Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： A new procedure is proposed to generate planar asymmetric coronas with multi-streamer structures, as shown in SOHO/LASCO observations. The initial coronal magnetic field is separated into potential part and non-potential part. We first fit the potential part by using the sum of magnetic multi-poles, whereas the non-potential part is approximated by the magnetic field induced by some properly fitted current densities. Then the total field is numerically modified in terms of Maxwell's equations. Based on the initial magnetic fields obtained in such a way, we can further compute various complex asymmetric corona structures by solving MHD equations. In order to verify this procedure, we compute the 2-D coronal structures prior to the December, 1996 CME and August, 1999 CME events. The numerical result is on the whole in agreement with observations, and hence set proper backgrounds for further studying the propagation of CME in various coronal structures using numerical computations. �Copyright 2001 by the American Geophysical Union.
Peer Review Status:
Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： Forecasting the solar proton event fluence is very important to guarantee the safety of spacecrafts and astronauts.Within various periods less than 1 year,the occurrence probabilities of the solar proton events and their fluences were analyzed for solar active years and solar quiet years, respectively.It is found that the probability distributions of solar proton event fluence basically satisfy the log-normal distributions.Based on this,solar proton event fluence can be forecasted with some given confidence levels for different duration space missions ranging from 1 day to 365 days.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： In this paper,in order to realize the high-resolution spectral measurement of low light,we propose a new spectral measurement method which is based on a digital micro-mirror device (DMD) and a photoelectric multiplier tube (PMT). Firstly, the spectrum of the measured light is imaged on a DMD by the dispersive optics system based on a small-size slit. Secondly, by the rotation of the micro-mirrors of the DMD per column,the spectrum is reflected to a PMT according to the different wavelengths. Lastly, the measurement of the spectrum is achieved through the scanning mode. The contrast experiments of our method and a charge-coupled device (CCD) spectrometer are performed,and the experiments for different low light conditions are also performed. At last,the signal-to-noise ratio (SNR) experiment of the system is conducted. The results show that the spectral resolution is 0.23 nm,the sensitivity of the spectral system is less than 4.6 pW,and the SNR performance is also perfect. Compared with the conventional spectroscopy technique, this spectral measurement method has the merits of low price, easy implementation and stable performance.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： This paper starts from the expression of frequency modulated continuous wave synthetic aperture radar(FMCW SAR)echo signal.Firstly,the characteristic of FMCW SAR echo isanalyzed,and then the accurate signal model and instantaneous spectrum are obtained.Based on these,the equivalent Dechirp signal model is obtained. Secondly,the signal model of FMCW SAR and pulse SAR are compared,and then the influence on the echo owing to the successive motion within a pulse sweep is revealed, based on which,the impact on the image reconstruction is quantitatively analyzed.At last,whether thestop-go-stopapproximation is valid in FMCW SAR is revealed.The simulation results verify the effectiveness and exactness of the above analysi.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： Cube-Sat is the research focus in the field of micro satellite in recent years. In this paper,mission that with a cube-sat in the Sun synchronous orbit ( SSO) is taken as an example,then the orbit evolution of SSO cube-sat is studied considering both the influence of atmosphere drag and that of J_2 coefficient (the Earth' s oblateness perturbations to the second-order zonal coefficient). Orbit altitude , solar activity index and atmosphere models are researched respectively to show their impacts on the evolution of orbit,and numerical simulations are carried out. The work above indicates some conclusions as follows : perturbation force that produced by air drag plays an important role to decide the lifetime of SSO cube-sat , and there is a nonlinear relationship between the orbit altitude and the magnitude of orbital decay which is induced by atmosphere drag. Orbital decay based on high solar activity is obviously different from that based on low solar activity, and the relationship between F10.7 and the magnitude of orbital change is not linear. Considering various air drag models separately, the orbit evolutions are not equal,but their order of magnitude are almost the same. The analysis above is helpful to both the orbital choosing of SSO CubeSat and its orbit control.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： The energetic charged particle in the radiation belts of earth is the main environmental factor which can result in performance degradation and even failure of the material and device on spacecraft, so the accuracy of radiation belts model which is being used during design phase of spacecraft is very important to spacecraft performance of space mission and survivability. In the development of radiation belts model based on our own country's data from exploration of radiation belts, the gridding of discrete data is a fundamental task. The key facts of data from Chinese exploration of radiation belts were introduced, the goal and road-map of modeling were described, the application of interpolation in gridding of modeling of radiation belts in low-earth orbit(LEO) was discussed, and the significant errors were analysed. The result of interpolation indicates that in mainly interpolation methods, inverse distance weighting (IDW), natural neighbor and nearest neighbor are most suitable for engineering calculation, the particle flux which is inverted from data grid produced by IDW has the highest precision, and the result from IDW will be more accurate when IDW uses small exponent of distance.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： Regarding the shutter of space imager as the research background,the advantages and disadvantages of different types of shutters are introduced. The rotary-disc shutter is selected as the research object. Starting from the mode of exposure, the control strategy of shutter is investigated. The reason for selecting PMSM motor is analyzed, and a controller based on Digital Signal Processor (DSP) is designed. Furthermore, the maximum error of exposure time is less than 3.0%, which meets the performance requirements of telescope imager.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract：AURIC是由美国计算物理公司CPI与空军Phillips实验室联合开发的中高层大气紫外-可见光-近红外气辉辐射传输模型, 是目前唯一用来进行中高层大气气辉辐射模拟研究的通用模型. 基于MODTRAN模型的理论, AURIC可以进行80 km高度以上的辐射传输模拟并将辐射波段扩展到远紫外波段(80 nm). 目前, CPI公司只面向全球发布了AURIC v1.2软件封装包, 其只能进行2000年以前的单点计算, 不适用于批量的中高层大气辐射模拟, 更不能用于星上大气成分的批量反演. 本文利用Matlab对AURIC v1.2地磁参数模块、大气电子密度模块、大气温度及各种中性气体成分密度模块进行了替代, 将更新模块与原有的辐射计算模块相结合, 将AURIC v1.2更新为AURIC-2012模型, 其可以批量地进行全球的大气辐射传输模拟, 可以与星载测量数据相结合进行中高层大气成分的批量反演, 如O/N_2、电子密度等, 同时也为模型辐射计算模块的进一步改进和辐射机制的参数更新奠定基础. 基于AURIC-2012模型, 进行了气辉临边柱辐射强度模拟和体辐射率计算, 并将结果分别与GUVI柱辐射强度和TIDI体辐射率实测值进行了比较, 得到两者峰值的模拟平均相对误差都小于20%. 最后,利用AURIC-2012对气辉临边柱辐射强度随纬度和高度的分布进行了二维模拟, 并基于模拟对昼、夜气辉辐射强度分布特性及影响因素进行了分析.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： Schmidt and Angel lobster-eye X-ray imaging system can realize total reflection focusing and imaging by simulating lobster-eye microchannel structure. Compared with traditional way of X-ray imaging, it is provided with large field of detection view, high resolution and energy acquisition ability. This paper studies on two lobster-eye basic structures. Based on the principle of grazing incidence, we analyzed Angel and Schmidt structure of light entering focal plane and space resolution. We use tracepro simulation software to model and verify the several focusing and imaging property parameters of these two lobster-eye structures, such as receiving/transmitting light, maximum/cross arm, maximum/background, cross arm/background. The theoretical analysis and simulation results show, when the focal length is longer and channel length-width ratio is about 50. Due to multiple reflection, focusing and imaging signal-to-noise ratio of some main parameters of Schmidt is higher than Angel model, and the spatial resolution is lower. When the focal length is shorter and channel length-width ratio is about 10. Due to simple reflection, focusing and imaging signal-to-noise ratio of some main parameters of Schmidt is lower than Angel model, and the spatial resolution is almost the same.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： The capability of the modern payloads on satellite is getting stronger and stronger， and the motor has been used widely. The life and reliability of the motor equipped on satellite would be the main characters that restrict long-time work of the satellites. So the design of motor system on satellites should be not only satisfied with the application requirements， but also the requirements of life and reliability should be fully taken into account simultaneously. In this paper， a two-phase hybrid stepper motor control system based on FPGA is introduced. In order to improve control accuracy and suppress low-frequency vibration， the system was designed based on subdivision control method and an acceleration process was designed to ensure that motor started properly. Large current was used to stop the motor quickly and small current was used to keep the motor motionless. The test results showed that this system has the advantages of low-power consumption， starting and stopping steadily.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： In the measurement of space particle， the interference caused by the particles is an important factor of the measure accuracy decline in the space particle detection， Anti-coincidence cup technology is an important means to eliminate particle interference. The paper introduces the origin of spatial interference particles and theory of anti-coincidence cup measuring system.An output pulse readout circuit based on A225F is designed， achieving in reshaping the quasi-Gaussian waveform at a high counting rate.The details of the application of A225F is described in the paper.The simulation and experimental results prove the reasonableness of the design.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： In order to ensure the success of space exploration mission， the small satellite formation requires reliable inter-satellite communications. Based on 802.11， small satellite formation network protocol architecture was designed. Firstly， network protocol stack was built according the OSI stack layers， the key parameters of physical layer and data link layer of was tuned to meet the requirement of inter-satellite communication， the network layer routing protocol was analysed， and then the satellite network formation model was made and analysed. With the aid of the network simulation tool NS3， performance of four typical formation network was simulated. Simulation results show that the network protocol architecture ensures inter-satellite communications based on 802.11. Although network performance varies greatly in different flyning formations， it can be adjusted according to the task requirements.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： In order to save channel resources， asynchronous digital multiplexer， which can multiplex different rate， different burst time slot digital source， has been widely applied. Aims to reduce the maximum extent possible source packet data transmission delay， improve channel utilization， design scheme of a greedy asynchronous dynamic digital multiplexer is proposed. The priority scheduling strategy of sources is given too. Two kinds of multiplex model are described by hardware description language. Simulations for greedy dynamic multiplexer and virtual channel multiplexer， under the condition of different physical frame length and two source model， have been carried out by Modelsim. The simulation results show that， for the average transmission delay and delay jitter， the greedy dynamic multiplexing is superior to the virtual channel multiplexing， and is more effective in saving resource of source cache.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： CCD is the core component for realizing space soft X-ray exploring mission. According to the requirements for space soft X-ray exploring， the scientific CCD42-10 BI AIMO produced by E2V Company has high sensitivity， low noise and high readout speed， and a driving circuit based on FPGA is designed. This design is developed on the XC3S500E hardware platform， using VHDL language to describe the driving timing. The CCD is driven by EL7202 chips. The simulation and testing results indicate that the CCD performed stably， and the design matches the driving requirements of CCD42-10 BI AIMO.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： For the small satellites formation flying， the distance between satellites must be determined and an adequate inter-satellites communication medium must be used to transmit the science data. In order to minimize device complexity， this paper studied a system capable of simultaneously transmitting high rate telecommunication and ranging. through simulations by Simulink in different ranging modulation index， obtained the bit error rate of telecommunication data. By analyzing the characteristics of GMSK+PN signal， an effective demodulation scheme for GMSK+PN is developed by this paper.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： This paper introduces the structure and working principle of the Neutral Atom Imaging System-High （NAIS-H） which is in the MIT project. Based on the testing needs of the instrument， we have designed ground test equipment， including the circuit system and the host computer system. In this paper， we show the structure and working principle of the ground test for NAIS-H， and tell structure and java programming of the sub modules of the host computer system in detail， such as API communicating system， data analyzing system and data saving system. At last， we test the equipment， and the result shows the ground test system has good performance and achieves the design requirement.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： With the ever-increasing of space data, a reasonable data-arrangement is strongly required for high efficiency in data accessing and visualization. In this paper, basing on the characteristics of solar-wind data, a SDOG-R grid model is employed, which is radial independent division in the adaptive SDOG grid. For huge Sun-Earth space, it is divided into multi-resolution grids. The original data, which is output from a SIP-CESE solar wind model, are re-sampled, and put into the subdivided grids. The grid model is applied to both regular and irregular sampling data, and fully maintains the characteristics of original data to the best and encodes grids with an improved CDZ curve. Specific examples of data organization are given. The experiments prove that the grid model not only resolves the problem that grids are too dense at two poles and the spherical center, but also meets the need for higher resolution in radius than in latitude and longitude. Besides, 3D LOD spatial data model can not only provide multi-resolution data, but also significantly improve the large-scale mass data retrieval and access efficiency, and can support the organization and management of massive spatial data effectively.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： The characteristics of current high orbit GPS (Global Positioning System) signal are of poor availability and low positioning accuracy. Positioning of high Earth orbit satellites using GPS/Beidou combined system is studied. The visibility of navigation satellites and the Geometric Dilution of Precision (GDOP) are analyzed. Through simulation and analyzing, it is verified that the GPS/Beidou combined system has better performance than that of single GPS system. On one hand, the GPS/Beidou combined system can receive more satellites' signal than single GPS system. On the other hand, GDOP of the GPS/Beidou combined system is smaller than that of single GPS system. At the same time, the use of high-precision atomic clock in the satellite receiver can realize positioning of three satellites, and reduce the technology requirements of receiver.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： Using the magnetic field data from Cluster spacecraft and the Interplanetary Magnetic Field (IMF) data from ACE spacecraft, the effect of IMF By component (IMF |By|<10nT) on the Field-Aligned Current (FAC) occurrence rate and density at the Plasma Sheet Boundary Layer (PSBL) in the magnetotail is investigated. 1657 FAC cases from July to October in 2001 and 2004 were selected for analysis. We present that the IMF By component plays a very important role in controlling the occurrence rate and density of the FAC in the PSBL in the magnetotail. The FAC occurrence is higher (about 55.6%) when the IMF By is positive compared with that when the IMF By is negative. When the IMF |By| is more than 4nT, the occurrence rate of FAC is about 77.4%. The FAC occurrence in the magnetotail has an obvious positive correlation with the IMF |By|, and when the IMF By is positive, this correlation is better. The FAC density also has an obvious positive correlation with the IMF |By|, and when the IMF By is positive, this correlation is better. The above results show that the IMF By component has strong control on the occurrence and density of the FAC cases in the magnetotail, and that the change of FAC is closely associated with the duskward IMF (the IMF By is positive).
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： Drawing the magnetic lines as streamlines is a general method of visualizing geomagnetic field. A key factor to evaluate the effect of the geomagnetic field visualization is whether the space distribution of geomagnetic field lines is consistent with that of magnetic field intensity, while the distribution of geomagnetic field lines is determined by seed point selection. The traditional algorithms that select seed points with uniform angles on magnetic meridian circles cannot objectively reflect the space distributions of magnetic field intensity. This paper proposes an algorithm of selecting seed points with equal line integral of magnetic field intensity. The algorithm is applied to draw the geomagnetic field lines with the data from T96 model and IGRF model. The redundant magnetic field lines existing in the result are removed. Statistical analysis and comparison between the space distribution of magnetic field lines and the geomagnetic field intensity reveals that this algorithm can effectively visualize the geomagnetic field.
Peer Review Status:Awaiting Review
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