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1.
《African Journal of Marine Science》2013,35(2):509-512
Predation by Cape fur seals Arctocephalus pusillus pusillus on seabirds has previously been attributed to a few individuals, mainly males. Scat samples were collected at three mainland breeding colonies of seals in Namibia to determine the extent of seabird predation. Mainly females were sampled. No scats from the van Reenen Bay and Atlas-Wolf Bay colonies, and only two from Cape Cross, contained feather remains, giving an overall frequency of occurrence of feathers in scats of 0.1%. The feathers found were of African penguin Spheniscus demersus and a species of cormorant (Phalacrocorax sp.). 相似文献
2.
《African Journal of Marine Science》2013,35(1):331-361
Assessment of the status of southern bluefin tuna (SBT) by Australia and Japan has used a method (ADAPT) that imposes a number of structural restrictions, and is similar to methods used for a number of stocks world-wide. A flexible method for assessment of the SBT population is presented that is much less restrictive and has potentially wide applicability. The three key features are: (1) all fitting to data is within the context of maximum likelihood, (2) catch-at-age data are not assumed to be without error (as in existing methods), but rather to be random variables, while age-specific selectivity is allowed to change over time within the bounds of specific structure, and (3) autocorrelation in recruitment processes is considered within the likelihood framework of the model. While the results suggest the stock has been depleted considerably from its virgin biomass, and are generally consistent with previous assessments, they also indicate that it is not as much below the biomass that will produce maximum suitable yield as previously estimated and that the extent of stock rebuilding necessary may not be as large as has been argued. The available data are shown to provide little information on the steepness parameter of the stock-recruitment function, and hence on sustainable catch levels for the stock. 相似文献
3.
《African Journal of Marine Science》2013,35(1):159-171
Aircraft observations were used to investigate contrasting weather conditions over the northern edge of the warm Agulhas Current south of George, South Africa, during June 1989. A sea surface temperature front of 7°C over 10 km was observed near 35°S, 23°E. Surface-sensible and latent heat fluxes increased by a factor of five on the warm side. A deepening of the moist unstable layer was indicated by increased equivalent potential temperatures over the warm side. Most significantly, convectively generated turbulence, as inferred from variances in air pressure, increased exponentially with sea surface temperature and surface layer winds doubled south of 35°S. The sea state, initially smooth over the continental shelf, became rough seawards of the northern edge of the Agulhas Current. Numerical model simulations were performed to assess air-sea interactions. Model-simulated thermodynamic variables responded in close agreement with observations, but the increase in cross-frontal winds was not fully resolved. The aircraft observations provide evidence that the Agulhas Current affects the large-scale pressure field and may enhance the rain-bearing capacity of transient weather systems. 相似文献
4.
《African Journal of Marine Science》2013,35(3):437-451
Long-term ecosystem changes, such as regime shifts, have occurred in several marine ecosystems world-wide. Multivariate statistical methods have been used to detect such changes. A new method known as the sequential t-test algorithm for analysing regime shifts (STARS) is applied to a set of biological state variables as well as environmental and anthropogenic forcing variables in the southern Benguela. The method is able to correct for auto-correlation within time-series by a process known as prewhitening. All variables were tested with and without prewhitening. Shifts that were detected with both methods were termed robust. The STARS method detected shifts in relatively short time-series and identified when these shifts occurred without a priori hypotheses. Shifts were generally well detected at the end of time-series, but further development of the method is needed to enhance its performance for auto-correlated time-series. Since 1950, two major long-term ecosystem changes were identified for the southern Benguela. The first change occurred during the 1960s, caused predominantly by heavy fishing pressure but with some environmental forcing. The second change occurred in the early 2000s, caused mainly by environmental forcing. To strengthen these findings, further analyses should be carried out using different methods. 相似文献
5.
《制图学和地理信息科学》2013,40(2):87-103
Mapping spatial change is a fundamental theme in geography. The analytical and numerical application of differential calculus to continuous geographic data produces first-derivative distributions that can be mapped to show gradient magnitude and gradient direction, and second-derivative measures that can be mapped to show the form (convexity, concavity) of the geographic surface. When these differential measures are obtained for spatially distributed temporal data, a velocity/acceleration change map can be constructed. Cartographic applications of the methodology presented in this paper include slope and curvature landform mapping, derivative trend-surface mapping of urban housing value gradients and the velocity/acceleration mapping of mobile-home residency in the United States from 1950 to 1980. 相似文献
6.
《制图学和地理信息科学》2013,40(3):151-166
We present new methods for analyzing geo-referenced statistical data. These methods combine visualization and direct manipulation techniques of exploratory data analysis and algorithms for data mining. The methods have been implemented by integrating two hitherto separate software tools: Descartes for interactive thematic mapping, and the data mining toolbox Kepler. In using these tools, data analysis may proceed as a steady interaction between visual inspiration and insights gained from mathematical–statistical calculations. After introducing the various components of the methods and tools, the paper guides the reader through in-depth examples of using the tools in the context of analysis of urban demographic data. In particular, it is shown how geography-based classifications of urban districts can be related to available thematic characteristics by applying the data mining algorithms classification tree derivation, attribute weighting, and subgroup discovery. 相似文献
7.
《制图学和地理信息科学》2013,40(4):199-217
Although modern imagery usually has latitude and longitude or similar coordinates to provide true world location, much potentially useful imagery lacks this information. This includes historical imagery, as well as modern imagery that may have lost its locational information through inappropriate processing. Its provision through the process of georeferencing is still primarily a manual procedure. This paper proposes an efficient, fully- automated solution for massively asymmetric image-to-vector georeferencing whereby an image of a relatively small geographic area is automatically located relative to a substantially larger vector map base. For control points, road intersections are automatically extracted from high resolution aerial or satellite imagery using the new concepts of reference circles and central pixels. For automated control point pair identification between image and vector map, an invariant point pattern matching approach is proposed based on shape invariance for similarity transforms and invariant area ratios for affine transforms. The matching algorithm necessitates only a small subset of image points and requires no additional information beyond pixel and map coordinates. Further, it tolerates inaccurate, missing and spurious points, and provides high performance with linear scalability. A final step performs transformation verification, globalization and optimization based upon an Iterative Closest Point Greedy algorithm. Experimentation shows that images covering a few city blocks with as few as 6 to 17 extracted road intersection points can be efficiently and correctly located using the road network of Dallas County, Texas, with over 80,000 intersections. 相似文献
8.
《The Cartographic journal》2013,50(4):261-273
AbstractParallel coordinates, re-orderable matrices, and dendrograms, widely used methods for visual exploration of multivariate data, are systematically integrated in a complementary manner for supporting multi-resolution visual data analysis with an enhanced overview + detail exploratory strategy. There are three main topics: (1) dynamic control across resolutions at which data are explored; (2) coordination and color mapping among the views; and (3) enhanced features of each view designed for the overview + detail exploratory tasks. A case study analysis is used to demonstrate the potential for boosting productivity for exploration tasks by coordinating the views through user-controlled resolutions within a highly interactive analysis environment. The case study is focused on a complex, geographically referenced dataset including public health, demographic and environmental components. 相似文献
9.
《The Cartographic journal》2013,50(3):179-213
AbstractTo what extent do European state topographic maps exhibit unique styles of cartography? This paper describes an investigation to classify and analyse stylistic diversity in the official 1 : 50 000 topographical mapping of 20 European countries. The method involves the construction of a typology of cartographic style, based upon the classification of distinct graphical legend symbols into mutually exclusive thematic categories. In order to identify stylistic similarities between national symbologies, hierarchical cluster analysis was performed to compare the relative proportions of symbols within each category. This was complemented by a qualitative analysis of various aspects of cartographic design: colour, 'white' space, visual hierarchy, and lettering. The results indicate a high degree of stylistic diversity throughout Europe, with the symbologies of Great Britain and Ireland demonstrating the strongest example of a supranational style. The typology of cartographic symbologies is shown to be an effective method for determining stylistic association among maps of differing geographical (and potentially historical) origins and it is suggested that the cartographic language paradigm should be revisited as a means for understanding why national differences persist in state cartography. A version of this paper was presented at the Twenty-third International Cartographic Conference in Moscow. 相似文献
10.
《制图学和地理信息科学》2013,40(2):89-101
Investigators in many fields are analyzing temporal change in spatial data. Such analyses are typically conducted by comparing the value of some metric (e. g., area, contagion, or diversity indices) measured at time T1 with the value of the same metric measured at time T2 . These comparisons typically include the use of simple interpolation models to estimate the value of the metric of interest at points in time between observations, followed by applications of differential calculus to investigate the rates at which the metric is changing. Unfortunately, these techniques treat the values of the metrics being analyzed as if they were observed values, when in fact the metrics are derived from more fundamental spatial data. The consequence of treating metrics as observed values is a significant reduction in the degrees of freedom in spatial change over time. This results in an oversimplified view of spatio-temporal change. A more accurate view can be produced by (1) applying temporal interpolation models to observed spatial data rather than derived spatial metrics; (2) expanding the metric of interest's computational equation by replacing the terms relating to the observed spatial data with their temporal interpolation equations; and (3) differentiating the expanded computational equation. This alternative, three-step spatio-temporal analysis technique will be described and justified. The alternative technique will be compared to the conventional approach using common metrics and a sample data set. 相似文献