Equatorial M(3000)F2 estimation of F2-layer models peak heights during low solar activity

M(3000)F2 estimation of h_mF2 based on four different formulated models viz: (1) Shimazaki (1955) (2) Bradley and Dudeney (1973), (3) Dudeney (1974) and (4) Bilitza et al. (1979) at an equatorial station in West Africa during low solar activity period (1995) are used to validate its conformity with observed and International Reference Ionosphere (IRI) model. Local time analyses of data from fifteen (15) selected days during the January and July solstices and April and October equinoxes are used. The results obtained show that the M(3000)F2 estimation of h_mF2 from the ionosonde-measured values using the Ionospheric Prediction Service (IPS-42) sounder compared to the observed values which were deduced using an algorithm from scaled virtual heights of quiet day ionograms are highly correlated with Bilitza model. International Reference Ionosphere (IRI 2007) model for the equatorial region also agrees with the formulation developed by Bilitza et al. (1979) for the four different seasons of the year. h_mF2 is highest (425 km) in summer (June solstice) season and lowest (386 km) in autumn (September equinox) season with daytimes peaks occurring at 1100–1200 LT during the solstices and at 1000 LT during the equinoxes respectively. Also, the post-sunset peaks are highest (362 km) at the spring (March equinox) and lowest (308 km) at the summer (June solstice) both occurring between 1800 and 2000 LT.     

电源线尖峰信号的分析与测试

针对感性负载在电源线尖峰信号试验过程中存在峰值难以捕获的问题,通过对感性负载在开关过程中的动态特性分析,研究了电源线尖峰信号的形成机理和影响因素,在此基础上,提出了在直流条件下电源线尖峰信号的替代测试方法。仿真实验结果表明,直流替代测试方法与理论结果基本一致,可用于解决标准试验方法的最大峰值随机问题,极大压缩峰值信号的动态范围,有效降低测试过程中的风险水平,对于电源线传导干扰的测试分析具有参考意义。     

台风影响电离层F2区的一种可能机制

在台风期间,特别是台风登陆前后,强烈的海气、陆气相互作用会增强低层大气中的湍流活动,并可能导致大气湍流层顶的抬升.这种抬升会改变高层大气结构,从而影响高层大气中的光化学过程,最终造成对电离层的影响.在台风活动抬升了湍流层顶的前提下,利用一个一维电离层物理模型,模拟了日本中纬地区(45°N,142°E)电离层F2区的响应.模拟结果很好地定性解释了如下观测事实,台风期间,电离层f0F2会下降,对给定频率电波的反射面会抬升;同时还表明以上过程会导致hmF2上升,这表明台风期间湍流层顶的抬升可能是台风影响电离层F2区的一种十分有效的机制.      

一种适合星载多光谱图像的压缩算法研究

文章提出了一种适合星载多光谱（4个谱段）图像压缩方法,根据多光谱图像之间相关性较强和卫星对地通道传输速率有限的特点,利用谱段变换,调整各谱段之间的信息量分配,形成新的谱段数据,并对新谱段数据压缩比进行适当调整,完成多光谱图像数据压缩。采用此算法后,可以使平均压缩比不变的情况下,4个谱段恢复的多光谱图像大部分峰值信噪比（Peak Signal Noise Ratio,PSNR）与直接压缩图像后的PSNR值相比有所提高。     

Lunar laser topography by LALT on board the KAGUYA lunar explorer – Operational history,new topographic data,peak height analysis of laser echo pulses

In this paper we review the lunar laser ranging conducted by the laser altimeter (LALT) on board the KAGUYA lunar explorer (2007–2009). Five aspects of LALT measurements are described: (1) General operational history, (2) Laser shot and data statistics, (3) Revisions to LALT topographic data, (4) Variations in laser output energy, and (5) Peak height analysis of laser echo pulses. LALT was able to range to the lunar surface despite some troubles with respect to laser output energy in the middle of the KAGUYA mission. The time series topographic data set was revised (Ver. 2) by incorporating new lunar gravity model based on KAGUYA and other historical lunar satellite’s orbit data, along with other improvements, for example by incorporating the accurate position of the laser collimator on board the KAGUYA; however, more than half of the acquired range data could not be converted properly due to problems with orbit accuracy during the extended phase of the mission. The spherical harmonic coefficients and the basic lunar figure parameters derived from LALT_LGT_TS agree very well with LRO-LOLA and the Chang’E-1 LAM model. It is possible that partial failure to the laser diode was responsible for the gradual degradation of laser power (0.835 mJ per million shots) and the rapid decrease that occurred over April 9–14, 2008. The laser power also proved to be extremely sensitive to the temperature of the laser oscillator. The peak height ratio – that is peak height telemetry data divided by calculated ratio – is about 19% on average using the mean slope and albedo data from LALT and Spectral Profiler on KAGUYA space craft, respectively, which suggests the performance of peak height measurement is more than 1/5 for more than 70 km altitude, if compared with calculated one. The peak height ratio may be better if we take the effect of small scale topography within a footprint into account.     

Statistical modelling of radio wave propagation under sporadic E-Layer influence

A technique of modelling the one-hop radio wave propagation at middle latitudes in the presence of sporadic E-Layer is presented. The technique is focused on the performance of the long-term forecast of the maximum usable frequency range and on the increase of the radio communication reliability. Examples of calculation for medium-distance paths are shown.     

组件组合方式对两相PDE总压损失和峰值压力影响

为了提高脉冲爆震发动机(PDE)的综合性能,在冷态条件下研究了螺旋钝体组件和扰流片钝体组件的总压损失,同时研究了它们在不同工作频率下的爆震波压力,将两者结合起来进行比较,确定相应组件的损失是有效总压损失还是无效总压损失。研究表明:激波反射器能反射、会聚强激波,增加爆震波峰值压力,因此它的总压损失大部分为有效损失;对于两相混气,平面火焰发生器和中心锥的总压损失基本为无效损失;总体上讲,螺旋钝体组件优于扰流片钝体组件。     

A Method of Inversing the Peak Density of Atomic Oxygen Vertical Distribution in the MLT Region From the OI (557.7nm) Night Airglow Intensity

In this paper, using the MSISE-90 model as the reference atmosphere, we discuss the feasibility and method of deducing the peak densities of the undisturbed atomic oxygen profiles in the MLT region (the mesosphere and lower thermosphere region) from OI (557.7 nm) night airglow intersities. The peak densities for different seasons, latitudes and longitudes are deduced from OI (557.7nm) airglow intensities through this expression. We analyze the features of inversion relative errors and discuss the influence of the variations in temperature on inversion errors. The results indicate that all inversion errors are less than 5% except for those at high altitudes in the summer hemisphere. And the impact of the variations in temperature on errors is not significant.      

基于BLACKFIN561的H.264视频编码优化

H.264视频压缩编码显示了强大的编码性能,较H.263和MPEG-4节省近50%的码率,但这是由H.264成倍增加的复杂度得到的。其代码容量和内存占用对硬件的存储器和计算能力提出了极为苛刻的要求,这就阻碍了其商用方案的发展。通过对H.264编码器的C语言级优化,使其对硬件的存储能力和计算能力的要求大大降低。在此基础上,利用Blackfin561的特性,再将代码进行汇编级优化,使代码更易于向DSP硬件平台移植。