Glonass Laser Ranging Accuracy With Satellite Signature Effect

GLONASS satellites have been tracked by the worldwide laser ranging networkas well as by the GLONASS-borne microwave-based technique. Owing to thelarge size of their corner cube reflector arrays, the amount of ranging data is enough to determine their orbits from laser ranging data alone. We found, however, that the large size of the array affected the accuracy of measurement to an extent that is dependent on the characteristics of the ranging systems. An azimuthal variation of the reflector array response was also detected in observations from single-photon laser ranging. Orbital analysis reveals that the effect makes the measured range on average 22 mm shorter than expected in the absence of the large array, which explains more than half of the offset of 39 mm previously discovered between microwave and laser orbits.     

Contributions of Satellite Laser Ranging to Past and Future Radar Altimetry Missions

Satellite laser ranging (SLR) has proven avery efficient method for contributingto the tracking of altimetric satellites anddetermining accurately their orbitalthough hampered by the non-worldwide coverageand the meteorologicalconditions. Indeed, in some cases it is the onlymethod available to determinethe satellite orbit (e.g., the orbits of the ERS-1and Geosat-Follow-On missions).Moreover, any operational and non-weather dependenttechniques, like GPS,DORIS, PRARE, can exhibit systematic errors inpositioning and orbitography. Acomparison with SLR results allows to evidence sucherrors and vice versa. Fordoing that, two different approaches for determiningprecise orbits can beconsidered: one based on global orbit determination,the other on a short-arctechnique used to locally improve a global orbitdetermined by another trackingtechniques, such as DORIS or GPS. We can thusvalidate a global orbit andachieve orbit quality control to a level of2 to 3 centimeters at present and expectto achieve a level of 1 to 2 centimeters inthe near future. Errors induced bystation coordinates or by the gravity field(geographically correlated errors, forexample) can be estimated from SLR tracking data.Colocation experiments withdifferent techniques in the same geodetic siteplay also a key role to ensure preciserelationships between the geodetic referenceframes linked to each technique. Inparticular, the role of the SLR technique is tostrengthen the vertical component(including velocity) of the positioning, whichis crucial for altimetry missions.The role of SLR data in the modelling of the firstterms of the gravity field has finally to be emphasized,which is of primary importance in orbitography,whatever the tracking technique used.Another application of SLR technology is thesatellite altimeter calibration. Examples of past calibrationand future experiments are given, including theaccuracy we can expect from the Jason-1 and EnviSatspace oceanography missions.     

激波在磁盔－电流片位场中的传播：（Ⅰ）激波与磁盔间的相互作用

利用新近获得的子午面磁盔－电流片背景太阳风稳态解，对激波从盔底沿电流片方向往外传播时与磁盔间的相互作用进行了数值模拟研究，重要新结果是：１．磁盔的存在使受扰介质速度跃变中央出现下凹，随着激波传出磁盔区并沿电流片方向传播，速度下凹逐渐减弱以致消失；２．激波将磁盔拉长并把盔顶的环形（垂直赤道面）磁场带到行星际空间，成为行星际磁场南向分量的来源之一；３．５个太阳半径（Ｒ⊙）内的磁盔部分将出现精细结构，沿盔外边界形成两条高速带，以及马蹄形密度（亮）环形结构等．这些结果表明，太阳附近高速等离子体与磁盔间存在重要的动力学相互作用过程，对行星际空间的太阳风三维结构有重要影响．     

由飞船观测数据求解激波关系

由Rankine-Hugoniot关系出发,导出一确定激波上、下游激波角θ_1和θ_2的方程组,该方程组系数完全由飞船观测数据确定,且不必借助磁场矢量方位角的测量.利用这一方法计算了1977-1980年由VOYAGER Ⅰ观测到的行星际快激波的激波角,并与由磁场共面性确定的激波角进行了比较.结果表明,在满足激波间断关系的前提下,用本文方法确定的上、下游激波角比用磁场共面性方法确定的激波角更为精确.     

太阳系质心参考系与地心参考系中的激光测距问题

给出了太阳系质心参考系（BRS）和地心参考系（GRS）中的相对论激光测距理论模型,并且利用现有的坐标变换关系证明两种模型在毫米级的精度上是完全等价的。最后指出,由IERS推荐的坐标变换公式与激光测距模型之间存在不自洽性,这种不自恰性对激光测月（LLR）的影响可达约10cm。     

1972年8月事件期间四个耀斑引起的日球层扰动的模拟研究

1972年8月发生的太阳耀斑事件是第20太阳周期内最重大的事件,我们在改进Hakamada-Akasofu方法（以下简称HA方法）的基础上,对事件期间四个较大的耀斑所引起的行星际扰动进行了计算机模拟研究,并取得了令人满意的结果。这些模拟包括赤道平面上一系列二维的激波形状、激波传播以及空间飞船先驱者9号、先驱者10号（以下简称P9、P10）和地球位置上的粒子速度-时间曲线。最后,本文还将该模拟结果与Dryer等人所做的同一事件的一维MHD模拟结果做了比较,并对模拟结果和HA方法本身做了一些讨论。     

近地大气物理现象与光电测距精度的关系

本文根据大气温度层结状态,讨论两种光电测距最佳观测时刻的理论。指出,在不稳定湍流状态下,更有利于获得高精度的观测值。     

利用SLR检核CHAMP卫星轨道

初步研究了利用SLR检核CHAMP卫星轨道的方法。采用2002年1月1日到16日的SLR观测数据对GFZ提供的事后科学轨道进行了检核实验，实验结果表明，GFZ事后科学轨道没有明显的系统偏差，其精度优于10cm。     

Magnetic clouds and interplanetary particle transport: a numerical model

Magnetic clouds modify the structure of the interplanetary magnetic field on spatial scales of tenth of AU. Their influence on the transport of energetic charged particles is studied with a numerical model that treats the magnetic cloud as an outward propagating modification of the focusing length. As a rule of thumb, the influence of the magnetic cloud on particle intensity and anisotropy profiles increases with decreasing particle mean free path and decreasing particle speed. Three cases are considered: (1) when the magnetic cloud is the driver of a shock that accelerates particles as it propagates outward, (2) when the magnetic cloud interacts with a prior solar energetic particle event, and (3) when a magnetic cloud already is present in interplanetary space at the time of a solar energetic particle event. In the latter case the cloud acts as a barrier, storing the bulk of the particles in its downstream medium.     

运用三维运动学模型对行星际磁场南北分量的预测

提出一种可能产生行星际磁场南北分量扰动的物理机制,并将此物理机制运用于三维运动学模型,对原模型作了改进. 使用改进后的模型模拟研究了1997年5月12日06:30UT爆发的晕状(halo)日冕物质抛射(CME)事件对行星际磁场和等离子体的扰动,以及1978-1981年间17个与CME有关的行星际扰动事件. 在17个事件中有14个事件可准确预测出行星际磁场南北分量的方向,准确率为82%. 结果表明,模型计算出的行星际磁场南北分量的扰动方向与观测的方向是基本一致的.