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541.
R.M. Laws D. Halliday J.-F. Hopperstad D. Gerez M. Supawala A. Özbek T. Murray E. Kragh 《Geophysical Prospecting》2019,67(6):1443-1471
Marine seismic vibrators are generally considered to be less intrusive than airguns from an environmental perspective. This is because they emit their energy spread out in time, rather than in a single, high-intensity pulse. There are also significant geophysical benefits associated with marine vibrators, and they stem from the ability to specify in detail the output acoustic waveform. The phase can be specified independently at each frequency. Such detailed control cannot be achieved with conventional airgun sources, where the phase can only be modified using simple overall time delays. The vibrator phase can be employed in several different ways: it can be applied to the overall source phase in a sequence so that it varies from one source point to the next; it can be applied to the individual vibrators within the source array so the source directivity is changed; it can be applied to the overall source phase of each source in a simultaneous source acquisition. Carefully designed phase sequences can attenuate the residual source noise, and this in turn allows extra source points to be interleaved between the conventional ones. For these extra source points, the relative phase of the vibrators within the array can be chosen to create a transverse gradient source, which illuminates the earth predominantly in directions out of the plane of the sail line without left/right ambiguity. If seismic vibrator data are acquired using interleaved conventional and transverse gradient sweeps, more information is collected per kilometre of vessel travel than is the case in conventional acquisition. This richer data acquisition leads to the possibility of acquiring all the necessary seismic data in a shorter time. Three-dimensional reconstruction techniques are used to recover the same image quality that would have been obtained using the conventional, more time-consuming acquisition. For a marine vibrator to be suitable for these techniques it must, in general terms, have ‘high fidelity’. The precise device specifications are defined through realistic end-to-end simulations of the physical systems and the processing. The specifications are somewhat more onerous than for a conventional vibrator, but they are achievable. A prototype vibrator that satisfies these requirements has been built. In a simulated case study of a three-dimensional deep-water ocean bottom node survey, the seismic data could have been acquired using marine vibrators in one third of the time that it would have taken using airguns. 相似文献
542.
Outflows at the Edges of an Active Region in a Coronal Hole: A Signature of Active Region Expansion?
Outflows of plasma at the edges of active regions surrounded by quiet Sun are now a common observation with the Hinode satellite. While there is observational evidence to suggest that the outflows are originating in the magnetic field surrounding
the active regions, there is no conclusive evidence that reveals how they are driven. Motivated by observations of outflows
at the periphery of a mature active region embedded in a coronal hole, we have used a three-dimensional simulation to emulate
the active region’s development in order to investigate the origin and driver of these outflows. We find that outflows are
accelerated from a site in the coronal hole magnetic field immediately surrounding the active region and are channelled along
the coronal hole field as they rise through the atmosphere. The plasma is accelerated simply as a result of the active region
expanding horizontally as it develops. Many of the characteristics of the outflows generated in the simulation are consistent
with those of observed outflows: velocities up to 45 km s−1, properties akin to the coronal hole, proximity to the active region’s draining loops, expansion with height, and projection
over monopolar photospheric magnetic concentrations. Although the horizontal expansion occurs as a consequence of the active
region’s development in the simulation, expansion is also a general feature of established active regions. Hence, it is entirely
possible and plausible that the expansion acceleration mechanism displayed in the simulation is occurring in active regions
on the Sun and, in addition to reconnection, is driving the outflows observed at their edges. 相似文献
543.
544.
Humphrey Murray Arko Lucieer Raymond Williams 《International Journal of Applied Earth Observation and Geoinformation》2010
This study was the first to use high-resolution IKONOS imagery to classify vegetation communities on sub-Antarctic Heard Island. We focused on the use of texture measures, in addition to standard multispectral information, to improve the classification of sub-Antarctic vegetation communities. Heard Island’s pristine and rapidly changing environment makes it a relevant and exciting location to study the regional effects of climate change. This study uses IKONOS imagery to provide automated, up-to-date, and non-invasive means to map vegetation as an important indicator for environmental change. Three classification techniques were compared: multispectral classification, texture based classification, and a combination of both. Texture features were calculated using the Grey Level Co-occurrence Matrix (GLCM). We investigated the effect of the texture window size on classification accuracy. The combined approach produced a higher accuracy than using multispectral bands alone. It was also found that the selection of GLCM texture features is critical. The highest accuracy (85%) was produced using all original spectral bands and three uncorrelated texture features. Incorporating texture improved classification accuracy by 6%. 相似文献
545.
Open data strategies are being adopted in disaster-related data particularly because of the need to provide information on global targets and indicators for implementation of the Sendai Framework for Disaster Risk Reduction 2015–2030. In all phases of disaster risk management including forecasting, emergency response and post-disaster reconstruction, the need for interconnected multidisciplinary open data for collaborative reporting as well as study and analysis are apparent, in order to determine disaster impact data in timely and reportable manner. The extraordinary progress in computing and information technology in the past decade, such as broad local and wide-area network connectivity (e.g. Internet), high-performance computing, service and cloud computing, big data methods and mobile devices, provides the technical foundation for connecting open data to support disaster risk research. A new generation of disaster data infrastructure based on interconnected open data is evolving rapidly. There are two levels in the conceptual model of Linked Open Data for Global Disaster Risk Research (LODGD) Working Group of the Committee on Data for Science and Technology (CODATA), which is the Committee on Data of the International Council for Science (ICSU): data characterization and data connection. In data characterization, the knowledge about disaster taxonomy and data dependency on disaster events requires specific scientific study as it aims to understand and present the correlation between specific disaster events and scientific data through the integration of literature analysis and semantic knowledge discovery. Data connection concepts deal with technical methods to connect distributed data resources identified by data characterization of disaster type. In the science community, interconnected open data for disaster risk impact assessment are beginning to influence how disaster data are shared, and this will need to extend data coverage and provide better ways of utilizing data across domains where innovation and integration are now necessarily needed. 相似文献
546.
Alan T. Murray Jing Xu Zifan Wang Richard L. Church 《International journal of geographical information science》2019,33(5):1106-1130
An essential location analytic method is GIS, able to support map-based display along with geographic data creation, management, manipulation in addition to functions for suitability evaluation. Location models have proven to be critical as well, with many prominent approaches found in popular GIS software. This paper reviews a class of location models and provides an overview of the methods used to solve these models. This is significant because of the broad use and application of location models in GIS to address important problems and issues facing society. Spatial analytical insights are essential. The implications of models and methods available through GIS are explored, particularly notions of solution quality. Case studies are offered to highlight ease of access to location models in GIS along with observed computational performance. 相似文献
547.
In this study, we provide the first absolute ages for a Big Circle megalithic structure in Jordan, using rock surface luminescence dating of the buried surface of rocks collected from circle J4 in southern Jordan. Five rocks were used for this study. All rocks showed evidence of previous daylight exposure before being used in the construction of the circle. The exposure was sufficient to bleach the latent luminescence signal to a negligible level compared to the subsequent burial dose. Three rocks gave indistinguishable ages, and were last exposed to daylight in 1500 ± 100 BCE; this is very likely to be the date of circle construction. Two others gave younger ages, indicating later disturbance or reworking. These new results provide very strong evidence for construction during the Late Bronze Age, and refute the earlier hypothesis of construction during Umayyad period (661–750 CE) as a hunting trap. 相似文献
548.