大气折射率干预引起电波折射误差的简便算法

提出了大气折射率干项引起电波折射误差的简便算法。重点给出了在现有条件下获得大气折射率干项的等值高度与地面温度实用模型的方法，并给出了中国某地的模型系数。     

基于高斯波束传输的高功率微波的大气击穿问题

提出了一种修正利用高斯波束传输高功率微波(High-Power Microwave,HPM)时的大气折射率的模型.在此模型中,把高斯波束横截面分成若干个同心圆环,并假定每一个同心圆环内的场强分布是均匀的.以基于电子流体力学方程和Maxwell方程的大气击穿理论,利用由实验数据拟合出来大气粒子的碰撞和大气电离参数,研究了高能量高斯波束的非线性传输,数值计算了在给定高斯波束参数时,在不同的压强下,波束以不同的电场强度、频率、脉冲宽度入射下的大气折射率.通过分析折射率的时间色散、空间色散以及时间空间色散,讨论了传输HPM脉冲的高斯波束的大气击穿问题,获得了一些有意义的结果.      

基于航天器解体事件的空间碎片寿命算法

研究了针对航天器解体事件所生成的空间碎片的寿命计算方法.给出了基于NASA标准航天器解体模型的航天器解体算法.该算法生成的一系列碎片参数,将作为寿命计算的初始条件.总结了现有求解碎片寿命的算法,并提出了一种半分析算法.该算法运用平均根数法的思路,计算了在J2摄动项的影响下,碎片的半长轴和偏心率的变化率;并采用微分积分法预报半长轴和偏心率随时间的变化.为了适应时变大气模型,该算法限制了计算步长.通过与数值法的比较分析了算法的计算速度和精度.选用了3种大气模型:SA76、GOST和MSIS-00,分析了不同大气模型在计算碎片寿命之间的差异.通过与P-78卫星解体事件的实测数据对比验证了整个算法的正确性.      

旋转大气下火星探测器轨道捕获

针对大气辅助捕获下多次穿越的方式,分别建立探测器气动捕获段在静止大气和旋转大气模型下的轨道动力学方程并进行相应的动力学仿真,分析旋转大气对轨道捕获的影响.根据仿真结果,给出了在两种大气模型下完成目标捕获时,任务耗时以及探测器所受的热量、过载情况,通过给定不同目标轨道近火点高度,得出两种大气模型下卫星轨道的轨道参数变化形式.结论表明:当目标轨道近火点高度较低时,旋转大气对探测器轨道参数的变化形式影响较大,应该考虑旋转大气的影响.     

长波定时ASF修正的GIS软件

论述的长波定时ASF修正的GIS软件能快速数字化可视化显示和调用服务区域的地形地理信息、大地电参数和大气折射率等多种数据源。使用此软件可以非常方便容易地用不同模型计算在广阔区域接收到的多个长波信号在各种典型路径上的ASF和地波传播时间延迟,并提高定时精度。     

大气闪烁对近似无衍射激光通信系统的影响

在近似无衍射激光通信系统中,大气湍流的作用导致接收端光强起伏不定,这将对通信系统的误码率产生影响.以光强起伏的概率分布为基础,忽略系统中的其他噪声,推导出折射率结构常数、通信距离和激光波长等影响因素与误码率的关系式.通过计算机模拟,研究了误码率随折射率结构常数的变化规律,讨论了一定湍流强度下通信距离和激光波长对误码率的影响,并以10-9为误码率标准,确定了通信距离的允许范围.结果表明,合理地选择天气和日照条件、减小通信距离以及选择长波长的激光器可以减弱大气湍流对误码率的影响.      

基于GPS掩星平均弯曲角的折射率反演研究

利用Abel积分变换通过掩星弯曲角计算折射率需要对高层弯曲角进行统计优化.目前由于所使用的背景场资料和具体反演方法不同,导致所发布的掩星大气数据气候统计值存在一定差异.本文使用2008年1,4,7,10月共4个月的COSMIC大气掩星附加相位数据,从纬圈平均弯曲角廓线反演相应月平均折射率,对反演结果进行比较分析.研究表明,利用掩星折射数据进行气候研究时无需逐一对掩星探测廓线进行统计优化,在40 km以下高度基于平均弯曲角的反演方法与传统统计相比能够获得几乎一致的月平均折射率,在50 km以上高度基于平均弯曲角的反演结果更加接近ECMWF资料统计.      

超新星爆发发射的γ射线的能量

本文用两箱模型导出了大气中的14C浓度与14C的产率、碳元素在大气和海洋中的贮存量及居留时间等量之间的关系,并进而给出根据树年轮14C数据计算超新星爆发后大气中增加的14C核子数ΔX₁（0）和估算超新星爆发发出的γ射线能量E_γ的公式。      

大气阻力摄动计算方法及误差分析

探索了大气阻力摄动精密计算方法，以提高卫星空间位置的预报精度。根据大气阻力摄动的基本原理，给出两种摄动计算方法，即半分析半数值方法和数值积分方法。选用三种高层大气模型：ＣＩＲＡ－１９８６、ＣＩＲＡ－１９７２和ＤＴＭ模型，分批 太阳活动中高年水平（Ｆ１０．７取为１５０，２００，２５０）和１０％－２０％的模型误差引起卫星空间位置的误差δＰ。结果显示：（１）太阳活动Ｆ１０．７的大小对δＰ的影响明显，在同     

Seasonal variation of surface refractivity over Nigeria

The seasonal variation of surface refractivity over Nigeria was studied using two years in-situ meteorological data from eight locations over Nigeria. The result shows that the surface refractivity generally has higher value during rainy season than dry season at all location studied. The results also show that the value of surface refractivity increases from arid region in the north to the coastal area in south. The results also show that local meteorology plays a very important role in refractivity variation.     

基于STK的GPS/LEO无线电掩星技术仿真研究

GPS/LEO无线电掩星技术反演地球大气参数剖面已经具有较高的精度. 国外开展了多个GPS/LEO掩星项目, 但中国还尚未深入进行相关的实验, 这制约了中国掩星技术的发展. 本文提出基于STK进行GPS/LEO掩星技术研究的方法; 根据GPS/LEO掩星的原理, 推导出掩星事件发生的条件和掩星切点的计算公式; 利用STK对掩星过程进行模拟, 得到掩星数据. 在大气球对称假设和大气模型已知的条件下, 反演得到中性大气折射指数. 通过比较模型和反演数据, 表明反演数据精度较高, 验证了利用STK模拟GPS/LEO掩星实验方法的可行性.      

大气层电波传播对星载SAR方位分辨率的影响

利用合成孔径原理和大气折射理论推导了大气层给SAR方位向分辨率带来的误差公式,针对不同时间、地点、高低年的电离层电子浓度和低层大气折射率剖面,对不同频段进行了计算,并对计算结果进行了分析讨论.得出了大气层中星载SAR的方位向分辨率误差为毫米量级,其绝对值随频率增高而减小的结论.      

Location of layered structures in the ionosphere and atmosphere by use of GPS occultation data

A method is introduced to locate the layered structures in the atmosphere and ionosphere based on simultaneous observations of radio wave intensity and phase variations in trans-ionospheric satellite-to-satellite links. The method determines location of a tangent point on the trans-ionospheric ray trajectory where gradient of refractivity is perpendicular to the ray trajectory and influence of a layered structure on radio wave parameters is maximal. An estimate of the location of a layer can be obtained from a combination of the phase and intensity variations. This new technique was applied to measurements provided during FORMOSAT-3 and CHAMP radio occultation (RO) missions. For the considered RO events the location of the inclined plasma layer in the lower ionosphere is found and the electron density distribution is retrieved. The method is checked by measuring the location of the tangent point on the ray trajectory in the neutral gas in the atmosphere. The results showed a fairly good agreement.     

Atmosphere sounding by GPS radio occultation: First results from TanDEM-X and comparison with TerraSAR-X

On 21 June 2010 the TerraSAR-X satellite was joined by the TanDEM-X satellite. A Global Positioning System (GPS) radio occultation (RO) experiment using the twin satellites has been carried out to estimate the precision of GPS atmospheric soundings. For the Day Of Year (DOY) 330–336, 2011, we analyze phase and amplitude data recorded by GPS receivers separated by a few hundred meters in a low earth orbit and derive collocated atmospheric refractivity profiles. In the altitude range 10–20 km the standard deviation between TerraSAR-X and TanDEM-X refractivity does not exceed 0.15%. The standard deviation is rapidly increasing for lower and higher altitudes; close to the surface and at an altitude of 30 km the standard deviation reaches 0.8% and 0.5%, respectively. Systematic deviations between TerraSAR-X and TanDEM-X refractivity in the considered altitude range (0–30 km) are negligible. The results confirm the anticipated high precision of the GPS RO technique. However, the difference in the retrieved refractivity in the lower troposphere for different Open Loop (OL) signal tracking parameters, altered onboard TanDEM-X for DOY 49–55, 2012, calls for an in depth analysis. At the moment we can not exclude that a potential bias in the OL Doppler model introduces a bias in our retrieved refractivity at altitudes <8$<8$ km.     

ROPP反演软件算法及其精度分析

介绍了ROPP反演软件中无线电掩星反演的算法与精度分析. 采用COSMIC卫星2008年1 月1日全天的附加相位数据, 反演得到折射率、温度、压强与湿度等参数, 并与CDAAC 相应结果进行对比. 实验结果表明, 在30km高度以下, 折射率、压强和湿度的相对 误差在2%以内, 温度误差不超过2K.      

FY-3D卫星的北斗掩星分布特征与误差特性

利用2018年1－3月FY-3D卫星的掩星折射率数据,研究了北斗导航卫星系统的掩星分布特点、数据精度以及误差统计特征。北斗导航卫星系统同步静止轨道掩星沿卫星轨道呈弧状分布在南北两极地区,倾斜轨道掩星在东西半球低纬度地区分别形成一小一大两个空洞,中地球轨道掩星则全球均匀分布。北斗掩星折射率数据精度在探测核心区域,即12~32 km范围内,与ERA5再分析资料计算的折射率相比,平均偏差的标准差约为1.5%,在核心区外,标准差从1.5%逐渐增大到6%。静止轨道掩星的平均偏差在高层略大于倾斜轨道和中地球轨道掩星。下降掩星在20 km以上区域的标准差大于上升掩星,20 km以下区域小于上升掩星。高纬地区北斗掩星标准差最小,低纬地区最大,对流层中下层尤其明显。分析结果表明,北斗掩星的数据精度和误差特征与GPS掩星数据相似。      

Tropospheric wet refractivity tomography using multiplicative algebraic reconstruction technique

Algebraic reconstruction techniques (ART) have been successfully used to reconstruct the total electron content (TEC) of the ionosphere and in recent years be tentatively used in tropospheric wet refractivity and water vapor tomography in the ground-based GNSS technology. The previous research on ART used in tropospheric water vapor tomography focused on the convergence and relaxation parameters for various algebraic reconstruction techniques and rarely discussed the impact of Gaussian constraints and initial field on the iteration results. The existing accuracy evaluation parameters calculated from slant wet delay can only evaluate the resultant precision of the voxels penetrated by slant paths and cannot evaluate that of the voxels not penetrated by any slant path. The paper proposes two new statistical parameters Bias and RMS, calculated from wet refractivity of the total voxels, to improve the deficiencies of existing evaluation parameters and then discusses the effect of the Gaussian constraints and initial field on the convergence and tomography results in multiplicative algebraic reconstruction technique (MART) to reconstruct the 4D tropospheric wet refractivity field using simulation method.     

Quantitative analyses of complexity and nonlinear trend of radio refractivity gradient in the troposphere

In this paper, the complexity and nonlinear trends of Radio Refractivity Gradient (RRG) in the troposphere over selected locations in Nigeria are analyzed and discussed extensively. The RRG is an important parameter in estimating path clearance and propagation effects such as ducting, surface reflection and multi-path on terrestrial line of-sights links. Also, radio wave signal propagating in the troposphere is affected by unpredictability of a weather condition which includes the variations of meteorological parameters such as temperature, pressure and relative humidity. The complex state of the atmosphere, which is the medium for the transmission of radio signals tend to have very strong influence such as scintillation and ducting on the quality of the radio signal, amplitude and phase. Variations in the meteorological parameters also induce variations in the refractive index of the atmosphere which in-turn results in the effect known as radio refractivity. For effective prediction and modeling of radio signal propagation, one should be able to characterize the nature and predictability of the computed RRG information. Chaotic Quantifiers (CQ) such as Phase Plot Reconstruction (PPR), Average Mutual Information (AMI), False Nearest Neighbor (FNN), Recurrence Plot (RP) and Recurrence Quantification Analyses (RQA) are used to assess the RRG. The information reveal, however, is based on the prediction techniques, design and frequency planning of microwave networks which may be useful for optimum performances during atmospheric turbulence.