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.     

F2 layer characteristics and electrojet strength over an equatorial station

The data presented in this work describes the diurnal and seasonal variation in hmF2, NmF2, and the electrojet current strength over an African equatorial station during a period of low solar activity. The F2 region horizontal magnetic element H revealed that the Solar quiet Sq(H) daily variation rises from early morning period to maximum around local noon and falls to lower values towards evening. The F2 ionospheric current responsible for the magnetic field variations is inferred to build up at the early morning hours, attaining maximum strength around 1200 LT. The Sq variation across the entire months was higher during the daytime than nighttime. This is ascribed to the variability of the ionospheric parameters like conductivity and winds structure in this region. Seasonal daytime electrojet (EEJ) current strength for June solstice, March and September equinoxes, respectively had peak values ranging within 27–35 nT (at 1400 LT) , 30–40 nT (at 1200 LT) and 35–45 nT (at 1500 LT). The different peak periods of the EEJ strength were attributed to the combined effects of the peak electron density and electric field. Lastly, the EEJ strength was observed to be higher during the equinoxes than the solstice period.     

Electron acoustic solitary waves in the Earth’s magnetotail region

Satellite observations have revealed solitary potential structures in the Earth’s magnetotail region. These structures have both positive (compressive) and negative (rarefactive) electrostatic potentials. In this paper we study the electron-acoustic solitary waves (EASWs) in an unmagnetized plasma consisting of cold plasma electrons and isothermal ions with two different temperatures. Using the reductive perturbation method, the nonlinear evolution of such structures is studied. The numerical computations are performed to study the role of two temperature ions in the generation of EASWs. In this case, the model supports the existence of both positive and negative electrostatic potentials with bipolar pulses. The electric field associated with these positive and negative solitary structures are numerically computed. The present study could be useful to construe the compressive and rarefactive electric field bipolar pulses associated with the BEN type emissions in the magnetospheric regions where the electron beams are not present.     

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。     

热电偶温度与电势互换公式

本文对铜—铜镍(康铜)(T)、镍铬—铜镍(康铜)(E)、铁—铜镍(康铜)(T)和铂铑13—铂(R)四种热电偶,根据温度 T→电势 E 的分度公式,采用多项式回归的方法,得出了电势 E→温度 T 的拟合公式,与分度公式比较,最大偏差在0.04℃以下,0℃以上的回归公式最大偏差小于0.02℃。     

电动轮廓仪相位校正滤波的一种新方法

介绍了电动轮廓仪中数字滤波的一种最新方法，其最大特点是：在轮廓信号传输过程中引起相移以及由相移导致的不对称畸变，使得计算被测信号的所有表面粗糙度参数和波度参数为可能；提出了用ＦＦＴ实现数字滤波中的卷积计算，给出了改进的快变计算公式及用汇编语言编程的具体方法。     

火工品控制电流和潜电流的自动化测试

火工品供电线路一直是火箭可靠性与安全性设计的重点，在控制系统的综合试验中都要对供电电流作专项测试。本文提出了一种替代传统手工测试的自动化测量方案，从软硬件的设计、试验的情况、效率、通用性以及扩展性等几个方面进行了探讨。     

一种用于分析旋转对称天线的扩展矩量法

为提高旋转对称天线的计算精度,在等效矩量法(MOM)的基础上,对旋转对称天线表面电流作离散处理,根据伽列金法给出了天线表面的电场积分方程(EFIE),用朱兰成公式求得天线远场。对某旋转对称天线不同频率处的方向图计算结果表明,与等效MOM相比,该法的精度更高。     

用于微小卫星推进装置的脉冲等离子体推力器

论述了脉冲等离子体推力器(PPT)的工作原理和研究状况。在分析其主要优缺点的基础上，讨论了PPT技术的发展方向，并就PPT的应用前景作了展望。分析认为PPT是一种先进的小推力动力装置，特别适合于微小卫星的轨道转移、姿态控制、位置保持以及星座编队飞行。     

导弹天线罩自动测试系统的设计与实现

为了对导弹天线罩电性能参数进行准确测量，利用虚拟仪器技术，采用LabView软件平台，通过多线程技术，实现一套基于测量仪器和转台协调工作的天线罩自动测试系统的设计。该设计充分挖掘了矢量网络分析仪器内在功能，可同时测量并导出四个通道的八组数据，可同时完成比幅、比相等功能，极大提高了对天线阵列等测试对象的测量效率、测试精度；可以实时显示测量数据的二维图或三维图，有利于实时掌握测试情况。本系统很好地满足了实验需要，它的实现为微波自动测试系统的设计提供了很好的借鉴。