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981.
传统的地震勘探数据采样必须遵循奈奎斯特采样定理,而野外数据采样可能由于地震道缺失或者勘探成本限制,不一定满足采样定理要求,因此存在数据重建问题.本文基于压缩感知理论,利用随机欠采样方法将传统规则欠采样所带来的互相干假频转化成较低幅度的不相干噪声,从而将数据重建问题转为更简单的去噪问题.在数据重建过程中引入凸集投影算法(POCS),提出采用e-√x(0≤x≤1)衰减规律的阈值参数,构建基于曲波变换三维地震数据重建技术.同时针对随机采样的不足,引入jitter采样方式,在保持随机采样优点的同时控制采样间隔.数值试验表明,基于曲波变换的重建效果优于傅里叶变换,jitter欠采样的重建效果优于随机欠采样,最后将该技术应用于实际地震勘探资料,获得较好的应用效果. 相似文献
982.
Dr. HUGO BOYKO 《水文科学杂志》2013,58(2):163-164
SUMMARY The evaporation tank consists of a square pan with a flat base, 2 metres long and 0, 7 metre deep, set into the ground with the rim 0, 1 metre above, and connected to a well on which is installed a limnigraph. This limnigraph records continuously fluctuations of the free water surface. The recordings show that a large amount of water can be evaporated during rainfall. This phenomenon is specific at every evaporation tank with a free water surface. It is only during the dry intervals that a strong correlation can be established between the evaporation measured in the tank and the potential evapotranspiration of the surrounding natural surfaces. In order to locate the dry intervals and to measure the evaporation only during these intervals, it is necessary to use an apparatus provided with a continuous recording mechanism 相似文献
983.
984.
提出了冰雷达数据处理的流程,详细论述了冰雷达数据处理中常规修正的关键技术:静态校正、增益控制、带通滤波以及偏移处理等。以中国第24次南极科学考察(CHINARE 24)所获取的Dome A 地区30 km×30 km范围冰雷达原始数据处理作为实例,提取得到了该区域冰盖内部等时层埋深以及冰盖的冰厚数据。通过插值展现了冰盖等时层以及冰岩界面的三维空间形态。结合该区域ICESat冰盖表面高程数据,构建出了Dome A地区涵盖冰盖表面、冰盖等时层以及冰岩界面形态特征的三维模型。 相似文献
985.
A. Rajabifard A. Binns I. Masser I. Williamson 《International journal of geographical information science》2013,27(7):727-741
A Spatial Data Infrastructure (SDI) facilitates and coordinates the exchange and sharing of spatial data between stakeholders in the spatial data community. With this objective in mind, countries throughout the world are developing SDIs to manage and utilize their spatial data assets more effectively. These countries are developing SDIs to assist in various kinds of decision‐making at different levels of government jurisdictions that have an important impact within their national boundaries. However, current research shows that SDI is understood and described differently by stakeholders from different disciplines and different jurisdictional levels. Therefore, in many cases, SDI initiatives remain very much an innovation, even among practitioners. There are still uncertainties regarding the benefits and identities of SDIs, particularly in connection with how they evolve over time to meet user needs. This paper reviews and assesses the development of SDIs throughout the world over the past 15 years and the leadership role of national governments in SDI creation. This assessment is based on the SDI activities of various jurisdictions including Asia‐Pacific, Australia, North America, and Europe, and research into the worldwide effects of spatial information clearing houses. This assessment includes a discussion on emerging trends in SDI development, with particular reference to the increasingly important role played by sub‐national governments and the private sector within the framework of SDI development. The paper concludes with a discussion of the implications for future SDI development, including the delivery of a virtual world that has a particular focus on facilitating decision‐making at a community level within a national context. 相似文献
986.
Jonathan L. Goodall David R. Maidment 《International journal of geographical information science》2013,27(2):233-247
Despite a long history of synergy, current techniques for integrating Geographic Information System (GIS) software with hydrologic simulation models do not fully utilize the potential of GIS for modeling hydrologic systems. Part of the reason for this is a lack of GIS data models appropriate for representing fluid flow in space and time. Here we address this challenge by proposing a spatiotemporal data model designed specifically for large‐scale river basin systems. The data model builds from core concepts in geographic information science and extends these concepts to accommodate mathematical representations of fluid flow at a regional scale. Space–time is abstracted into three basic objects relevant to hydrologic systems: a control volume, a flux and a flux coupler. A control volume is capable of storing mass, energy or momentum through time, a flux represents the movement of these quantities within space–time and a flux coupler insures conservation of the quantities within an overall system. To demonstrate the data model, a simple case study is presented to show how the data model could be applied to digitally represent a river basin system. 相似文献
987.
The objective of the study is to evaluate the potential of a data assimilation system for real-time flash flood forecasting over small watersheds by updating model states. To this end, the Ensemble Square-Root-Filter (EnSRF) based on the Ensemble Kalman Filter (EnKF) technique was coupled to a widely used conceptual rainfall-runoff model called HyMOD. Two small watersheds susceptible to flash flooding from America and China were selected in this study. The modeling and observational errors were considered in the framework of data assimilation, followed by an ensemble size sensitivity experiment. Once the appropriate model error and ensemble size was determined, a simulation study focused on the performance of a data assimilation system, based on the correlation between streamflow observation and model states, was conducted. The EnSRF method was implemented within HyMOD and results for flash flood forecasting were analyzed, where the calibrated streamflow simulation without state updating was treated as the benchmark or nature run. Results for twenty-four flash-flood events in total from the two watersheds indicated that the data assimilation approach effectively improved the predictions of peak flows and the hydrographs in general. This study demonstrated the benefit and efficiency of implementing data assimilation into a hydrological model to improve flash flood forecasting over small, instrumented basins with potential application to real-time alert systems. 相似文献
988.
Climatological fields of dissolved oxygen and phosphates in the Bering Sea during the spring, summer, and fall seasons were generated on the basis of an extensive dataset of hydrochemical observations (16,356 stations, beginning in 1928) and a novel 3D variational algorithm for interpolation of a passive ocean tracer. The resulting patterns comply with maps produced earlier using an optimal interpolation method, though they also provide more detail and contain no “missing data” regions. Vertical, spatial, and temporal variability of both parameters follow large-scale patterns of circulation, upper mixed layer depth, and phytoplankton productivity in the Bering Sea. 相似文献
989.
Rooted aquatic macrophytes affect abiotic conditions in low-gradient rivers by altering channel hydraulics, consuming biologically available nutrients, controlling sediment transport and deposition, and shading the water surface. Due to seasonal macrophyte growth and senescence, the magnitude of these effects may vary temporally. Seasonal changes in aquatic macrophyte biomass, channel roughness and flow velocity, were quantified and trends were related to spatiotemporal patterns in water temperature in a low-gradient, spring-fed river downstream from high-volume, constant-temperature groundwater springs. Between spring and summer, a nearly threefold increase in macrophyte biomass was positively correlated with channel roughness and inversely related to flow velocity. On average, flow velocity declined by 34% during the study period, and channel roughness increased 63% (from 0.064 to 0.104). During the spring and fall period, the location of a minimum water temperature variability “node” migrated upstream more than 4 km, whereas daily maximum water temperature cooled by 2–3°C. Water temperature modelling shows that the longitudinal extent of cold-water habitat was shortened due to increased channel roughness independent of seasonal surface water diversions. These results suggest that macrophyte growth mediates spatiotemporal patterns of water temperature, constraining available cold-water habitat while simultaneously improving its quality. Understanding complex spatial and temporal dynamics between macrophyte growth and water temperature is critical to developing regulatory standards reflective of naturally occurring variability and has important implications for the management and conservation of cold-water biota. 相似文献
990.
Yonghai Zhang 《Geophysical Prospecting》2010,58(6):915-924
Seismic data acquired along rugged topographic surfaces present well‐known problems in seismic imaging. In conventional seismic data processing, datum statics are approximated by the surface consistence assumption, which states that all seismic rays travel vertically in the top layer. Hence, the datum static for each single trace is constant. In case this assumption does not apply, non‐constant statics are required. The common reflection surface (CRS) stack for rugged surface topography provides the capability to deal with this non‐vertical static issue. It handles the surface elevation as a coordinate component and treats the elevation variation in the sense of directional datuming. In this paper I apply the CRS stack method to a synthetic data set that simulates the acquisition along an irregular surface topography. After the CRS stack, by means of the wavefield attributes, a simple algorithm for redatuming the CRS stack section to an arbitrarily chosen planar surface is performed. The redatumed section simulates a stack section whose acquisition surface is the chosen planar surface. 相似文献