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161.
Tangtang Zhang Jun Wen Zhongbo Su Rogier van der Velde Joris Timmermans Rong Liu Yuanyong Liu Zhenchao Li 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
In this paper, we used the available algorithm for soil moisture estimation over LOPEX05 (the Loess Plateau land surface process Experiment (2005)) area. The available algorithm used ENVISAT/ASAR AP mode VV polarization observational data at a low incidence angle and ground measured soil moistures. The ground measurements were performed in the summer of the 2005 during the LOPEX05 field campaign. The validated results indicate that an average difference between the soil moistures estimated from the microwave remote sensing and ground measurements is less than 0.02 cm3/cm3, with a RMS error of 2.0%, and a maximum less than 0.04 cm3/cm3. The algorithm was applied to the surface soil moisture mapping later. The results show that this algorithm is suitable for monitoring soil moisture information of the agricultural fields over the Chinese Loess Plateau, when ground land cover situation and the resolution of imagery data are taken into account. However, we also find that there are large differences over the steep slope region, the edge of mesa. The results are not acceptable for surface soil moisture estimation in these regions. Thus, the surface soil moisture retrieval in the steep slope region of the Loess Plateau need to be further investigated in the future. 相似文献
162.
Jun Chen Shoujing Yin Rulin Xiao Qianxiang Xu Changsong Lin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The objectives of this study are to validate the applicability of a shortwave infrared atmospheric correction model (SWIR-based model) in deriving remote sensing reflectance in turbid Case II waters, and to improve that model using a proposed green-shortwave infrared model (GSWIR-based model). In a GSWIR-based model, the aerosol type is determined by a SWIR-based model and the reflectance due to aerosol scattering is calculated using spectral slope technology. In this study, field measurements collected from three independent cruises from two different Case II waters were used to compare models. The results indicate that both SWIR- and GSWIR-based models can be used to derive the remote sensing reflectance at visible wavelengths in turbid Case II waters, but GSWIR-based models are superior to SWIR-based models. Using the GSWIR-based model decreases uncertainty in remote sensing reflectance retrievals in turbid Case II waters by 2.6–12.1%. In addition, GSWIR-based model’s sensitivity to user-supplied parameters was determined using the numerical method, which indicated that the GSWIR-based model is more sensitive to the uncertainty of spectral slope technology than to that of aerosol type retrieval methodology. Due to much lower noise tolerance of GSWIR-based model in the blue and near-infrared regions, the GSWIR-based model performs poorly in determining remote sensing reflectance at these wavelengths, which is consistent with the GSWIR-based model’s accuracy evaluation results. 相似文献
163.
164.
《中国航空学报》2020,33(2):465-475
Mach reflection in steady supersonic flow is an important phenomenon having received extensive studies, among which simplified theoretical models to predict the size of Mach stem and other flow structure are of particular interest. Past efforts for such models were based on inviscid assumption while in real cases the flow is viscous. Here in this paper we consider the influence of wedge boundary layer on the Mach stem height. This is done by including a simplified boundary layer model into a recently published inviscid model. In this viscous model, the wedge angle and the trailing edge height, which control the Mach stem height, are replaced by their equivalent ones accounting for the displacement effect of the wedge boundary layer, with the boundary layer assumed to be laminar or fully turbulent. This viscous model is shown to compare well with numerical results by computational fluid dynamics and gives a Mach stem height as function of the Reynolds number and Mach number. It is shown that due to the viscous effect, the Mach stem height is increased, through increasing the effective wedge angle. 相似文献
165.
基于落点预测的高旋火箭弹弹道修正算法 总被引:1,自引:0,他引:1
高旋火箭弹的修正控制是基于等效力实现的二维弹道修正控制,由于弹体存在陀螺进动和马格努斯效应,在控制力作用下产生的附加攻角引起的升力与控制力的矢量合为等效力,其大小与方向在控制过程中不断变化,不能简单根据偏差量(修正量)的比例关系来确定控制力的方向。基于此,分析了控制力与等效力的关系,提出了一种基于弹道落点预测的控制算法。首先利用弹道落点预测模型实时预测落点与目标的偏差量,然后利用小扰动法构造偏差量对控制量的敏感系数矩阵,通过偏差量与敏感系数矩阵解算出纵、横两个方向的需用控制量。采用修正前后速度矢量的位置关系得到控制量的合矢量及其方位角,并利用控制量的合矢量与等效力计算出控制周期,在控制周期内按照等效力方位角调整控制力的方向实现对高旋火箭弹的精确控制,解决了非线性耦合问题。仿真结果表明该算法具有较高的控制精度,为工程应用提供理论依据。 相似文献
166.
根据弹道导弹中段飞行近似为二体运动的特点,应用二体运动理论分析了弹道导弹中段防御的拦截窗口。假设最低拦截点由拦截弹末段寻的飞行正常工作的最低地面高度决定,最高拦截点由拦截弹投射能力决定,给出了根据当前时刻弹道导弹位置和速度求解拦截窗口的算法。对采用最小能量弹道飞行的弹道导弹,给出了根据射程求解拦截窗口的算法,并对不同射程的最小能量弹道,给出了求解拦截窗口的算例。 相似文献
167.
根据目前训练飞行不挂炸弹,起飞质量较轻,冬季飞行发动机推力较大这一特点,通过理论分析及计算,得出了正常起飞质量下起飞所需转速随大气温度的关系,并通过反复试飞证明这一结论是正确的,且对使用小转速起飞的优点作了分析。 相似文献
168.
GPS广域增强系统电离层延迟网格修正算法的研究 总被引:5,自引:0,他引:5
建立了一种广域增强系统地面监测网对电离层延迟的观测数据生成网格修正值算法,并在天津,长春,西安三地通过用双频接收机同时采集的电离层延迟实测数据,对广域增强系统的电离层网格修正法的修正精度进行验证,并与一般用户目前采用的Klobuchar模型修正法进行了比较,结果表明,电离层延迟网格修正法的修正精度普遍大于80%,优于Klobuchar模型修正法,是一种精度较高的电离层实时修正法。 相似文献
169.
利用校正环节提高三级电液伺服阀动态响应的探讨 总被引:2,自引:0,他引:2
许明理 《航空精密制造技术》1997,(5)
论述了通过三级电液伺服阀控制器的改进,利用校正环节提高三级电液伺服阀的阻尼,降低谐振峰值,进而提高三级电液阀的动态响应. 相似文献
170.
分析了经纬仪横轴与竖轴垂直度误差的产生原因及该误差对水平方向观测值的影响,给出了该误差的检定方法,对高低点法和高平点法检定精度进行了分析,并以实验进行了验证。 相似文献