powers
obtained from the Yamaguchi \emph{et. al.,} 4-component (Y4O) decomposition and
the Yamaguchi \emph{et. al.,} 4-component Rotated (Y4R) decomposition for the
same data sets. The proportion of negative power pixels is also computed. The
results show an improvement on all these attributes by using the proposed
methodology.Comment: Accepted for publication in Remote Sensing Letter
Target scattering characterization in sar polarimetry using model-free approaches
Target decomposition methods for polarimetric Synthetic Aperture Radar (PolSAR) data aim at explaining the scattering information. In this regard, several conventional model-based methods use scattering power components to analyze polarimetric SAR data. However, the typical hierarchical process to enumerate power components uses various branching conditions, leading to several limitations. This study uses the 3D Barakat degree of polarization (DoP) to obtain the scattered wave polarization state. We employ the DoP to obtain the even bounce, odd-bounce, and diffuse scattering power components. Besides, we propose a measure of target scattering asymmetry, which is subsequently utilized to obtain the helicity power. All the power components in our approach are roll-invariant and non-negative, and the decomposition preserves the total power. We utilized C-band full polarimetric RADARSAT-2 data to show the effectiveness of the proposed decomposition. © 2021 IEEE.Peer ReviewedPostprint (author's final draft
Quad-Polarimetric Multi-Scale Analysis of Icebergs in ALOS-2 SAR Data: A Comparison between Icebergs in West and East Greenland
Icebergs are ocean hazards which require extensive monitoring. Synthetic Aperture Radar (SAR) satellites can help with this, however, SAR backscattering is strongly influenced by the properties of icebergs, together with meteorological and environmental conditions. In this work, we used five images of quad-pol ALOS-2/PALSAR-2 SAR data to analyse 1332 icebergs in five locations in west and east Greenland. We investigate the backscatter and polarimetric behaviour, by using several observables and decompositions such as the Cloude–Pottier eigenvalue/eigenvector and Yamaguchi model-based decompositions. Our results show that those icebergs can contain a variety of scattering mechanisms at L-band. However, the most common scattering mechanism for icebergs is surface scattering, with the second most dominant volume scattering (or more generally, clouds of dipoles). In some cases, we observed a double bounce dominance, but this is not as common. Interestingly, we identified that different locations (e.g., glaciers) produce icebergs with different polarimetric characteristics. We also performed a multi-scale analysis using boxcar 5 × 5 and 11 × 11 window sizes and this revealed that depending on locations (and therefore, characteristics) icebergs can be a collection of strong scatterers that are packed in a denser or less dense way. This gives hope for using quad-pol polarimetry to provide some iceberg classifications in the future
General model-based decomposition framework for polarimetric SAR images
2017 Spring.Includes bibliographical references.Polarimetric synthetic aperture radars emit a signal and measure the magnitude, phase, and polarization of the return. Polarimetric decompositions are used to extract physically meaningful attributes of the scatterers. Of these, model-based decompositions intend to model the measured data with canonical scatter-types. Many advances have been made to this field of model-based decomposition and this work is surveyed by the first portion of this dissertation. A general model-based decomposition framework (GMBDF) is established that can decompose polarimetric data with different scatter-types and evaluate how well those scatter-types model the data by comparing a residual term. The GMBDF solves for all the scatter-type parameters simultaneously that are within a given decomposition by minimizing the residual term. A decomposition with a lower residual term contains better scatter-type models for the given data. An example is worked through that compares two decompositions with different surface scatter-type models. As an application of the polarimetric decomposition analysis, a novel terrain classification algorithm of polSAR images is proposed. In the algorithm, the results of state-of-the-art polarimetric decompositions are processed for an image. Pixels are then selected to represent different terrain classes. Distributions of the parameters of these selected pixels are determined for each class. Each pixel in the image is given a score according to how well its parameters fit the parameter distributions of each class. Based on this score, the pixel is either assigned to a predefined terrain class or labeled unclassified
Polarimetric Synthetic Aperture Radar
This open access book focuses on the practical application of electromagnetic polarimetry principles in Earth remote sensing with an educational purpose. In the last decade, the operations from fully polarimetric synthetic aperture radar such as the Japanese ALOS/PalSAR, the Canadian Radarsat-2 and the German TerraSAR-X and their easy data access for scientific use have developed further the research and data applications at L,C and X band. As a consequence, the wider distribution of polarimetric data sets across the remote sensing community boosted activity and development in polarimetric SAR applications, also in view of future missions. Numerous experiments with real data from spaceborne platforms are shown, with the aim of giving an up-to-date and complete treatment of the unique benefits of fully polarimetric synthetic aperture radar data in five different domains: forest, agriculture, cryosphere, urban and oceans
Gravitational waves and geometrical optics in scalar-tensor theories
The detection of gravitational waves (GWs) propagating through cosmic
structures can provide invaluable information on the geometry and content of
our Universe, as well as on the fundamental theory of gravity. In order to test
possible departures from General Relativity, it is essential to analyse, in a
modified gravity setting, how GWs propagate through a perturbed cosmological
space-time. Working within the framework of geometrical optics, we develop
tools to address this topic for a broad class of scalar-tensor theories,
including scenarios with non-minimal, derivative couplings between scalar and
tensor modes. We determine the corresponding evolution equations for the GW
amplitude and polarization tensor. The former satisfies a generalised evolution
equation that includes possible effects due to a variation of the effective
Planck scale; the latter can fail to be parallely transported along GW
geodesics unless certain conditions are satisfied. We apply our general
formulas to specific scalar-tensor theories with unit tensor speed, and then
focus on GW propagation on a perturbed space-time. We determine corrections to
standard formulas for the GW luminosity distance and for the evolution of the
polarization tensor, which depend both on modified gravity and on the effects
of cosmological perturbations. Our results can constitute a starting point to
disentangle among degeneracies from different sectors that can influence GW
propagation through cosmological space-times.Comment: 42 pages. V2: Improved discussion, in particular on gauge conditions,
and references added. Results unchanged. V3: Updated version to be published
in JCA
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