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71.
72.
GPS中CCD技术的原理与应用 总被引:2,自引:2,他引:0
码/载波相位扩散技术可使单频GPS接收机的测程从20km急剧扩大到400km。本文叙述其简单原理与实际应用。 相似文献
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74.
Brisk, persistent easterly trade wind influences define Holocene patterns of carbonate sedimentation across the Caicos Platform (southeastern Bahamas). Resultant predictive sedimentary facies models based on trade wind influences are more widely applicable to the exploration for subsurface carbonate plays than are existing models based on the northern Bahamas facies patterns, which are characterized by gentle trade winds and strong platform-margin-related oceanic processes (swells and tidal currents). The Caicos Platform relationships may be more applicable because many ancient shallow carbonate depositional environments were within the trade wind belts and commonly within broad intracratonic seas that were little influenced by oceanic processes.The grainstone-dominated Caicos Platform exhibits reservoir potential over much of its surface, in contrast to northern Bahamian platforms, where oceanic tidal currents or swells and gentle easterly trade winds confine higher energy environments with reservoir potential to platform margins. Strong easterly trade winds across Caicos Platform promote widespread Holocene platform-interior oolitic, skeletal and grapestone grainstone bodies on this platform. Orientations of ooid sand bodies vary depending on preexisting topography, water depth and bottom energy. Shallow subtidal ooid sand shoals orient parallel to these winds. Ooid sands developed along older shorelines orient parallel to the shorelines but prograde perpendicular into these winds. Deeper platform-interior oolitic sands exist as widespread, sheet-like deposits. These trade winds allow reefs and ooids to coexist in many settings, permit isolated linear reefs to flourish on certain leeward platform margins, and promote effective off-bank transport of carbonate sands that create onlapping grainstone wedges. These relationships are very applicable to the rock record.Strong trade wind influences, such as seen on Caicos Platform, better explain the occurrence of Cretaceous reef and/or oolitic grainstone reservoirs developed well in from platform margins (Fairway Field in East Texas; Black Lake Field in Louisiana) than do existing northern Bahamian models. Depositional models based on conditions in the northern Bahamian models would predict low-energy facies in these platform-interior settings. A trade-wind-driven depositional model, characterized by strong persistent easterlies, also better explains the origin of the onlapping wedge of skeletal grainstones at Poza Rica oilfield in Mexico.The Caicos Platform easterly trade-wind-driven depositional model should generally apply to any ancient shallow carbonate environment that developed 5–22° north or south of the paleoequator, whether or not a platform margin was near by. Future carbonate exploration or exploitation should always factor in not only geological age, but also physiographic, latitudinal and climatic setting at a global and local scale. 相似文献
75.
The accurate surface wind in the equatorial Indian Ocean is crucial for modeling ocean circulation over this region. In this study, the surface wind analysis generated at the European Center for Medium Range Weather Forecasts (ECMWF) and the National Centers for Environmental Prediction (NCEP) are compared with NASA QuikSCAT satellite derived Level2B (swath level) and Level3 (gridded) surface winds for the year 2005. It is observed that the ECMWF winds exhibit speed bias of 1.5 m/s with respect to QuikSCAT Level3 in the southern equatorial Indian Ocean. The NCEP winds are found to exhibit speed bias (1.0–1.5 m/s) in the southern equatorial Indian Ocean specifically during January–February 2005. The biases are also observed in the analysis when compared with Level2B product as well; however, it is less in comparison to Level3 products. The amplitude of daily variations of both ECMWF and NCEP wind speed in Bay of Bengal and parts of the Arabian Sea is about 80% of that in QuikSCAT, while in the equatorial Indian Ocean it is about 60% of that of QuikSCAT. 相似文献
76.
Surface energy and water vapor fluxes observed in a desert plantation in central Iran 总被引:1,自引:0,他引:1
A. Oliphant P. Zawar-rezaG. Azizi A. DehghanpourJ. Harrison 《Journal of Arid Environments》2011,75(10):926-935
Summertime observations of surface radiation budget, energy balance and atmospheric surface layer meteorology were made on an arid valley floor planted with Haloxylon aphyllum to combat desertification in central Iran. The surface microclimate is characterized and compared with other arid regions and the role of ‘desert greening’ on surface fluxes is considered. A high surface albedo (0.265) and large longwave radiation loss produced relatively low net radiation. Energy partitioning was dominated by sensible and ground heat fluxes with opposing diurnal asymmetry governed by strong diurnal variability in eddy diffusivity. The Bowen ratio was 2.53, which fell inside the range of other vegetated arid surfaces. Surface temperature gradients were strong both in the atmospheric surface layer and in the substrate, with consistent lapse conditions by day and inversions at night. The wind regime included a moderate daytime regional wind which displayed Coriolis turning and weaker nocturnal slope flows. Actual evapotranspiration (1 mm dy−1) was only a small fraction of potential evapotranspiration. The diurnal pattern of AET indicates strong stomatal control. The desert greening effect of Haloxylon plantations provided atmospheric water and reduced sensible heat flux by up to 40%. 相似文献
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78.
In recent years a number of double-humped supernovae (SNe) have been discovered. This is a feature predicted by the dual-shock Quark-Nova (QN) model where an SN explosion is followed (a few days to a few weeks later) by a QN explo- sion. SN 2009ip and SN 2010mc are the best observed examples of double-humped SNe. Here, we show that the dual-shock QN model naturally explains their light curves including the late time emission, which we attribute to the interaction between the mixed SN and QN ejecta and the surrounding circumstellar matter. Our model applies to any star (O-stars, luminous blue variables, Wolf-Rayet stars, etc.) provided that the mass involved in the SN explosion is ~ 20 Mo which provides good conditions for forming a QN. 相似文献
79.
THREE-DIMENSIONAL NUMERICAL SIMULATION OF THE MESOSCALE WIND STRUCTURE OVER SHANDONG PENINSULA
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General features of 3-dimensional mesoscale wind and temperature structure over ShandongPeninsula are described in this paper.Results are achieved by numerical simulation with the 3-dimensional non-hydrostatic mesoscale model METRAS.For the onset and cessation time of sea-land breezes,the simulation results agree well with the statistical analyses of observational dataavailable for the studied area.One interesting result is the 3 hour response time of wind field to thethermal change.Further statistic analysis based on the observational data is needed to make sure ofthis correlation.Important effects of coastal mountains on the wind structure are also exposed indetail by the model.Convergence and divergence centers resulting from the conjunction of sea-landbreezes and complex terrain are clearly shown,which are not noticed before by conventionalsynoptic observation and theoretical analysis. 相似文献
80.
Naoto Ebuchi 《Journal of Oceanography》2000,56(2):161-172
In order to validate wind vectors derived from the NASA scatterometer (NSCAT), statistical distributions of wind speeds and directions retrieved by the NSCAT-2 geophysical model function have been investigated by comparison with wind data retrieved by the other model functions such as SASS-2 and NSCAT-1 and those derived from the wind analyses of the European Centre for Medium Range Weather Forecasts (ECMWF). The histogram of the NSCAT-2 wind speeds has a similar shape to those of the ECMWF and NSCAT-1 winds, but is slightly shifted toward higher wind speed to adjust negative bias which has been found in the NSCAT-1 winds by previous buoy comparison studies. Variations of the standard deviation of the NSCAT-2 wind speeds with incidence angle are greater than those of the ECMWF and NSCAT-1 winds. The frequency distribution of wind directions relative to spacecraft flight direction has been calculated to assess the self-consistency of the wind directions. It was found that the NSCAT-2 wind vectors exhibit systematic directional preference relative to antenna beams. This artificial directivity is considered to be caused by imperfections in the antenna beam balancing and the geophysical model function. The skill of the ambiguity removal procedure is discussed as a function of wind speed and incidence angle, and is found to be improved compared to the NSCAT-1 winds, especially at high incidence angles. It is concluded that systematic errors in wind directions might be increased by modifications from NSCAT-1 to NSCAT-2, though the wind speed bias is removed and the ambiguity removal skill is improved. 相似文献