Lu Bai

Effect of window function on absorbing layers top boundary in parabolic equation

Constructing parabolic wave equation model, with the algorithm of discrete mixed Fourier transform, has become the mainstream approach to describe the atmospheric duct. To determine the absorption layer top boundary of parabolic equation is the significant step of the step calculation process. This paper discusses on the relevant problems about setting window function for absorption boundary. Firstly, we proved that two commonly used window: Tukey window and Hanning window are in the same coincident configuration mathematical expressions. Secondly, we put forward some new window functions and verify their availability under a numerical example. And we draw a conclusion on some conditions which should be added to the absorbing top boundary and discussed the effect on one-way path loss in different window functions. Numerical results showed in the paper could verify that the condition of window function we proposed is right.

Evolution of linear edge dislocation in atmospheric turbulence and free space

ABSTRACT In accordance with the extended Huygens–Fresnel principle, the evolution of linear edge dislocation propagating through atmospheric turbulence is studied, and the effects of waist width and the slope of linear edge dislocation are investigated. It is shown that when linear edge dislocation beams propagate through atmospheric turbulence, if the waist width is not equal and the slope is not zero, then the linear edge dislocation vanishes and transforms into an optical vortex with a topological charge of −1 or +1. The optical vortex and an optical vortex that is created annihilate when the transmission distance is far enough. The linear edge dislocation vanishes when the slope is zero. If the waist width is equal, then the linear edge dislocation will vanish regardless of the slope value. For linear edge dislocation beams in free space, when selecting specific parameters, linear edge dislocation always exists.

Density and temperature characteristics of hypersonic aircraft outflow field near the wall

When flying at a high speed or ultra-high speed, The hypersonic aircraft will react violently with the flow nearby. So some density and temperature distribution characteristics appear near the wall. These features will affect the optical imaging system resolution of the target image, and generate pneumatic optical effect. In this paper, we established two optical-hood models of aircraft with different half cone angles by using CFD simulation technology. Fluent were then used to simulate the temperature and density distribution of flow field near the models with different Mach numbers on the same flight altitude. Finally, we studied the variation characteristic of temperature and density with distance increasing from the wall. These studies have reference value on the design of ultra high-speed aircraft and aero-optical bias correction. Besides, improving the optical imaging system in the target image sharpness.

Bidirectional reflection distribution function modeling of material surface in different temperature

Based on the Plancks law and integrality the directional hemisphere reflectivity (DHR) and the Kirchhoffs law. And referred to the Torrance-Sparrow model and the five-parameter semi-empirical model, a new Bidirectional reflection distribution function model (BRDF) is developed in different temperature of material surface, this model will be applicable for various materials.

The application of PE in the propagation of VLF wave in earth-ionosphere waveguide

This paper presents a new method for the calculation of VLF propagation in the earth-ionosphere waveguide using the parabolic equation (PE) method. The PE is commonly used to solve the problem of radio wave propagation within atmospheric ducts at high frequencies. The required initial field, refractive index, and boundary conditions for the calculation of the PE under the environment of the earth ionosphere waveguide are studied. Further, the path loss of VLF after long-distance propagation is simulated. Compared with the waveguide mode theory as well as other commonly used methods for the propagation calculation of VLF, the presented method is simpler.

Ultraviolet bidirectional reflectance distribution function measurement and analysis of typical roughness surface

An experiment measuring system is introduced. Angle-resolved single-band and multispectral bidirectional reflectance distribution function measurements are operated in ultraviolet band. Hemisphere spectral reflectivity of some samples is measured. An optimizing modeling method, particle swarm optimization (PSO) is used to model the laser BRDF data of typical samples. The results are fitted with the models developed above using optimize algorithm to get the parameters. Spectral BRDF of samples calculated with the model are in good agreement with the measured data. And these studies about measuring and optimizing modeling of typical roughness target samples in ultraviolet band have significant meanings in a lot of related fields.