Sea surface emissivity observations at L-band: first results of the Wind and Salinity Experiment WISE 2000

Sea surface salinity can be measured by passive microwave remote sensing at L-band. In May 1999, the European Space Agency (ESA) selected the Soil Moisture and Ocean Salinity (SMOS) Earth Explorer Opportunity Mission to provide global coverage of soil moisture and ocean salinity. To determine the effect of wind on the sea surface emissivity, ESA sponsored the Wind and Salinity Experiment (WISE 2000). This paper describes the field campaign, the measurements acquired with emphasis in the radiometric measurements at L-band, their comparison with numerical models, and the implications for the remote sensing of sea salinity.     

Tests of sequential data assimilation for retrieving profile soilmoisture and temperature from observed L-band radiobrightness

Sequential data assimilation (Kalman filter optimal estimation) techniques are applied to the problem of retrieving near-surface soil moisture and temperature state from periodic terrestrial radiobrightness observations that update soil heat and moisture diffusion models. The retrieval procedure uses a time-explicit numerical model to continuously propagate the soil state profile, its error of estimation, and its interdepth covariances through time. The model's coupled soil moisture and heat fluxes are constrained by micrometeorology boundary conditions drawn from observations or atmospheric modeling. When radiometer data are available, the Kalman filter updates the state profile estimate by weighing the propagated state, error, and covariance estimates against an a priori estimate of radiometric measurement error. The Kalman filter compares predicted and observed radiobrightnesses directly, so no inverse algorithm relating brightness to physical parameters is required. The authors demonstrate Kalman filter model effectiveness using field observations and a simulation study. An observed 1 m soil state profile is recovered over an eight-day period from daily L-band observations following an intentionally poor initial state estimate. In a four-month simulation study, they gauge the longer term behavior of the soil state retrieval and Kalman gain through multiple rain events, soil dry-downs, and updates from radiobrightnesses     

准直光束的温度场影响分析

在激光准直技术中,产生误差的主要因素有激光光束漂移、光线弯曲和随机抖动。对大尺寸激光准直测量,后两项误差的影响尤其突出。近年来产生了自适应准直的思想,即控制反射镜等元件的运动,使光束通过两个基准孔径,以期得到光线基准。这种方法是建立在“光直线传播”的基础上,然而这个条件在真实大气中是不满足的。本文根据对长距离激光准直光束特性的分析,提出了多点监测、综合补偿的准直方法,这种方法的特点是建立一个任意曲线的光束轨迹模型。由于这个模型是根据现场实测数据建立的,综合考虑了三个误差因素的相互影响和作用,因而具有较高的精度,较广泛的适应性和较大的应用范围     

A lamp power control scheme for dimmable electronic ballasts to minimize the temperature effect on the lamp brightness

A hybrid lamp power control scheme for dimmable electronic ballasts is proposed. Apart from adjusting the brightness of the lamp, the proposed method can also minimize the ambient temperature effect on light output. Instead of regulating the lamp current, the proposed method is based on regulating the power supplying the lamp. First, the dimming operation is achieved by regulating the dc voltage at the ballast inverter input. Second, variation of the lamp power (due to the temperature effect) is regulated by sensing the inverter average input current to adjust the switching frequency of the inverter. An 18 W prototype has been built and tested. The lamp power and luminous output of the prototype at the ambient temperature from 5/spl deg/C to 35/spl deg/C have been studied.     

A new method for temperature mapping on GaAs field effect transistors

In this paper, a method is described, how to apply the technique of spatially resolved photoluminescence (PL) spectroscopy for the measurement of the local channel temperature in GaAs-based field effect transistors. This spectroscopic technique uses a focused laser beam which scans directly the surface of a chip inside its package. The temperature is deduced from the corresponding wavelength shift of the PL peak. In the case of a typical heterostructure-based transistor (like the pseudomorphic high electron mobility transistors studied here) a spatial resolution of 1 pm and a temperature resolution of °C is demonstrated.     

基于磁流体磁体积效应的磁场与温度双参量传感器

为了实现磁场与温度的同时测量,提出并制作了一种基于磁流体(magnetic fluid,MF)磁体积效应的法布里-珀罗(Fabry-Perot,FP)腔与光纤布拉格光栅(fiber Bragg grating,FBG)级联的复合传感结构。注入空芯光纤(hollow-core fiber,HF)的MF液面与单模光纤端面形成的FP腔同时对磁场和温度敏感,与之级联的FBG只对温度敏感。通过同时监测FP腔特征峰与FBG布拉格反射峰的波长漂移,利用传感器磁场与温度敏感系数矩阵,同时获取温度与磁场信息。实验成功制备了初始腔长为56.1μm的FBG-FP温度磁场双参量传感器,磁场与温度灵敏度分别达到了16.21 pm/Oe和9.96 pm/℃,具有体积微小、结构简单、成本低等特点。该传感器可解决常规光纤磁场传感器的磁场-温度交叉敏感问题。     

Impact of horizontal and vertical heterogeneities on retrievals using multiangle microwave brightness temperature data

This paper investigates the impact of heterogeneity at the land surface on geophysical parameters retrieved from multiangle microwave brightness temperature data, such as would be obtained from the Soil Moisture and Ocean Salinity (SMOS) mission. Synthetic brightness temperature data were created using the Common Land (land surface) Model, coupled with a microwave emission model and set within the framework of the North American Land Data Assimilation System (NLDAS). Soil moisture, vegetation optical depth, and effective physical temperature were retrieved using a multiobjective calibration routine similar to the proposed SMOS retrieval algorithm for a typical on-axis range of look angles. The impact of heterogeneity both in the near-surface profiles of soil moisture and temperature and in the land cover on the accuracy of the retrievals was examined. There are significant errors in the retrieved parameters over regions with steep gradients in the near-surface soil moisture profile. These errors are approximately proportional to the difference in the soil water content between the top (at 0.7 cm) and second layer (at 2.7 cm) of the land surface model. The errors resulting from heterogeneity in the land cover are smaller and increase nonlinearly with increasing land-surface heterogeneity (represented by the standard deviation of the optical depth within the pixel). The most likely use of retrieved soil moisture is through assimilation into an LDAS for improved initiation of weather and climate models. Given that information on the soil moisture profile is already available within the LDAS, the error in the retrieved soil moisture as a result of the near-surface profile can be corrected for. The potential errors as a result of land-surface heterogeneity can also be assessed for use in the assimilation process.     

Tissue cooling and its effect on brightness temperatures by contact-type microwave applicators

Contact of an applicator on the skin surface may cool the tissues so that the resulting brightness temperature measured by the applicator is varied. The tissue cooling effect on the brightness temperature was quantitatively evaluated. From the experimental results, it was concluded that an accurate temperature control was needed in order to reduce the errors in the brightness temperature. A new method of temperature control which permits continuous measurement of the thermal responses of a human body was attempted, and advantages and disadvantages of the method are discussed. The research results may be practical and useful for the accurate measurement of brightness temperature.     

“电磁场与电磁波”无线电测向课外实验

电磁场与电磁波是电子信息工程专业中学习难度较大的课程,其公式繁多,概念抽象,学生入门较难。在无线电测向运动中需要使用发射电台、接收机等电子设备,要求在实践中应用电磁波的传播、矢量叠加等相关知识。以无线电测向运动为载体,开发无线电测向接收机天线方向图绘制课外实验,将抽象的天线理论知识变得直观,并与工程实践进行结合,让学生在实践中理解天线方向图、天线转台、测试方法等相关理论知识,能够极大增强学生学习兴趣,提升电磁场与电磁波课程教学质量。     

红外高温温度场中非完全温度点重建方法与预测精度的研究

在高温温度场重建过程中,仍然需要通过温度场的单点温度值来构建整个温度场的温度分布情况。以焊接温度场为例,通过反距离加权法、克里格法和样条函数法三种插值方法,分别对其空间变异和布局进行了分析和重建。结果表明:不同插值方法对预测精度影响不显著,而采样点数量则显著影响了温度场空间分布的重建精度。在温度场重建过程中,25个采样点进行重建是比较适宜的采样数量。将得出的结论与最佳采样公式进行比较,发现使用公式计算的最佳采样数量相对偏低,说明不考虑采样点实际的空间变异情况,仅使用最佳公式得到的采样数量进行温度场的重建会导致重建结果的不准确。     

Immunity against temperature variability and bias point invariability in double gate tunnel field effect transistor

The weak dependence of the Tunnel Field Effect Transistor (TFET) device characteristics on temperature provides an edge over the conventional MOSFETs in terms of its reliable operation over a wide temperature range applications. This study focusses on the analog/RF performance comparison of DG-TFET and DG-MOSFET, and the impact of temperature variations on some of the key parameters like VIP₃ and intrinsic device gain (g_m * R_out) and the variation of the optimum bias point. In the study of linearity and analog performance, g_m3 (third order derivative of I_ds ? V_gs), VIP₃ in conjunction with intrinsic gain are considered to select the optimum bias point to achieve high gain and better linearity performance. The impact of temperature variations on the ambipolar behavior of a TFET has also been studied.     

温度对液晶波前校正器响应速度及LUT的影响研究

温度起伏会对液晶器件的相位调制特性、响应速度有影响,从而影响自适应光学系统中的液晶波前校正器的相位调制精度。针对该问题,本文研究了温度对512×512像素的硅基液晶波前校正器(LCOS)的LUT(look-up table)的影响,正是由于LUT的变化导致其相位调制特性不同;实验测量了不同温度下LCOS的时间和相位响应特性,由此计算了对应的LUT,利用最小二乘拟合方法对得到的数据进行拟合,给出了16～26℃范围内的关系式,利用此关系式可以获得该温度范围内不同温度下合理的LUT。我们在LCOS上施加闪耀光栅灰度图后,对不同LUT下入射光束的衍射效率分别进行测量,结果表明我们利用关系式内对应温度下的LUT取代LCOS中固定值的LUT方法可以克服温度的起伏带来的影响,提高LCOS的相位调制能力。本方法对于液晶器件在自适应光学、显示等领域的应用也有帮助。     

MEMS器件WLP封装温度特性的有限元模拟分析与实验

圆片级封装(WLP)技术是一种常用于微电子机械系统(MEMS)器件封装的有效方法。对于具有可动结构的MEMS器件来说,WLP的温度特性会对其性能和可靠性产生重要影响。通过对具有不同面阵列凸点分布形式的WLP封装结构进行有限元模拟,分析了封装过程中芯片有源面在温度载荷影响下的应力分布和变形情况,并通过实验对有限元模拟结果进行了修正。结果表明:对于具有3×3,6×6,9×9面阵列凸点分布形式的WLP封装结构来说,其芯片有源面变形的实际测试结果与修正后的模拟结果非常吻合,误差量分别为5.4%,4.1%和0.3%。     

基于温度和发射率场的涂层损伤检测方法

在现代化国防和航空航天领域,目标表面涂覆具有热防护、电磁屏蔽、降低红外辐射等性能的材料,可有效保护目标,但其处于目标的表面,长期受到周围环境影响,易出现气泡、划痕、脱落等不同类型的损伤,造成涂层性能大幅度降低,无法有效保护目标。因此,需要定期对目标涂层进行检测和维护。通过研究涂层损伤与温度和发射率之间的关系,结合热辐射定律、比色测温技术、发射率测量方法,搭建一套红外热像仪的检测装置,提出一种基于涂层温度和发射率场的涂层损伤检测方法。将研制的检测装置应用于以铝为基底的氧化铝涂层,通过分析氧化铝的温度和发射率准确识别涂层内部和外部损伤,验证了基于温度和发射率场的涂层损伤检测方法的理论模型,以及检测装置的可行性与适用性。     

Influence of annealing temperature on field emission from tetrapod-shaped ZnO-whisker films obtained by screen printing

Tetrapod-shaped zinc oxide whisker-film emitters were fabricated on indium tin oxide glass substrates using a screen-printing method. The influence of annealing temperature on field emission of tetrapod-whisker ZnO-based emitters was investigated. X-ray diffraction and scanning electronic microscopy were applied to characterize the structure and the surface morphology of the deposited films. It was found that ZnO-based emitters annealed at 250 °C have the best field emission properties with the lowest turn-on field of 2.6 V/μm at a current density of 1 μA/cm², the lowest threshold field of 5.2 V/μm at a current density of 1 mA/cm² and high field emission enhancement factor of 4129. Moreover, films with homogeneous, fine and dense light spots with low emission current fluctuation of 1.7% were obtained from samples annealed at 250 °C.     

基于降维算法从少量测量数据中重构温度场

由于测量环境及测量技术的制约,工业中温度信息的获取主要依据少量测点数据,难以得到被测对象完整温度信息。计算方法可以获得被测对象完整温度信息,但计算量大,信息再现实时性差。为了解决这个问题,实现快速、有效、准确的实时温度分布测量,提出一种基于Gappy POD低维表示的温度分布降维重建算法,从少量局部温度测量数据准确中重建温度场,并分析采用上述算法进行温度场重构时POD基个数、测点数量和测点位置对其的影响。通过双峰温度场模型重建结果和误差分析表明,重建误差在1×10^-10以下,且该算法显著地减少了测量传感器的数量,降低了温度分布测量的复杂性与测量成本,为工业测量中数据缺失提供新的解决思路。     

激光扫描速率与熔覆层组织性能的规律研究

为了研究在激光熔覆修复工艺中，激光扫描速率对最终形成的熔覆层性能的影响，采用同步送粉法，利用激光熔覆工艺在QT500球墨铸铁上制备了不同扫描速率下的镍基合金熔覆层样本；利用金相显微镜观察熔覆层的显微金相，并使用显微硬度计对熔覆层显微硬度进行了测定与分析，取得了熔覆层样品的硬度、显微金相组织以及样品稀释率等数据。结果表明，在其它条件不变下，随着激光扫描速率的增加，熔覆层组织更加致密、均匀，熔覆层的平均显微硬度得到了显著提高；以激光功率为1.9kW、扫描速率为5mm/s、光斑直径为4mm等参量得到的熔覆层组织与性能最优。此研究对激光熔覆表面强化工艺中合理选择工艺参量提供了理论依据。