Predicting ordinary kriging errors caused by surface roughness and dissectivity

The magnitude of kriging errors varies in accordance with the surface properties. The purpose of this paper is to determine the association of ordinary kriging (OK) estimated errors with the local variability of surface roughness, and to analyse the suitability of probabilistic models for predicting the magnitude of OK errors from surface parameters. This task includes determining the terrain parameters in order to explain the variation in the magnitude of OK errors. The results of this research indicate that the higher order regression models, with complex interaction terms, were able to explain 95 per cent of the variation in the OK error magnitude using the least number of predictors. In addition, the results underscore the importance of the role of the local diversity of relief properties in increasing or decreasing the magnitude of interpolation errors. The newly developed dissectivity parameters provide useful information for terrain analysis. Our study also provides constructive guides to understanding the local variation of interpolation errors and their dependence on surface dissectivity. Copyright © 2005 John Wiley & Sons, Ltd.     

Bayesian and multivariate methods applied to favorability quantification in Recôncavo Basin and Ribeira Belt, Brazil

A methology to define favorable areas in petroleum and mineral exploration is applied, which consists in weighting the exploratory variables, in order to characterize their importance as exploration guides. The exploration data are spatially integrated in the selected area to establish the association between variables and deposits, and the relationships among distribution, topology, and indicator pattern of all variables. Two methods of statistical analysis were compared. The first one is the Weights of Evidence Modeling, a conditional probability approach (Agterberg, 1989a), and the second one is the Principal Components Analysis (Pan, 1993). In the conditional method, the favorability estimation is based on the probability of deposit and variable joint occurrence, with the weights being defined as natural logarithms of likelihood ratios. In the multivariate analysis, the cells which contain deposits are selected as control cells and the weights are determined by eigendecomposition, being represented by the coefficients of the eigenvector related to the system’s largest eigenvalue. The two techniques of weighting and complementary procedures were tested on two case studies: 1. Recôncavo Basin, Northeast Brazil (for Petroleum) and 2. Itaiacoca Formation of Ribeira Belt, Southeast Brazil (for Pb-Zn Mississippi Valley Type deposits). The applied methdology proved to be easy to use and of great assistance to predict the favorability in large areas, particularly in the initial phase of exploration programs.     

Waterfall notch-filtering for restoration of acoustic backscatter records from Admiralty Bay,Antarctica

A series of multibeam sonar surveys were conducted from 2009 to 2013 around Admiralty Bay, Shetland Islands, Antarctica. These surveys provided a detailed bathymetric model that helped understand and characterize the bottom geology of this remote area. Unfortunately, the acoustic backscatter records registered during these bathymetric surveys were heavily contaminated with noise and motion artifacts. These artifacts persisted in the backscatter records despite the fact that the proper acquisition geometry and the necessary offsets and delays were applied during the survey and in post-processing. These noisy backscatter records were very difficult to interpret and to correlate with gravity-core samples acquired in the same area. In order to address this issue, a directional notch-filter was applied to the backscatter waterfall in the along-track direction. The proposed filter provided better estimates for the backscatter strength of each sample by considerably reducing residual motion artifacts. The restoration of individual samples was possible since the waterfall frame of reference preserves the acquisition geometry. Then, a remote seafloor characterization procedure based on an acoustic model inversion was applied to the restored backscatter samples, generating remote estimates of acoustic impedance. These remote estimates were compared to Multi Sensor Core Logger measurements of acoustic impedance obtained from gravity core samples. The remote estimates and the Core Logger measurements of acoustic impedance were comparable when the shallow seafloor was homogeneous. The proposed waterfall notch-filtering approach can be applied to any sonar record, provided that we know the system ping-rate and sampling frequency.     

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近30 年渤海水文和气象状况的长期变化及其相互关系

利用线性回归方法对渤海和北黄海西部沿岸 7个海洋站 1 965— 1 997年实测海洋表层水温和盐度及地面气温和降水等 4个水文气象要素的长期变化趋势作了分析 ,得出渤海在这 32年期间海表温度年变率为 0 .0 1 5℃ /a ,由此推算得出 32年升高 0 .48℃ ;海表盐度年变率为 0 .0 4 2 /a ,32年升高 1 .34;气温年变率为 0 .0 34℃ /a ,32年升高 1 .0 9℃ ;降水年变率为- 2 .73mm/a,32年减少 87mm。这 4个要素之间及其与厄尔尼诺指数之间的超前 /滞后线性回归分析表明 ,海温与气温的年际变化相关关系最密切 ,相关系数达到 76.5 % ,置信度高于0 .99。其次是盐度与降水 ,它们之间亦有良好关系。同年盐度和降水之间的相关系数为- 43.6% ,盐度落后降水一年时相关系数为 - 39.2 % ,置信度均高于 0 .95。由此可推知 ,盐度变化平均落后降水约半年。渤海水文气象状况变化与厄尔尼诺有一定关系 ,其中以降水与厄尔尼诺关系最密切 ,1 982— 1 983年厄尔尼诺期间渤海气温和水温较高 ,降水显著偏少且海水盐度显著偏高。     

Trophic structure and functioning in a eutrophic and poorly flushed lagoon in southwestern Taiwan

Tapong Bay, a eutrophic and poorly flushed tropical lagoon, supports intensive oyster culture. Using the Ecopath approach and network analysis, a mass-balanced trophic model was constructed to analyze the structure and matter flows within the food web. The lagoon model is comprised of 18 compartments with the highest trophic level of 3.2 for piscivorous fish. The high pedigree index (0.82) reveals the model to be of high quality. The most-prominent living compartment in terms of matter flow and biomass in the lagoon is cultured oysters and bivalves, respectively. The mixed trophic impacts indicate that phytoplankton and periphyton are the most-influential living compartments in the lagoon. Comparative analyses with the eutrophic and well-flushed Chiku Lagoon and non-eutrophic tropical lagoons show that high nutrient loadings might stimulate the growth and accumulation of phytoplankton and periphyton and therefore support high fishery yields. However, net primary production, total biomass, fishery yields per unit area, and mean transfer efficiency of Tapong Bay were remarkably lower than those of Chiku Lagoon. The lower transfer efficiency likely results from the low mortality of cultured oysters and invasive bivalves from predation or the lower density of benthic feeders constrained by the hypoxic bottom water as a result of poor flushing. This might therefore result in a great proportion of flows to detritus. However, the hypoxic bottom water might further reduce the recycling of the entering detritus back into the food web. In contrast to many estuaries and tropical lagoons, poor flushing of this eutrophic tropical lagoon might induce a shift from detritivory to herbivory in the food web.     

Study of cavernous underground conduits in Nam La (Northwest Vietnam) by an integrative approach

This paper presents the result of an investigation of underground conduits, which connect the swallow holes and the resurgence of a blind river in the tropical, highly karstified limestone Nam La catchment in the NW of Vietnam. The Nam La River disappears underground in several swallow holes near the outlet of the catchment. In the rainy season this results in flooding upstream of the sinkholes. A hypothesis is that the Nam La River resurges at a large cavern spring 4.5 km east of the catchment outlet. A multi-thematic study of the possible connections between the swallow holes and the resurgence was carried out to investigate the geological structure, tectonics, cave structure analysis and discharge time series. The existence of the underground conduits was also tested and proven by tracer experiments. On the basis of a lineament analysis the location of the underground conduits were predicted. A remote sensing derived lineament-length density map was used to track routes from the swallow holes to the resurgence, having the shortest length but highest lineament density. This resulted in a plan-view prediction of underground conduits that matches with the cave and fault development. The functioning of the conduits was further explained by analysing flooding records of a nearby doline, which turns out to act as a temporary storage reservoir mitigating flooding of the catchment outlet area.

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Resumen Este artículo presenta el resultado de una investigación de conductos subterráneos, los cuales conectan dolinas y la resurgencia de un río ciego en la cuenca tropical Nam La, compuesta por calizas altamente karstificadas, en el noroeste de Vietnam. El Río Nam La desaparece en el subsuelo por medio de varias dolinas cerca de la salida de la cuenca. Durante la estación lluviosa esto resulta en inundaciones aguas arriba de las dolinas. Una hipótesis es que el Río Nam La resurge en un manantial de caverna grande a 4.5 km al oriente de la salida de la cuenca. Se llevó a cabo un estudio multi-temático de las conexiones posibles entre las dolinas y la resurgencia para investigar la estructura geológica, tectónica, análisis estructural de cavernas, y series de tiempo de descarga. Se evalúa y se demuestra también la existencia de conductos subterráneos por medio de experimentos con trazadores. En base a análisis de lineamientos se predice la localización de los conductos subterráneos. Se utiliza un mapa de densidad de longitudes de lineamientos construido a partir de sensores remotos para seguir las rutas de las dolinas a la resurgencia, teniendo longitudes más cortas pero densidad de lineamientos más altas. Esto da por resultado una predicción en vista de planta de conductos subterráneos que se ajustan con el desarrollo de cavernas y fallas. El funcionamiento de los conductos se explica posteriormente mediante el análisis de registro de inundaciones de una dolina cercana la cual actúa como un reservorio de almacenamiento temporal que mitiga inundaciones en el área de salida de la cuenca.

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Résumé Cet article présente les résultats de linvestigation de conduits souterrains, qui mettent en connexion les pertes et les résurgences dune rivière souterraine dans le bassin versant de Nam La, dans une région tropicale fortement karstique du NW du Vietnam. La rivière Nam La disparaît dans le sous-sol via plusieurs pertes à proximité de lexutoire du bassin. Durant la saison des pluies, les pertes se mettent en charge et des inondations apparaissent. Une hypothèse serait que la rivière ressort 4.5 km à lEst de lexutoire du bassin, dans une grande caverne. Une étude multi-thématique visant les connexions possibles entre les pertes et les résurgences a été réalisée. Elle comprend létude de la structure géologique, la tectonique, lanalyse de la structure karstique et des chroniques de débits. Lexistence des conduits souterrains est également testée et prouvée par des essais de traçages. Sur base de lanalyse des linéaments, la localisation des conduits souterrains est prédite. Grâce à la télédétection et une cartographie de la densité et de la longueur des linéaments, on peut deviner le cheminement de leau entre les pertes et la résurgence (via le chemin le plus court et la densité de fracturation la plus importante). Il en résulte une vue en plan prédisant la localisation des conduits, qui correspond par ailleurs avec le développement des cavités et des failles. Le fonctionnement des conduits est ensuite expliqué sur base de lanalyse des chroniques de débits enregistrés à proximité dune doline, qui joue le rôle dun réservoir temporaire, mitigeant les inondations à la zone de lexutoire du bassin-versant.

     

The carbonate system in the East China Sea in winter

Measurements of dissolved inorganic carbon (DIC), pH, total alkalinity (TA), and partial pressure of CO₂ (pCO₂) were conducted at a total of 25 stations along four cross shelf transects in the East China Sea (ECS) in January 2008. Results showed that their distributions in the surface water corresponded well to the general circulation pattern in the ECS. Low DIC and pCO₂ and high pH were found in the warm and saline Kuroshio Current water flowing northeastward along the shelf break, whereas high DIC and pCO₂ and low pH were mainly observed in the cold and less saline China Coastal Current water flowing southward along the coast of Mainland China. Difference between surface water and atmospheric pCO₂ (ΔpCO₂), ranging from ~ 0 to ? 111 μatm, indicated that the entire ECS shelf acted as a CO₂ sink during winter with an average flux of CO₂ of ?13.7 ± 5.7 (mmol C m^? 2 day^? 1), and is consistent with previous studies. However, pCO₂ was negatively correlated with temperature for surface waters lower than 20 °C, in contrast to the positive correlation found in the 1990s. Moreover, the wintertime ΔpCO₂ in the inner shelf near the Changjiang River estuary has appreciably decreased since the early 1990s, suggesting a decline of CO₂ sequestration capacity in this region. However, the actual causes for the observed relationship between these decadal changes and the increased eutrophication over recent decades are worth further study.     

Climate extremes in the United States: recent research by physical geographers

This paper reports our review of research on domestic climate extremes conducted by US physical geographers over the past 15?years. Sections cover extremes in wind, precipitation, lightning, and temperature, as well as derivative climate extremes (droughts, floods, and storm surges). Themes considered include: the spatial and temporal distribution of the climate extreme; its implications for our understanding of the physical processes that produce it; the spatial and temporal distributions of the extreme’s economic and human costs; lessons for assessment, policy, and management; and scale. We conclude that most of the works reviewed inadequately address the human basis of vulnerability to climate extremes, and encourage physical geographers to work with colleagues from the other subfields of geography and the social sciences to develop the holistic understanding of vulnerability needed to effectively adapt to the more extreme climate projected under climate change.