1,720,965 research outputs found
Optical remote sensing of oil in the marine environment : an investigation into the optical properties of surface and dispersed oil and the means by which pollution may be detected using airborne optical instruments at visible and near-infrared wavelengths
No full textRemote sensing has played an increasing role in the routine monitoring of oil pollution and in support of the operational response to major oil pollution incidents. This study develops the technique of optical measurement for the detection of oil in the Marine Environment.A theoretical model is proposed, which relates upwelling radiance from surface oil to the optical properties of the oil in question, to the thickness of the oil layer, and to a number of ancillary environmental parameters. It is used to interpret the results of laboratory experiments in artificial and natural light, and ultimately as a tool in the analysis of airborne optical data of surface oil in the field, including the Sea Empress oil spill.Laboratory experiments showed that the thickness of surface oil may be determined using spectral ratios, and the result compared well with the predictions made by the theoretical model. Using the peak to near-infrared ratio, relative thickness estimates can be made from remote sensing data, without extensive data processing. Absolute thickness measurements are more complex, and require the knowledge of a number of environmental parameters.Both the laboratory and airborne data show that classification of oils into broad groups is possible using spectral analysis. However, the number of environmental parameters that must be considered makes this a complex task for field data.The model predicts that sheen detection will be most reliable in regions of the spectrum where the sub-surface signal is low, such as the violet to deep blue and the near-infrared. This is confirmed by the laboratory experiments in natural light, and by the airborne data from the field experiments. When water-leaving radiance is high in the near-infrared, sheen detection may be more difficult, although it should still be possible in the violet to deep blue.The theoretical model and the field data suggest that dispersed oil may be detected if concentrations are sufficiently high. The presence of suspended sediment or high concentrations of planktonic algae will, however, make this task more difficult, and success depends on a good knowledge of the background conditions.</p
Slicks as Indicators for Marine Processes
Full text linkMonomolecular surface films ("sea slicks") are well known to dampen small-scale waves at the water surface, thereby influencing transport processes at the air-sea interface. Because of their strong wave-damping capacity, they can often be observed, not just on synthetic aperture radar imagery, but also on imagery acquired in the visible and infrared spectral ranges. Because sea slicks tend to accumulate at the water surface along lines of, for example, current shear in fronts and eddies, they can be used as proxies for observing such marine processes from space. We demonstrate how well sea slicks are suited to indicate marine processes in the coastal zone. A slick's damping capability depends on the surfactant concentration on the sea surface and, thus, on the compression status of the slick-forming material. Furthermore, we show that slick signatures can be used to derive surface current vectors at higher spatial resolution than that of numerical models
Application of clustering techniques to multispectral optical data over the ocean
Full text linkMERIS, on Envisat, provides high-resolution radiometric data at nine discrete channels in the visible band. This paper looks at the potential of an unsupervised classification technique for utilizing these multi-spectral data to provide better discrimination between water masses according to their optical properties, and in particular whether phytoplankton groups can be distinguished. Although the majority of data do show a spectral peak associated with chlorophyll's red fluorescence line, clustering using only the red bands was found to separate out coastal waters according to their sediment content. Red-end classification also appeared to identify sub-pixel cloud, and demonstrate that the smile correction had not removed all the striping from the data. Classification using bands from the blue-green end showed a response to changes in chlorophyll concentration, but also indicated other variations. However, without in situ data no firm conclusions can be drawn on which phytoplankton groupings are present
Characterisation of the sea surface microlayer - using Langmuir films and ellipsometry
No full textThe sea-surface microlayer (SSM) is a hugely complex system comprised of many different organic materials that has a considerable influence on the physical and chemical properties of the ocean surface. Under certain conditions, involving wind, internal waves and currents, the SSM is compressed and forms biogenic slicks. These biogenic slicks have a wave dampening effect and when using satellite data to monitor the ocean surfaces look indistinguishable from anthropogenic slicks. It is important to understand the physical properties of these biogenic slicks to identify oil pollution.
For this project the physical properties of biogenic slicks from the Solent (UK) and the Black Sea (Ukraine) are being investigated. Model compounds that display similar properties to the slicks are also being characterized; these simpler systems are easier to interpret and parallels to the biogenic slicks can be made increasing understanding.
The tools used to characterize these Langmuir films involve the analysis of the phase and amplitude change of polarized light upon surface reflection (ellipsometry). The film can be compressed and expanded monitoring changes in surface pressure. In conjunction, ellipsometry can be used to determine optical properties, thickness, phase changes and hysteresis effects of the film, offering both spectroscopic information and images. The changes of the film on compression are important as they mimic natural events that have the potential to be of use in satellite data interpretation.
Results show, in images, the domain separation of different chemical species within the SSM and co-existence of phases. Upon compression and expansion of the films, aggregation of the different phases along with hysteresis effects are seen – phenomena that has only been hypothesized so far. Work on the model compounds demonstrates that it is possible to determine thicknesses of thin films at different surface pressures offering valuable information on phase changes
The application of hyperspectral image techniques on MODIS data for the detection of oil spill in RSA
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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
BILKO and African capacity development in coastal and marine remote sensing
No full textIn much of Africa barriers still exist to the effective use of Earth observation in marine and coastal research and management. To remedy this, the development of data access and processing capacity must go hand in hand with hands-on training in the use of satellite data. The Bilko project has been providing training resources suitable for this for 25 years. In recent years marine scientists from Africa and Europe have been using Bilko to develop lessons based on African examples taken from image data disseminated via GEONETCast in two EC funded projects. The work is part of current efforts to develop MSc level and professional training courses for use in Africa, and shows how the contribution of African experts in the development of new lessons contributes to making these more relevant
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