共查询到20条相似文献,搜索用时 15 毫秒
1.
针对空间大地测量技术对中性大气折射延迟改正精度的要求,阐述了折射延迟改正值应随测站和随方位而异的必要性.指出,在尚不能直接测定天文大气折射值的情况下,现有的各种改正模型对大气分布模型的依赖性,不能达到预期的精度和降低观测的截止角.根据云南天文台低纬子午环的特殊结构,和测定大气折射的实践,提出了提高折射延迟改正精度的新方法,即:利用各观测站不同方位从天顶附近直到低地平高度角的天文大气折射实测数据,求解得到折射率差和映射函数的参数,从而建立随测站和随方位而异的大气折射延迟改正模型.这一新方法的实施,将能在不需采用大气分布模型的情况下,把天顶延迟的改正精度提高到1 mm以内,低地平高度角的折射延迟改正精度提高到厘米级,并且把截止高度角压缩到5°以内. 相似文献
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Focusing on lowering the cut-off elevation in the neutral atmosphere refraction delay correction and on raising the accuracy of the correction, we derive the formulae for calculating the correction for the bending of the light path caused by atmospheric refraction. This is the sort of correction that is given after the principal term in theoretical models of neutral atmospheric refraction delay correction, but is often neglected because it is a small quantity. However, in practice, for a not too low elevation like 15°, this term reaches 1 cm order of magnitude and can not be neglected. Li Yan-xing et al. specially gave a derivation of this correction and a computational method by successive approximation and some calculated values. Yan Hao-jian also proposed a formula of direct calculation but his calculated result was more than 3 times smaller than that of Li Yan-xing, which shows that further study of this correction is called for. Here we give a simple, convenient and reliable formula for calculating the correction. 相似文献
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电磁波折射延迟的弯曲改正 总被引:1,自引:1,他引:0
针对中性大气折射延迟改正中压缩截止高度角和提高改正精度的要求,推导了电磁波折射延迟中由天文大气折射引起的路径弯曲改正的计算公式,这是在许多理论模型中给出中性大气折射延迟改正的公式时,都会在主项后边给出的,却又因为它是小量而常被忽略的一项改正.实际上,在不太低的高度角,例如15°,这一项就达到1 cm量级,是不能忽略的.李延兴等人专门对这一改正作了推导,给出了逐步逼近的计算方法和计算值;严毫健也曾给出了直接计算的公式,计算结果却比李延兴等人的小3倍多,这说明对该项改正有必要作进一步的研究,拿出简便可靠的计算公式. 相似文献
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电磁波信号在地球大气中的传播受到折射的影响,传播的方向发生了改变,传播的路径变为曲线,长度大于直线距离,相应的传播时间也被延长了,采用一个简化的球对称大气模型计算了光线在不同天顶距下由于路径弯曲而引起的延迟改正. 相似文献
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A hypothesis is proposed for the mechanism of superrotation of the atmosphere of Venus involving the following processes. Winds near the planet's surface, making up part of the Hadley cell, flow past the surface relief and excite internal atmospheric gravity waves. While moving upward, these waves become unstable and collapse generating turbulent eddies. Some portion of the energy of these eddies is transferred to a two-dimensional flow, which is maintained also at the expense of instability of large-scale motions. In this flow, the inverse energy cascade (transition from smaller eddies to larger eddies), or negative viscosity, appears as a key element of this mechanism. Large-scale quasi-two-dimensional turbulent eddies transfer their energy to Rossby planetary waves which, in turn, transmit it to a zonal flow. Based on this hypothesis and the existing experimental data, the time period over which superrotation is established, as well as the vertical and horizontal eddy viscosity coefficients, is estimated. In parallel, arguments in favor of the proposed hypothesis are obtained. 相似文献
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Light refraction by the Sun's atmosphere is calculated.As detected from the Earth, the refraction can deflect a light ray emitted from the Sun's limb by 13 or a starlight ray grazing the solar limb by 26, an effect 15 times larger than the gravitational deflection. 相似文献
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回顾了作为实用天文学和大地测量学中基本研究课题之一的大气折射函数研究的最新进展;介绍了近几年发展的大气折射母函数方法。对如今广泛地应用在空间测量技术中的几种映射函数,如CfA2.2、MTT等模型作出评述;特别分析了NMF模型的优点和不足之处。还介绍了由大气折射母函数方法引出的大气延迟新连分式映射函数和天文大气折射的映射函数方法,利用VLBI实验中高度截止角与基线长变化的关系和探空气球(radios 相似文献
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根据经典天体定位测量受天文大气折射的影响和现代空间大地测量对中性大气折射延迟改正的要求,分析了这些修正没有达到预期精度要求的原因:主要在于不能直接测定天文大气折射;文章针对这些影响量对大气分布模型的依赖性,改正值应随着不同的观测站和不同方位而异的要求,提出了提高这两种改正精度的有效途径:在各观测站不同方位的各天顶距,测定天文大气折射值,分别建立不同方位的大气折射实测模型,并利用实测数据,求解出折射率差和映射函数的参数,建立和采用随着观测站、随着方位而异的折射延迟改正模型。这一新方法的实施,将能在避免采用大气分布模型的情况下,把较低高度角的折射延迟改正精度从现在的米级提高到厘米级,并且把截止高度角压缩到5°以内。文章还论述了在各观测站多方向测定天文大气折射值的可能性。 相似文献
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We have obtained the temporal correlation function, Q(t), from time sequences of Caii K filtergrams and Dopplergrams from Antarctica, Taiwan Oscillation Network (TON) and Solar and Heliospheric Observatory (SOHO). Q(t) gives the time evolution of the pattern under examination, supergranulation in this case. It has been found that Q(t) shows oscillatory signals of both 5-min and long-term periods. The 5-min oscillations are suppressed by averaging the images over 10 min. An exponential decay curve which represents the lifetime trend of supergranules, is fitted to Q(t) and subtracted out. The Q(t) residuals thus obtained contain the oscillatory component and are then subjected to a periodogram analysis. Significant periodicities in the range of 1.4–10 hours have been noted. The causes of these oscillations are not fully known at present, but the instrumental and atmospheric factors can be ruled out, pointing to solar origin. Various possibilities are discussed. Some of the observed periodicities may be considered as probable candidates for long-term oscillations in the Sun, such as the elusive gravity modes. 相似文献
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Using the annual GPS observational tropospheric zenith delay data and meteorological data obtained at 36 globally distributed IGS stations in 2003, we have estimated the accuracy and range of application of two often-used models of tropospheric delay correction (the Hopfield and Saastamoinen models), and of a more recent model (the EGNOS model). We point out some defects in the Hopfield model and show that the EGNOS model can be used as the correction model of the tropospheric zenith delay for the GNSS real-time positioning and navigation. 相似文献
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The point source of neutral gas undergoing ionization and expanding into an uniform magnetic field is considered. Friction
between the neutral and ionized particles results in the formation of the magnetic field barrier and diamagnetic cavity surrounding
the source. At least one neutral point inevitably arises at the boundary of the cavity. When the neutral gas production rate
grows, two neutral points may arise at this boundary. In the vicinity of these points magnetic field lines converge, along
with the plasma flow which is magnetic field aligned in the steady state. As a result, two plasma jets originate from the
neutral points. Possible relation of these jets to cometary rays is discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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进行低高度角观测是GPS(Global Positioning System)气象学的发展趋势,其中发展高精度的低高度角的大气静力学延迟修正是主要的关键技术.比较了3种计算无线电波从空间到地面接收机的大气静力学延迟修正方法:(1)在大气球对称假设下用探空气球资料路径积分得到大气静力学延迟;(2)在大气球对称假设下用NCEP(National Centers for Environmental Prediction)再分析资料得到大气静力学延迟;(3)用Niell的大气静力学映射函数得到大气静力学延迟.与2001年中国地区89个探空气球站资料计算得到的大气静力学映射函数比较结果显示:NCEP再分析资料路径积分的方法在低高度角(5°以下)的精度好于Niell映射函数模型约5倍. 相似文献
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Elizabeth Bass Meers Oppenheim Jorge Chau Alice Olmstead 《Earth, Moon, and Planets》2008,102(1-4):379-382
This paper examines current techniques used to determine meteoroid mass from high-power, large aperture (HPLA) radar observations.
We demonstrate why the standard approach of fitting a polynomial to velocity measurements gives inaccurate results by applying
this technique to artificial datasets. We then suggest an alternate approach, fitting velocity data to an ablation model.
Using data taken at the Jicamarca Radio Observatory in July 2005, we compare the results of both methods and demonstrate that
fitting velocity data to an ablation model yields a reasonable result in some instances where alternate methods produce physically
unrealistic mass estimates. 相似文献
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测定天文大气折射和建立电磁波折射延迟实测模型(Ⅲ)-专用测量仪器 总被引:1,自引:0,他引:1
针对用天文大气折射测定值,建立随观测站和随方位而异的电磁波折射延迟改正模型的高精度要求,提出了新的仪器误差理论,其主要内容是允许仪器误差存在,并看成是不断变化的,采用相应的测量方法作实时的测定和修正,同时消除仪器的各种变形和误差的影响,排除观测数据中的各种系统误差来源,并达到提高单次测定精度目的;文中还针对不同纬度的观测站、多方位、从天顶直到低空的观测需要,给出了仪器总体结构的安排,和采用视频CCD作为接收器的终端设计方案,也给出了各种仪器误差的测定方法和测量装置的设计要求。 相似文献
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