1,721,056 research outputs found
Theoretical Performance Bounds on the Estimation of Forest Structure Parameters From Multibaseline SAR Data
No full textGiven their central role in the carbon budget, the SAR remote sensing of forests has become during the last two decades a “hot” research topic. A powerful way to analyze forest scattering consists in the coherent combination of multibaseline (MB) SAR data, possibly also polarimetric. For instance, SAR Tomography is a powerful technique whose natural output is the 3-D imaging in the range-azimuth-height space, thus allowing the resolution of multiple scatterers in height in the same cell. As a consequence, the extraction of a high amount of information is made possible, e.g. forest height and biomass, radar reflectivities, sub-canopy topography, soil humidity, volume extinction [1].
In the last years, many tomographic algorithms have been conceived for the estimation of forest structure parameters in both parametric and non parametric frameworks and their performance have been judged against the available in-situ measurements [2-5]. However, not so many efforts have been spent in the analytical derivation of theoretical performance bounds, despite their primary importance. In fact, such tools provide a benchmark against which it is possible to compare the performance of any estimator. Not only, but they alert to the physical impossibility of finding an estimator whose performance is lower than the bounds.
This work offers a contribution to tackle the performance bounding problem by resorting to the Cramér-Rao bound (CRB) theory. The CRB is a result of the information theory which provides a lower bound on the variance of any unbiased estimator of an unknown parameter. Given also its relative easiness of calculation, the CRB is widely used in the statistical signal processing to judge the efficiency of the parameter estimators. In the specific MB SAR field, it could also be a very useful instrument to characterize the potentials of acquisition configurations and possibly as a guideline in designing acquisition patterns (mission planning) and systems. An interesting extension of the CRB is represented by the Hybrid CRB (HCRB), in which the presence of random phase offsets between different acquisitions (e.g. due to non perfect baseline estimation and/or propagation effects through the atmosphere) can be taken into account.
In particular, in this work the CRB and HCRB derivations are focused to the analysis of forest areas by assuming a two-layer model for the MB data vector, i.e. a ground layer and a canopy layer, with different characteristics of their vertical structure. Starting from the very general formulations of MB bounds in [6] and [7], ready-to-use CRB and HCRB formulas are given for forest scenarios. Moreover, the obtained precision limits on the parameters of interest are calculated numerically for some realistic acquisition patterns and for different observed scenarios. The presence of temporal decorrelation is considered in the model, which is recognized to be one of the main application barriers of MB repeat-pass forest observations, especially from space [8].
References
[1] A. Reigber, A.Moreira, “First Demonstration of Airborne SAR Tomography Using Multibaseline L-Band Data,” IEEE Trans. on Geoscience and Remote Sensing, vol. 38, 2000.
[2] F. Lombardini, M. Pardini, “Experiments of Tomography-Based SAR Techniques with P-Band Polarimetric Data”, Proc. of the 2009 ESA PolInSAR Workshop.
[3] M. Nannini, R. Scheiber, et al., “Estimation of the Minimum Number of Tracks for SAR Tomography,” IEEE Trans. on Geoscience and Remote Sensing, vol. 47, 2009.
[4] M. Neumann, L. Ferro-Famil, et al., “Estimation of Forest Structure, Ground, and Canopy Layer Characteristics From Multibaseline Polarimetric Interferometric Data,” IEEE Trans. on Geoscience and Remote Sensing, vol. 48, 2010.
[5] S. Tebaldini, “Single and Multipolarimetric SAR Tomography of Forested Areas: A Parametric Approach,” IEEE Trans. on Geoscience and Remote Sensing, vol. 48, 2010.
[6] F. Gini, F. Lombardini, M. Montanari, “Layover Solution in Multibaseline SAR Interferometry,” IEEE Trans. on Aerospace and Electronic Systems, vol. 38, 2002.
[7] M. Pardini, F. Lombardini, F. Gini, “The Hybrid Cramér-Rao Bound for Broadside DOA Estimation of Extended Sources in Presence of Array Errors,” IEEE Trans. on Signal Processing, vol. 56, pp. 1726–1730, Apr 2008.
[8] F. Lombardini, F. Cai, M. Pardini, “Parametric Differential SAR Tomography of decorrelating Volume Scatterers,” Proc. of the 2009 European Radar Conference (EURAD)
Phase Calibration of Multibaseline SAR Data Stacks: A Minimum Entropy Approach
No full textNon-perfectly compensated platform motions and/or atmospheric propagation delays introduce phase errors in repeat pass multibaseline synthetic aperture radar (SAR) data stacks. Such errors affect dramatically the extraction of information about the observed scene. In this paper, a new phase self-calibration approach is proposed. Its effectiveness is assessed by processing both simulated and real data
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Sub-Canopy Topography Estimation: Experiments With Multibaseline SAR Data at L-Band
No full textSynthetic aperture radar (SAR) systems in L-band and P-band are characterized by deep penetration capabilities into volumes, enabling new opportunities for the radar remote sensing of forests. In the last years, the interest has been continuously growing in the estimation of the sub-canopy topography, especially by exploiting multibaseline (possibly polarimetric) SAR data.
This work intends to contribute on this topic by presenting further experiments with real L-band data about ground topography estimation and by quantifying the obtained performance. Different forest scenarios are considered. Potentials and limitations are analyzed with particular reference to a multibaseline relaxation-based algorithm
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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