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991.
Frank A. van den Heuvel 《ISPRS Journal of Photogrammetry and Remote Sensing》1998,53(6):354-368
Photogrammetry has many advantages as a technique for the acquisition of three-dimensional models for virtual reality. But the traditional photogrammetric process to extract 3D geometry from multiple images is often considered too labour-intensive. In this paper a method is presented with which a polyhedral object model can be efficiently derived from measurements in a single image combined with geometric knowledge on the object. Man-made objects can often be described by a polyhedral model and usually many geometric constraints are valid. These constraints are inferred during image interpretation or may even be extracted automatically. In this paper different types of geometric constraints and their use for object reconstruction are discussed. Applying more constraints than needed for reconstruction will lead to redundancy and thereby to the need for an adjustment. The redundancy is the basis for reliability that is introduced by testing for possible measurement errors. The adjusted observations are used for object reconstruction in a separate step. Of course the model that is obtained from a single image will not be complete, for instance due to occlusion. An arbitrary number of models can be combined using similarity transformations based on the coordinates of common points. The information gathered allows for a bundle adjustment if highest accuracy is strived for. In virtual reality applications this is generally not the case, as quality is mainly determined by visual perception. A visual aspect of major importance is the photo-realistic texture mapped to the faces of the object. This texture is extracted from the same (single) image. In this paper the measurement process, the different types of constraints, their adjustment and the object model reconstruction are treated. A practical application of the proposed method is discussed in which a texture mapped model of a historic building is constructed and the repeatability of the method is assessed. The application shows the feasibility of the method and the potential of photogrammetry as an efficient tool for the production of 3D models for virtual reality applications. 相似文献
992.
993.
Watershed mean transit times (MTTs) are used to characterize the hydrology of watersheds. Watershed MTTs could have important implications for water quality, as relatively long MTTs imply lengthier water retention, thereby allowing more time for pollutant transformation and more moderate release of pollutants into streams. Although estimates of MTTs are common for undisturbed watersheds, only a few studies to date have applied MTT models to urbanized watersheds. In the present study, we use δ18O to compare estimates of MTTs for paired suburban‐industrial and agricultural watersheds in Toronto, Canada. Although differences in precipitation δ18O between the two watersheds were negligible, there were significant differences in stream δ18O, suggesting differences in water transport pathways. Less damping between input precipitation δ18O and output stream δ18O in the suburban‐industrial watershed indicated a larger streamflow contribution from quick‐flow transport pathways. We applied three transit time models to quantify MTTs. Considering overall model fit, root mean square error, and uncertainty in model parameters, the exponential model performed the best of the three models. Optimized MTTs using this distribution across the suburban‐industrial subwatersheds ranged from 2.1 to 2.9 months, whereas those in the agricultural subwatersheds ranged from 2.7 to 7.5 months. The relatively small difference between urban and agricultural MTTs coincides with observations elsewhere. Model efficiencies could potentially be improved, and MTTs estimated more reliably, with a higher sampling frequency that captures a greater volume of overall discharge. Overall, this work provides a distinct first glimpse into the separation of MTTs between paired watersheds with such a large contrast in their land use. 相似文献
994.
Northern Svalbard represents a basement high surrounded by the Norwegian‐Greenland Sea/Fram Strait, Eurasian Basin, the Barents Shelf and the onshore Central Tertiary Basin (CTB). Published apatite fission track (AFT) data indicate Mesozoic differential, fault‐controlled uplift and exhumation of the region. Thermal history modelling of published and new AFT and (U–Th–Sm)/He ages of 51–153 Ma in the context of regional stratigraphy and geomorphology implies at least two, possibly three, uplift and exhumation stages since late Mesozoic, separated by episodes of subsidence and sediment deposition. Late Cretaceous/Palaeocene exhumation and subsequent burial appear to be related with the transition of compressional to transpressional collision of Svalbard and Greenland during the Eurekan Orogeny. Renewed exhumation since the Oligocene probably results from passive margin formation after the separation of Svalbard and Greenland, when a new offshore sedimentary basin opened west of Svalbard. Final uplift since the Miocene eventually re‐exposed the palaeosurface of northern Svalbard. 相似文献
995.
Assessment of a 2016 mission concept: The search for trace gases in the atmosphere of Mars 总被引:1,自引:0,他引:1
Richard W. Zurek Augustin Chicarro Mark A. Allen Jean-Loup Bertaux R.Todd Clancy Frank Daerden Vittorio Formisano James B. Garvin Gerhard Neukum Michael D. Smith 《Planetary and Space Science》2011,59(2-3):284-291
The reported detection of methane in the atmosphere of Mars as well as its potentially large seasonal spatial variations challenge our understanding of both the sources and sinks of atmospheric trace gases. The presence of methane suggests ongoing exchange between the subsurface and the atmosphere of potentially biogenic trace gases, while the spatial and temporal variations cannot be accounted for with current knowledge of martian photochemistry. A Joint Instrument Definition Team (JIDT) was asked to assess concepts for a mission that might follow up on these discoveries within the framework of a series of joint missions being considered by ESA and NASA for possible future exploration of Mars. The following is based on the report of the JIDT to the space agencies (Zurek et al., 2009); a synopsis of the report was presented at the Workshop on Mars Methane held in Frascati, Italy, in November 2009. To summarize, the JIDT believed that a scientifically exciting and credible mission could be conducted within the evolving capabilities of the science/telecommunications orbiter being considered by ESA and NASA for possible launch in the 2016 opportunity for Mars. 相似文献
996.
Frank Chew 《Marine Geodesy》2013,36(1):103-116
Western boundary currents, such as the Gulf Stream, are often modeled as flows in near cross‐stream geostrophic balance with paths that are straight or nearly straight. The effect of planetary vorticity advection on the downstream sea‐level slope in these rectilinear flows is re‐examined and found negligible. Instead, the re‐examination reveals a much greater effect of the ageostrophic component of the horizontal divergence in determining the downstream slope. Overlooked in previous studies is the geostrophic component of the horizontal divergence because of a hidden assumption of parallel flow. To avoid this pitfall, we employ a natural coordinate system to follow precisely the downstream direction. Further, we differentiate between weak geostrophic flows with small accelerations and flows in cross‐stream geostrophic balance where downstream acceleration might be appreciable. Two Rossby numbers are employed: a small cross‐stream number (≤0.01) to describe the near cross‐stream balance, and a large downstream number (≤0.1) to describe the large downstream accelerations that are found in western boundary flows. Finally, by means of a scale analysis we show that over the whole range of possible Rossby numbers, the advection effect of planetary vorticity on downstream sea level slope is negligible compared to the effect of the ageostrophic component of the horizontal divergence. Some new data on the nearshore gradient of the Reynolds stress are also included. 相似文献
997.
四极杆电感耦合等离子体质谱仪(Inductively Coupled Plasma-Quadrupole Mass Spectrometry,简称ICP-QMS)可用于U和Th同位素分析.目前,ICP-QMS能实现精度大约为0.3%(U)和1%(Th)的测量分析,可提供误差在1%~10%的230Th/U年代数据.本文用ICP-QMS分析了采自意大利南都Loreto旧石器地点的4颗马牙化石样品,并对已发表的UTEVA树脂提纯U和Th的流程做了进一步改进,使其适用于动物牙化石样品.样品中的U和Th含量的平均测量精度(2σ)分别为0.3%和0.6%;234U/235U和230Th/238U活度比平均精度(2σ)分别为0.3%和0.8%.数据表明同一颗牙化石的不同组织的U含量可有数量级差别,同时它们的U -Th同位素活度比也可显著地离散(>2σ),从而导致不一致的230Th/U年代结果.如今测定的各牙组织的U-Th同位素数据可用于模拟U的迁移历史;U-系分析与电子自旋共振测年技术相结合或可更好地估计样品的地质年代. 相似文献
998.
Sewer model development under minimum data requirements 总被引:1,自引:1,他引:0
Planning, design and operation of urban drainage systems is often based on hydraulic sewer modelling. Sewer models are also
increasingly used to quantify pollution loads discharged to aquatic ecosystems (e.g. via combined sewer overflows), which
ultimately allows an estimation of the ecological impact emanating from urban drainage systems. The establishment of such
network models, however, requires detailed and accurate information about the sewer network structure and the connected surface
area. This infrastructure data is often unavailable, confidential or available in ‘paper’ format only. The present paper outlines
a novel approach to develop a hydraulic sewer model constrained by a minimum amount of data. The approach combines the application
of a surface flow accumulation algorithm to a selectively manipulated Digital Elevation Model (DEM) with a routine for hydraulic
network dimensioning to generate a close-to-reality sewer network ready to be implemented in a hydraulic modelling platform.
The method is tested for three real-life catchments of which characteristics vary in scale, topography, state of development
and network complexity. For all cases the generated network is implemented on the EPA-SWMM platform to allow hydrodynamic
simulations. Model performance is assessed by (1) evaluating the spatial match of existing and generated network layout, (2)
comparing the estimated hydraulic dimension with real-life infrastructure data and (3) benchmarking simulated runoff with
measured data for a defined validation period. The analysis shows that the presented method is capable of reproducing the
original network layout, network length and corresponding discharge rates based on little, freely available information. Further
research potential is identified to improve the hydraulic dimensioning and the application to complex systems that include
control structures. The presented approach is useful to estimate the scope of drainage networks including layout and design
(e.g. for preliminary planning in emerging areas) to screen existing networks and to identify critical spots where more precise
information is required. 相似文献
999.
Frank Herrmann Georg Berthold Johann-Gerhard Fritsche Ralf Kunkel Hans-Jürgen Voigt Frank Wendland 《Environmental Earth Sciences》2012,67(8):2239-2250
A regional conceptual hydrogeological model has been developed for evaluating residence times of both, percolate water in the unsaturated zone and groundwater in upper aquifers. The model is based on digitally geo-data bases available at the regional level and has been applied for the entire Federal State of Hesse (Germany) with a spatial resolution of 60?×?60?m. Residence times determined for unconsolidated rock areas typically ranged between 10 and 25?years, whereas residence times of <5?years were assessed for consolidated rock areas. With regard to the implementation of the EU Water Framework Directive, the determined residence times may help to assess the time periods between the introduction of well-targeted groundwater protection measures and their impact on groundwater and surface water quality, respectively. 相似文献
1000.
Frank S. Spear Kyle T. Ashley Laura E. Webb Jay B. Thomas 《Contributions to Mineralogy and Petrology》2012,164(6):977-986
Quartz inclusions in garnet from samples collected from the staurolite zone in central New England are zoned in cathodoluminescence (CL). The CL intensity is interpreted to be a proxy for Ti concentration and the zoning attributed to Ti diffusion into the quartz grains driven by Ti exchange between quartz and enclosing garnet as a function of changing temperature. The CL zoning has been interpreted using a numerical diffusion model to constrain the time scales over which the diffusion has occurred. Temperature–time histories are sensitive to the presumed peak temperature but not to other model parameters. The total time of the metamorphic heating and cooling cycle from around 450?°C to the peak temperature (550–600?°C) back to 450?°C is surprisingly short and encompasses only 0.2–2 million years for peak temperatures of 600–550?°C. The metamorphism was accompanied by large-scale nappe and dome formation, and it is suggested that this occurred as a consequence of in-sequence thrusting resulting in a mid-crustal ductile duplex structure. 相似文献