Terrain correcting Australian gravity observations using the national digital elevation model and the fast Fourier transform

The release of a digital elevation model (DEM) for Australia on a 9″ (～250 m) grid has enabled the computation of gravimetric terrain corrections thus allowing the computation of complete Bouguer anomalies across the continent. The terrain correction was calculated through a two‐dimensional fast Fourier transform algorithm applied to a linear, planar approximation of the terrain‐correction formula, and with a constant topographic density of 2670 kg.m^‐3. The technique was applied to two datasets in order to test for instabilities in the terrain‐correction algorithm: the original 9″ DEM, and a 27″ DEM averaged from the 9″ data. The 27″ terrain corrections were compared with values supplied by the Australian Geological Survey Organisation in Tasmania: 86% of these data were found to agree within 3.91 μm.s^‐2; 98% agreed to within 5.32 μm.s^‐2 (1σ).     

Topographic analysis for the prairie pothole region of Western Canada

The unique topography of the pothole region of the North American prairies creates challenges for properly determining basin contributing area. Numerous depressions or potholes within the landscape impound runoff. However, potholes can ‘fill‐spill’ resulting in surface water connections between the potholes. Surface water connectivity between potholes ultimately influences basin contributing area. Currently, automated methods, such as landscape analysis tools, treat depressions in the landscape as artifacts and simply fill the depressions to delineate a drainage basin. Using this method to calculate contributing area assumes that all surface storage has been satisfied (threshold) and the drainage basin will contribute 100% of its area for all runoff events. However, most runoff events in the prairie pothole region are pre‐threshold events that contribute only a portion of surface runoff to the outlet. These pre‐threshold events have surface storage that varies because of antecedent water levels and have a variable or dynamic potential to store further runoff in the basin. Government agencies have developed methodologies for determining pre‐threshold contributing areas, but these methodologies do not incorporate current technologies and, as a result, have limitations. We propose an automated method for determining contributing area that incorporates the fill‐spill of prairie potholes. The algorithm, which uses the D‐8 drainage direction method, automates a methodology for identifying and quantifying runoff contributing area. Any algorithm that determines pre‐threshold contributing area, must allow the DEM to be filled in an incremental manner. This will simulate increasing pond levels, and the resulting decrease in available storage in the basin, in response to runoff events. The SPILL algorithm is an iterative solution that increases the magnitude of input runoff events and records the decreasing change in available surface storage and the increase in contributing area until the storage threshold is reached and the contributing area reaches 100%. Through application of the algorithm on prairie pothole region basins, we test proposed conceptual curves that describe a hypothesized non‐linear relationship between decreasing potential storage in the landscape and contributing area. Results indicate that the proposed conceptual curves represent the relationship between potential surface storage and contributing area in the test basins very well. Copyright © 2012 John Wiley & Sons, Ltd.     

小尺度深凹地形大气边界层流场演变过程的非静力数值模拟研究

针对小尺度深凹地形的特点,建立了一个高分辨的、非静力的二维边界层模式,采用能量（Ｅ－ε）闭合方案,考虑了太阳短波辐射及其在地表面的不均匀分布,地－气系统的长波辐射、潜热和感热输送,以及地表面与土壤层的热传导物理过程。利用该模式。模拟了某深凹露天矿实际地形上的大气边界层流场的演变过程。     

Wind Flow Over Complex Terrain: A Historical Perspective and the Prospect for Large-Eddy Modelling

The development of our understanding of turbulent flow overcomplex terrain is described. Despite considerable advances, there are still gaps in our knowledge. Large-eddy simulation of such flows is now becoming possible. This may stimulate further advances but it is computationally very demanding. The application of this technique to flow over hills is discussed.     

基于VisualC 平台的多边形裁剪算法实现

详细叙述了利用ＶｉｓｕａｌＣ＋＋提供的函数进行多边形裁剪的算法实惠过程,并给出了多边形带“岛”情况的具体处理方法。     

Hydrogeochemistry of seepage water collected within the Youngcheon diversion tunnel,Korea: source and evolution of SO4‐rich groundwater in sedimentary terrain

In the Youngcheon Diversion Tunnel area, South Korea, 46 samples of tunnel seepage water (TSW) and borehole groundwater were collected from areas with sedimentary rocks (mainly sandstone and shale) and were examined for hydrogeochemical characteristics. The measured SO₄ concentrations range widely from 7·7 to 942·0 mg/l, and exceed the Korean Drinking Water Standard (200 mg/l) in about half the samples. The TDS (total dissolved solid) content generally is high (171–1461 mg/l) from more shale‐rich formations and also reflects varying degrees of water–rock interaction. The water is classified into three groups: Ca? SO₄ type (61% of the samples collected), Ca? SO₄? HCO₃ type (15%) and Ca? HCO₃ type (24%). The Ca? HCO₃ type water (mean concentrations=369 mg/l Ca, 148 mg/l HCO₃ and 23 mg/l SO₄) reflected the simple reaction between CO₂‐recharged water and calcite, whereas the more SO₄‐rich nature of Ca? SO₄ type water (mean concentrations=153 mg/l Ca, 66 mg/l HCO₃ and 416 mg/l SO₄) reflected the oxidation of pyrite in sedimentary rocks and fracture zones. Pyrite oxidation resulted in precipitation of amorphous iron hydroxide locally within the tunnel as well as in high concentrations of Ca (mean 153 mg/l) and Na (mean 49 mg/l) for TSW, and is associated with calcite dissolution resulting in pH buffering. The pyrite oxidation required for the formation of Ca? SO₄ type water was enhanced by the diffusion of oxygenated air through the fractures related to the tunnel's construction. The subsequent outgassing of CO₂ into the tunnel resulted in precipitation of iron‐bearing carbonate. Copyright © 2001 John Wiley & Sons, Ltd.     

Towards High-Resolution Habitat Suitability Modeling of Vulnerable Marine Ecosystems in the Deep-Sea: Resolving Terrain Attribute Dependencies

Recent habitat suitability models used to predict the occurrence of vulnerable marine species, particularly framework building cold-water corals, have identified terrain attributes such as slope and bathymetric position index as important predictive parameters. Due to their scale-dependent nature, a realistic representation of terrain attributes is crucial for the development of reliable habitat suitability models. In this paper, three known coral areas and a noncoral control area off the west coast of Ireland were chosen to assess quantitative and distributional differences between terrain attributes derived from bathymetry grids of varying resolution and information content. Correlation analysis identified consistent changes of terrain attributes as grain size was altered. Response characteristics and dimensions depended on terrain attribute types and the dominant morphological length-scales within the study areas. The subsequent effect on habitat suitability maps was demonstrated by preliminary models generated at different grain sizes. This study demonstrates that high resolution habitat suitability models based on terrain parameters derived from multibeam generated bathymetry are required to detect many of the topographical features found in Irish waters that are associated with coral. This has implications for marine spatial planning in the deep sea. Supplemental materials are available for this article. Go to the publisher's online edition of Marine Geodesy to view the free supplemental file.     

RTM Gravity Forward-Modeling Using Topography/Bathymetry Data to Improve High-Degree Global Geopotential Models in the Coastal Zone

We apply the residual terrain modeling (RTM) technique for gravity forward-modeling to successfully improve high-resolution global gravity fields at short spatial scales in coastal zones. The RTM scheme is combined with the concept of rock-equivalent topography, allowing to use a single uniform constant mass-density in the RTM forward-modeling, both at land and sea. SRTM30_PLUS bathymetry is merged with higher-resolution SRTM V4.1 land topography, and expanded into spherical harmonics to degree 2160, yielding a new and consistent high-degree RTM reference surface. The forward-modeling performance is demonstrated in coastal zones of Greece and Canada using ground-truth vertical deflections, gravity from land and shipborne gravimetry, and geoid heights from GPS/leveling, with improvements originating from bathymetry clearly identified. We demonstrate that the SRTM30_PLUS bathymetry carries information on gravity field structures at spatial scales less than 5 arc minutes, which can be used to augment EGM2008 in (rugged) coastal zones, both over land and marine areas. This may be of value (i) to partially reduce the signal omission error in EGM2008/GOCE-based height transfer in areas devoid of dense gravity data, (ii) to fill the gap between land gravity and shipborne gravity along rugged coastlines, and (iii) for the development of next-generation altimetric gravity fields.     

基于1∶10000比例尺数字影像地图的开发与制作

通过介绍1∶10 000比例尺数字影像地图的设计开发、技术路线等情况,从而提出应用Illustrator,Photoshop软件制作1∶10 000比例尺数字影像地图的作业方法,初步探讨了以软件为核心的生产体系,倡导在生产实践中不断完善和充实,为今后数字影像地图制作的应用提供建设性的指导意见。     

The structural evolution of the Fyfe Hills‐Khmara Bay region,Enderby Land,East Antarctica

The Table Hill Volcanics of the Officer Basin were first dated as approximately 1100 m.y. from Rb‐Sr model ages for total‐rock samples of basalt from the Yowalga No. 2 bore. Later regional mapping, however, places the Volcanics as Marinoan (very late Precambrian) or younger, and receives support from discordant K‐Ar ages ranging from 330 m.y. to 445 m.y. New total‐rock analyses confirm the original Rb‐Sr data, but analyses of separated minerals do not confirm the low value for the initial ⁸⁷Sr/⁸⁶Sr that had been assumed to calculate the 1100 m.y. model age. Instead, apparently‐unaltered primary pyroxenes indicate that the initial ⁸⁷Sr/⁸⁶Sr could be as high as 0.718. Combined with the total‐rock results, this yields an apparent age for the basalt of 575 ± 40 m.y. It is possible in principle that the high ⁸⁷Sr/⁸⁶Sr in the pyroxenes could be due to Sr isotope exchange during a Palaeozoic metamorphism, but there is absolutely no field or petrological evidence for such an event. Consequently, and in view of the stratigraphic evidence for their age, the Rb‐Sr data are best interpreted as signifying an original extrusion of the basalts at 575 ± 40 m.y., together with a prehistory of the magma that includes contamination with radiogenic Sr and alkalis from Precambrian crustal material.