Subjects: Geosciences >> Space Physics submitted time 2017-03-10
Abstract：锁相环频率合成器环路带宽值的选取直接影响其输出相位噪声。基于此，本文首先介绍了锁相环的基本组成部分，然后分析了晶振、集成锁相芯片和压控振荡器相位噪声对频率合成器环路输出端的噪声影响，从而导出了最优环路带宽计算公式。并且通过基于PE3236芯片的频率合成器的输出相位噪声测量对最优环路带宽公式正确性进行了验证。结果表明：当根据最优环路带宽公式取值时，锁相环频率合成器的输出相位噪声满足实际应用需求。
Peer Review Status:
Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2017-03-10
Abstract：本文提出了一种应用于 L 波段的锁相频率合成电路的设计方案。给出了基于 PE3236 芯片的锁相 环电路设计方案。通过仿真验证和实验结果重点论述锁相环环路带宽与环路输出相位噪声和环路捕获时间 之间的关系。实验结果表明，该方案可以被应用于导航接收机射频前端，该频率合成器电路性能稳定，满 足实际应用需求。
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2017-01-22
Abstract： Combining the GRO (Global Navigation Satellite System Radio Occultation GRO) and LRO (Low Earth Orbit Radio Occultation) techniques to probe the Earth's atmosphere is a main development direction of RO. In this study, the mathematical criteria of a RO event have been described. Then the effects of the main orbit parameters of LEO satellite on the RO events amount and their global distribution have discussed by a simulation study. The results showed that the lower the LEO satellite orbit is, the more GRO events are; when the inclination is between 30癮nd 75� there are more GRO events and their Earth coverage is higher. The LRO events distribute on the Earth evenly when the LEO-LEO RO satellite set in the polar orbits. This study can provide a scientific reference for GRO and LRO satellite constellation design.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2017-01-22
Abstract： A technique of using a semiconductor diode volt-ampere characteristic to test Langmuir probe performance is presented. The Langmuir probe is an important technique for in-suit detecting the space plasma, and its performance test is the key to ensure that its technical indicators can meet the mission requirements. The technique of using a semiconductor diode volt-ampere characteristic demands less of external factors, so it can be carried out in a laboratory environment. The test results can be used as preliminary performance verification before calibration test of ground plasma environment, and it is proved that the method is effective and feasible in a lab environment test.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2017-01-22
Abstract： The unique combination of global coverage, high precision, high vertical resolution, long-term stability and all-weather viewing of radio occultation will enhance the data sets of numerical weather prediction and improve the precision of Numeric Weather Prediction (NWP). And data assimilation requires preprocessing of the raw radio signals into the bending angles and refractivity. Then the atmospheric parameters such as temperature, pressure and humidity can be retrieved through data variational assimilation. The procedures for processing of radio occultation data, especially several important steps are introduced. And comparative analysis between these results and those from CDAAC shows that below the altitude of 30 km, the relative errors of refractivity, pressure and humidity are within 2% and the deviation of temperature is below 2K. The results are also compared with the data from ERA-interim model of ECMWF and similar conclusion is obtained.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-13
Abstract： By utilizing data obtained on Chinese satellite in the middle Earth orbit from solar activity descending phase to solar activity ascending phase, the properties of high energy electron environment in the middle Earth orbit are analyzed, such as spatial distribution, flux intensity, temporal variations, and response to geomagnetic storms. The investigating results indicate that the spatial distribution of high energy electron in the middle Earth orbit is stable;the fluxes of electrons decrease with energy increasing;the high energy electron environment is a dynamical system which disturbs evidently on different timescales;the evolvement of this system is stimulated by geomagnetic storms, but the correlation between the evolvement and the storms is nonlinear.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-13
Abstract： A technique of using a semiconductor diode volt-ampere characteristic to test Langmuir probe performance is presented. The Langmuir probe is an important technique for in-suit detecting the space plasma, and its performance test is the key to ensure that its technical indicators can meet the mission requirements. The technique of using a semiconductor diode volt-ampere characteristic demands less of external factors, so it can be carried out in a laboratory environment. The test results can be used as preliminary performance verification before calibration test of ground plasma environment, and it is proved that the method is effective and feasible in a lab environment test.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-13
Abstract： The unique combination of global coverage, high precision, high vertical resolution, long-term stability and all-weather viewing of radio occultation will enhance the data sets of numerical weather prediction and improve the precision of Numeric Weather Prediction (NWP). And data assimilation requires preprocessing of the raw radio signals into the bending angles and refractivity. Then the atmospheric parameters such as temperature, pressure and humidity can be retrieved through data variational assimilation. The procedures for processing of radio occultation data, especially several important steps are introduced. And comparative analysis between these results and those from CDAAC shows that below the altitude of 30 km, the relative errors of refractivity, pressure and humidity are within 2% and the deviation of temperature is below 2K. The results are also compared with the data from ERA-interim model of ECMWF and similar conclusion is obtained.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-13
Abstract： FY-3A satellite can measure the radiation dose data from different directions during the missions from 2008 to 2012. In this paper, we describe total radiation dose from two directions, and dose rate variation with energetic particle flux. The result shows that different sections of the spacecraft receive different amounts of radiation dose, which is always consistent with space distribution of energetic particles. Absorbed dose rate changed greatly from several rad (Si).d~(-1) during quite time to even more than tenfold during disturbances. The increased high energy electrons in polar regions during disturbances are responsible for significant increase of radiation dose. At last, FY-3A radiation dose during the operational period of the mission is compared with the results calculated by SPENVIS. It is obvious that observation data is more realistic to reflect the real space radiation environment.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics Subjects: Geosciences >> Marine Sciences submitted time 2016-05-13
Abstract：全球卫星导航定位系统的反射信号(GNSS-R)遥感是反演陆地和海洋表面地球物理参数的有力工具.而机载GNSS-R是一个很重要的实验平台,因为它不仅可以为空基实验提供校准依据,而且在中小尺度目标(比如河流和湖泊)的遥感方面独具优势.机载实验的研究主要包括海面风场的反演、海面高度的测量和土壤湿度的探测.首次反演海面风场和土壤湿度的机载GNSS-R实验都是由美国NASA和科罗拉多州立大学组织实施的.之后在西班牙IEEC(Institut d'Estudis Espacials de Catalunya)/CSIC(Consejo Superior de Investigaciones Cientificas)、Starlab实验室与NASA的联合实验中,海面风场的反演精度已经能够达到2 m/s.两个最早利用GNSS-R探测海面高度的机载GNSS-R实验都是美国的JPL(Jet Propulsion Laboratory)组织实施的,其中海面平均高度的探测精度已经达到了厘米级.在中国,北京航空航天大学和中国科学院遥感与数字地球研究所也组织了相应的机载GNSS-R实验.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： Large planar plasma sheets with size of 60 cm*60 cm, maximum current of 3 A and duration of 200 mus, were obtained in a pulsed linear hollow cathode discharge device under 15 mT magnetic field confinement. The electron density 2-D distribution in the thickness direction and its evolution of plasma sheets with pressures between 90 Pa to 210 Pa were obtained by Langmuir probe using the fast frame function of oscilloscope and the rotating hollow cathode method. The effects of pressure on the time needed to reach the maximum peak density in the thickness direction, the maximum peak density and the full width at half maximum (FWHM) peak density, were investigated. The results show that, as the pressure decreased, the time reaching the maximum peak density in the thickness direction and the FWHM peak density diminished, while the maximum peak density in the thickness direction increased. These results could be utilized to manipulate the parameters of large planar plasma sheets.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： Large planar plasma sheets, generated by a linear hollow cathode in pulse discharge mode under magnetic confinement, can be used in the field of plasma antenna, plasma stealth, and simulation of a plasma layer surrounding vehicles traveling at hypersonic velocities within the Earth's atmosphere. Firstly, to investigate the propagation properties of electromagnetic waves at different frequencies and polarization, the transverse field transfer matrix method is introduced. Secondly, the measured electron density temporal and spatial distribution and the transverse field transfer matrix method are utilized to calculate the reflection, transmission and absorption of electromagnetic waves by large planar plasma sheets with different currents. Finally, 1 GHz (less than the critical cut-off frequency) electromagnetic waves and 4 GHz (greater than the critical frequency) electromagnetic waves are chosen to investigate the evolution of propagation properties during the pulsed discharge period. Results show that both the reflection and absorption of the electromagnetic waves are greater for their polarization direction parallel to that of magnetic field, and their frequencies lower than the critical cut-off frequency, and as the discharge currents rise, the reflection increases while the absorption decreases. However both the reflection and absorption of the electromagnetic waves with their polarization direction perpendicular to the magnetic field direction and their frequency greater than the critical cut-off frequency become less, and as the discharge currents rise, both the reflection and absorption will increase. For the electromagnetic waves with their polarization direction perpendicular to the magnetic field direction, there is an upper hybrid resonance absorption band near the upper hybrid resonance frequencies, in which the absorption is significant but the absorption peak value is not affected by the discharge current. The propagation characteristics of the electromagnetic waves with polarization direction perpendicular to the magnetic field direction are the same as that of the electromagnetic waves with the polarization direction parallel to the magnetic field direction, except the upper hybrid resonance absorption. During the pulse discharge period, the propagation characteristic of the electromagnetic waves experiences an unstable phase before reaching steady states. The transition time is about 100 mu s and increases as the discharge current rises. The upper hybrid resonance absorption is significant during the phase of steady state for waves with frequency lower than the critical cut-off frequency and polarization direction parallel to the magnetic field direction. For the applications of a large planar plasma sheet to reflect electromagnetic waves effectively and steadily, the pulse discharge period should be larger than 100 mu s, and its discharge current should be large enough to make the critical cut-off frequency greater than the frequency of incident wave, and its polarization direction should be parallel to the magnetic field direction.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： Radiation risk of astronauts during the flight in low earth orbit (LEO) and deep space exploration is mainly from the exposure of galactic cosmic ray (GCR). The radiation dose from GCR is the basis for the assessment of astronauts' radiation risk. In 2013, a new estimation method for the assessment of astronauts' radiation dose was presented by the International Committee on Radiological Protection (ICRP), so as to improve the assessment's accuracy of the radiation dose from heavy ions in space. Based on this method, a Monte Carlo program was developed for simulation of the particle transportation in materials and a voxel phantom of Chinese adult male was realized in this program to represent the astronaut. With this program, the fluence to dose conversion coefficients for the organs of astronauts were calculated for the isotropic exposure by particles with the atomic number from 1 to 92. The radiation dose to astronauts in LEO from GCR was also estimated. �2015, Beijing University of Aeronautics and Astronautics (BUAA). All right reserved.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-03
Abstract： The radio occultation (RO) technique using signals from the global navigation satellite system, is widely used to observe the atmosphere for applications such as numerical weather prediction (NWP) and global climate monitoring. Since 1995, there have been turborogue sounder on board global positioning system/meteorology, black jack sounder on board challenging minisatellite payload and gravity recovery and climate experiment, IGOR sounder on board constellation observing system for meteorology, ionosphere and climate, GRAS on board meteorological operational, which have been recieving a large number of RO data, but their observed signals come only from global positioning system (GPS). These RO data have been wildly used in NWP and climate monitoring, however they cannot meet the requirements for high accuracy and real time atmosphere observation, in this case compatible RO sounder to obtain more RO observations is significant. Global navigation satellite system occultation sounder (GNOS) on board the fengyun3 C (FY3 C) satellite, which is the first Bei Dou system (BDS)/GPS compatible RO sounder in the world, was launched on 23 September 2013. Up to now, lots of RO observations have been obtained. In this study, the components of GNOS are introduced; one-day GNOS RO events and their global distribution are analyzed; compared with the GPS RO observations, the accuracy and consistency of BDS real-time positioning results and BDS RO products are analyzed. The preliminary results show that the BDS can enhance the number of RO events by 33.3%; the average deviation and standard deviation of BDS real time positioning results are 6 m and 7 m, respectively; the BDS/GPS difference standard deviation of refrectivity, temperature, humidity, pressure and ionospheric electron density are lower than 2%, 2 K, 1.5 g/kg, 2%, and 15.6%, respectively. The BDS observations/products are consistent with those of GPS, therefore BDS RO products can bring benefit to numerical wheather prediction and global chlimate change analysis.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract：为了研究大面积等离子体片的分层特性,利用脉冲磁约束线形空心阴极放电装置,在150 Pa氦气中产生了持续时间为200μs、面积为60 cm×60 cm的大面积等离子体片。采用快帧法和旋转空心阴极法利用郎缪尔探针首次获得了等离子体片分层时厚度方向电子密度分布及其演化构成的二维分布图;基于获得的二维分布图,研究了分层等离子体片厚度方向电子密度的分布特征与磁场强度和放电电流的关系。实验发现,等离子体片分层时厚度方向电子密度呈现双峰曲线分布特征;当放电电流为2 A,磁场强度为1.5×10-2,2.25×10-2,3×10-2T时,双峰间距分别为0,3.2,8.4 mm;当磁场为3×10-2T,电流为1,2,3,4 A时,双峰间距分别为8.6,8.2,6.8,5 mm。结果表明:分层等离子体密度峰值间距随着磁场的增强和放电电流的降低而增大。
Peer Review Status:Awaiting Review
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