二维线性与非线性海面的宽带散射特性仿真及分析

Simulation and Analysis for Wide-band Scattering Characteristics of 2-D Linear and Nonlinear Sea Surfaces

该文基于加权曲率近似方法（Weighted Curvature Approximation, WCA），实现了对2维线性与非线性海面的宽带电磁散射信号的仿真，并通过大量的蒙特卡洛仿真研究了距离高分辨率条件下各距离单元内海杂波统计特性，特别是尖峰特性。研究结果表明，当雷达分辨率提高、雷达入射视线方向由侧风转向逆风、海面风速增加时，海杂波强度概率密度曲线（Probability Density Function, PDF）的长拖尾现象将更加明显。同时，非线性海面的宽带散射回波信号中出现尖峰现象的概率更高。此外，对海杂波统计分布曲线的拟合结果表明，与传统的K分布和Weibull分布相比，Pareto分布在较小擦地角条件下能够更好描述海杂波强度的统计特性。

Objective The study was conducted to establish the warning baseline according to the condition in Beijing to make scientific and effective early warning of influenza epidemic. Methods Weekly numbers of influenza-like illness cases in level 2 or 3 hospitals and weekly data of virologic surveillance from 2007 to 2014 in Beijing were used to establish the warning baseline. Results The baseline of influenza ear- ly warning in Beijing was 2. 30%, sensitivity and specificity were 50. 67% and 97.03%, respectively. The result of Kappa analysis was 0. 55（ P 〈 0. 001）. Conclusions The baseline of influenza early warning had good sensitivity and specificity, which can play certain roles in early warning.