用CHAMP加速仪数据校验太阳活动峰年的大气模型精度

介绍CHAMP星载加速仪数据的处理方法.通过对实测数据的分析证实仪器的x轴存在故障.为了研究太阳活动峰年大气模型的精度,处理了2001至2002年的加速仪数据,利用切向非引力加速度反算大气密度.然后从统计的角度分析DTM94和MSIS90大气模型的误差,得到一些定量的结论,太阳活动峰年DTM94的误差为30%-35%,MSIS90的误差为25%-30%,MSIS90比DTM94误差小,模型间最大差异约10%.     

加速仪数据在CHAMP卫星精密定轨中的贡献

通过用几个实例计算，评估了CHAMP卫星加速仪数据对SLR数据定轨精度的贡献．结果显示用加速仪数据代替非保守力对CHAMP卫星进行精密定轨时，其SLR的残差从原来的16．5cm减少到2．7cm，与精密轨道相比，卫星位置误差由18．9cm减少到6．2cm(一天资料)．     

星载测高仪交叉点数据定轨研究

从海洋测高卫星的发展状况入手,介绍了用测高仪数据进行定轨的意义.然后,分析了测高仪数据的误差修正模型及交叉点数据计算方法,详细介绍了JASON-1测高数据文件中所涉及的误差修正量和采用的模型.最后,通过仿真数据和实测数据的计算,分析了单用测高仪数据和交叉点数据进行轨道确定所能达到的精度,为未来的实际应用提供了有价值的参考.     

CHAMP加速仪资料的快速校标研究

对星载加速仪进行校标是有效利用星载加速仪测量数据的基础,目前校标方法都是建立在星载GPS资料处理的基础上,对处理软件和计算设备的要求都非常高.为了满足高层大气阻力研究的需要,提出了一种快速高效的校标方法,即利用GFZ公布的CHAMP卫星快速轨道作为观测资料,采用有尺度因子和线性偏差的加速仪测量值代替非引力模型摄动加速度...     

星载GPS精密测轨研究及应用

星载ＧＰＳ定轨系统由于其全天侯、价格低、不受卫星高度的影响可达到米级、分米级乃至厘米级的测轨精度等特点已成为低轨道卫星精密定轨的要求,概述了星载ＧＰＳ系统的组成和定轨原理,给出了星载ＧＰＳ测轨的几种主要方法和数学模型,同时根据ＴＯＰＥＸ卫星星载ＧＰＳ实测数据分析了各种定轨方法的测轨精度以及影响定轨精度的各种因素。     

分布逼近的卡尔曼滤波及其在星载GPS卫星定轨中的应用

探讨了利用推广卡尔曼滤波估计非线性系统状态时存在的问题，进而简要介绍了目前自动控制领域广泛使用的分布逼近的卡尔曼滤波UKF(Unscented Kalman Filter)，考虑到卫星定轨中系统的动态方程和量测方程存在严重非线性的情形，提出了将UKF用于星载GPS卫星定轨．实例计算结果表明，UKF的性能要优于推广卡尔曼滤波．     

LP估计在星载GPS运动学定轨中的应用及精度分析

为得到高精度的星载GPS运动学定轨,必须利用观测精度高的相位观测值,但是相位观测值预处理后,仍然存在残余小周跳．在残差服从正态分布情况下LS法是最佳参数解算方法,但该方法不能解决资料的系统误差消除问题,LP估计是处理资料残差分布含有系统误差的有效方法之一．基于LS、LP方法的有效条件和GPS数据预处理的特性,将LP估计方法引入星载GPS运动学定轨数据处理中,以CHAMP卫星资料为例,研究了LP估计在星载GPS运动学定轨中的应用及其精度分析．实践表明:在处理含有残余小周跳的相位观测值时,LP估计比LS更有效,提高了星载GPS运动学定轨精度,但随着残余周跳的进一步修复,LP估计相对于LS估计的优越性越来越弱,在资料完全没有系统误差,残差服从正态分布的情况下,LP估计不能很好地体现其优越性,精度反而低于LS估计．     

卡尔曼滤波在VLBI数据处理中的应用

本文探讨卡尔曼滤波技术用于VLBI天体测量和大地测量数据处理的原理和方法;并深入地对Herring等提出的软件系统（SOLVK）进行详细研究,提出一些具体的办法以便应用．然后用1993—1994年的VLBI观测资料,精确计算了几种天文学和地球动力学参数作为例证．     

中点检测技术及在BPM定时仪中的应用

由于采用了中点检测技术,才使BPM定时仪的精度得到保证,本文介绍了它的基本原理。     

抗差估计在星载GPS卫星非差运动学定轨中的应用

针对星载GPS卫星非差运动学定轨的特点,提出将抗差估计应用于星载GPS卫星运动学定轨,一方面尽量保留来自每颗GPS卫星的观测值,保持较强的卫星几何强度,避免轨道求解出现奇异;另一方面,采用等价权思想,有效地降低质量较差的观测值对定轨结果的影响,保证定轨精度．还采用CHAMP卫星的实测GPS数据验证了新方案的可行性和有效性．     

Stochastic Models of Hot Planetary and Satellite Coronas: Suprathermal Nitrogen in Titan's Upper Atmosphere

The processes of dissociation and dissociative ionization of molecular nitrogen by solar UV radiation and by the accompanying flux of photoelectrons, as well as sputtering of the atmosphere by fluxes of magnetospheric ions and pick-up ions, are the main sources of translationally excited (hot, or suprathermal) nitrogen atoms and molecules in Titan's upper atmosphere. Since Titan does not possess an intrinsic magnetic field, ions from Saturn's magnetosphere can penetrate into the outer layers of Titan's atmosphere and sputter atoms and molecules from the atmosphere in momentum-transfer and charge exchange collisions. Atmospheric sputtering by corotating nitrogen ions and carbon-containing pick-up ions, as well as photodissociation-related losses, was considered previously by Lammer and Bauer (1993) and Shematovich et al. (2001, 2003). In this paper we investigate the processes of the formation and evolution of the fraction of suprathermal nitrogen atoms and molecules in the transition region of Titan's upper atmosphere using the previously developed Monte Carlo model for hot satellite and planetary coronas (Shematovich, 1999, 2004). It is established that the suprathermal nitrogen fraction in the transition region of Titan's upper atmosphere includes nitrogen atoms and molecules but the suprathermal nitrogen concentration is relatively small owing to high rates of escape from the atmosphere and to the efficient thermalization of suprathermal nitrogen at the altitudes of the relatively dense lower thermosphere. However, the scale height for suprathermal nitrogen in the transition region is much higher than that for the ambient atmospheric gas. Therefore, suprathermal nitrogen becomes one of the dominant components in the outer exosphere.     

Application of Accelerometer Data in Precise Orbit Determination of GRACE -A and -B

We investigate how well the GRACE satellite orbits can be determined using the onboard GPS data combined with the accelerometer data.The preprocessing of the accelerometer data and the methods and models used in the orbit determination are presented.In order to assess the orbit accuracy,a number of tests are made,including external orbit comparison,and through Satellite Laser Ranging (SLR) residuals and K-band ranging (KBR) residuals.It is shown that the standard deviations of the position differences between the so-called precise science orbits (PSO) produced by GFZ,and the single-difference (SD) and zero-difference (ZD) dynamic orbits are about 7 cm and 6 cm,respectively.The independent SLR validation indicates that the overall root-mean-squared (RMS) errors of the SD solution for days 309-329 of 2002 are about 4.93cm and 5.22cm,for GRACE-A and B respectively; theoverall RMS errors of the ZD solution are about 4.25 cm and 4.71 cm,respectively.The relative accuracy between the two GRACE satellites is validated by the KBR data to be on a level of 1.29 cm for the SD,and 1.03 cm for the ZD solution.     

The CH4 Density in the Upper Atmosphere of Titan

Previous modeling by Banaszkiewicz et al. (2000a,b) showed that the CH₄ thermospheric mixing ratio on Titan could vary as much as 35-40% due to ion-neutral chemical reactions. A new vertical methane profile has been computed by simultaneously modifying the stratospheric methane mixing ratio and the K(z) previously considered by Lara et al. (1996) and Banaszkiewicz et al. (2000a,b). A satisfactory fit of the methane thermospheric abundance and stratospheric mixing ratio of other minor constituents is achieved by placing the homopause at ∼1000 km and increasing the methane stratospheric mixing ratio (q_CH4) up to 3.8%. The new proposed eddy diffusion coefficient steadily rises from 1×10⁷ cm² s⁻¹ at 700 km to 1×10¹⁰ cm² s⁻¹ at 1500 km, whereas the stratospheric values are in the range (4-20)×10³ cm² s⁻¹. Other likely ionization sources that can influence the methane distribution are (i) a metallic ion layer produced by micrometeoroid infall and (ii) frequent X-rays solar flares. Analysis of the effects of these ionization sources on the methane distribution indicates that, unlike previously assumed, CH₄ can suffer considerable variations. These variations, although proved in this work, must be cautiously regarded since several assumptions have to be made on the rate of N₂ and CH₄ ionization by the processes previously mentioned. Hence, these results are only indicative of methane sensitivity to ionospheric chemistry.     

行星大气定理及其天灾预测应用

在界定行星大气运动范围后,提出行星大气运动三定理。从行星磁场角度研究不完全电离磁流体(incompleteionospheregaseousfluid)得到行星磁力线绝热压缩反弹致冷效应,给出大气运动出现的冷池(coolpool)现象的物理机制。最后从天文学角度讨论和展望大气灾害的可预报性。     

The Accuracy of Atmospheric Models in Solar Maximum Years Checked with the Data of CHAMP Accelerometer

A method of processing the data obtained with the CHAMP satelliteborne accelerometer is introduced. Through an analysis of the data the fault in the x-axis of the instrument is verified. We examined the accuracy of the atmospheric models in solar maximum years with the accelerometer data obtained from 2001 to 2002 and the inversion of the atmospheric density from the tangential non-gravitational acceleration. Then from a statistical analysis of the errors of the models, DTM94 and MSIS90, we obtained the following quantitative conclusions. During the solar maximum years the error of DTM94 is 30% to 35%, and that of MSIS90 is smaller at 25% to 30%. The greatest difference between the two models is about 10%.     

卫星导航技术在PDA上的应用研究

对卫星导航技术在PDA(personal digital assistant,个人数字助理)上的应用作了研究。主要介绍GPS卫星信号的提取、发送及其与PDA之间的数据通信格式。     

The Data Depth-weight-kernel Estimation of the Model Error of Satellite Orbit Determination

It is an objective fact that there exists error in the satellite dynamic model and it will be transferred to satellite orbit determination algorithm, forming a part of the connotative model error. Mixed with the systematic error and random error of the measurements, they form the unitive model error and badly restrict the precision of the orbit determination. We deduce in detail the equations of orbit improvement for a system with dynamic model error, construct the parametric model for the explicit part of the model and nonparametric model for the error that can not be explicitly described. We also construct the partially linear orbit determination model, estimate and fit the model error using a two-stage estimation and a kernel function estimation, and finally make the corresponding compensation in the orbit determination. Beginning from the data depth theory, a data depth weight kernel estimator for model error is proposed for the sake of promoting the steadiness of model error estimation. Simulation experiments of SBSS are performed. The results show clearly that the model error is one of the most important effects that will influence the precision of the orbit determination. The kernel function method can effectively estimate the model error, with the window width as a major restrict parameter. A data depth-weight-kernel estimation, however, can improve largely the robustness of the kernel function and therefore improve the precision of orbit determination.     

开展我国云量分布的卫星资料统计研究的建议

收集连续三年每小时的静止卫星红外云图，用温度阈值法判断有云或晴空，从而统计出我国全国范围中２０×２０ｋｍ２网格上晴天和云量分布概率，以供天文台选址参考。     

卫星光电跟踪资料处理

介绍了云南天文台卫星目视观测组新使用的一种卫星光电资料的平滑处理方法—多直线选优法。文中给出了此方法的基本原理, 计算公式, 计算结果以及实际应用情况。