巴丹吉林沙漠北缘拐子湖流沙下垫面近地层湍流强度和陆面过程特征

利用巴丹吉林沙漠北缘拐子湖流沙下垫面2013年7、10月和2014年1、4月的湍流通量资料,计算并分析了研究区近地层湍流强度,同时针对风速分量、温度、水汽和CO₂归一化标准差随稳定度的变化关系和总体输送系数等陆面过程特征进行分析。结果表明：（1）风速各分量的湍流强度均随风速的增加逐渐减小,风速处于2 m·s^-1以下时湍流发展最为旺盛。湍流强度主要由水平方向风速分量决定,垂直方向风速的作用较小,且近中性和不稳定层结利于湍流的发展。与其他地区相比,平坦且没有建筑物的沙漠地区,机械湍流较弱,湍流强度相应较小。（2）风速各分量的归一化标准差与稳定度（z/L）均满足1/3次方函数规律,其中垂直方向风速分量的拟合曲线方程较好。（3）动量输送系数C_d具有明显的夏季高、冬季低的变化状态且各月的日变化形态均呈夜间低、日间高的循环形态。热量输送系数C_h的不同月份日变化间并没有明显的排列次序,且日出日落前后具有明显的波动。不稳定层结时,C_d和C_h均随风速的增加逐渐减小;稳定层结时,C_d和C_h均随着风速的增加逐渐上升。     

Nonlinear numerical simulation on extreme-wave kinematics

A fully nonlinear numerical model based on a time-domain higher-order boundary element method (HOBEM) is founded to simulate the kinematics of extreme waves. In the model, the fully nonlinear free surface boundary conditions are satisfied and a semi-mixed Euler-Lagrange method is used to track free surface; a fourth-order Runga-Kutta technique is adopted to refresh the wave elevation and velocity potential on the free surface at each time step; an image Green function is used in the numerical wave tank so that the integrations on the lateral surfaces and bottom are excluded. The extreme waves are generated by the method of wave focusing. The physical experiments are carried out in a wave flume. On the horizontal velocity of the measured point, numerical solutions agree well with experimental results. The characteristics of the nonlinear extreme-wave kinematics and the velocity distribution are studied here.     

Nonlinear transfer function modelling of beach morphology at Duck,North Carolina

This paper presents a simple nonlinear data-based modelling approach for predicting the beach profile volume at Duck, North Carolina, USA. The state-dependent parameter form of the general transfer function (SDP TF) model is used to describe nonlinearity influencing these morphological data in two case examples. Case 1 investigates the nonlinearity associated with the dependency of wave forcing on the preceding beach volume. Case 2 investigates the ability to model the variables within the well-known diffusion equation for beach volume using this data-based approach. The results of this study show that the SDP TF approach can be used successfully to develop statistically robust models for describing nonlinearity in beach morphological systems. Furthermore, these models are shown to predict the beach volumes over both short (1 month ahead) and long (2 years ahead) time periods, and thus show great potential for practical applications in coastal zone management and engineering.     

改进型经验正交函数海洋声速剖面预报方法

鉴于深海温跃层以下往往声速值缺乏,声速剖面不完整的原因,提出一种声速剖面的预报方法:在传统经验正交函数预报法基础上,首先改进协方差矩阵的求解方法,将原始数据的空间信息和时间信息有效地融合到协方差矩阵中,通过由大量实测数据统计得出的时间函数的经验公式,得到合成剖面,将二者结合,把不完整剖面垂直向下延拓到海底,较为有效地解决了传统方法求解协方差矩阵和时间函数较粗糙的问题,给出了完整的海洋声速剖面的准确预报.实测数据检验结果表明,改进方法的预报精度比传统方法有了很大提高.     

一个波浪破碎散射模型的改进

为了得到与实测数据更为一致的散射模型,对KHCC03散射模型进行了改进.研究了考虑波浪破碎影响的KHCC03散射模型的适用范围.研究结果表明,KHCC03散射模型在入射角为25°～40°范围内,模型结果与实测数据吻合较好,在入射角小于25°和入射角大于40°的情况下,模型结果与实测数据差异较大.针对这一问题,对KHCC03模型进行了改进,结果表明:与原KHCC03模型相比,改进后的模型结果与实测数据吻合程度明显提高.     

An Efficient Model for Transient Surface Waves in Both Finite and Infinite Water Depth

A numerical model is developed to simulate fully nonlinear extreme waves in finite and infinite water-depth wave tanks. A semi-mixed Eulerian-Lagrangian formulation is adopted and a higher-order boundary element method in conjunction with an image Green function is used for the fluid domain. The boundary values on the free surface are updated at each time step by a fourth-order Runga-Kutta time-marching scheme at each time step. Input wave characteristics are specified at the upstream boundary by an appropriate wave theory. At the downstream boundary, an artificial damping zone is used to prevent wave reflection back into the computational domain. Using the image Green function in the whole fluid domain, the integrations on the two lateral walls and bottom are excluded. The simulation results on extreme wave elevations in finite and infinite water-depths are compared with experimental results and second-order analytical solutions respectively. The wave kinematics is also discussed in the present study.     

一种自适应匹配子空间亚像元目标探测方法

为了克服基于线性混合模型的高光谱遥感影像亚像元目标探测方法的缺陷, 提出了一种基于全限制性线性分解的自适应匹配子空间探测方法。首先利用交叉相关光谱匹配技术求得各个像元所含端元类别信息, 然后根据端元类别信息和全限制性分解的结果构造自适应匹配子空间探测算子, 利用端元类别信息在探测中动态选择端元, 降低端元数目估计偏差对探测结果的影响, 提高探测器对目标与背景的可分性。实验证明, 该方法与其他基于线性混合模型的亚像元目标探测方法相比, 可以更好地克服端元数目估计偏差对探测结果的影响, 无论是端元个数低估还是     

植被电磁散射的半空间模型研究

本文给出了地面植被电磁散射的半空间模型研究方法.在以往的相关文献中,均采用自由空间格林函数求解单个叶片散射体的散射场,本文利用半空间并矢格林函数求出了单个散射体的散射场,然后运用Monte Carlo方法模拟生成地面植被层,得到了在半空间下植被层的电磁散射特性,计算出了单、双站雷达散射截面,并与自由空间下的散射场做了相互对比.结果表明,在半空间格林函数下得到的散射场更为适用于描述地面植被的电磁散射特性.     

基于EOS/MODIS数据的NDVI与EVI比较研究

作为NOAA/AVHRR 归一化植被指数(NDVI) 的延续和发展, EOS/MODIS 归一化植被指 数(NDVI) 和增强植被指数( EVI) 在许多领域得到广泛应用。应用数理统计和地统计学方法对二 者进行的对比研究表明: NDVI 在植被生长旺盛期容易达到饱和, 而EVI 则能克服这一现象, 比 较真实地反映植被的生长变化过程; 相同空间分辨率下, EVI 取值范围、标准差与变异系数均高 于NDVI, NDVI 数据比较均一, 其空间相关性高于EVI, EVI 更能反映研究区域内植被空间差异。 关键词:MODIS; 归一化植被指数(NDVI) ; 增强植被指数( EVI) ; 对比     

Annual Frequency of Tropical Cyclones Directly Affecting Guangdong Province:Prediction Based on LSTM-FC

Tropical cyclone(TC) annual frequency forecasting is significant for disaster prevention and mitigation in Guangdong Province. Based on the NCEP-NCAR reanalysis and NOAA Extended Reconstructed global sea surface temperature(SST) V5 data in winter, the TC frequency climatic features and prediction models have been studied.During 1951-2019, 353 TCs directly affected Guangdong with an annual average of about 5.1. TCs have experienced an abrupt change from abundance to deficiency in the mid to late ...