Fast algorithms for automatic mapping with space-limited covariance functions     

Ben Ingram  Dan Cornford  David Evans 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(5):661-670

In this paper we discuss a fast Bayesian extension to kriging algorithms which has been used successfully for fast, automatic mapping in emergency conditions in the Spatial Interpolation Comparison 2004 (SIC2004) exercise. The application of kriging to automatic mapping raises several issues such as robustness, scalability, speed and parameter estimation. Various ad-hoc solutions have been proposed and used extensively but they lack a sound theoretical basis. In this paper we show how observations can be projected onto a representative subset of the data, without losing significant information. This allows the complexity of the algorithm to grow as O(n m ²), where n is the total number of observations and m is the size of the subset of the observations retained for prediction. The main contribution of this paper is to further extend this projective method through the application of space-limited covariance functions, which can be used as an alternative to the commonly used covariance models. In many real world applications the correlation between observations essentially vanishes beyond a certain separation distance. Thus it makes sense to use a covariance model that encompasses this belief since this leads to sparse covariance matrices for which optimised sparse matrix techniques can be used. In the presence of extreme values we show that space-limited covariance functions offer an additional benefit, they maintain the smoothness locally but at the same time lead to a more robust, and compact, global model. We show the performance of this technique coupled with the sparse extension to the kriging algorithm on synthetic data and outline a number of computational benefits such an approach brings. To test the relevance to automatic mapping we apply the method to the data used in a recent comparison of interpolation techniques (SIC2004) to map the levels of background ambient gamma radiation.

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Ben IngramEmail:

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The use of large bottomless lysimeters in the determination of water balances for a raised mire     

Julia C. Kelemen  Hugh A. P. Ingram 《水文研究》1999,13(1):101-111

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Climate warming alters thermal stability but not stratification phenology in a small north‐temperate lake          下载免费PDF全文

A. M. Paterson  E. A. Stainsby  N. Michelutti  H. Yao  J. A. Rusak  R. Ingram  C. McConnell  J. P. Smol 《水文研究》2014,28(26):6309-6319

Recent climate change represents one of the most serious anthropogenic threats to lake ecosystems in Canada. As meteorological and hydrological conditions are altered by climate change, so too are physical, chemical and biological properties of lakes. The ability to quantify the impact of climate change on the physical properties of lakes represents an integral step in estimating future chemical and biological change. To that end, we have used the dynamic reservoir simulation model, a one‐dimensional vertical heat transfer and mixing model, to hindcast and compare lake temperature‐depth profiles against 30 years of long‐term monitoring data in Harp Lake, Ontario. These temperature profiles were used to calculate annual (June–September) thermal stability values from 1979 to 2009. Comparisons between measured and modelled lake water temperature and thermal stability over three decades showed strong correlation (r² > 0.9). However, despite significant increases in modelled thermal stability over the 30 year record, we found no significant change in the timing of the onset, breakdown or the duration of thermal stratification. Our data suggest that increased air temperature and decreased wind are the primary drivers of enhanced stability in Harp Lake since 1979. The high‐predictive ability of the Harp Lake dynamic reservoir simulation model suggests that its use as a tool in future lake management projects is appropriate. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Scarifying and fingering surfaces of plunging jets     

Ayumi Saruwatari  Yasunori Watanabe  David M. Ingram 《Coastal Engineering》2009,56(11-12):1109-1122

The local surface deformation resulting from the oblique impact of a columnar water jet has been computed, using a three-dimensional large eddy simulation, as a model of the overturning jet of a breaking wave. The emergence of the secondary jet from the front face of the initial jet has been examined and the organisation of the vortices within the jet characterised. As the secondary jet emerges, the vorticity field becomes unstable under the action of the strong shear beneath the jet surface and pairs of longitudinal counter-rotating vortices stretched along the direction of the jet projection are formed. The presence of these longitudinal vortex pairs creates convergent surface flows, resulting in the formation of longitudinal scars on the rear face of the projecting jet. Following significant growth of the scars on both its upper and lower surfaces, the jet decouples into fingers. The lateral widths of the longitudinal vortices provide a minimum measure of the finger size. A horizontal Froude number Fr_h, representing a measure of strength of horizontal shear in a gravity-dominated impacting flow is defined, which characterises the organisation of the longitudinal vortices occurring in the shear flow, and the resultant formation of scars and fingers. For higher Fr_h, stronger longitudinal vortices and deeper scars are formed at longer lateral intervals, enhancing the fingering process during the splashing event. Fundamental features of material transport in the vicinity of the surface of jets (e.g. gas transfer across a sea surface) are related to the entrainment of surface fluid by the longitudinal vortices, and is thus also characterised by Fr_h.  相似文献   

Physical processes within the North Water (NOW) polynya     

D. Barber  R. Marsden  P. Minnett  G. Ingram  L. Fortier 《大气与海洋》2013,51(3):163-166

Abstract

Two‐state, first‐order, single‐site Markov models for daily precipitation occurrence were developed for each winter rainy season over the historical period of record at five long‐term meteorological stations in the lower Fraser Valley of British Columbia, Canada. Monotonic temporal trends in the independent elements of the transition matrices were then assessed. Although the results remain tentative, there is some evidence for a regionally coherent long‐term negative trend in the probability of wet‐to‐dry state transitions, P10 (or a positive trend in the probability of a wet day being followed by another wet day, P11). In contrast, there is no evidence for a regionally coordinated and consistent trend in the probability of dry‐to‐wet state transitions, P01 (or, therefore, in the probability of a dry day being followed by another dry day, P00). These results appear loosely consistent with previous statistical climate change impact studies in the region, and might be physically interpreted as suggesting a gradual increase in the local typical duration of a Pacific frontal storm during hydrologic winter, with no systematic trend in the average duration of a dry‐day interlude. Additionally, the probability of any day‐to‐day precipitation state transition (from wet to dry, or from dry to wet), PST, has been tentatively interpreted to exhibit an area‐wide negative long‐term trend, suggesting an overall increase in precipitation memory. The findings provide some additional regional context for several issues in hydrometeorological modelling, climatology, and environmental impact assessment.  相似文献   

Some implications of a new approach to the water vapour feedback     

William Ingram 《Climate Dynamics》2013,40(3-4):925-933

The water vapour feedback is the largest physical climate feedback. It also gives the second-largest contribution to the range of uncertainty in climate sensitivity in General Circulation Models (GCMs). Tracing these differences back to their physical causes in the hope of constraining climate sensitivity requires an appropriate quantification. Yet the Intergovernmental Panel on Climate Change judge that the conventional diagnosis of a “water vapour feedback” and a “lapse rate feedback” provides little insight into differences between GCMs’ climate sensitivities. We show that the conventionally diagnosed water vapour feedback is in fact formally useless for investigating differences between GCMs’ climate sensitivities—the anticorrelation between conventional “water vapour feedback” and “lapse rate feedback” makes the correlation between the “water vapour feedback” and their sum insignificant: i.e. statistically, knowing this “feedback” allows one to conclude nothing about the sum and thence about climate sensitivity. This follows primarily from how little relative humidity (RH) changes with climate change in GCMs. A more detailed physical analysis concludes that the overall mean decrease of RH on warming seen in GCMs is robustly physically based. This and other physical arguments then suggest that the stronger the positive “water vapour feedback”, the less sensitive climate can be expected to be. A diagnosis based on the “partly-Simpsonian” model of water vapour feedback avoids these problems. On the conventional view of the water vapour feedback, naive extrapolation of variations within present-day climate suggests that parts of our planet are close to locally reaching conditions that would allow a run-away water vapour greenhouse effect once they were extensive enough. Of course this has never occurred in geological history, and is not seen in Earth-like GCMs. Again, the “partly-Simpsonian” approach provides a simple qualitative explanation, by showing that the water vapour feedback can only cancel part of the basic Planck’s Law negative feedback.  相似文献   

From accessing to assessing forecasts: an end-to-end study of participatory climate forecast dissemination in Burkina Faso (West Africa)   总被引：1，自引：0，他引：1  

Carla Roncoli  Christine Jost  Paul Kirshen  Moussa Sanon  Keith T. Ingram  Mark Woodin  Léopold Somé  Frédéric Ouattara  Bienvenue J. Sanfo  Ciriaque Sia  Pascal Yaka  Gerrit Hoogenboom 《Climatic change》2009,92(3-4):433-460

This study compares responses to seasonal climate forecasts conducted by farmers of three agro-ecological zones of Burkina Faso, including some who had attended local level workshops and others who had not attended the workshops. While local inequalities and social tensions contributed to excluding some groups, about two-thirds of non-participants interviewed received the forecast from the participants or through various means deployed by the project. Interviews revealed that almost all those who received the forecasts by some mechanism (workshop or other) shared them with others. The data show that participants were more likely to understand the probabilistic aspect of the forecasts and their limitations, to use the information in making management decisions and by a wider range of responses. These differences are shown to be statistically significant. Farmers evaluated the forecasts as accurate and useful in terms of both material and non-material considerations. These findings support the hypothesis that participatory workshops can play a positive role in the provision of effective climate services to African rural producers. However, this role must be assessed in the context of local dynamics of power, which shape information flows and response options. Participation must also be understood beyond single events (such as workshops) and be grounded in sustained interaction and commitments among stakeholders. The conclusion of this study point to lessons learned and critical insights on the role of participation in climate-based decision support systems for rural African communities.  相似文献   

Anthropogenic climate change for 1860 to 2100 simulated with the HadCM3 model under updated emissions scenarios   总被引：3，自引：8，他引：3  

T. C. Johns  J. M. Gregory  W. J. Ingram  C. E. Johnson  A. Jones  J. A. Lowe  J. F. B. Mitchell  D. L. Roberts  D. M. H. Sexton  D. S. Stevenson  S. F. B. Tett  M. J. Woodage 《Climate Dynamics》2003,20(6):583-612

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Spatial and temporal variability in the stable isotope systematics of modern precipitation in China: implications for paleoclimate reconstructions   总被引：19，自引：0，他引：19  

Kathleen R. Johnson  B.Lynn Ingram 《Earth and Planetary Science Letters》2004,220(3-4):365-377

The stable isotopic composition of materials such as glacial ice, tree rings, lake sediments, and speleothems from low-to-mid latitudes contains information about past changes in temperature (T) and precipitation amount (P). However, the transfer functions which link δ¹⁸O_p to changes in T or P, dδ¹⁸O_p/dT and dδ¹⁸O_p/dP, can exhibit significant temporal and spatial variability in these regions. In areas affected by the Southeast Asian monsoon, past variations in δ¹⁸O and δD of precipitation have been attributed to variations in monsoon intensity, storm tracks, and/or variations in temperature. Proper interpretation of past δ¹⁸O_p variations here requires an understanding of these complicated stable isotope systematics. Since temperature and precipitation are positively correlated in China and have opposite effects on δ¹⁸O_p, it is necessary to determine which of these effects is dominant for a specific region in order to perform even qualitative paleoclimate reconstructions. Here, we evaluate the value of the transfer functions in modern precipitation to more accurately interpret the paleorecord. The strength of these transfer functions in China is investigated using multiple regression analysis of data from 10 sites within the Global Network for Isotopes in Precipitation (GNIP). δ¹⁸O_p is modeled as a function of both temperature and precipitation. The magnitude and signs of the transfer functions at any given site are closely related to the degree of summer monsoon influence. δ¹⁸O_p values at sites with intense summer monsoon precipitation are more dependent on the amount of precipitation than on temperature, and therefore exhibit more negative values in the summer. In contrast, δ¹⁸O_p values at sites that are unaffected by summer monsoon precipitation exhibit strong relationships between δ¹⁸O_p and temperature. The sites that are near the northern limit of the summer monsoon exhibit dependence on both temperature and amount of precipitation. Comparison with simple linear models (δ¹⁸O_p as a function of T or P) and a geographic model (δ¹⁸O_p as a function of latitude and altitude) shows that the multiple regression model is more successful at reproducing δ¹⁸O_p values at sites that are strongly influenced by the summer monsoon. The fact that the transfer function values are highly spatially variable and closely related to the degree of summer monsoon influence suggests that these values may also vary temporally. Since the Southeast Asian monsoon intensity is known to exhibit large variations on a number of timescales (annual to glacial–interglacial), and the magnitude and sign of the transfer functions is related to monsoon intensity, we suggest that as monsoon intensity changes, the magnitude and possibly even the sign of the transfer functions may vary. Therefore, quantitative paleoclimate reconstructions based on δ¹⁸O_p variations may not be valid.  相似文献   

Effects of structural faults on ground control in selected coal mines in southwest Virginia     

M. Molinda  D. K. Ingram 《Geotechnical and Geological Engineering》1990,8(4):332-347

Summary Two faults related to the Pine Mountain overthrust sheet near Buchanan County, Virginia, were investigated to determine their effect on ground control and to develop recognition criteria for prediction. Both faults are right lateral, strike-slip faults overprinted simultaneously with thrust faulting. Offsets of the coal seam due to thrust faulting average 6 ft with severe roof conditions (20 ft high roof falls) occurring through an average 30 ft wide zone of disturbance. Recognition criteria include characteristic overthrusting, coalbed swag, bedding plane slippage, and fault gouge. Ground control strategies include mine designs that minimize fault exposure.  相似文献