排序方式: 共有36条查询结果,搜索用时 31 毫秒
11.
Amii R. Darnell Andrew A. Lovett Jenni Barclay Richard A. Herd 《International journal of geographical information science》2013,27(8):1171-1191
Terrain is a surface phenomenon that is measured, modelled, and mapped. However, it is continuously variable and must be simulated by points or mathematical equations that are inherently approximations. The error induced by digitally represented terrain can propagate to surface derivatives and geographical information science (GIS) applications where topography is considered. This can lead to uncertainty in model predictions and the use of data that are unfit for the application to which they are intended. This article outlines the problem of uncertainty in terrain representation and demonstrates the consequences for volcanic mudflow modelling. The response of a simple least-cost single flow algorithm to input parameters was investigated in order to assess output variation from the different sources of input variation. Elevation error was modelled with a probability density function (PDF) and propagated through stochastic simulation (Monte Carlo). Such combined uncertainty and sensitivity analyses enabled a qualitative judgement of the relative significance of elevation error on the flow model prediction. Different methods for terrain model construction were considered and show that supplementing global positioning system (GPS) measurements with information from field notes and reconnaissance photographs greatly improved the model performance and reduced the uncertainty. It is concluded that in terms of validity of model results, there is no substitute for constructing an elevation model that is informed by the terrain. 相似文献
12.
Mikko Kaasalainen Petr Pravec Lenka Šarounová Jenni Virtanen Anders Erikson Josef ?urech Johan S.V. Lagerros Claes-Ingvar Lagerkvist John Davies Peter Kušnirák Vasilij G. Shevchenko Irina N. Belskaya 《Icarus》2004,167(1):178-196
We present new observations and models of the shapes and rotational states of the eight near-Earth Asteroids (1580) Betulia, (1627) Ivar, (1980) Tezcatlipoca, (2100) Ra-Shalom, (3199) Nefertiti, (3908) Nyx, (4957) Brucemurray, and (5587) 1990 SB. We also outline some of their solar phase curves, corrected to common reference geometry with the models. Some of the targets may feature sizable global nonconvexities, but the observable solar phase angles were not sufficiently high for confirming these. None is likely to have a very densely cratered surface. We discuss the role of the intermediate topographic scale range in photometry, and surmise that this scale range is less important than large or small scale lengths. 相似文献
13.
Jan Alexander Jenni Barclay Janez Sušnik Sue C. Loughlin Richard A. Herd Amii Darnell Sian Crosweller 《Journal of Volcanology and Geothermal Research》2010
On 20th May 2006 the Soufrière Hills Volcano on the Caribbean island of Montserrat experienced a large dome collapse and intense rainfall generated flash floods. The floods had very high loads of volcanic debris derived both from this and previous eruptions and can thus be classified as lahars. The floods reached unusually high water levels and caused substantial geomorphic change in the Belham Valley. Detailed rainfall and geomorphological data, coupled with the precise timing of events and yewitness accounts have facilitated an assessment of the relative importance of rainfall volume and intensity, older volcanic debris, pre- and syn-flood tephra fall and the extent of pre-flood vegetation damage for the behavior of this and subsequent sediment-laden floods in this setting. The change in runoff behavior was controlled by preexisting vegetation damage and synchronous tephra fall and this was critically important in controlling the impact of these flash floods. Although rainfall intensity and volume have some control on flood occurrence they are not the critical control on flash flood impact on the geomorphology in the Belham Valley. A significant conclusion of this study is that the extreme nature of the flash floods was not caused by extreme rainfall (as is commonly believed to be the primary cause of flash floods) but rather it was the result of changed runoff behaviour caused by the widespread syn-flood tephra deposition and importantly the widespread vegetation damage by volcanic-associated acid rain in the preceding weeks. 相似文献
14.
Mikael Granvik Jenni Virtanen Dagmara Oszkiewicz Karri Muinonen 《Meteoritics & planetary science》2009,44(12):1853-1861
Abstract— We are making an open‐source asteroid orbit computation software package called OpenOrb publicly available. OpenOrb is built on a well‐established Bayesian inversion theory, which means that it is to a large part complementary to orbit‐computation packages currently available. In particular, OpenOrb is the first package that contains tools for rigorously estimating the uncertainties resulting from the inverse problem of computing orbital elements using scarce astrometry. In addition to the well‐known least‐squares method, OpenOrb also contains both Monte‐Carlo (MC) and Markov‐Chain MC (MCMC; Oszkiewicz et al. [2009]) versions of the statistical ranging method. Ranging allows the user to obtain sampled, non‐Gaussian orbital‐element probability‐density functions and is therefore optimized for cases where the amount of astrometry is scarce or spans a relatively short time interval. Ranging‐based methods have successfully been applied to a variety of different problems such as rigorous ephemeris prediction, orbital element distribution studies for transneptunian objects, the computation of invariant collision probabilities between near‐Earth objects and the Earth, detection of linkages between astrometric asteroid observations within an apparition as well as between apparitions, and in the rigorous analysis of the impact of orbital arc length and/or astrometric uncertainty on the uncertainty of the resulting orbits. Tools for making ephemeris predictions and for classifying objects based on their orbits are also available in OpenOrb. As an example, we use OpenOrb in the search for candidate retrograde and/or high‐inclination objects similar to 2008 KV42 in the known population of transneptunian objects that have an observational time span shorter than 30 days. 相似文献
15.
Julie A. Winkler Suzanne Thornsbury Marco Artavia Frank-M. Chmielewski Dieter Kirschke Sangjun Lee Malgorzata Liszewska Scott Loveridge Pang-Ning Tan Sharon Zhong Jeffrey A. Andresen J. Roy Black Robert Kurlus Denys Nizalov Nicole Olynk Zbigniew Ustrnul Costanza Zavalloni Jeanne M. Bisanz Géza Bujdosó Lesley Fusina Yvonne Henniges Peter Hilsendegen Katarzyna Lar Lukasz Malarzewski Thordis Moeller Roman Murmylo Tadeusz Niedzwiedz Olena Nizalova Haryono Prawiranata Nikki Rothwell Jenni van Ravensway Harald von Witzke Mollie Woods 《Climatic change》2010,103(3-4):445-470
A conceptual framework for climate change assessments of international market systems that involve long-term investments is proposed. The framework is a hybrid of dynamic and static modeling. Dynamic modeling is used for those system components for which temporally continuous modeling is possible, while fixed time slices are used for other system components where it can be assumed that underlying assumptions are held constant within the time slices but allowed to vary between slices. An important component of the framework is the assessment of the “metauncertainty” arising from the structural uncertainties of a linked sequence of climate, production, trade and decision-making models. The impetus for proposing the framework is the paucity of industry-wide assessments for market systems with multiple production regions and long-term capital investments that are vulnerable to climate variations and change, especially climate extremes. The proposed framework is pragmatic, eschewing the ideal for the tractable. Even so, numerous implementation challenges are expected, which are illustrated using an example industry. The conceptual framework is offered as a starting point for further discussions of strategies and approaches for climate change impact, vulnerability and adaptation assessments for international market systems. 相似文献
16.
Estimating the hydraulic properties of fractured aquifers is challenging due to the complexity of structural discontinuities that can generally be measured at a small scale, either in core or in outcrop, but influence groundwater flow over a range of scales. This modeling study uses fracture scanline data obtained from surface bedrock exposures to derive estimates of permeability that can be used to represent the fractured rock matrix within regional scale flow models. The model is developed using PETREL, which traditionally benefits from high resolution data sets obtained during oil and gas exploration, including for example seismic data, and borehole logging data (both lithological and geophysical). The technique consists of interpreting scanline fracture data, and using these data to generate representative Discrete Fracture Network (DFN) models for each field set. The DFN models are then upscaled to provide an effective hydraulic conductivity tensor that represents the fractured rock matrix. For each field site, the upscaled hydraulic conductivities are compared with estimates derived from pumping tests to validate the model. A hydraulic conductivity field is generated for the study region that captures the spatial variability of fracture networks in pseudo-three dimensions from scanline data. Hydraulic conductivities estimated using this approach compare well with those estimated from pumping test data. The study results suggest that such an approach may be feasible for taking small scale fracture data and upscaling these to represent the aquifer matrix hydraulic properties needed for regional groundwater modeling. 相似文献
17.
Paul Duuring Stephen M. Rowins Bradley S. M. McKinley Jenni M. Dickinson Larry J. Diakow Young-Seog Kim Robert A. Creaser 《Mineralium Deposita》2009,44(4):435-462
Kemess South is the only Cu–Au–Mo mine in the Toodoggone district and a major Cu and Au producer in British Columbia. Porphyry-style
Cu–Au–Mo mineralization is mainly hosted by the tabular, SW-plunging, 199.6 ± 0.6-Ma Maple Leaf granodiorite, which intrudes
tightly folded, SW-dipping, Permian Asitka Group siltstone and limestone and homogeneous Triassic Takla Group basalt. Southwest-dipping
194.0 ± 0.4-Ma Toodoggone Formation conglomerate, volcaniclastic, and epiclastic rocks overlie the granodiorite and Asitka
Group rocks. Minor Cu–Au–Mo mineralization is hosted by the immediate Takla Group basalt country rock, whereas low-tonnage
high-grade Cu zones occur beneath a 30-m-thick leached capping in supergene-altered granodiorite and in exotic positions in
overlying Toodoggone Formation conglomerate. Granodiorite has an intrusive contact with mineralized and altered Takla Group
basalt but displays a sheared contact with unmineralized and less altered Asitka Group siltstone. The North Block fault is
a deposit-scale, E-striking, steeply S-dipping normal fault that juxtaposes the granodiorite/basalt ore body against unmineralized
Asitka Group rocks. Younger NW- and NE-striking normal–dextral faults cut all rock types, orebodies, and the North Block fault
with displacements of up to 100 m and result in the graben-and-horst-style block faulting of the stratigraphy and ore body.
Both basalt and granodiorite host comparable vein sequence and alteration histories, with minor variations in hydrothermal
mineral assemblages caused by differing protolith chemistry. Early potassic alteration (and associated early-stage Cu ± Au ± Mo
mineralization) is partly replaced by phyllic and intermediate argillic alteration associated with main-stage Cu–Au–Mo mineralization.
Two main-stage veins have Re–Os molybdenite ages of 201.3 ± 1.2 and 201.1 ± 1.2 Ma. These mineralization ages overlap the
199.6 ± 0.6-Ma U–Pb zircon crystallization age for the Maple Leaf granodiorite. Late-stage pyrite-rich stringer veins and
related phyllic alteration assemblages are cut by anhydrite-rich, carbonate-rich, and chlorite veins. Fluids and metals associated
with early-, main-, and late-stage veins were probably derived principally from the same deep magma chamber as the Maple Leaf
granodiorite. These magmatic-derived fluids interacted with Asitka and Takla Group country rocks and possibly with meteoric
and metamorphic fluids prior to mineralization. 相似文献
18.
A case study of airborne and satellite remote sensing of a spring bloom event in the Gulf of Finland
Sampsa Koponen Jenni Attila Jouni Pulliainen Kari Kallio Timo Pyhälahti Antti Lindfors Kai Rasmus Martti Hallikainen 《Continental Shelf Research》2007
The concentrations of chlorophyll-a (chl-a), total suspended solids (TSS) and the absorption coefficient of colored dissolved organic matter (aCDOM(400)) are estimated in Case II waters using medium resolution imaging spectrometer (MERIS) satellite (full resolution [FR] level 1b, 300 m resolution) and AISA airborne spectrometer data acquired during a spring bloom in the Gulf of Finland, Baltic Sea on April 27, 2004. The accuracy of the estimation is analyzed using empirical band-ratio algorithms together with in situ observations that include water samples analyzed in a laboratory (variation ranges: 22–130 μg/l, 2.9–20 mg/l, and 1.29–2.61 m−1 for chl-a, TSS and aCDOM(400), respectively). Additional in situ estimates (transects) on these characteristics are available through absorption and scattering coefficients measured with an ac-9 absorption and attenuation meter installed in a flow-through system. The retrieval accuracy (R2) of all three water quality characteristics with MERIS data is close to or above 0.9, while the RMSE is 7.8 μg/l (22%), 0.74 mg/l (16%) and 0.08 m−1 (5%), for chl-a, TSS and aCDOM(400), respectively. The validity of the chl-a algorithm is tested using nine additional data points. The BIAS-error for these points is 5.2 μg/l and the RMSE is 10.6 μg/l. The effects of changes in the atmospheric characteristics on band-ratio algorithms in cases where no concurrent in situ reference data are available are analyzed using the MODerate spectral resolution atmospheric TRANSmittance algorithm and computer model (MODTRAN). The additional error due to these changes is estimated to be below 20% for the applied ratio algorithms. The water quality data available in the level 2 MERIS-product distributed by the European Space Agency did not include valid results for the date investigated here. 相似文献
19.
James Rose Jenni Turner Elaine Turton James B. Riding Adrian Palmer John K. Wright Jonathan R. Lee Nicholas S. J. Q. Bullimore 《第四纪科学杂志》2021,36(4):547-569
This paper provides a record and analysis of a site in east-midland England, at which organic and soil material are found between two Middle Pleistocene tills. This is the first discovery of its kind in the area, and demonstrates unequivocally that the region was glaciated on two separate occasions, something that has long been inferred and articulated, but not actually demonstrated. The landforms, sediments and soils are studied with respect to their geomorphological, lithological, pedological, palaeobotanical and structural properties. The organic and soil material along with soil structures indicate, sequentially, a periglacial climate, a long period of warm temperate weathering and a cool temperate climate. Evaluation of this evidence in terms of existing published work identifies a number of problems with existing models and suggests that the most likely model for the glacial history of this part of midland England is an early Middle Pleistocene glaciation which is represented only by trace erratics, a Marine Isotope Stage (MIS) 12 age glaciation which moved across the area from the NW and deposited a chalk-free till, and an MIS 8 age glaciation that transported and deposited an upper chalky till from the NE. © 2021 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd. 相似文献
20.
This paper investigates trust in the scientists, government authorities and wider risk management team during the ongoing
volcanic crisis in Montserrat, WI. Identifying the most trusted communicator and how trust in information can be enhanced
are considered important for improving the efficacy of volcanic risk communication. Qualitative interviews, participant observations
and a quantitative survey were utilised to investigate the views and attitudes of the public, authorities and scientists.
Trust was found to be dynamic, influenced by political factors made more complex by the colonial nature of Montserrat’s governance
and the changing level of volcanic activity. The scientists were viewed by the authorities as a highly trusted expert source
of volcanic information. Mistrust among some of the local authorities towards the scientists and British Governor was founded
in the uncertainty of the volcanic situation and influenced by differences in levels of acceptable risk and suspicions about
integrity (e.g. as a consequence of employment by the British Government). The public viewed friends and relatives as the
most trusted source for volcanic information. High trust in this source allowed competing messages to reinforce beliefs of
lower risk than were officially being described. The scientists were the second most trusted group by the public and considered
significantly more competent, reliable, caring, fair and open than the authorities. The world press was the least trusted,
preceded closely by the British Governor’s Office and Montserratian Government officials. These results tally well with other
empirical findings suggesting that government ministers and departments are typically distrusted as sources of risk-related
information. These findings have implications for risk communication on Montserrat and other volcanic crises. The importance
and potential effectiveness of scientists as communicators, because of, and despite, the existence of political, cultural
and institutional barriers, is exemplified by this study.
相似文献
Katharine HaynesEmail: Email: |