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161.
A new technique to determine geoid and orthometric heights from satellite positioning and geopotential numbers 总被引:1,自引:0,他引:1
L. E. Sjöberg 《Journal of Geodesy》2006,80(6):304-312
This paper takes advantage of space-technique-derived positions on the Earth’s surface and the known normal gravity field to determine the height anomaly from geopotential numbers. A new method is also presented to downward-continue the height anomaly to the geoid height. The orthometric height is determined as the difference between the geodetic (ellipsoidal) height derived by space-geodetic techniques and the geoid height. It is shown that, due to the very high correlation between the geodetic height and the computed geoid height, the error of the orthometric height determined by this method is usually much smaller than that provided by standard GPS/levelling. Also included is a practical formula to correct the Helmert orthometric height by adding two correction terms: a topographic roughness term and a correction term for lateral topographic mass–density variations. 相似文献
162.
163.
A cross-sectional non-hydrostatic model with idealized topography was used to examine the processes influencing tidal mixing
in the region of sills. Initial calculations with appropriate parameters for the sill at the entrance to Loch Etive showed
that the model could reproduce the main features of the observed mixing in the region. In particular, the hydraulic jump in
the sill region was reproduced, as was an intense mid-water jet that was observed to separate from the lee side of the sill.
Shear instabilities associated with the jet appeared to be a source of mixing within the thermocline. In addition, internal
lee waves were generated on the lee side of the sill, with the observed amplification because of trapping during the flood
stage. Their magnitude and hence the mixing increased with increasing Froude number (F
r). In the case of vertically varying buoyancy frequency, its value near the sill top determined the F
r number, with its value below influencing internal waves magnitude at depth. At high F
r values particularly with strong currents, short waves and overturning occurred. 相似文献
164.
During the last 50 years, the management of agroecosystems has been undergoing major changes to meet the growing demand for food, timber, fibre and fuel. As a result of this intensified use, the ecological status of many agroecosystems has been severely deteriorated. Modeling the behavior of agroecosystems is, therefore, of great help since it allows the definition of management strategies that maximize (crop) production while minimizing the environmental impacts. Remote sensing can support such modeling by offering information on the spatial and temporal variation of important canopy state variables which would be very difficult to obtain otherwise.In this paper, we present an overview of different methods that can be used to derive biophysical and biochemical canopy state variables from optical remote sensing data in the VNIR-SWIR regions. The overview is based on an extensive literature review where both statistical–empirical and physically based methods are discussed. Subsequently, the prevailing techniques of assimilating remote sensing data into agroecosystem models are outlined. The increasing complexity of data assimilation methods and of models describing agroecosystem functioning has significantly increased computational demands. For this reason, we include a short section on the potential of parallel processing to deal with the complex and computationally intensive algorithms described in the preceding sections.The studied literature reveals that many valuable techniques have been developed both for the retrieval of canopy state variables from reflective remote sensing data as for assimilating the retrieved variables in agroecosystem models. However, for agroecosystem modeling and remote sensing data assimilation to be commonly employed on a global operational basis, emphasis will have to be put on bridging the mismatch between data availability and accuracy on one hand, and model and user requirements on the other. This could be achieved by integrating imagery with different spatial, temporal, spectral, and angular resolutions, and the fusion of optical data with data of different origin, such as LIDAR and radar/microwave. 相似文献
165.
Crustal contamination and fluid/rock interaction in the carbonatites of Fuerteventura (Canary Islands, Spain): a C, O, H isotope study 总被引:7,自引:0,他引:7
Fuerteventura—the second largest of the Canary Islands consists of Mesozoic sediments, submarine volcanic rocks, dike swarms and plutons of the Basal Complex, and younger subaerial basaltic and trachytic series. Carbonatites are found in two Basal Complex exposures: the Betancuria Massif in the central part of the island and the Esquinzo area in the north.
values of the carbonatites increase progressively from south to north of the island. This phenomenon is attributed to different degrees of assimilation of sedimentary carbonate. Homogeneous, typically magmatic
values for carbonatites which have preserved primary igneous textures and minerals suggest a well-mixed reservoir where changes in
values result from the storage of carbonate magmas at different structural levels. The magma storage allowed assimilation of sediment to varying degrees before final emplacement of carbonatites. Shifts in
towards more positive and negative values from presumed primary compositions are observed in the carbonatites. On the basis of the oxygen isotope compositions of calcite, mica and K-feldspar, and the hydrogen isotope compositions of micas, the changes in the
values of the carbonatites can be related to fluid/rock interactions. 相似文献
166.
167.
The atmospheric spectral transparency variations at 344 nm and 369 nm, averaged at eight Soviet stations between 69°N and 55°N, have been compared with sunspot numbers, or Wolf numbers (WN). The data were taken for the seasonal interval May-August during the period 1972 – 1989. Good negative correlations –0.76 and –0.82 have been found. The correlation coefficient between aerosol extinction at 344 nm and WN is equal to +0.75. Insignificant correlation is found for the transparency variations at 344 nm for stations situated to the south of latitude 50°. The best correlation with WN for both transparency and aerosol extinction at northern stations occurs for the shift of WN ahead of the optical parameters by 6 months.
The connection of transparency with cosmic rays in Apatity is also examined. It displays a sign opposite to that for WN, smaller values of the correlation coefficient, and an improbable shift of transparency ahead of cosmic ray intensity.
The relative changes of the transparency during a solar cycle can be evaluated at 10% in the ozone-free UVA region 相似文献
168.
Abstract The physically-based flood frequency models use readily available rainfall data and catchment characteristics to derive the flood frequency distribution. In the present study, a new physically-based flood frequency distribution has been developed. This model uses bivariate exponential distribution for rainfall intensity and duration, and the Soil Conservation Service-Curve Number (SCS-CN) method for deriving the probability density function (pdf) of effective rainfall. The effective rainfall-runoff model is based on kinematic-wave theory. The results of application of this derived model to three Indian basins indicate that the model is a useful alternative for estimating flood flow quantiles at ungauged sites. 相似文献
169.
The curve number (CN) method is widely used for rainfall–runoff modelling in continuous hydrologic simulation models. A sound continuous soil moisture accounting procedure is necessary for models using the CN method. For shallow soils and soils with low storage, the existing methods have limitations in their ability to reproduce the observed runoff. Therefore, a simple one‐parameter model based on the Soil Conservation Society CN procedure is developed for use in continuous hydrologic simulation. The sensitivity of the model parameter to runoff predictions was also analysed. In addition, the behaviour of the procedure developed and the existing continuous soil moisture accounting procedure used in hydrologic models, in combination with Penman–Monteith and Hargreaves evapotranspiration (ET) methods was also analysed. The new CN methodology, its behaviour and the sensitivity of the depletion coefficient (model parameter) were tested in four United States Geological Survey defined eight‐digit watersheds in different water resources regions of the USA using the SWAT model. In addition to easy parameterization for calibration, the one‐parameter model developed performed adequately in predicting runoff. When tested for shallow soils, the parameter is found to be very sensitive to surface runoff and subsurface flow and less sensitive to ET. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
170.
Abstract A simplified method has been developed for solving leaky aquifer non-Darcian flow hydraulics. The principle of volumetric approach is combined with the confined-aquifer, time-dependent drawdown equation in an observation well. The groundwater flow in the leaky aquifer is assumed to obey a non-Darcian flow law of exponential type. The results are obtained in the form of type-curve expressions from which the necessary bundles of curves are drawn for a set of selective non-Darcian flow aquifer parameters. Although application of the methodology appears as rather limited but it provides a scientific contribution and extension of leaky aquifer theory towards nonlinear flow conditions. The methodology developed herein is applied to some actual field data from the eastern sedimentary basin in the Kingdom of Saudi Arabia. 相似文献