Modeling position error probability density functions for statistical inversions using a Goff–Jordan rough surface model     

Stacy L. Tantum  Quan Zhu  Peter A. Torrione  Leslie M. Collins 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(2):155-167

Buried unexploded ordnance (UXO) continues to be a difficult remediation problem from both a sensing and a discrimination point of view. Modern approaches to both the sensing and discrimination problems utilize high bandwidth electromagnetic induction (EMI) sensors to collect geo-referenced data which is then inverted, or fit, using a forward model in order to obtain features that can be directly interpreted using the physics associated with electromagnetic induction-based sensing. These features are then used in a variety of classification architectures. One aspect of this process that has captured recent interest is that uncertainty in the positions at which data was collected can degrade the inversion performance and thus the subsequent classification. Several mechanisms to address this issue have been explored that range from filtering and prediction of actual positions to exploiting Bayesian approaches for uncertainty mitigation. In the Bayesian approach, a statistical model of the position errors is used as a prior for integrating over the uncertainty in the inversion process. In this study, we demonstrate that errors in the statistical priors used in this process can negatively impact subsequent classification performance, thus highlighting the need for an accurate statistical model for the position errors. Next, we propose a mechanism by which to obtain such models. Specifically, we utilize a Goff–Jordan rough surface model and simulate the sensor data collection system motion over the simulated ground or ocean surfaces to calculate errors and generate statistical models. Our results suggest that this approach can be used to develop the statistical models necessary for mitigating uncertain position information.  相似文献   

Hurricane predictability: are there simple linear invariants within these complex nonlinear dynamical systems?     

L. M. Leslie  R. F. Abbey Jr. 《Meteorology and Atmospheric Physics》2000,74(1-4):57-62

Summary Forecasting the tracks of hurricanes is a problem of immense importance. It is a major scientific exercise in solving the complicated set of mathematical equations that govern the behavior of atmospheric flow in general and hurricanes in particular. Moreover, hurricanes rank as the most devastating of all natural phenomena, in terms of loss of life and destruction of property. Hitherto, unlike many other atmospheric and oceanic systems, hurricanes have defied rapid advances in prediction of their motion, and progress has been of the order of a mere one percent or so reduction per annum in mean 48 hour forecast position errors over the past two decades. A research program aimed at estimating inherent and actual mean absolute forecast position errors, has produced an apparent paradox. Despite the fact that the equations governing hurricane motion are a complex, coupled, nonlinear set of dynamical equations, there is very strong evidence for the existence of an underlying simple, linear, invariant behavior. The original aim of the research program was to determine the lower limits of mean hurricane forecast position errors and to quantify them out to 72 hour leadtime. The appearance of the paradox meant that the focus shifted first to examining and explaining the paradox. Attention then turns to showing that the mean forecasts errors are still a very large 40 to 50 percent lower than the mean position errors currently being achieved in practice by state-of-the-art models numerical weather prediction (NWP) models. Revised December 14, 1999  相似文献   

The role of endolithic cyanobacteria in the formation of lithified laminae in Bahamian stromatolites   总被引：5，自引：0，他引：5  

Ian G. Macintyre  Leslie Prufert-Bebout  & R. Pamela Reid 《Sedimentology》2000,47(5):915-921

The microboring activity of endolithic cyanobacteria plays a major role in the formation of the dominant lithified laminae in modern marine stromatolites in the Exuma Cays, Bahamas. These stromatolites are composed primarily of fine-grained carbonate sand that is trapped and bound by the filamentous cyanobacteria Schizothrix sp.. Periodic introduction of coccoid endolithic cyanobacteria Solentia sp. during hiatuses in stromatolite growth associated with very low rates of sedimentation results in the formation of lithified horizons, 200–1000 μm thick. These layers consist of micritized grains that are welded together at point contacts. The micritization is caused by extensive microboring and carbonate precipitation within boreholes concurrent with endolithic activity. Grain welding occurs when boreholes cross from one grain to another at point contacts. Thus, microboring destroys original grain textures but, at the same time, plays a constructional role in stromatolite growth by forming lithified layers of welded grains. These lateral bands of fused carbonate grains help to stabilize and preserve the stromatolite deposits.  相似文献   

The influence of low-density granite bodies on extensional basins     

Louis Howell  Stuart Egan  Graham Leslie  Stuart Clarke  Andrew Mitten  Jamie Pringle 《Geology Today》2020,36(1):22-26

The Carboniferous northern Pennine Basin remains the type locality for the ‘block and basin’ tectonic framework model. It has been widely believed that during periods of tectonic extension, large low-density bodies within the basement permit buoyant blocks to resist isostatic subsidence. However, lithosphere-scale structural and geodynamic modelling experiments dispute this; suggesting instead that the formation of intra-basinal highs occurs prior to lithospheric extension. In northern UK, this tectonic framework is controlled by a combination of tectonic stress, isostasy and the buoyancy forces of low-density granite, lithospheric flexure and, importantly, the inherited structural framework. It is hoped that further study can lead to a greater appreciation of the interplay of structural and geodynamic process that control the ‘block and basin’ framework.  相似文献   

The Monitor project: rotation periods of low-mass stars in M50     

Jonathan Irwin  Suzanne Aigrain  Jerome Bouvier  Leslie Hebb  Simon Hodgkin  Mike Irwin  Estelle Moraux 《Monthly notices of the Royal Astronomical Society》2009,392(4):1456-1466

We report on the results of a time-series photometric survey of M50 (NGC 2323), a  ∼130 Myr  open cluster, carried out using the Cerro Tololo Inter-American Observatory (CTIO) 4-m Blanco telescope and Mosaic-II detector as part of the Monitor project. Rotation periods were derived for 812 candidate cluster members over the mass range  0.2 ≲ M /M_⊙≲ 1.1  . The rotation period distributions show a clear mass-dependent morphology, statistically indistinguishable from those in NGC 2516 and M35 taken from the literature. Due to the availability of data from three observing runs separated by ∼10 and 1 month time-scales, we are able to demonstrate clear evidence for evolution of the photometric amplitudes, and hence spot patterns, over the 10 month gap. We are not able to constrain the time-scales for these effects in detail due to limitations imposed by the large gaps in our sampling, which also prevent the use of the phase information.  相似文献   

Verification of model simulated mass balance, flow fields and tabular calving events of the Antarctic ice sheet against remotely sensed observations     

Diandong Ren  Lance M. Leslie  Mervyn J. Lynch 《Climate Dynamics》2013,40(11-12):2617-2636

The Antarctic ice sheet (AIS) has the greatest potential for global sea level rise. This study simulates AIS ice creeping, sliding, tabular calving, and estimates the total mass balances, using a recently developed, advanced ice dynamics model, known as SEGMENT-Ice. SEGMENT-Ice is written in a spherical Earth coordinate system. Because the AIS contains the South Pole, a projection transfer is performed to displace the pole outside of the simulation domain. The AIS also has complex ice-water-granular material-bedrock configurations, requiring sophisticated lateral and basal boundary conditions. Because of the prevalence of ice shelves, a ‘girder yield’ type calving scheme is activated. The simulations of present surface ice flow velocities compare favorably with InSAR measurements, for various ice-water-bedrock configurations. The estimated ice mass loss rate during 2003–2009 agrees with GRACE measurements and provides more spatial details not represented by the latter. The model estimated calving frequencies of the peripheral ice shelves from 1996 (roughly when the 5-km digital elevation and thickness data for the shelves were collected) to 2009 compare well with archived scatterometer images. SEGMENT-Ice’s unique, non-local systematic calving scheme is found to be relevant for tabular calving. However, the exact timing of calving and of iceberg sizes cannot be simulated accurately at present. A projection of the future mass change of the AIS is made, with SEGMENT-Ice forced by atmospheric conditions from three different coupled general circulation models. The entire AIS is estimated to be losing mass steadily at a rate of ~120 km³/a at present and this rate possibly may double by year 2100.  相似文献   

Improved Bell's method for the stability analysis of slopes     

Hong Zheng  Leslie George Tham 《国际地质力学数值与分析法杂志》2009,33(14):1673-1689

A new procedure based on the approximation to the total normal pressure along the slip surface is developed to compute the factor of safety of slopes for slip surfaces of all shapes. By taking the whole sliding body, instead of an individual slice, as the loaded object, all the equilibrium equations are formulated according to the three‐moment equilibrium conditions rather than the two force equilibrium conditions and one‐moment equilibrium condition. The system of nonlinear equations deduced in this way is well‐scaled and enjoys excellent numerical properties such as the existence of solution with a positive factor of safety, a nearly unlimited scope of convergence and a rapid convergence rate associated with the Newton method. In the case of ?_u =0—the situation where no drainage and no consolidation are involved, furthermore, the system has a unique solution and the factor of safety has an explicit expression. Some typical examples are analyzed to demonstrate the numerical properties of the proposed procedure. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Tree-ring record of hillslope erosion and valley floor dynamics: Landscape responses to climate variation during the last 400 yr in the Colorado Plateau, northeastern Arizona   总被引：2，自引：0，他引：2  

Joseph R. McAuliffe  Louis A. Scuderi  Leslie D. McFadden   《Global and Planetary Change》2006,50(3-4):184-201

Dendrogeomorphologic approaches were used to study hillslope erosion and valley floor dynamics in a small drainage basin in the Colorado Plateau of northeastern Arizona, U.S.A. Root exposure in pinyon pines indicated hillslope erosion averaged 1.9 mm/yr over the last 400 yr, but erosion has been highly episodic. Negative increment growth anomalies in hillslope trees are interpreted as the consequence of rapid aerial exposure of roots by erosion. During the last 300 yr, two of three major episodes of these growth anomalies occurred after abrupt transitions from prolonged, multi-year droughts to sustained, lengthy periods of above-average precipitation. The most recent episode of these growth anomalies began within a few years after 1905 and was associated with the largest precipitation shift (drought to wet interval) in the last 400 yr. In contrast to trees on eroding hillslopes, increment growth of trees in more geomorphically stable landscape positions closely tracked the regional precipitation signal. Two major alluvial fills on the adjacent valley floor are also linked to the abrupt changes in precipitation regimes and the associated increases in delivery of runoff and sediments from slopes. The clay-cemented sandstones weather rapidly; rapid weathering and sediment production make slopes highly responsive to decadal precipitation changes. Significant vegetation declines on slopes during extreme drought make hillslope soils more prone to erosion if heavy precipitation follows soon thereafter.  相似文献   

The utility and risk of local ecological knowledge in developing stakeholder driven fisheries management: The Foveaux Strait dredge oyster fishery,New Zealand     

Nicholas A.O. Hill  Keith P. Michael  Allen Frazer  Stefan Leslie 《Ocean & Coastal Management》2010,53(11):659-668

Local ecological knowledge (LEK) has been recognised as an important source of information for resource management in data-poor fisheries. Our case study of the Foveaux Strait dredge oyster fishery in New Zealand shows LEK can also make a significant contribution to the management of data-rich fisheries, but highlights the importance of appropriate data collection design and interpretation and presentation of LEK. We formalise a structure for interpreting LEK, illustrate the importance of design by comparing two LEK studies, and discuss how the inclusion of LEK into the fisheries plan process has provided unexpected benefits for better management of the fishery.  相似文献   

A Postcolonial Approach to Urban Studies: Interviews,Mental Maps,and Photo Voices on the Urban Farms of Dar es Salaam,Tanzania     

Leslie McLees 《The Professional geographer》2013,65(2):283-295

To examine a postcolonial approach to urban experience is to inquire about how cities and people operate beyond the structures and analytical frameworks that have emerged from Western urban theory. Much of the emerging research in the field is looking for ways to valorize the myriad efforts that residents put forth to live and thrive in the city. Many methodological approaches, however, are still directed by the researcher, who determines the data-collection activities and the guidelines by which they are carried out. Using a case study of urban farmers in Dar es Salaam, Tanzania, this article is an effort to articulate a postcolonial methodology where the research and data collection methods were designed to give voice to the people marginalized by narrow definitions of the city, who are often seen as victims rather than as active agents constructing their own lives. This approach reveals the very real and tangible experiences and relationships that constitute daily life for the urban farmers of Dar es Salaam. Key Words: mental mapping, photo voice, postcolonial methods, Tanzania, urban farming.  相似文献