用于火星电离层探测的星-星无线电掩星技术

火星和地球类似,周围束缚了不同密度的电离层.利用无线电掩星技术可以对火星电离层进行观测.星-地无线电掩星在探测精度和探测区域方面都受到一定的限制.中俄联合火星探测计划将于2011年10月一箭双星发射俄罗斯的Phobos-Grunt探测器和中国的萤火1号火星探测器.该计划将开展国际上首次火星电离层的星-星无线电掩星观测试验,重点是对星-地无线电掩星无法观测的正午和子夜区域的火星电离层进行探测.星-星无线电掩星观测试验采用双频工作模式,接收机灵敏度为-145dBm,相位测量精度优于5%周.在地面对接收机进行了动态模拟测试,测试得到的相位数据能很好地反演出火星电离层电子密度廓线.     

火星重力场研究现状及发展趋势

针对近年来月球与火星探测成为各航天大国的热点,以及中国首个火星探测计划"萤火1号"拟定的科学研究目标,文章对火星重力场模犁的历史、现状及展望做了简要描述.文中首先探讨了火星探测的多重意义和火星重力场在火星探测中起到的重要作用;接着介绍了火星重力场模型发展的历史和现状;最后介绍了利用中国"萤火1号"轨道跟踪数据对火星重力场模型的可能贡献,在此基础上对中国未来火星重力场探测提出了设想.     

AIRS与COSMIC反演大气温湿廓线比较

将福卫三号星系计划(COSMIC)气象、电离层及气候卫星探测系统、大气红外探测器(AIRS)反演的大气温度和湿度廓线与时间、空间匹配的欧洲中心中期天气预报(ECMWF)、美国环境预报中心(NCEP)分析值和无线电探空观测值进行比较, 结果表明, COSMIC具有垂直分辨率高、全天候的观测特点, 反演的大气温度和湿度廓线相对于AIRS而言与无线电探空观测值更接近, 能提供大气廓线的更精细结构, 但受掩星事件发生时所能探测最低高度的限制, 不能得到该高度以下的大气信息。AIRS在晴空时大气温湿廓线反演精度较高, 但受云天的限制, 在云层以下, 反演精度就大大降低。     

COSMIC掩星电离层资料反演以及结果验证

通过COSMIC掩星电离层观测资料L1和L2相位组合,得到相对总电子含量TEC;利用非掩星的辅助观测数据校正TEC,消除LEO卫星高度以上的TEC部分;在电子密度局部球对称假设和信号直线传播的近似下,通过Abel积分变换可以得到电子密度垂直廓线.将2007年度中与电离层测高仪站点经度差小于10°,纬度差小于2°的4903个COSMIC掩星电离层资料与相对应的电离层测高仪数据进行比较,F₂层的临界频率f₀F₂的标准差约为059 关键词： COSMIC GPS/LEO掩星 电离层测高仪 电离层反演     

"火星快车"下视雷达对火星电离层探测简介

火星是近年来深空探测的热点,对火星电离层的观测和研究是火星探测的主要内容之一.欧洲航天局2003年发射了火星探测器"火星快车",它所搭载的下视雷达MARSIS(火星地表和电离层探测雷达)为火星电离层探测提供了大量数据,文章简单介绍了利用MARSIS探测火星电离层的基本原理,探测数据的结构和利用这些探测数据进行电离层研究的现状.     

火星空间环境磁场探测研究——"萤火1号"磁强计的研制与应用

文章介绍了"萤火1号"卫星对火星空问环境磁场进行探测的目的、意义及采用的方式方法.研究火星的空间环境离不开火星磁场,它对于火星弓激波、磁鞘、电离层、大气等绝大多数空间环境效应都有着深刻的影响,因此"萤火1号"卫星安装了一台重要的科学探测载荷--高精度磁强计,以满足科学研究和应用目标的需求.磁强计从原理选择到具体没计,都考虑到了火星轨道严酷的工作环境和科学目标所需的测量要求.通过"萤火1号"装星前的地面标定测试实验,验证了高精度磁强计可以在-140-75℃温度范围内测量±256nT以内的磁场,分辨率达到了0.01nT,带宽内总噪声小于0.03nT,能够胜任"萤火1号"对火星空间环境探测的科学任务."萤火1号"火星探测器将于2011年与俄罗斯的"福布斯-土壤"一同飞往火星,这是人类送往火星最精密的磁场探测器之一,将对火星空间环境磁场结构和动力学过程进行精密而详细的探测.     

应用一维变分法反演GPS掩星大气温湿廓线

GPS掩星观测的折射率是大气温度、湿度状态的函数, 应用一维变分方法 (1DVAR) 可以从折射率资料中同时反演出大气温、湿度廓线, 利用COSMIC 2011年中国区域掩星观测数据对这一方法进行了测试, 背景场采用ECMWF大气廓线, 反演结果与相匹配的探空观测有较好一致性. 重点研究了一维变分反演方法中非理想气体效应 (non-ideal effect) 对温度、湿度反演误差的影响, 不同月份的比较结果表明, 非理想气体效应对掩星反演大气廓线是一种系统性影响, 考虑这一效应可对温度反演改进0.1 K的偏差 (bias), 对比湿可改进约0.5%偏差. 掩星资料作为数值天气预报资料同化中少数无需偏差改正的卫星遥感资料, 非理想气体效应改正是无疑是非常重要的, 此外, 考虑这一效应对掩星资料的气候应用也有重要价值. 关键词： 一维变分 掩星 非理想气体效应     

GPS/LEO掩星正则变换反演方法

利用无线电全息方法, 如正则变换方法或全谱反演方法, 可以有效地解决大气多路径条件下GPS掩星信号的反演问题. 本文采用正则变换方法反演掩星资料, 模拟仿真反演结果显示正则变换方法可以准确地反演包含大气多路径效应的信号. 在模拟信号的相位中加入不同程度的高斯相位噪声后, 正则变换方法的反演结果会受到不同程度的影响. 用正则变换方法对2007年第71天至73天共约4500个COSMIC数据进行处理. 将其折射率反演结果和atmPrf资料 (利用全谱反演方法计算得到) 一起, 与对应的ECMWF 分析场资料进行统计比较, 结果表明: 在5 km以下, 正则变换方法计算的折射率的相对误差的平均值普遍大于atmPrf资料. 其原因可能为: 正则变换方法将信号从LEO轨迹后传播至辅助屏, 造成孔径缩小, 精度下降. 同时也讨论了信号截断对低对流层中反演精度和掩星个数的影响. 关键词： 无线电掩星 大气多路径 多相位屏技术 正则变换方法     

非球对称电离层掩星数据反演

电离层掩星数据的传统反演方法是电离层球对称假设下的Abel变换反演方法,但是实际的电离层电子密度分布不是球对称的,电离层的非球对称分布给电离层电子密度反演带来误差.发展了一种新的非球对称电离层掩星反演方法,利用国际参考电离层模型提供的三维电离层电子密度分布先验信息来修正掩星总电子含量 ,再通过球对称假设下的Abel变换反演出电离层电子密度.利用新方法反演了星座气象、电离层和气候观察系统掩星实测数据,并将得到的反演结果与电离层探测器资料进行了比较.结果表明,新方法能够较好地反演出电离层电子密度. 关键词： 电离层掩星 电子密度 国际参考电离层模型     

基于火星巡视器车载激光诱导击穿光谱仪系统设计米散射激光雷达可行性研究

火星大气气溶胶的地基探测对研究火星大气环境具有重要意义,为了能够在节约火星巡视器/着陆器体积、重量的条件下进行气溶胶探测,论证了基于巡视器车载激光诱导击穿光谱仪系统设计米散射激光雷达方案的可行性。所设计的米散射激光雷达系统使用巡视器车载激光诱导击穿光谱仪的既有硬件资源,加入分光元件和探测器模块,构成与激光诱导击穿光谱仪系统集成的米散射激光雷达,米散射激光雷达与激光诱导击穿光谱仪在火星地表分时工作,互不影响。为了论证所设计的米散射激光雷达的探测性能,对Phoenix火星探测任务中独立的米散射激光雷达得到的一组原始回波信号数据进行了处理,反演得到一组典型火星大气消光系数廓线,结合消光系数廓线与系统硬件参数计算了所设计的米散射激光雷达的回波信噪比,结果表明该系统在所用原始数据被记录的当日在火星大气边界层顶4 km高度处信噪比达到26 dB,在10 km高度附近下降到0 dB,说明基于火星巡视器车载激光诱导击穿光谱仪系统设计米散射激光雷达进行气溶胶探测具有现实可行性。对比Phoenix的独立米散射激光雷达设计方案,基于激光诱导击穿光谱仪的米散射激光雷达不但能够节省巡视器体积、重量,而且发射能量更高,回波接收方案更为简单,数据反演步骤更为简洁。     

Localization of plasma layers in the ionosphere based on observing variations in the phase and amplitude of radiowaves along the satellite-to-satellite path

We propose a method for localization of layered structures in the ionosphere, which is based on simultaneous observations of time variations in the intensity and phase of radio waves along transionospheric paths. The method determines the position of the turning point, where the gradient of the refraction index is perpendicular to the ray trajectory and the influence of the layered structure on the parameters of radio waves is maximal. The layer position is estimated by analyzing the variations in the phase and intensity of radio waves in combination. The method was used to analyze the experimental data obtained by the radio occulation mission CHAMP. The position for inclined plasma layers was determined and the electron density distribution was found for the considered radio occultation sessions. The method was verified by measuring the turning point on the ray trajectory in a neutral gas in the atmosphere. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 1, pp. 1–9, January 2008.     

风云三号C星全球导航卫星掩星探测仪首次实现北斗掩星探测

全球导航卫星掩星探测仪(GNOS)是国际首台北斗系统(BDS)和全球定位系统(GPS)双系统兼容掩星探测仪, 2013年9月23日随风云三号卫星C星(FY3 C)发射入轨, 目前已测得大量掩星数据. 介绍了FY3 C-GNOS的组成; 统计了2013年10月12日全天的FY3 C-GNOS掩星事件及其全球分布情况; 通过与GPS精密定轨结果进行对比分析, 测试了BDS在轨实时定位精度, 检验了BDS掩星产品的可靠性和一致性. 初步分析结果表明: 14颗BDS卫星在轨运营的条件下, BDS和GPS兼容掩星探测仪可将掩星事件数提高约33.3%; BDS实时定位平均偏差优于6 m, 标准偏差优于7 m; 5-25 km高度范围内, BDS与GPS内符合精度大气折射率优于2%, 温度优于2 K, 湿度优于1.5 g/kg, 压强优于2%, 电离层峰值密度优于15.6%. GNOS的在轨正常运行及BDS与GPS掩星定位精度及反演产品的一致性为北斗掩星探测的业务化运行奠定了基础.     

Ground-Based and Space-Borne Studies of Midlatitude F-Spread

We present the results of the first space-borne SURA-WIND experiment aimed at studying the features of short-radiowave propagation in the case of radio occultation of the near-Earth plasma in the presence of a developed midlatitude F-spread. We discover the effect of screening of a signal at frequency 4525 kHz that is 0.8 MHz higher than the minimum observed frequency for the SURA-WIND radio path determined using the ionograms obtained by the ground-based vertical-sounding station. The screening effect is explained by the effect of large-scale irregularities of the number density of ionospheric electrons of sizes about a few tens of kilometers, which lead to the appearance of electron-density depletion regions in the ionosphere stretched along the geomagnetic field. These depletion regions are separated by the ordinary plane-parallel distribution of the electron number density. The features of the frequency spectra of intensity fluctuations of the HF radiation over the SURA-WIND radio path in the presence of a developed midlatitude F-spread are considered.     

Vertical Velocities and Temperature of the Neutral Component in the Upper Atmosphere

Results of measurements of the velocity of the vertical plasma motion and the temperature of the neutral component in the upper atmosphere and comparison of variations in these parameters have been described. The measurements have been carried out by the resonance scattering of radio waves by artificial periodic irregularities in the ionospheric plasma. The irregularities arise when the ionosphere is modificated by a powerful high-frequency radio emission from a Sura midlatitude heating facility. Comparison has been conducted using experimental data on altitude- and time-dependent variations in the above parameters obtained in experiments of 2010 and 2014. It has been shown that, above 100 km, wavelike variations in temperature and velocity are commonly observed simultaneously. In the absence of wavelike variations, there is a tendency to an increase in temperature with an increase in the velocity of the vertical plasma motion regardless of direction. This tendency can be attributed to thermal flows directed upward from the turbulent region of the ionosphere.     

Amplitude and Phase Fluctuations of Decimeter Radio Waves Raying the Atmosphere via Satellite-to-Satellite Paths

We present the results of experimental studies of the atmospheric phase and amplitude fluctuations of decimeter radio waves in radio occultation measurements using paths connecting the MICROLAB satellite and the satellites of the GPS navigation system. The dependences of the amplitude- and phase-fluctuation variance on the minimum altitude of the ray trajectory and the frequency spectra of the fluctuations are presented. The experimental data are compared with the theory of radio-wave propagation in random media. We determine the spectral index of irregularities of the atmospheric refractive index, the external scale of the irregularities, and the variance of the refractive-index fluctuations. It is shown that the radio occultation technique allows one to monitor small-scale irregularities of the atmosphere.     

基于改进的单差法计算GPS掩星附加相位

从GPS掩星探测数据中反演的参数可同化入数值天气预报模式. 附加相位的计算精度受参考链电离层噪音及L2噪音影响, 在L2信号加密情况下噪音影响更为显著.为提高附加相位处理精度, 减少一般单差法(single difference, SD)从参考链传入掩星链的噪音,本文采用改进的单差法 (updated single difference, USD)计算大气附加相位.参考链数据采用组合频率LC观测数据, 并以一定时间窗口(2 s)做平滑处理,逐项考虑天线相位中心改正、 相对论效应改正等因素的影响.利用COSMIC掩星观测数据对上述方法进行了验证. 上升及下降典型掩星事件分析表明:USD计算的附加相位与 COSMIC官方发布的附加相位有很好的一致性;计算了全球分布的440次掩星事件附加相位, 结果表明USD法可明显改进附加相位平均偏差与标准差的分布, 证明了我们算法的可靠性. USD法可应用于风云三号气象卫星掩星仪器半无码跟踪L2得到的数据处理中.     

Radiowave fluctuations in the polar ionosphere on the satellite-to-satellite paths under high solar activity

We analyze ionospheric fluctuations of decimeter radio waves on occultation polar paths between the navigational GPS satellites and the satellite CHAMP. Time dependences of the variance of the signal amplitude and amplitude fluctuation spectra under high solar activity in October–November 2003 are presented. The behavior of the signal amplitude fluctuations during occultation ionospheric sounding in the polar regions in different time of the day and in the equatorial regions in the daytime are considered. Radio-wave fluctuations are related to the solar-activity manifestations. It is shown that during strong solar-flare activity, intense small-scale plasma irregularities are excited in the polar ionosphere. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 3, pp. 185–193, March 2006.     

Influence of an artificially disturbed ionosphere on the mesospheric ozone

The results of microwave measurements of ozone emission in the middle atmosphere during modification of the ionosphere by high-power short radio waves on March 14–19, 2009 and on March 27–28, 2011. The modification was carried out using a SURA heating facility (Radiophysical Research Institute) in conjunction with two microwave ozonometers aimed at different parts of the sky. A new physical phenomenon of decrease of the intensity of microwave emission from the mesosphere in the ozone line upon the modification of the ionosphere with high-power short radio waves is discovered.