1,720,982 research outputs found
Addressing the rain effects on the ocean scattering: a theoretical model of the ocean surface backscattering coefficient in presence of both wind and rain
No full textAtmospheric rain has a strong impact on spaceborne scatterometer observations at Ku-band and higher frequencies. Several semi-empirical techniques have been developed in the past years to address the rain effects on scatterometer backscattered signal but, a theoretical model is still an open issue [Weissman et al., 2012]. A theoretical model would contribute to establish an accurate approach in deriving winds as well as in studying the sensibility to the rain intensity. It would also ingest the opportunity to develop new techniques to estimate both wind and rain simultaneously. Therefore, in this perspective, the goal of this work is to describe our approach in developing such model.
Here, we have focused on modelling the ocean surface backscattering coefficient in presence of rain. The inclusion of rain attenuation and volume backscattering will be the goal of future works. To describe the surface backscattering coefficient, we have used the Two Scale Model, where a new ocean surface roughness model is proposed to account for the ocean surface modification induced by the rain [Contreras and Plant, 2006]. This new spectrum consists on an extension of the ocean wave spectrum model proposed by Elfouhaily et al., (1997) (hereafter E). However, the E spectrum has been firstly tuned to best match the empirical geophysical model functions (GMF). The tuning strategy has been defined such that it does not depend on any instrumental parameters like frequency, incidence angle or polarization as well as on the different available GMFs, in order to allow the model to work in any conditions. Two main rain effects have been included in this spectrum, such as: the short wave damping according to the theory proposed by Nystuen, (1990) and the generation of the ring waves, as shown by Bliven et al., (1997).
The results of the modeled Normalized Radar Cross Section (NRCS), in non-rainy conditions, show a very good agreement with the GMF developed for the Ku-band QuikSCAT scatterometer, at vertical polarization. Good results are also obtained at C-band, in vertical polarization, using the CMOD5.N GMF for validation but, in this case, some discrepancies can be seen at wind speed higher than 15 m/s so, further investigation are needed. Moreover, at Ku-band, the horizontal polarization shows a bias which increases with the wind speed. This bias can be ascribed to the presence of the steep breaking waves which are known to introduce an additional scattering to the wind wave backscattering coefficient. Future investigations will focus on modeling such additional scattering, according to the theory proposed by Kudryavtsev et al., (2003).
On the other hand, in rainy conditions, the results are consistent to what expected. The Ku-band NRCS increases with the rain rate at low, medium and high winds, demonstrating that the ring waves are the dominant contribution. The rain smooths the directional component of the NRCS at lower winds but does not affects the directional component at moderate and high winds. Moreover, it is shown that the sensibility of the NRCS to rain decreases with the wind speed. Additional tests, using real data, are also planned
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
Addressing the polarization signature of the ocean scattering at Ku band in presence of both non homogenous winds and rain
No full textKu-band spaceborne scatterometer observations are affected by rain and these effects need to be corrected to avoid errors in wind retrievals. We propose a theoretical model of the ocean surface backscattering coefficient accounting for both wind and rain. The rain effects are included in the ocean wind wave spectrum. In this work we describe our model and the approach used to address the discrepancies found at horizontal (H) and vertical (V) polarizations
Addressing the rain effects on ocean wind scatterometry at C and Ku band: modification of the ocean surface backscattering coefficient
No full textOcean surface winds are the main factors affecting the scatterometer backscattered radiation. In clear weather conditions, the surface wind modifies the ocean surface roughness which plays a key role in the regulation of the backscattered radiation and, in turn, in the wind estimates. However, in presence of atmospheric precipitation, the surface roughness is also modified by the impact of the raindrops imping on the surface. Therefore, modeling the ocean surface modification combining both wind and rain offers an opportunity to physically understand the contribution of the rain in the ocean backscattering coefficient. It opens the way towards a complete theoretical forward model to simulate the scatterometer observations in both rainy and non-rainy conditions once the contributions due to rain attenuation and volume backscattering are introduced. Such model allows also possible correction techniques of the wind retrievals and synergistic estimates of rain parameters as well. In this perspective, our work focuses on the development of a physical model of the ocean surface backscattering coefficient accounting for the modification of the surface roughness due to both wind and rain.
The ocean surface roughness is described by the equilibrium ocean wind wave spectrum which can be defined as the distribution of the mean waves’ energy considering the spectral sources as balanced, such as wind contributions, breaking dissipation and non-linear interactions. Several representations of the ocean surface spectrum in equilibrium range already exist and, in term of wavenumbers, they describe the ocean surface as composed by two scale of roughness such as large scale gravity waves and small scale capillary waves. Our approach consists in modifying the spectrum in the region of capillary waves in order to include the rain-induced wave damping and the generation of ring waves [Contreras and Plant, 2006]. We have modeled these effects by introducing an attenuation factor accounting for the variation of the water viscosity [Nystuen, 1990] and an additive contribution representing the increase of the surface roughness due to ring waves [Bliven et al., 1997]. The main features of our approach is that the rain model does not depend on the representation of the surface wind wave spectrum so that it can be applied to any equilibrium spectrum as long as it shows a separation between gravity and capillary waves. We have first analyze the spectrum developed by Donelan and Pierson (1987) and the preliminary results are as expected, however analysis using further spectra will follow. To compute the co-polar ocean surface backscattering coefficient, the ocean surface two scale model with the new rain affected wind wave spectrum, has been used. We have first focused on Ku band simulations in non-rainy conditions and comparison to the empirical geophysical model function developed for the NASA scatterometer QuikSCAT show good agreement especially at vertical polarization. Then, we have focused on low-medium wind regime to analyze the ocean surface backscattering coefficient at different rain intensities. As expected, the backscattering coefficient increases when the rain rate becomes higher due to the increasing roughness and this shows that our approach is physically consistent. Analysis at C band will be also carried out. The validation in non-rainy conditions will be performed using the CMOD5.N geophysical model function developed for C band scatterometer such as European Remote Sensing Satellite-2 (ERS-2) and Advanced Scatterometer (ASCAT). Analysis of the ocean response at different rain rates as well as comparisons between C and Ku bands are planned in order to study the impact on the backscattering coefficient, at different frequencies, of the rain induced surface modification
Variations on the Author
Get PDF“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
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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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