大气传输特性对激光雷达探测系统的影响

大气探测激光雷达的实际探测能力与激光的大气传输衰减有密切的关系.详细阐述了大气对激光传输的各种衰减效应,包括大气中气体分子和气溶胶粒子对激光信号的吸收和散射、大气分子的荧光吸收及大气湍流等.不仅有助于加深对激光雷达方程的理解,且对激光雷达系统的设计与研制也具有重要的指导意义.     

光机电

世界首台车载钠层激光雷达中国科学院空间科学与应用研究中心自主研制的车载钠层测风测温激光雷达完成观测试验,成功获得了中间层顶区域80km～105km高度的大气三维风场、温度及钠原子数密度等参数。这标志着世界首台车载钠层测风测温激光雷     

我国成功研制机载大气污染探测系统

正中国科学院合肥物质科学研究院安徽光学精密机械研究所成功研制出1种用于机载、可快速获取区域环境大气污染成分的环境大气成分探测系统,并通过了安徽省科技成果转化服务中心组织的科技成果鉴定。该机载环境大气成分探测系统由大气环境激光雷达、差分吸收光谱仪和多角度偏振辐射计及主控管理器等4个子系统组成。研究人员研制出了国内首台探测气溶胶和云的双波长偏振航空遥感激光雷达。     

螺旋桨的永磁无刷直流电机绕组换接驱动方法

螺旋桨转矩与大气密度成正比,飞艇最高飞行高度海拔30 km处大气密度为0 km处的1/66,若保持相同转速,0 km的转矩是30 km处的66倍,常规永磁无刷直流电机(brushless DC machines,BLDCM)难以兼顾对高、低空螺旋桨负载的匹配,限制了飞艇飞行高度范围。为此提出利用调节BLDCM磁链的解决思路,进而提出一种BLDCM绕组换接方法,绕组并联减小磁链,满足高空下电机高速运行需求,绕组串联增加磁链,减小电机电流,满足电机低空低速大转矩需求。对不同绕组模式电机性能进行了理论分析,研究了绕组换接BLDCM的设计方法,设计并测试了1台3.5 k W BLDCM样机,样机不同绕组模式下性能测试结果与理论分析相吻合,证明该绕组换接方法可使BLDCM满足0~30 km高度空间内螺旋桨负载驱动的转矩和转速需求。     

极区中层尘埃粒子的带电效应

利用轨道运动限制和尘埃带电理论,分析了在极区中层顶中,尘埃等离子体受高功率无线电磁波的影响下,尘埃粒子的带电效应。此外,利用数值模拟及实验方法对理论分析结果进行了验证。通过理论分析可知,尘埃粒子带电数由尘埃半径大小、电子温度、离子温度的高低以及离子数密度和电子数密度决定。通过数值模拟及统计分析火箭探测数据得到,平均尘埃带电数随等离子体中尘埃电荷数密度的增加而降低,而随尘埃半径、电子温度和电子密度的增加而增加。在一定程度上,仿真及实验结果与理论研究结果较一致,当尘埃带电量为0.4e时,尘埃半径值与文献结果一致。     

激光雷达在大气和海洋污染探测中的应用及其发展趋势初探

激光是一种新型光源,激光与普通光相比,具有很好的单色性、方向性、相干性和高亮度以及高功率、高能量等特点。激光雷达是利用了激光的优良性能,集激光技术、光学技术和微弱信号探测技术于一体而发展起来的一种现代化光学探测手段。激光雷达的探测波长短、波束定向性强,能量密度高,因此,具有探测灵敏度高、空间分辨率高,能分辨被探测的物种和不存在探测盲区等优点,已经成为目前对大气、海洋和陆地进行高精度遥感探测的有效方法,广泛地应用于环境监测、航天、通信、导航和定位等高新技术领域。本文简述了激光的特性,重点阐述了激光雷达特点及其在大气污染和海洋烃类污染等方面的应用情况和发展趋势。     

大气折射率结构常数CN2的研究

根据温度变化规律,将地表上方几何高度71km 以下的大气分为6层,分别导出各层的温度和压强的计算公式,由这些公式计算出这一范围内任意高度的温度和压强值与美国标准大气表中所列值极好地吻合,据此可求出在自适应光学中起重要作用的大气折射率结构常数 C_N~2及相关长度 r_0的解析表达式。     

劈窗算法LST精度评价和参数敏感性分析

介绍了大气模拟数据法，并用此方法分析和评价了作提出的劈窗算法．采用模拟大气参数计算得到的地表温度平均精度为0．46℃；利用间接方法(即大气透过率是由大气水汽含量计算得到)得到的平均精度为0．60℃．同时对MODIS地表温度产品与我们用MODIS影像反演出来的结果对比分析表明作提出的劈窗算法是可行的．敏感性分析表明此算法对参数透过率、比辐射率都不敏感．     

激光大气传输相干长度实验研究

通过激光水平大气传输实验,对接收的光强闪烁和光斑尺度特征进行记录。在强湍流条件下,利用光强闪烁计算出大气折射率结构常数Cn2,并以此反演大气相干长度r0,从而计算出光斑尺度;通过与实际测量得到的等效光斑尺度进行对比分析发现：二者存在一定偏差,在rn小于O．055m的条件下相差大约200μm2,但是其量级和时间变化趋势上基本一致,分析了误差产生的原因。     

利用FY-3C气象卫星GNSS掩星估计全球重力波变化与分析

大气重力波是地球大气层中广泛存在的重要大气动力学扰动,研究其分布和变化规律对理解大气物理、大气结构以及大气动力学等具有重要意义.传统大气重力波探测手段,如雷达和探空气球等,均存在探测时间短、有效探测高度低等缺点,全球卫星导航系统(GNSS)掩星观测具有全天候、低成本、高精度等优点,被广泛应用于地球大气探测和研究,为研究区域或全球重力波变化和活动特征提供了新的观测手段.本文利用中国第一颗搭载GNSS掩星设备气象卫星——风云3C(FY-3C)获得的掩星数据,反演得到2014年8月—2016年12月大气温度轮廓线,并首次估计重力波参数分布,分析了重力波参数的时空变化分布特征.结果表明,海陆季节性对流导致冬夏两季的重力波势能强于春秋两季,赤道对流作用导致赤道区域重力波强于两极,夏季南半球中低纬度地区重力波活动频繁,冬季北半球中低纬度区域重力波活动频繁.重力波随着高度的上升,势能逐渐下降.另外,地形是低层大气重力波的主要来源.     

Climatology of global gravity wave activity and dissipation revealed by SABER/TIMED temperature observations

Gravity wave activity and dissipation in the height range from the low stratosphere to the low thermosphere(25–115 km)covering latitudes between 50°S and 50°N are statistically studied by using 9-year(January 22,2002–December 31,2010)SABER/TIMED temperature data.We propose a method to extract realistic gravity wave fluctuations from the temperature profiles and treat square temperature fluctuations as GW activity.Overall,the gravity wave activity generally increases with height.Near the equator(0°–10°),the gravity wave activity shows a quasi-biennial variation in the stratosphere(below 40 km)while from 20°to 30°,it exhibits an annual variation below 40 km;in low latitudes(0°–30°)between the upper stratosphere and the low thermosphere(40–115 km),the gravity wave activity shows a semi-annual variation.In middle latitudes(40°–50°),the gravity wave activity has a clear annual variation below 85 km.In addition,we observe a four-monthly variation with peaks occurring usually in April,August,December in the northern hemisphere and in February,June,October in the southern hemisphere,respectively,above 85 km in middle latitudes,which has been seldom reported in gravity wave activity.In order to study the dissipation of gravity wave propagation,we calculate the gravity wave dissipation ratio,which is defined as the ratio of the gravity wave growth scale height to the atmosphere density scale height.The height variation of the dissipation ratio indicates that strong gravity wave dissipation mainly concentrates in the three height regions:the stratosphere(30–60 km),the mesopause(around 85 km)and the low thermosphere(above 100 km).Besides,gravity wave energy enhancement can be also observed in the background atmosphere.     

卫星自主导航中星光大气折射模型的研究方法

研究了卫星自主导航的大气折射原理及平流层大气变化规律，根据光在湍流大气中的传播机理，给出了一种采用球形大气分层的可行研究方法．应用理想气体理论，根据卫星、地球及星光切高度之间的几何关系及光学定律，建立了星光大气折射的通用模型，给出了影响导航精度高度范围内的经验公式．仿真结果表明，新模型符合大气折射的变化规律，与现有的经验公式相比，形式简单、精度较高、使用方便，而且包含了大气的实际物理状态和变化过程，更具有实际应用价值．     

大气电场倒转与突发钠层及突发E层的相关性

突发钠层(Sporadic Sodium Layer, Na_S)是中高层大气金属层最为显著的一种现象,其发生机制目前尚无定论。突发E层(Sporadic E layer, E_S)是等离子体密度异常增大的薄层,被认为与Na_S密切相关。为进一步研究Na_S及E_S事件之间相关性及影响因素,利用中国科学院“子午工程”2010～2018年合肥科大站宽带钠荧光共振激光雷达观测结果,并结合武汉左岭镇站数字测高仪及九峰站大气电场仪数据,分析大气电场倒转(即北向电场)对Na_S以及E_S事件的影响。在统计的91例Na_S事件中,发生于大气电场倒转时的比例为20/91; 同时,在发生Na_S事件的事例中,E_S消失或中断的比例较大(14/20),表明E_S可能以提供钠源的形式转化为Na_S。此外,在分析武汉左岭镇站数字测高仪数据的同时进行概率统计,结果表明:当大气电场倒转时,E_S临界频率减小甚至消失的概率较大(187/242),少数情况下可能造成临界频率增大甚至激发E_S生成(55/242); E_S虚高消失比例为179/242,E_S不变比例为27/242,E_S上升比例为23/242。综上所述,大气北向电场在一定程度上对E_S事件的发生有抑制作用,并对E_S事件的发生高度有明显影响。最后,对一种与电场倒转相关的突发钠层机制也进行了讨论。     

Shock wave standoff distance of near space hypersonic vehicles

The shock wave standoff distances of near space hypersonic vehicles,which execute missions mainly at the altitude of 25 km to55 km,are vital in aerothermodynamic analysis.The implicit finite volume schemes are derived from axisymmetric Navier-Stokes equations for chemical equilibrium flow,and programmed in FORTRAN.Taking a sphere cone for example,the effects of Mach numbers(from 22 to 36) on the shock wave standoff distance and the average density behind the shock are simulated at different altitudes from 25 km to 55 km.The numerical results illustrate that the turning point of the standoff distance is corresponding to that of the average density with the variation of Mach numbers.Based on the numerical results,we propose a formula for shock wave standoff distance,which is the function of the radius of the blunt body,the Mach number and the altitude in the atmosphere.Compared with previous correlations,the new formula can overcome the drawbacks of larger relative errors and complex calculations of the average density.     

Atmospheric Drag Perturbation in an Autonomous Orbit Determination for Satellite

In this paper, an autonomous orbit determination method for satellite using a large field of view star sensor is presented. The simulation of orbit under atmospheric drag perturbation are given with expanded Kalman filtering.The large field of view star sensor has the same precision as star sensor and a sufficient filed of view. Therefore ,the refraction stars can be observed more accurately in real time. The geometric relation between the refracted starlight and the earth can be determined by tangent altitude of the refraction starlight. And then the earth center can be determined in satellite body frame. The simulation shows that the precision of the mean square deviation of satellite‘s position and velocity is 5m and 0.01m/s respectively. The calculated decrement of the semi-major axis in one day is close to the theoretical result, and the absolute error is in the range of decimeter when the altitude of orbit is 750 km. The simulateion of orbit of different initial semi-major axis shows that the higher the altitude of orbit is, the smaller the decrement of the semi-major axis is, and when the altitude of orbit is 1700 km the decimeter of the semi-major axis is 10^-7km.     

高功率微波大气传输轨迹模拟

高功率微波在大气中传输时，会发生大气折射效应，折射效应的显著程度主要依赖于沿路径的折射指数变化梯度和射线初始仰角。本文根据低层大气剖面数据，将高功率微波在大气未击穿时的传输轨迹划分为若干个点，分析计算出各点对目标的仰角、高度、地心夹角和到发射站的真实距离，实现了对高功率微波大气传输轨迹模拟。     

Thermal conductivity measurements on xonotlite-type calcium silicate by the transient hot-strip method

The experimental results of the thermal conductivities of xonotlite-type calcium silicate insulation materials were presented at different temperatures and pressures.Two appropriative surroundings,i.e.an elevated temperature surrounding from ambient temperature to 1450 K and a vacuum surrounding from atmosphere pressure to 10-3 Pa,were designed for the transient hot-strip (THS) method.The thermal conduetivities of xonotlite-type calcium silicate with four densities from ambient temperature to 1000 K and 0.045 Pa to atmospheric pressure were measured.The results show that the thermal conductivity of xunotlite-type calcium silicate decreases apparently with the fall of density,and decreases apparently with the drop of pressure,and reaches the least value at about 100 Pa.The thermal conductivity of xonotlite-type calcium silicate increases almost linearly with T3,and increases more abundantly with low density than with high density.The thermal conductivity measurement uncertainty is estimated to be approximately 3% at ambient temperature,and 6% at 800 K.     

探空温度传感器受太阳辐射影响的仿真分析

随着高空温度探测精度要求的日益提高,如何减小温度传感器测量误差已成为亟需解决的问题,而太阳辐射作为影响温度传感器探测性能的重要因素已成为该领域研究的热点.利用计算机仿真技术,引入太阳高度角、引线夹角2个影响因子,根据流体动力学模型模拟分析探空温度传感器从海平面上升到32km高空时所受太阳辐射的影响,最终得到辐射误差与海拔高度的关系曲线族,仿真结果将为开展高空温度传感器误差分析提供基础依据,从而提高传感器测量准确度.     

Effective approach for outdoor obstacle detection by clustering LIDAR data context

A method of environment mapping using laser-based light detection and ranging (LIDAR) is proposed in this paper. This method not only has a good detection performance in a wide range of detection angles, but also facilitates the detection of dynamic and hollowed-out obstacles. Essentially using this method, an improved clustering algorithm based on fast search and discovery of density peaks (CBFD) is presented to extract various obstacles in the environment map. By comparing with other cluster algorithms, CBFD can obtain a favorable number of clusterings automatically. Furthermore, the experiments show that CBFD is better and more robust in functionality and performance than the K-means and iterative self-organizing data analysis techniques algorithm (ISODATA).