Calibration for CHAMP Accelerometer Data Based on Crossover Points of the Satellite

The German CHAlleging Minisatellite Payload （CHAMP） was launched in July 2000. It is the first satellite that provides us with position and accelerometer measurements, with which the gravity field model can be determined. One of the most popular methods for geopotential recovery using the position and accelerometer measurements of CHAMP is the energy conservation method, The main aim of this paper is to determine the scale and bias parameters of CHAMP accelerometer data using the energy conservation method. The basic principle and mathematical model using the crossover points of CHAMP orbit to calibrate the accelerometer data are given based on the energy balance method. The rigorous integral formula as well as its discrete form of the observational equation is presented, This method can be used to estimate only one of the scale and bias parameters or both of them. In order to control the influence of outliers, the robust estimator for the calibration parameters is given. The results of the numerical computations and comparisons using the CHAMP accelerometer data show the validity of the method.     

FY-3微波成像仪遥感图像地理定位方法研究

MWRI (MicroWave Radiation Imager) is one of the payloads on our next generation polar meteorological satellite FY-3. MWRI conically scans with a fixed incident angle on the earth surface. It is the first time for Chinese remote sensor to use this scan mode. In this work, we present a geolocation method for FY-3 MWRI’s remote sensing image based on its special scan geometry. The integrated coordinate systems and the specific relationships with these coordinate systems are defined. A spatial relationship model between the remote sensing data and the earth-based coordinate system is established. This method also includes an algorithm of satellite orbit computation, which is used to get the satellite’s instantaneous velocity vector from its position. This method has been applied to MWRI’s remote sensing image geolocation. The results show that the accuracy of this method can achieve 1 pixel. The 33 GCPs (Ground Control Points) which are in the regiones of FY-3 MWRI’s observation have been collected and used to analyze the precision of the geolocation. By statistical analysis, the error along-track is about 1.5km, and the error along-scan is about 3.0km. It is obvious that this method fulfills the requirement of precision for FY-3 MWRI whose space resolution exceeds 5km.     

Analyses and Solutions of Errors on GPS／GLONASS Positioning

This paper focuses mainly on the major errors and their reduction approaches pertaining to combined GPS/GLONASS positioning.To determine thd difference in the time reference systems,different receiver clock offsets are introduced with respect to GPS and GLONASS system time.A more desirable method for introducing a independent unknown parameter of fifth receiver,which can be canceled out when forming difference measurements,is discussed.The error of orbit integration and the error of transformation parameters are addressed in detail.Results of numerical integration are give.To deal with the influence of ionospheric delay,a method for forming dual-frequency ionospheric free carrier phase measurements is detailed.     

A spatially weighted degree model for network vulnerability analysis

Using degree distribution to assess network vulnerability represents a promising direction of network analysis.However,the traditional degree distribution model is inadequate for analyzing the vulnerability of spatial networks because it does not take into consideration the geographical aspects of spatial networks.This paper proposes a spatially weighted degree model in which both the functional class and the length of network links are considered to be important factors for determining the node degrees of spatial networks.A weight coefficient is used in this new model to account for the contribution of each factor to the node degree.The proposed model is compared with the traditional degree model and an accessibility-based vulnerability model in the vulnerabil-ity analysis of a highway network.Experiment results indicate that,although node degrees of spatial networks derived from the tra-ditional degree model follow a random distribution,node degrees determined by the spatially weighted model exhibit a scale-free distribution,which is a common characteristic of robust networks.Compared to the accessibility-based model,the proposed model has similar performance in identifying critical nodes but with higher computational efficiency and better ability to reveal the overall vulnerability of a spatial network.     

Object Extraction Based on Evolutionary Morphological Processing

This paper introduces a novel technique for object detection using genetic algorithms and morphological processing. The method employs a kind of object oriented structure element, which is derived by genetic algorithms. The population of morphological filters is iteratively evaluated according to a statistical performance index corresponding to object extraction ability, and evolves into an optimal structuring element using the evolution principles of genetic search. Experimental results of road extraction from high resolution satellite images are presented to illustrate the merit and feasibility of the proposed method.     

Doppler properties of spaceborne/airborne hybrid bistatic synthetic aperture radar

In this paper,a special geometry case of spaceborne-airborne bistatic SAR(SA-BiSAR) is considered,in which satellite and aircraft flight paths are parallel and their antennas are steering at the strip map.This case is a simple but typical application example,which is applicable for non-cooperative illumination.The integration time of SA-BiSAR system is derived via the motion of transmitter and receiver footprint.In parallel and stripmap mode,Doppler frequency is obtained through the combination be-tween spaceborne and airborne SAR.Other Doppler properties have been envisaged,including Doppler bandwidth and azimuth resolution.The overall simulation experiments are conducted and some characteristics are exhibited.The critical parameters,which have the significant effect on the SA-BiSAR Doppler properties,are extracted by analytical expressions and numerical simulations.In parallel and strip map mode and with reference to ENVISAT-1,SA-BiSAR system possesses the potential of yielding 10 m azi-muth resolution and 0.5 s integration time for C-band via the analysis of simulation results.     

一种新型遥感影像快速匹配算法

An iterative algorithm to calculate mutual correlation using hierarchical key points and the search space mark principle is proposed. An effective algorithm is designed to improve the matching speed. By hierarchical key point algorithm and mutual correlation coefficients of the matching images, the important points can be iteratively calculated in the images hierarchically, and the correlation coefficient can be obtained with satisfactory precision. Massive spots in the parameter space which are impossible to match can be removed by the search space mark principle. Two approximate continuities in the correlation image matching process, the image gray level distribution continuity and the correlation coefficient value in the parameter space continuity, are considered in the method. The experiments show that the new algorithm can greatly enhance matching speed and achieve accurate matching results.     

Integration of neural networks and cellular automata for urban planning

This paper presents a new type of cellular automata (CA) model for the simulation of alternative land development using neural networks for urban planning. CA models can be regarded as a planning tool because they can generate alternative urban growth. Alternative development patterns can be formed by using different sets of parameter values in CA simulation. A critical issue is how to define parameter values for realistic and idealized simulation. This paper demonstrates that neural networks can simplify CA models but generate more plausible results. The simulation is based on a simple three-layer network with an output neuron to generate conversion probability. No transition rules are required for the simulation. Parameter values are automatically obtained from the training of network by using satellite remote sensing data. Original training data can be assessed and modified according to planning objectives. Alternative urban patterns can be easily formulated by using the modified training data sets rather than changing the model.     

Estimation of Geodetic Parameters with VLBI Data of Last 5 Years

The meaning to research the potential of VLBI for geodetic applications is summarized. And the observation models and their related parameters of geodetic interest are investigated. Then, the principle and method of using the random model in VLBI data processing are investigated. With the world wide VLBI data from 2000-2004, the conditions to compute the parameters of geodetic interest are introduced, and so are the computing methods and processes. And the computed results of the parameters of geodetic interest are analyzed.     

VLBI在探月卫星定位中的应用分析

中国实施的"嫦娥"探月工程中,探月卫星的定轨测控系统由我国现有的S频段航天测控网(USB)和甚长基线干涉测量(VLBI)系统组成。系统中,VLBI技术主要为绕月卫星定轨提供卫星的角位置。本文分析了在探月项目中,VLBI单点定位的必要性。探讨了VLBI技术用于探月卫星单点定位的基本原理及其实现方法。通过算例对模拟数据进行处理,检验了方法的正确性。对结果进行分析,得出一些结论。     

USB-VLBI综合确定SMART-1环月探测器轨道

我国绕月探测工程中"嫦娥一号"(CE-1)卫星将综合使用统一S波段系统(USB)和甚长基线干涉仪(VLBI)完成测定轨任务。为了检验USB-VLBI综合测定轨精度,测控系统于2006年5月利用欧空局(ESA)的SMART-1环月探测器进行了USB-VLBI综合测定轨试验。本文对这次试验的测轨数据进行了分析,研究了不同观测弧长和不同类型观测数据组合情况下的定轨和预报精度,得出了一些结论。     

我国发射射电卫星的作用及关键技术研究

论述了我国发射射电卫星对于天文学和射电天文方法的发展、我国月球及深空探测计划、大地测量和天文地球动力学的研究和发展等方面的意义;根据VLBI卫星的技术和应用特点,分析了射电望远镜及相关设施的技术要求和指标,比较全面地分析和总结了VLBI卫星及相关设施的关键技术和方法。     

GPS卫星精密星历的实时确定

建立了一种GPS卫星实时轨道确定的新算法。该算法用法方程叠加方法更新卫星轨道参数,然后根据卫星轨道与卫星轨道参数之间的数值微分关系计算新的卫星轨道,并详细分析了用中国GPS跟踪网数据实时定轨的结果。     

星地跟踪网的导航卫星精密轨道确定及预报

针对区域跟踪网不能覆盖导航卫星全弧段从而导致卫星定轨精度低的问题,简述了导航卫星和低轨卫星联合定轨模型,然后利用星地跟踪网观测数据同时确定了低轨卫星和导航卫星精密轨道,并根据实验结果详细分析了低轨卫星在联合定轨中所起到的作用。计算结果表明,引入低轨卫星之后,全球网和区域网定轨精度分别平均提高了20.0%和44.3%,区域网6h和24h的轨道预报精度分别优于10cm、13cm,利用星地跟踪网观测数据联合定轨方案是一种提高定轨精度并削弱对地面站依赖性的有效方法。     

USB-VLBI综合快速确定环月飞行器短弧轨道

2006-05-29~2006-06-02,有关单位利用欧空局(ESA)的SMART-1环月飞行器进行了USB-VLBI综合测定轨试验,其中一个重要目标就是考察环月飞行器的短弧快速轨道确定能力。这里对综合测轨数据的精度进行了评估,分析了不同类型测轨数据组合和定轨弧长对短弧定轨和预报的影响。利用5 d测量数据进行统计:VLBI时延的RMS约为1 m,时延率的RMS约为0.25 cm/s,USB测速的RMS约为3~6 cm/s,测距的RMS约为1~3 m。30 min定轨及预报一个环月轨道周期(5 h)位置的RMS约为250 m,速度的RMS约为15 cm/s。     

VLBI在GEO卫星精密定轨中的应用

影响GEO轨道确定精度的原因主要有两方面:一是高轨卫星的几何跟踪条件受到局部测轨网的限制;二是卫星相对于地面的动力学约束信息较弱。利用一个针对GEO卫星的简化动力法定轨的协方差分析模型,研究了联合测距跟踪网和甚长基线干涉测量(VLBI)对定轨精度的改善情况。指出测距系统的校正误差是常规测距跟踪网定轨精度的主要误差源;当附加一条东西向VLBI基线时,仅利用不定期的少量VLBI高精度数据就能够显著改善测距偏差对轨道的影响,从而保证了卫星的整体位置解算精度。     

Orbit determination of the SELENE satellites using multi-satellite data types and evaluation of SELENE gravity field models

The SELENE mission, consisting of three separate satellites that use different terrestrial-based tracking systems, presents a unique opportunity to evaluate the contribution of these tracking systems to orbit determination precision. The tracking data consist of four-way Doppler between the main orbiter and one of the two sub-satellites while the former is over the far side, and of same-beam differential VLBI tracking between the two sub-satellites. Laser altimeter data are also used for orbit determination. The contribution to orbit precision of these different data types is investigated through orbit overlap analysis. It is shown that using four-way and VLBI data improves orbit consistency for all satellites involved by reducing peak values in orbit overlap differences that exist when only standard two-way Doppler and range data are used. Including laser altimeter data improves the orbit precision of the SELENE main satellite further, resulting in very smooth total orbit errors at an average level of 18 m. The multi-satellite data have also resulted in improved lunar gravity field models, which are assessed through orbit overlap analysis using Lunar Prospector tracking data. Improvements over a pre-SELENE model are shown to be mostly in the along-track and cross-track directions. Orbit overlap differences are at a level between 13 and 21 m with the SELENE models, depending on whether 1-day data overlaps or 1-day predictions are used.     

月球探测器捕获分析及评估

国外深空探测活动的实践表明:深空探测器在整个飞行过程中要进行多次轨道控制才能实现其使命轨道。以我国嫦娥一号(Chang’e-1)探月卫星轨道为例,对探月卫星进行月球制动捕获所需脉冲速度增量ΔV进行了分析,通过仿真计算指出ΔV最小达到约200 m/s,即可保证制动后卫星飞行轨道的远月点在地月系统作用范围内。针对捕获制动过程,参考国外经验并结合我国现有测定轨设备及方法的实际条件,分析了通过监视多普勒测速和VLBI时延率残差变化的趋势进行轨道控制效果评估方法的可行性。     

多星定轨条件下北斗卫星钟差的周期性变化

基于地面监测网的多星精密定轨可以同时解算出北斗卫星轨道和卫星钟差。由于轨道和钟差的耦合影响,卫星钟差时序难免会出现周期性波动。此外,受限于目前并不完善的北斗全球监测网络分布、系统导航文件缺失以及定轨后处理软件的设置问题,3类卫星的钟差均存在大量数据间断问题。本文利用适用于间断数据的谱分析方法,对多星定轨条件下的北斗卫星钟差数据进行了周期项提取,并利用周期项改进后的钟差预报模型评估了24h以内的预报精度。基于近一年的数据分析表明,北斗GEO卫星钟差3个主周期依次为12、24和8h,IGSO卫星钟差的3个主周期依次为24、12和8h,而MEO卫星钟差的3个主周期依次为12.91、6.44和24h。与改进前相比,周期项改进后的钟差预报模型将北斗卫星钟差在24h以内的预报精度提高了20%~40%。