Swarm – An Earth Observation Mission investigating Geospace

The Swarm mission was selected as the 5th mission in ESA’s Earth Explorer Programme in 2004. This mission aims at measuring the Earth’s magnetic field with unprecedented accuracy. This will be done by a constellation of three satellites, where two will fly at lower altitude, measuring the gradient of the magnetic field, and one satellite will fly at higher altitude. The measured magnetic field is the sum of many contributions including both magnetic fields and currents in the Earth’s interior and electrical currents in Geospace. In order to separate all these sources electric field and plasma measurements will also be made to complement the primary magnetic field measurements. Together these will allow the deduction of information on a series of solid earth processes responsible for the creation of the fields measured. The completeness of the measurements on each satellite and the constellation aspect, however, implies simultaneous observations of a unique set of important electrodynamical parameters crucial for the understanding of the physical processes in Geospace, which are an important part of the objectives of the International Living With a Star Programme, ILWS. In this paper an overview of the Swarm science objectives, the mission concept, the scientific instrumentation, and the expected contribution to the ILWS programme will be summarized.     

Analysis on coverage ability of BeiDou navigation satellite system for manned spacecraft

To investigate the service ability of the BeiDou Navigation Satellite System (BDS) for manned spacecraft, both the current regional and the future-planned global constellations of BDS are introduced and simulated. The orbital parameters of the International Space Station and China׳s Tiangong-1 spacelab are used to create the simulation scenario and evaluate the performance of the BDS constellations. The number of visible satellites and the position dilution (PDOP) of precision at the spacecraft-based receiver are evaluated. Simulation and analysis show quantitative results on the coverage ability and time percentages of both the current BDS regional and future global constellations for manned-space orbits which can be a guideline to the applications and mission design of BDS receivers on manned spacecraft.     

运载火箭发射场无人值守加注发射技术研究

针对我国火箭在发射场射前操作项目多、保障人员多的问题，分析了国内外火箭发射场无人值守加注发射的现状。结合火箭射前状态，从火箭系统、地面测发控系统和发射场系统等方面提出了无人值守加注发射总体方案，通过火箭状态远程监测及故障处理技术、连接器零秒脱落技术、箭地接口组合连接技术、连接器自动对接技术和火工品自动短路保护与解保技术等关键技术研究，可提高人员和产品的安全性，为后续我国火箭实现无人值守加注发射提供参考。     

Satellite range scheduling with the priority constraint: An improved genetic algorithm using a station ID encoding method

Satellite range scheduling with the priority constraint is one of the most important problems in the field of satellite operation.This paper proposes a station coding based genetic algorithm to solve this problem,which adopts a new chromosome encoding method that arranges tasks according to the ground station ID.The new encoding method contributes to reducing the complexity in conflict checking and resolving,and helps to improve the ability to find optimal resolutions.Three different selection operators are designed to match the new encoding strategy,namely random selection,greedy selection,and roulette selection.To demonstrate the benefits of the improved genetic algorithm,a basic genetic algorithm is designed in which two cross operators are presented,a single-point crossover and a multi-point crossover.For the purpose of algorithm test and analysis,a problem-generating program is designed,which can simulate problems by modeling features encountered in real-world problems.Based on the problem generator,computational results and analysis are made and illustrated for the scheduling of multiple ground stations.     

Validation of GOME (ERS-2) NO2 vertical column data with ground-based measurements at Issyk-Kul (Kyrgyzstan)

Here we present the results of comparison between operational NO₂ vertical column data by Global Ozone Monitoring Experiment (GOME) onboard ERS-2 satellite and ground-based measurements at Issyk-Kul station in Kyrgyzstan, northern Tien Shan. The data of GOME, taken for the period of 1996–2002, was found to be reasonably close to the results of ground-based sunrise measurements. The latter were adjusted to the time of GOME overpass nearby noon, providing direct comparison between satellite and ground-based data. According to the results, there is 0.6 × 10¹⁵ mol/cm² (18%) overestimation of NO₂ vertical column by GOME, compared to our ground-based data.     

Boundary layer aerosol retrieval from thermal infrared nadir sounding – Preliminary results

A non-empirical algorithm is presented to retrieve the optical depth in the 750–1250 cm⁻¹ spectral range, of aerosol located in the boundary layer over the ocean, from nadir high-resolution radiance spectra in the thermal infrared. The algorithm is based on a line-by-line radiative transfer forward model and used the Optimal Estimation Method for the retrieval. Its performance strongly depends on the quality of the a priori temperature and H₂O atmospheric profiles. To demonstrate the relevance of the algorithm, distributions of maritime aerosol parameters have been retrieved from IMG/ADEOS data for December 1996, using the algorithm with the LBLRTM radiative transfer code, and ERA40 (ECMWF) a priori atmospheric profiles and surface conditions.     

卫星转发器载波互调噪声比的工程计算

阐述了卫星转发器在多载波工作时载波互调噪声比的工程计算方法，并给出了一个实际的计算例子。     

滤波器的相频特性对像质影响的仿真

利用计算机仿真的方法,研究了椭圆低通滤波器和Butterworth滤波器的相频特性对像质的影响。这种影响主要有边缘退化、分辨率损失、产生新的干扰条纹和几何畸变以及多波段图像配准精度降低等。     

椭圆轨道卫星编队燃料最优机动实时算法

文章针对椭圆轨道编队卫星最优燃料机动的实时计算问题进行研究。利用LGL伪谱法对问题进行快速求解。由于最优燃料控制为非连续控制,如直接采用伪谱法则只有当离散点数目很大时,才能实现较高精度的编队机动控制,而这会影响算法的实时计算效率。为了克服这方面的不足,文章提出了一种时间尺度变换策略,并结合模型预测的滚动优化方法,设计了一种编队实时机动控制算法。该算法在兼顾解的全局最优性的同时改善了解的局部精确性,最后通过数值仿真验证了所设计算法的有效性。     

Radiance calibration of CRISTA-NF

The CRISTA-NF instrument is the airborne version of the CRISTA satellite infrared limb sounder. It has been successfully flown on the Geophysica research airplane during a test campaign in July 2005, during the SCOUT-O3 Tropical Aircraft Campaign in November/December 2005 and during the AMMA campaign in August 2006. Radiance calibrations of the airborne instrument are more complex compared to the satellite instrument because the vacuum shell of CRISTA-NF is confined by a ZnSe (zinc–selenide) window and the detectors can thermally drift during measurement flights. By comprehensive radiance calibrations with a blackbody source the window’s emissivity and transmissivity are determined and the dependence of the instrument sensitivity on the detector temperature is characterized. Taking these effects into account, the remaining radiance error of the calibration is smaller than 3%.