99,219 research outputs found
Dominant Scattering Mechanism Identification from Quad-Pol-SAR Data Analysis
Get PDFPolarimetric decompositions are used to separate scatterers and identify their physical parameters by analyzing backscattering, coherence, or covariance matrices. Each cell within polarimetric SAR data is seen as a coherent or incoherent combination of different scattering mechanisms. However, targets are not perfectly characterized by these matrices due to the presence of noise components. The main objective of this study is to remedy the latest issue through proper noise effect elimination. Hence, we propose the re-estimation of the coherence matrix, by incorporating a processing phase that searches for the number of elementary scattering mechanisms in each cell. This first step is based on the eigenvalues, which exploit the advantage of polarization basis independent of the eigenvectors. In the second step, a reduced space is defined by the eigenvectors selected, according to the cases of the first step, as those contributing to the construction of the target, excluding those judged to contribute to noise. The characteristic vector and/or the coherence matrix of the average target is then reconstructed in this new space in three different ways: summation of the elementary coherence matrices, applying Bernoulli's probability law, and orthogonal projection on the reduced space. Finally, the Freeman Durden polarimetric decomposition and the H-alpha Wishart classification are used to show the effectiveness of the process in terms of dominant scattering mechanism identification. Their application on simulated data and on fully-polarized RadarSat-2 images of the city of Algiers attests to the performance of the proposed methodology to improve the identification of dominant scattering mechanisms
Beyond the Grid: GLRT-Based TomoSAR Fast Detection for Retrieving Height and Thermal Dilation
No full textThe Tomographic Synthetic Aperture Radar (TomoSAR) technique is widely used for monitoring urban infrastructures, as it enables the mapping of individual scatterers across additional dimensions such as height (3D), thermal dilation (4D), and deformation velocity (5D). Retrieving this information is crucial for building management and maintenance. Nevertheless, accurately extracting it from TomoSAR data poses several challenges, particularly the presence of outliers due to uneven and limited baseline distributions. One way to address these issues is through statistical detection approaches such as the Generalized Likelihood Ratio Test, which ensures a Constant False Alarm Rate. While effective, these methods face two primary limitations: high computational complexity and the off-grid problem caused by the discretization of the search space. To overcome these drawbacks, we propose an approach that combines a quick initialization process using Fast-Sup GLRT with local descent optimization. This method operates directly in the continuous domain, bypassing the limitations of grid-based search while significantly reducing computational costs. Experiments conducted on both simulated and real datasets acquired with the TerraSAR-X satellite over the Spanish city of Barcelona demonstrate the ability of the proposed approach to maintain computational efficiency while improving scatterer localization accuracy in the third and fourth dimensions
Covariance Matrix Estimation via Geometric Median in Highly Heterogeneous PolSAR Images
Get PDFThe Wishart distribution is a well-established statistical model for characterizing the density of random variables in Polarimetric SAR (PolSAR) data, particularly within homogeneous regions where Gaussian assumptions hold. However, as PolSAR applications expand into heterogeneous environments, alternative statistical models have been developed to better capture the complexity of such areas, playing an important role in tasks such as classification. In this study, we examine the effectiveness of covariance matrix estimation using the median matrix, a technique grounded in optimal transport theory and validated in prior research for its effectiveness. Building on this foundation, we propose the application of a statistical model tailored for heterogeneous regions, i.e., following the G0P distribution, addressing the limitations of traditional assumptions. This method is particularly suitable for high-resolution PolSAR datasets, where the homogeneity hypothesis often does not hold. The experimental results obtained using L-band PolSAR images acquired over Foulum in Denmark demonstrate the robustness of our proposed variant
Non-Parametric Tomographic SAR Reconstruction via Improved Regularized MUSIC
No full textHeight estimation of scatterers in complex environments via the Tomographic Synthetic Aperture Radar (TomoSAR) technique is still a valuable research field. The parametric spectral estimation approach constitutes a powerful tool to identify the superimposed scatterers with different complex reflectivities, located at different heights in the same range–azimuth resolution cell. Unfortunately, this approach requires prior knowledge about the number of scatterers for each pixel, which is not possible in practical situations. In this paper, we propose a method that analyzes the scree plot, generated from the spectral decomposition of the multidimensional covariance matrix, in order to estimate automatically the number of scatterers for each resolution cell. In this context, a properly improved regularization step is included during the reconstruction process, transforming the parametric MUSIC estimator into a non-parametric method. The experimental results on two data sets covering high elevation towers, with different facade coating characteristics, acquired by the TerraSAR-X satellite highlighted the effectiveness of the proposed regularized MUSIC for the reconstruction of high man-made structures compared with classical approaches
Joshua Davis: Author of Spare Parts
Get PDFCitation: K-State First (2016). Joshua Davis: Author of Spare Parts [Flier]. Manhattan, Kansas: K-State First.Flyer advertising Joshua Davis's author talk at Kansas State University
Norman K. Denzin (1991), Images of Postmodern Society. Social theory and Contemporary Cinema
No full textHadj-Moussa Ratiba. Norman K. Denzin (1991), Images of Postmodern Society. Social theory and Contemporary Cinema. In: Communication. Information Médias Théories, volume 13 n°2, automne 1992. Spectateurs. pp. 231-233
Steven Johnson Author Talk Poster
No full textK-State Book NetworkA poster advertising an author talk by Steven Johnson at Kansas State University on September 3, 2014. Steven Johnson's book "The Ghost Map" was the 2014-2015 common book
REE and Y distribution and speciation in fossil water: The northwestern African Continental Intercalaire aquifer, Algerian Sahara
No full textThe Continental Intercalaire aquifer is a part of the Northwestern Sahara Aquifer System
which, extending through Algeria, Tunisia and Libya with over one million km2, is one of the
largest fossil aquifers in the world, with an age of about 775,000 years, water resource
estimated at ~31000×109 m3 and negligible recharge rate at 1×109 m3/year. The fossil water
of the Algerian Sahara, part of the Continental Intercalaire aquifer, was examined, for the
first time, for its REE+Y composition, speciation, and geochemical significance in order to
constrain the processes affecting the REE+Y distribution and fractionation pattern in a
peculiar aquatic system.
The fossil water of the Algerian Sahara has total mineralization in the 1170 and 2309 mg/l
range and the prevailing hydrochemical facies is Na-Cl-SO4. The recorded REE+Y
concentrations increase downstream, along with the dissolved silica content and temperature,
as a function of water flow. The water samples are in equilibrium with 2:1 and 1:1 clay
minerals with the exception of few upstream samples, characterized by alkaline pH values,
that are in equilibrium with Na- and K-feldspars.
The REE+Y speciation is mainly controlled by carbonate species. The Ln(CO3)+ species
increase and the Ln(CO3)2
- species decrease downstream as the carbonate rocks of the aquifer
dissolve and the PCO2 equilibrating pressure increases. The LnSO4
+ species are mostly LaSO4
+
downstream the aquifer and, more in general, LaSO4
+ largely prevails up to pH between 6.9
and 7.2.
The low negative cerium anomalies affecting most of the samples might be explained by the
CeO2 precipitation following Ce3+ transformation to Ce4+. Ce oxidation is probably promoted
by Mn-minerals by oxidative scavenging, whereas positive Ce anomaly could be due to the
preferential desorption of Ce3+ over Ce4+. Finally, the pronounced negative samarium anomaly observed in some samples may reflect depletion of organic matter and Sm
adsorption onto clay minerals
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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