1,721,041 research outputs found
Electromagnetic modeling of scattered signals of opportunity: challenges and approaches
No full texthe possibility of exploiting signals of opportunity such as navigation signals for remote-sensing applications has been the object of extensive scientific research. Over the years, the potential of this technique has been mainly investigated for wind scatterometry and sea-surface altimetry, resulting in mission concepts and prototypes currently in orbit or under study. More recently, the potential of the Global Navigation Satellite System (GNSS) has attracted significant scientific and industrial interest, especially for land applications. The possibility of retrieving soil moisture and vegetation biomass by means of GNSS reflections, originally demonstrated through theoretical models and simulations, has been confirmed through the analysis of ground-based and airborne measurements. Even if these campaigns significantly contributed to consolidating the physics that is behind the interaction between navigation signals and some important geophysical parameters of the illuminated surface, a complete understanding of the experiments still needs further scientific efforts, especially for satellite observations. In this work, we review the main progress that has recently been made at two universities of Rome, Sapienza and Tor Vergata, as well as by some other research groups. Current challenges and modeling approaches are summarized, focusing the attention on the potential offered by GNSS reflectometry with respect to more established passive and active remote-sensing techniques. An electromagnetic model and the corresponding numerical simulator designed to characterize the field scattered under bistatic illumination and for the study of the signal at the receiver generated by sources of opportunity are reviewed and summarized
Design and evaluation of a cloud-oriented procedure based on SAR and Multispectral data to detect burnt areas
Full text linkThis article presents the design and an experimental evaluation study of a novel procedure based on the synergistic use of SAR and Multispectral data to detect burnt area over vegetated natural surfaces. The procedure is designed to take advantages of open satellite datasets and cloud computing services. The underpinning data processing workflow exploits the variation of the backscattering coefficients and the spectral signature of surfaces affected by fire damages by applying a threshold-based technique optimized for different land cover classes. The presented experimental study focuses on three large wildfires occurred over Europe during the last four years. By comparing the burnt areas detected by the procedure with data from the European Forest Fire Information Service, we obtained an overall accuracy higher than 0.88 for all the considered test cases. The presented data also include various metrics that allow to compare the results achievable by using in synergy SAR and Multispectral data with respect to the individual use of them. Overall, the results of our study show that the presented procedure, and more in general the exploited design approach, can be of interest for researchers and practitioners for the development of efficient automated solutions for the detection of burnt areas
Analysis of multi-frequency SAR data for evaluating their sensitivity to soil moisture over an agricultural area in Argentina
No full textIn this paper, a joint analysis of multi-frequency SAR data has been performed to assess their sensitivity to soil moisture variations over an agricultural area. The main objective was evaluating the performances offered by C and L bands in terms of sensitivity to soil moisture. We used L-band quad-polarimetric data acquired by SAOCOM-1A and C-band dual-polarimetric data collected by Sentinel-1A over an agricultural area located in the Córdoba Province, Argentina. We analyzed the temporal evolution of the backscattering coefficient at different polarizations with respect to in-situ soil moisture measurements collected during a field campaign conducted by the Argentinian Space Agency as well as data recorded by a permanent network of ground stations. Sensitivity to other variables, such as the NDVI, is also discussed and analyzed
Bistatic radar with large baseline for bio-geophysical parameter retrieval
No full textThis work aims at defining applications, products and user requirements, as well as the hardware and ground processing design of a companion satellite mission which shall carry aboard a 'passive' radar working in tandem with the Argentinian L-band radar developed by CONAE and denoted as SAOCOM. The primary objective (i.e., science driver) of the SAOCOM companion satellite mission (SAOCOM-CS) is forest tomography, which will be carried out by exploiting small baselines between active and passive systems (order of km) changing with time. Conversely, this paper summarizes the investigation carried out for different bistatic radar configurations that are characterized by much larger spatial baselines (up to hundreds of km) and bistatic angles with very large components both in azimuth and in elevation. Soil moisture and vegetation biomass retrieval takes advantage from the combined exploitation of monostatic and bistatic measurements. The retrieval ambiguity related to target azimuthal anisotropy could also be reduced by bistatic observations, like in the case of the ocean surface. The bistatic system shall collect data with suitable directions and polarizations. The expected performances of a multistatic system have been predicted using electromagnetic model
Polarimetric SAR decompositions for soil moisture retrieval over corn fields in Argentina
No full textIn this study, we investigate the synergic use of polarimetric Synthetic Aperture Radar (SAR) decompositions and electromagnetic models for soil moisture retrieval over corn fields. The Generalized Freeman-Durden decomposition (GFD) is applied to a time-series of L-band full-polarimetric SAOCOM-1A data collected during the 2019-2020 growing season over an agricultural area. The scattering mechanisms (i.e., surface, double-bounce, and volume) derived from the decomposition are compared with the ones simulated using the Tor Vergata electromagnetic model. The goal of the work is to evaluate the capabilities of the GFD to consistently assign each scattered power to the corresponding scattering mechanism, so that the sensitivity to soil moisture and vegetation can be highlighted. Results point out significative discrepancies, especially for the volume term, while a good agreement is found for the double-bounce contribution. Differences are further confirmed when a simple linear regression model is applied to retrieve soil moisture using the GFD scattered powers or the model powers
Joint analysis of Sentinel-1 and SAOCOM data sensitivity to soil moisture content over an agricultural area
No full textA joint analysis of C-band dual-pol Sentinel-1A data and L-band full-pol SAOCOM-1A data is presented to investigate their sensitivity to soil moisture over an agricultural area located near the city of Monte Buey in the Córdoba Province, Argentina. The temporal evolution of the backscattering coefficient σ0 at different polarizations is analyzed with respect to in-situ soil moisture measurements collected during a field campaign as well as data recorded by ground stations from a permanent network. Sensitivity to vegetation parameters is also discussed. The fully polarimetric electromagnetic model developed at Tor Vergata University is used to compare simulated and measured σ0 for corn fields
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
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