数字滤波弱约束四维变分同化在台风初始化中的应用(Ⅱ):数字滤波权重选择

数字滤波权重的选择是影响台风路径和强度预报的重要因素,某些个例中直接决定着台风数值模拟的成功与否,合适的数字滤波权重非常重要.本文利用2010年3个台风7个不同初始时刻个例,开展数字滤波弱约束四维变分同化(4D-Var)台风初始化试验,分析不同数字滤波权重对台风路径和强度预报的影响;基于上述台风路径和强度预报后验统计信息,以及台风中心区域800 km范围和整个模拟区域3 h平均地面气压倾向信息,提出一种bogus资料同化台风初始化中数字滤波权重优选方案,并进行理论解释说明;同时,指出bogus资料同化台风初始化中,常规数字滤波权重为1000更合理,明显有别于常规天气和暴雨天气权重设置.     

基于100 m色散位移光纤的超连续谱实验研究

利用被动锁模掺铒光纤激光器输出的重复频率13.9 MHz、中心波长1557.28 nm的光脉冲作泵浦源,在100 m的色散位移光纤中产生总宽度达488 nm的超连续谱,不平坦度小于±3.0 dB,利用法布里-珀罗滤波器获得163路多波长脉冲,利用可调谐滤波器得到C波段内脉宽为1.2～2.0 ps的近变换限超短光脉冲.分析了泵浦脉冲的功率、光纤长度等因素对SC光谱展宽的作用,并与色散平坦光纤和较长的色散位移光纤作了比较.     

A novel spectroscopic filter used in rotational Raman lidar for the temperature profiling

We perform the rotational Raman temperature measurements in the troposphere and lower stratosphere with high performance. Depending on the aerosol content and presence of clouds in the lower troposphere, the rotational Raman lidar (RRL) is the lidar technique of choice for temperature measurements. However, the Raman filter design is a technical difficulty in RRL systems. Considering the higher spectral resolution and compactness, we select several photonic crystals to construct a novel spectroscopic filter for extracting the required rotational Raman spectrum (RRS) signals of atmospheric molecules. We describe in detail the principle to design the photonic-crystal filter. To verify the feasibility of the novel spectroscopic filter, we carry out some numerical calculations, and our results show that the novel spectroscopic filter has the capability to fine draw the required RRS signal and suppress sufficiently elastic signals. For the RRL system which uses the novel spectroscopic filter, we obtain that a statistical temperature error is less than 1 K up to a height of 3.2 and 5.6 km for daytime and nighttime measurements, respectively. Our simulation conditions are as follows: 532 nm laser with 500 mJ energy, and 10 Hz pulse repeating rate, a 300 mm diameter Cassegrain reflecting telescope with 1000 mm focus length, 0.2 mm diameter multimode optical fiber which sets the field of view (FOV) of receiving system to 0.2 mrad, 45 m range resolution, 9 min observation time, overall optical-system efficiency of 0.6, and a special atmospheric model which integrates the US standard model of 1976 with an actual Mie scattering profile obtained from practical observations.     

Ultraviolet Raman lidar for high-accuracy profiling of aerosol extinction coefficient

An ultraviolet （UV） Raman lidar system at 354.7 nm has been developed for accurately measuring the aerosol extinction profiles. A spectroscopic filter combining a high-spectral-resolution grating with two narrowband mirrors is used to separate the vibrational Raman scattering signal of N2 at a central wavelength of 386.7 nm and the elastic scattering signal at 354.7 nm. The aerosol extinction is derived from the Raman scattering of N2 and the elastic scattering by the use of Raman method and Klett method, respectively. The derived results of aerosol extinction are used to compare the difference of two retrieval methods, and the preliminary experiment shows that the Raman lidar system operated in analog detection mode has the capability of measuring aerosol profiles up to a height of 3 km with a laser energy of 250 mJ and an integration time of 8 min.     

TUNABLE FIBER FABRY-PEROT FILTER FOR OPTICAL CARRIER-SUPPRESSION AND SINGLE-SIDEBAND MODULATION IN RADIO OVER FIBER LINKS

A novel method of simultaneous realization of optical carrier-suppression and single-sideband modulation using fiber Fabry-Perot tunable filter is presented. In order to enhance transmission performance of radio over fiber links, we use a fiber Fabry-Perot tunable filter to filter out one sideband as well as suppress the optical carrier power. The results demonstrate 20.5dB and 14.2dB improvement in the signal noise ratios when 18GHz and 10GHz microwave signals carrying 5Mbit/s quadrature-phase-shift-keyed (QPSK) format data is transmitted over 35 km single mode fiber, respectively.     

X频段连续波100 kW吸收式谐波滤波器研制

为了抑制深空探测高功率发射机谐波能量对接收机的干扰,提出了一种基于渐变漏壁式波导加载吸收负载结构的超大功率谐波滤波器.分析了该结构滤波器衰减损耗特性,并结合电磁场仿真软件,对滤波器整体结构进行了仿真,依据仿真尺寸对滤波器进行了结构设计和样件加工,经过对样件测试,滤波器通带最大插入损耗小于0.3 dB,二次、三次及四次谐波抑制度分别大于75, 50, 35 dB,测试结果与仿真结果基本一致.对滤波器样件进行了高功率实验,在外加液冷条件下,连续波功率容量可达100 kW以上,成功研制出了一种X频段吸收式超大功率谐波滤波器,并已经应用于某型号大功率地面发射机,指标性能良好.     

联合方位-径向速度的粒子滤波目标运动分析

纯方位目标运动分析方法要求观测平台有效机动才能估计目标运动状态,针对这一问题,联合径向速度与方位角作为测量信息对目标进行运动分析,但基于卡尔曼滤波算法进行解算需要已知粗略的目标状态初始值,且收敛时间较长、误差较大,不利于目标实时跟踪.针对以上问题,提出了一种基于粒子滤波的方位径向速度联合目标运动分析方法,建立目标运动状态分析的粒子滤波算法模型,对目标位置和速度等运动要素进行估计.在目标初始状态未知的情况下,一定程度上缩短了收敛时间,减小了估计误差,海试数据处理结果显示:相同条件下,与原有方法相比,本文所提方法收敛时间从35.1 min缩短至30.0 min;跟踪精度从6.1%提高至3.8%,且无需已知目标状态初始值。     

A detection of atmospheric relative humidity profile by UV Raman lidar

A new spectroscopic filter constructed with a high-spectral-resolution grating and two narrow-band mirrors is designed to separate the elastic scattering and the vibrational Raman scattering spectra in an ultraviolet (UV) Raman lidar system. The density of humidity and water vapor mixing ratio are calculated from the vibrational Raman scattering signals of N₂ and H₂O. Water vapor mixing ratio is retrieved from this development. With this measured water vapor mixing ratio, the relative humidity is calculated with atmospheric temperature profile obtained by another Raman temperature lidar. Preliminary experiments and comparison results between lidar and radiosonde showed that the UV Raman lidar system has the capability for profiling the water vapor mixing ratio up to a height of 2 km with less than 10% of the uncertainty under the conditions of laser energy of 300 mJ and signal-averaging time of 10 min.     

Where the ocean influences the impulse response and its effect on synchronous changes of acoustic travel time

In 1983, sounds at 133 Hz, 0.06 s resolution were transmitted in the Pacific for five days at 2 min intervals over 3709 km between bottom-mounted instruments maintained with atomic clocks. In 1989, a technique was developed to measure changes in acoustic travel time with an accuracy of 135 microseconds at 2 min intervals for selected windows of travel time within the impulse response. The data have short-lived 1 to 10 ms oscillations of travel time with periods less than a few days. Excluding tidal effects, different windows exhibited significant synchronized changes in travel time for periods shorter than 10 h. In the 1980s, this phenomenon was not understood because internal waves have correlation lengths of a few kilometers which are smaller than the way sound was thought to sample the ocean along well-separated and distinct rays corresponding to different windows. The paradox's resolution comes from modern theories that replace the ray-picture with finite wavelength representations that predict sound can be influenced in the upper ocean over horizontal scales such as 20 km or more. Thus, different windows are influenced by the same short-scale fluctuations of sound speed. This conclusion is supported by the data and numerical simulations of the impulse response.     

40 Gbit/s非等幅编码光时分复用传输系统

4× 10Gb s非等幅编光时分复用 (OTDM)传输系统采用增益开关分布反馈式激光器 (GS DFB)产生超短光脉冲 ,通过色散补偿光纤 (DCF)和梳状色散光纤链 (CDPF)实现了脉冲的线性和非线性压缩 ;利用啁啾光纤光栅实现色散补偿 ;在接收端 ,利用电吸收调制器 (EAM)实现了光时分复用信号的解复用 ;同时采用非等幅编码方案提取帧时钟。整个系统经过 12 2km的G .6 5 2光纤传输之后 ,误码率小于 10 - 9。     

Analysis of Multiple Melting of High-Speed Melt Spun Polylactide Fibers Based on Kinetic Modeling

Multiple melting behavior of high-speed melt-spun polylactide (PLA) fibers was investigated by temperature modulated differential scanning calorimetry (TMDSC) in the heating process with various modulation periods in the calorimeter. In the case of the as-spun PLA fibers taken-up at 1 km/min, a melting endothermic peak and a recrystallization exothermic peak appeared at the same peak temperature of 151°C in the reversing and non-reversing heat flows (RHF and NRHF), respectively, whereas at 168°C, an endothermic peak was observed in both the RHF and NRHF. On the other hand, the as-spun PLA fibers taken-up at a high-speed of 6 km/min showed the melting in both the RHF and NRHF, but the recrystallization behavior was not obvious in the NRHF at the shorter modulation period conditions. The obtained data were analyzed based on the kinetic modeling of melting proposed by Toda et al. The real and imaginary parts of the complex apparent heat capacity in the melting region showed a strong modulation period dependence for both the low- and high-speed spun fibers. The endothermic heat flow of melting was separated by extrapolating the frequency to zero. For the PLA fibers spun at 1 km/min, a set of melting and recrystallization peaks in the RHF and NRHF appeared even for the melting at 168°C. In other words, the simultaneous occurrence of melting and recrystallization was confirmed through this extrapolation. For the 6 km/min PLA fibers, the presence of an exothermic heat of recrystallization was clearly confirmed at a peak temperature of 164°C.     

单矢量水听器的高分辨目标方位跟踪算法研究

根据单矢量水听器自身具有阵列流型的特点,提出了适用于对目标保持连续跟踪的空域预滤波MUSIC算法。通过调整滤波器通带中心角使其保持在目标估计方位角附近,可以消除滤波器通带中心角偏离目标真实方位角时传统预滤波MUSIC算法产生的目标方位估计误差。仿真结果表明,改进预滤波MUSIC算法可以减小甚至消除低信噪比情况下目标方位估计存在的较大误差。海试数据结果表明,阵元域MUSIC和改进预滤波MUSIC都可实现对单频脉冲信号和线性调频信号的目标方位估计,且估计结果与GPS舰位推算结果一致,但改进预滤波MUSIC算法主瓣更尖锐。对宽带航船噪声处理结果显示,改进预滤波MUSIC算法使单矢量水听器在存在目标干扰时的探测距离从2 km提升到了5 km,验证了改进预滤波MUSIC算法可实现弱目标情况下的高分辨目标方位跟踪。     

Ultraviolet high-spectral-resolution Rayleigh-Mie lidar with a dual-pass Fabry-Perot etalon for measuring atmospheric temperature profiles of the troposphere

We report what is believed to be the first demonstration of measurement of tropospheric temperature profiles in daytime by use of a high-spectral-resolution Rayleigh-Mie lidar at an eye-safe wavelength of 355 nm. Atmospheric temperature is determined from the linewidth of the Rayleigh spectrum. Two Rayleigh signals are detected with Fabry-Perot etalon filters with a dual-pass optical layout. The Mie signal is detected with a third etalon filter for correcting the Mie component in the Rayleigh signals. The temperature statistical uncertainties are below 1 K up to a height of 3 km in nighttime and 2 km in daytime with a relatively compact system that uses laser energy of 180 mJ and a 25-cm telescope. Good agreement between lidar and radiosonde measurements is obtained.     

Experimental study of mode selection in shallow-water sea

The possibilities of matching low-frequency underwater sound pulses to the parameters of an oceanic waveguide are considered. The objective is to optimize the system of few-mode tomographic observation in a shallow-water sea. Experimental data are analyzed for two methods of selecting the low-frequency fewmode pulses propagating in a shallow-water sea. The first method excites probe pulses by vertically elongated arrays, with spatial filtering after vertical or horizontal arrays receive the pulses. The second method is based on exciting broadband signals with linear frequency modulation by a single transmitter. The selection of the few-mode signal is performed by time strobing the signals at the output of the matched filter after a horizontal array receives the pulses. The distance between the sound sources and receiving systems varied from 10 to 300 km.     

56 Gb/s direct-detection polarization multiplexing multi-band CAP transmission

Carrierless amplitude and phase(CAP) modulation is generating increasing interest for short-reach optical communications. Polarization multiplexing(Pol Mux) is a good way to improve the CAP system's data rate further with the limited bandwidth of electrical devices. In this Letter, we experimentally demonstrate a 56 Gb/s directdetection Pol Mux CAP system over a 15 km fiber link for the first time, to our best knowledge. Two-band CAP modulation with different modulated orders for each band is employed. An optical filter at the receiver is utilized to realize the polarization separation. No extra digital signal processing for polarization-dependent distortion is required.     

An algorithm for the automatic detection of anomalous temperature variations at ground level: its application to the METEOSAT-2 satellite

Summary The algorithm, starting from techniques typical of image processing and information theory, is an instrument for the detection of anomalous variations in any physical parameter measured by remote sensing. Within a software system capable of checking the validity of such a measurement, comparing it with extant historical data and reporting it, the algorithm acts as a filter able to amplify the anomaly. The aim of this work is to see if it possible to detect anomalous temperature variations in some way connected with fire at ground level by means of the sensors in the infrared heat band of the METEOSAT-2 satellite. The choice of this geostationary satellite was made because, despite low spatial resolution (at the latitude of Sardinia pixels are about 7 km square), it has good time resolution (one slot every 30 minutes).     

不同滤波方法对揭示全球海洋条带结构的比较

海洋条带结构是近年物理海洋学研究的一个新热点. 在海洋中, 条带结构往往被大尺度环流过程所掩盖. 把这种隐蔽的海水运动现象显现出来的办法是对时间平均的速度场进行空间滤波. 利用全球简单海洋资料同化分析系统资料和中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室的气候系统海洋模式模拟数据对三种一维滤波方法进行了比较, 分别是常用的高斯和汉宁滤波方法, 以及本文引入的切比雪夫滤波方法. 结果表明, 尽管三种方法均可获得条带结构, 但以切比雪夫方法为最佳; 另外, 设计高通滤波器时需设定截断频率, 而它的选定取决于对具体数据的频谱分析, 当选取的归一化的截断频率值在0.1和0.4之间时, 可以有效地揭示出条带结构在全球海域内的分布. 因此本文的研究方法为海洋条带结构的深入研究提供了一个有力工具.     

Initial spring temperature profiles of the mesopause region over Fort Collins,CO, measured by the Colorado State Na temperature lidar

After its first measurement in late August, 1989, the new Na temperature lidar has been in operation during springs 1990 and 1991 at Fort Collins, CO. A total of nine nights (over 2600 profiles) of mesopause temperature measurements, each for a period longer than 4 hours, have been taken. We present these high quality initial profiles which demonstrate the effectiveness of the new two-frequency narrowband lidar technique for mesopause temperature measurements. The average temperature profiles suggest that the spring mesopause temperatures range from 168 K to 205 K. The mesopause heights are around 88 km before the midnight and around 99 km after the midnight. The nightly averaged temperature profiles in the mesopause region display considerable variability. The richness in new geophysical information obtainable with a Na temperature lidar is made evident by noting strong perturbations in a short time scale (15 min) in the data taken on March 11, 1990 and March 18, 1991.     

Generation of ionospheric irregularities upon propagation of solitary internal gravity wave during the major magnetic storm of October 29–31, 2003

Using the technique of global detection of ionospheric disturbances, based on processing the data of the global GPS-receiver network, we obtain experimental proof of the existence of a solitary wave (soliton) in the atmosphere during the main phase of the major magnetic storm of October 30, 2003. The soliton with a characteristic duration of about 40 min and a relative amplitude of up to 40%, originated at the moment of the maximum disturbance of the Earth’s magnetic field, traveled without changing its shape at a distance of up to 4500 km with a velocity of 1400 m/s, which exceeded the atmospheric sound velocity at the heights of the main electron-density maximum in the ionosphere (about 300 km) by a factor of 1.5. The intensity of variations in the total electron content in the period range 1–10 min increases by an order of magnitude as the soliton propagates from the North-East to the South-West of the USA in the regions with the maximum amplitude of the large-scale disturbance. This corresponds to enhancement of ionospheric irregularities with scales from 10 to 100 km, and also of small-scale irregularities (SSI) with scales of 100 to 1000 m, since the spectrum of the ionospheric irregularities has a power-law shape. Spatio-temporal characteristics of the density distribution of phase slips of GPS signals are close to the corresponding characteristics of the SSI intensity. This agrees with the existing concept that the phase slips result from scattering of GPS radio signals by SSIs. Both the SSI amplitude and the density of phase slips decrease as the soliton decays in amplitude. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 2, pp. 89–104, February 2006.     

Fiber Structure,Tensile Behavior and Antibacterial Activity of Polylactide/Poly(butylene terephthalate) Bicomponent Fibers Produced by High-Speed Melt-Spinning

Abstract

Various types of bicomponent fibers composed of polylactide (PLA) and poly(butylene terephthalate) (PBT) with different molecular weights, arranging the polymers separately in the skin or core, were produced by high-speed melt-spinning. The bicomponent spinning, arranging the PLA with high molecular weight (melt flow rate =1.9?g/10?min, L-lactide content = 98.7%) in the skin and the PBT with low molecular weight (IV = 0.835–0.865 dL/g) in the core, resulted in orientation-induced crystallization in the PLA component at the spinning speed of 2?km/min. This crystallization effect was ascribed to a chain-extending treatment applied to the original PLA (MFR = 4.0?g/10?min) to increase its molecular weight. By the treatment the PLA could crystallize when spun even at 1?km/min in its single-component spinning. On the other hand, the bicomponent spinning system interfered with the orientation-induced crystallization of PBT in the core. As a result, the critical spinning speed needed to generate the orientation-induced crystallization in the core PBT was elevated to 4?km/min. The inferior tensile behavior of the bicomponent fibers, as compared to the single-component PLA or PBT fibers, suggested poor compatibility between PLA and PBT. Transesterification reactions rarely occurred at the interface of the two polymers. The bicomponent fibers prepared from high molecular weight PLA and low molecular weight PBT, however, showed sufficient antibacterial activity and physical properties to be suitable for designing medical clothing materials.