Surface temperature estimation in Singhbhum Shear Zone of India using Landsat-7 ETM+ thermal infrared data

Land surface temperature (LST) is an important factor in global change studies, heat balance and as control for climate change. A comparative study of LST over parts of the Singhbhum Shear Zone in India was undertaken using various emissivity and temperature retrieval algorithms applied on visible and near infrared (VNIR), and thermal infrared (TIR) bands of high resolution Landsat-7 ETM+ imagery. LST results obtained from satellite data of October 26, 2001 and November 2, 2001 through various algorithms were validated with ground measurements collected during satellite overpass. In addition, LST products of MODIS and ASTER were compared with Landsat-7 ETM+ and ground truth data to explore the possibility of using multi-sensor approach in LST monitoring. An image-based dark object subtraction (DOS3) algorithm, which is yet to be tested for LST retrieval, was applied on VNIR bands to obtain atmospheric corrected surface reflectance images. Normalized difference vegetation index (NDVI) was estimated from VNIR reflectance image. Various surface emissivity retrieval algorithms based on NDVI and vegetation proportion were applied to ascertain emissivities of the various land cover categories in the study area in the spectral range of 10.4–12.5 μm. A minimum emissivity value of about 0.95 was observed over the reflective rock body with a maximum of about 0.99 over dense forest. A strong correlation was established between Landsat ETM+ reflectance band 3 and emissivity. Single channel based algorithms were adopted for surface radiance and brightness temperature. Finally, emissivity correction was applied on ‘brightness temperature’ to obtain LST. Estimated LST values obtained from various algorithms were compared with field ground measurements for different land cover categories. LST values obtained after using Valor’s emissivity and single channel equations were best correlated with ground truth temperature. Minimum LST is observed over dense forest as about 26 °C and maximum LST is observed over rock body of about 38 °C. The estimated LST showed that rock bodies, bare soils and built-up areas exhibit higher surface temperatures, while water bodies, agricultural croplands and dense vegetations have lower surface temperatures during the daytime. The accuracy of the estimated LST was within ±2 °C. LST comparison of ASTER and MODIS with Landsat has a maximum difference of 2 °C. Strong correlation was found between LST and spectral radiance of band 6 of Landsat-7 ETM+. Result corroborates the fact that surface temperatures over land use/land cover types are greatly influenced by the amount of vegetation present.     

车模比例和风洞截面对轿车气动性能影响

采用三维不可压缩N-S(Navier-Stokes)方程和RNG k-ε(renormalization group k-ε)湍流模型仿真计算汽车流场特性.控制界面的物理量应用二阶迎风差分格式获得,并运用SIMPLEC压力修正法进行迭代.选用不同车模比例和风洞截面形状进行仿真计算,分析了车模比例和风洞截面形状对轿车气动性能的影响.结果表明:车模比例在一定范围内,汽车气动参数变化平缓;选用不同的车模比例在三种典型风洞模型中进行仿真计算,结果相差很大.      

阴阳极进气量对附加场磁等离子体推力器性能的影响

针对附加场磁等离子体推力器阴阳极供气量对推力器性能的影响进行了研究。采用试验方法测量了稳态AF MPDT的束流参数以及放电电压、放电电流、附加磁感应强度等工况参数,测量计算了推力、效率等性能参数。通过改变阴阳极供气比例,分析研究了初始气体分布对推力器性能及物理机制的影响。研究结果显示,阴极供气比重增大时,推力器推力及效率相应增大,但增大到一定比例,推力器出现工作不稳定导致性能下降,说明阴阳极存在最佳的供气比例,表明供气比例对推力器性能具有重要影响。     

基于微分对策的导弹攻击策略

利用建立的垂直平面内交战双方攻击模型,应用微分对策理论,得到导弹的最优攻击策略,对比微分对策导引律与比例导引律在多种仿真环境下的结果,说明在近距离交战中,基于微分对策理论的导引律设计具有更大的优越性。     

基于预测模型迭代优化的改进比例导引律

为了提高对加速度时变机动目标的制导精度,将预测决策理论与传统比例导引(PN)相结合,提出了一种通过泰勒级数预测模型迭代控制加速度修正项的改进比例导引律。首先,以预设的低阶泰勒级数预测模型预测特定时间的位移,并计算位移预测值与测量值的差值;然后,通过迭代方法逐阶增加泰勒级数预测模型阶数,直至满足精度要求;最后,计算泰勒级数预测模型的二阶导数,修正比例导引律的加速度指令。仿真结果表明,传统PN和APN的脱靶量分别约为195 m和95 m,提出的改进比例导引律的脱靶量约为8.3 m,极大地提高了制导精度。     

空间磁场环境模拟线圈驱动恒流源设计

针对空间磁场环境模拟线圈磁感应强度0~20 Gs连续可调,磁场稳定度优于1%的要求,采用前级电压源与后级电流源串联的主电路拓扑结构,结合电压双闭环控制和电流闭环负反馈控制的方法,实现了稳定的电流输出,减小了功率金属-氧化物半导体场效应晶体管(MOSFET)的功耗,提高了恒流源的效率.测试结果表明:恒流源输出电流0~10 A连续可调,霍姆赫兹线圈中心磁感应强度能达到20 Gs的设计要求,电流稳定度优于0.1%,磁场稳定度优于1%.      

铺层比例对层合板连接结构损伤特性影响分析

复合材料螺栓连接结构,其铺层比例、铺层顺序对整体结构连接效率具有重要影响.基于ABAQUS有限元软件平台,对其进行二次开发定义材料损伤退化方法,建立三维渐进损伤模型对不同铺层比例复合材料层合板螺栓连接结构的损伤扩展及破坏特性进行数值模拟分析,计算结果与验证试验结果吻合较好.分析仿真与试验结果表明:对于CCF300/BA9916Ⅱ型复合材料层合板螺栓连接结构,铺层比例对结构连接效率有重要影响,合理确定±45°层比例可以显著提高孔边应力集中区的抗挤压和抗剪切能力,有效改善连接结构的破坏模式;在±45°层比例增加到50％之后,复合材料层合板螺栓连接结构的连接强度将不再显著提高.     

Ni含量及超声振动对激光熔覆中裂纹的影响

增加熔覆粉末中N i含量可以减少熔覆层中的硬质相,使熔覆层脆性降低,韧性提高,因而提高熔覆层在冷却过程中对拉应力的承受能力,减少熔覆层裂纹;而在熔覆过程中施加超声振动,则可以打碎枝晶,细化晶粒,减少或消除拉应力产生的根源,并使熔池化学成分、温度分布趋于均匀,从而减少裂纹的产生几率。     

企业领导力综合评价模型构建与实证研究

通过对三家国有工业企业的问卷调查,搜集了相关数据,利用因子分析法,确定了各指标的权重,构建了企业领导力综合评价模型,并利用综合评价模型对企业的领导力分别进行了评价。     

仿真输出非平均性能测度的Bayes估计

考虑离散事件仿真中一个非平均性能测度－－比例的估计问题，在对有关比例的已有估计方法的概述和分析的基础上，提出了一种比例的Ｂａｙｅｓ估计方法和贝塔分布的区间估计方法，从实验上对这些方法进行了研究和比较，从而证明了Ｂｅｙｅｓ方法能合理地给出比例的估计，而且仿真精度在大样本情形比已有方法略有提高，在小样本情形有明显的改进。