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521.
Hodgkiss W.S. Ensberg D.E. Murray J.J. D'Spain G.L. Booth N.O. Schey P.W. 《Oceanic Engineering, IEEE Journal of》1996,21(4):393-401
Accurate knowledge of array shape is essential for carrying out full wavefield (matched-field) processing. Direct approaches to array element localization (AEL) include both nonacoustic (tilt-heading sensors) and acoustic (high-frequency, transponder-based navigation) methods. The low-frequency signature emitted from a distant source also can be used in an inversion approach to determine array shape. The focus of this paper is on a comparison of the array shape results from these three different methods using data from a 120-m aperture vertical array deployed during SWellEx-3 (Shallow Water evaluation cell Experiment 3). Located 2 m above the shallowest array element was a self-recording package equipped with depth, tilt, and direction-of-tilt sensors, thereby permitting AEL to be performed non-acoustically. Direct AEL also was performed acoustically by making use of transponder pings (in the vicinity of 12 kHz) received by high-frequency hydrophones spaced every 7.5 m along the vertical array. In addition to these direct approaches, AEL was carried out using an inversion technique where matched-field processing was performed on a multitone (50-200 Hz), acoustic source at various ranges and azimuths from the array. As shown, the time-evolving array shape estimates generated by all three AEL methods provide a consistent picture of array motion throughout the 6-h period analyzed 相似文献
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David C. Booth Stuart Crampin Russ Evans Graham Roberts 《Geophysical Journal International》1985,83(1):61-73
Summary. The Turkish Dilatancy Projects (TDP1 in 1979 and TDP2 in 1980) recorded small earthquakes near the North Anatolian Fault with closely-spaced networks of three-component seismometers in order to investigate the possibility of diagnosing dilatancy from its effects of shear-wave propagation. This paper examines the polarizations of shear wavetrains recorded in the shear-wave window immediately above the earthquake foci. Abrupt changes in the orientation and/or ellipticity of the shear-wave polarizations are almost always observed during the first few cycles following the initial shear-wave arrival on each seismogram. The horizontal projections of the polarizations of the first shear-wave arrivals at any given station show nearly parallel alignments with approximately the same orientations at each of the recording sites (with one exception). It is difficult to explain this uniform alignment over a wide area in terms of scattering at the irregular surface topography or by earthquake focal mechanisms. We demonstrate that the shear-wave splitting is likely to be the result of anisotropy in the region above the earthquake foci, which could produce polarizations displaying the observed alignments. The temporal change of the azimuth of alignment, observed at one locality between 1979 and 1980, may be due to the release of a local stress anomaly by a very near earthquake. 相似文献
525.
Johannes Feddema Keith Oleson Gordon Bonan Linda Mearns Warren Washington Gerald Meehl Douglas Nychka 《Climate Dynamics》2005,25(6):581-609
This study assesses the sensitivity of the fully coupled NCAR-DOE PCM to three different representations of present-day land
cover, based on IPCC SRES land cover information. We conclude that there is significant model sensitivity to current land
cover characterization, with an observed average global temperature range of 0.21 K between the simulations. Much larger contrasts
(up to 5 K) are found on the regional scale; however, these changes are largely offsetting on the global scale. These results
show that significant biases can be introduced when outside data sources are used to conduct anthropogenic land cover change
experiments in GCMs that have been calibrated to their own representation of present-day land cover. We conclude that hybrid
systems that combine the natural vegetation from the native GCM datasets combined with human land cover information from other
sources are best for simulating such impacts. We also performed a prehuman simulation, which had a 0.39 K ~higher average
global temperature and, perhaps of greater importance, temperature changes regionally of about 2 K. In this study, the larger
regional changes coincide with large-scale agricultural areas. The initial cooling from energy balance changes appear to create
feedbacks that intensify mid-latitude circulation features and weaken the summer monsoon circulation over Asia, leading to
further cooling. From these results, we conclude that land cover change plays a significant role in anthropogenically forced
climate change. Because these changes coincide with regions of the highest human population this climate impact could have
a disproportionate impact on human systems. Therefore, it is important that land cover change be included in past and future
climate change simulations. 相似文献
526.
Linda Werner Hartman 《Mathematical Geology》2006,38(2):113-133
Spatial datasets are common in the environmental sciences. In this study we suggest a hierarchical model for a spatial stochastic field. The main focus of this article is to approximate a stochastic field with a Gaussian Markov Random Field (GMRF) to exploit computational advantages of the Markov field, concerning predictions, etc. The variation of the stochastic field is modelled as a linear trend plus microvariation in the form of a GMRF defined on a lattice. To estimate model parameters we adopt a Bayesian perspective, and use Monte Carlo integration with samples from Markov Chain simulations. Our methods does not demand lattice, or near-lattice data, but are developed for a general spatial data-set, leaving the lattice to be specified by the modeller. The model selection problem that comes with the artificial grid is in this article addressed with cross-validation, but we also suggest other alternatives. From the application of the methods to a data set of elemental composition of forest soil, we obtained predictive distributions at arbitrary locations as well as estimates of model parameters. 相似文献
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528.
Orbital forcing of continental climate during the Pleistocene: a complete astronomically tuned climatic record from Lake Baikal, SE Siberia 总被引:1,自引:0,他引:1
Alexander A. Prokopenko Linda A. Hinnov Douglas F. Williams Mikhail I. Kuzmin 《Quaternary Science Reviews》2006,25(23-24):3431
A new composite BDP-96 biogenic silica record over the entire Pleistocene was generated by splicing BDP-96-1 and BDP-96-2 drill cores from Lake Baikal, crosschecked against a similar record from a nearby BDP-98 drill core. A new astronomically tuned age model is proposed based on correlating peak biogenic silica responses with the timing of September perihelia. This target is derived from analysis of regional climate proxy responses during the Holocene, the last interglacial and around paleomagnetic reversals. By resolving virtually every precessional cycle during the Pleistocene, the new age model represents a major improvement compared with previously reported Lake Baikal timescales. The astronomically tuned ages of the Pleistocene paleomagnetic reversals are consistent with published dates. The minimal tuning approach we used (precession only) has also aligned high signal power in a narrow obliquity band, confirming the strong presence of orbital forcing. There are also strong ca 100-ka scale cycles, but these are not aligned with the orbital eccentricity.Despite the location of Lake Baikal in a continental interior that is highly sensitive to insolation forcing, the tuned biogenic silica record reveals a consistent phase difference of −32° (ca 4 ka) relative to insolation in the obliquity band. An inherent lag embedded in a continental proxy record, not driven by global ice volume, is an intriguing finding. Another new observation is that long-term changes in sedimentation rates in Lake Baikal appear to be related to the amplitude of orbital forcing; both amplitudes and sedimentation rates undergo significant changes during MIS 24-MIS 19 interval corresponding to the Middle Pleistocene Transition. With potential for linking continental and marine climato-stratigraphies, the new Baikal record serves a new benchmark correlation target in continental Eurasia, as an alternative to June 65°N insolation and ODP-correlated timescales. 相似文献
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Linda Sorg Neiler Medina Daniel Feldmeyer Arlex Sanchez Zoran Vojinovic Jörn Birkmann Alessandra Marchese 《Natural Hazards》2018,92(1):257-282
Vulnerability and disaster risk assessment has been evaluated from different perspectives with focus on global or national scale. There is a lack of methodologies on city scale, which are able to capture inner-city disparities with regard to socioeconomic aspects. Therefore, the main objective was to develop a transparent and comprehensive indicator-based approach which is flexible in terms of data availability and is not tied to a specific case study side. This research proposes two flexible methodological approaches on how to perform socioeconomic vulnerability assessment. Susceptibility, Coping and Adaptation are the main elements of a modular hierarchical structure to capture the societal sphere of vulnerability. The first method is completely based on official census data at block scale. The second method is an expansion and includes data derived from a field survey to add components of risk perception. The proposed methodologies were developed and applied in the city of Genoa (Italy). The results are displayed spatially explicit on maps. Furthermore statistical analysis, to reveal the driving forces which influence vulnerability, was performed. The census-based approach revealed that vulnerability is forced along the river by the inherent susceptibility, as well as the lack of adaptation. The two approaches can be used effectively in gaining different insights. The flexibility of the framework proved to be suitable to the objective of the research. However, the values computed in this research do not claim completeness, and the aim was to provide useful information for stakeholders in decision making process to reduce vulnerability and risk. 相似文献