Zhen Sen Wu

Automatic Classification of Dayside Aurora in All-Sky Images Using a Multi-Level Texture Feature Representation

In this paper, we propose an aurora classification method using a multi-level feature representation aimed to capture both global and local texture information, and to reduce the feature space dimension substantially. First-order and second-order statistics are computed for an input image and its low-frequency scaled images at three lower levels obtained using wavelet decomposition. The features include gray level distribution, co-occurrence matrix features, and run-length matrix features. A support vector machine (SVM) classifier was trained and tested on a Chinese Arctic Yellow River Station dayside aurora image dataset. Classification performance was evaluated and compared with those of k-nearest neighbor (KNN) classifiers and back-propagation neural networks (BPNN). To explore the possibility of using a smaller feature space, we used a Minimum-Redundancy Max-Relevance feature selection strategy. The result shows that there is only indistinct performance decrease by reducing the feature vector from a total of 88 to the most discriminatory 38 features. This proves that our multi-level feature representation is very robust.

The Angle Distribution of the Spheroid Particle upon Optical Surface

The angle distribution of the spheroid particle upon optical surface is discussed in this paper. Taking the advantage of the Bobbert-Vlieger (BV) theorem, the scattering model between optical surface and spheroid particles is established. The scattering process is analyzed and the scattering coefficients are derived by using of the vector spherical harmonic function. The differential scattering cross section (DSCS) of a spheroid particle upon the optical surface is calculated which is compared with the Discrete Sources Method (DSM) proved the validity of the method and the influences of the incident angle and scattering angle on the DSCS are analyzed numerically in details. The results show that the influence of the incident angle on the scattering intensity is less at the smaller scattering angle, which can be concluded that the influence of the incident angle is more serious to the back scattering .The polarization effect and back scattering effect become weaker and weaker with the increase of the incident angle, which provide strong theoretical foundation to the nondestructive detector engineer.

Coding Algorithms of Aurora Image Compression Based on Wavelet Transformation

This paper introduced some significant applications of aurora images, listed the main factors of choosing wavelet basis in image compression coding and analyzed the influence of aurora image compression effect caused by different wavelet basis were experimentally. The results of two kinds of significant wavelet transform algorithms EZW and SPIHT were analyzed, compared and also experimentally improved.

Decomposing the Non-Gaussian Surface in Sum of Gaussian Surfaces

The decomposition of the multivariate Non-Gaussian PDF in the sum of a Gaussian PDF instead of the Gram-Charlier series is investigated. Four parameters need to be found by minimizing the integrated square of the difference between Cox-Munk function and its approximation. The backscattering radar cross section (RCS) of the surface is calculated by the Kirchhoff approximation (KA) under different value of k using the formula of decomposition of the Non-Gaussian. The condition of KA satisfying electromagnetic scattering scale from Gaussian and Non-Gaussian surfaces is taken into account by computing the backscattering coefficients in HH and VV polarity.

Scattering Characteristics of Complex Target from Solar Irradiance and Sky-Ground Background Radiance in Infrared Spectrum

Scattering characteristic of complex target from the solar irradiance and sky-ground background radiance plays an important role in both theoretical researches and practical engineering. The solar irradiance and sky-ground background radiance and scattering property are discussed in this paper. BRDF (Bidirectional Reflectance Distributional Function) relates incident irradiance with scattering radiance while LRCS (Laser Radar Cross Section) shows the scattering characteristic of complex target. By using KA (Kirchhoff Approximation) method, we calculate the LCRS of facet of target and then get BRDF of each facet. Then all the visible faces are added up. Due to the complexity of the atmosphere model, MODTRAN is used to calculate the solar irradiance and background radiance. Finally, to give an example, a model airplane is taken for instance. The results indicate the effectiveness of the method we proposed.

Phase-Only Beam Optimization for GaAs Optical Waveguide Phase Array

Optical waveguide phased arrays have highlighted advantages than other electro-optical material optical arrays in scanning angle, response speed etc. For diffraction fields of uniform waveguide have strong side-lobes, which have influence on scanning performance of phased arrays. So side-lobes compression is one of the main issues for optical waveguide phased array device development. Based on photoelectric effect, the relations of voltage and phase are analysised. Phase-only array beam control using a Genetic Algorithm, an efficiency-optimized scheme, for uniform optical waveguide array with process errors is proposed. Phase distributions are arranged as randomly increasing distributions and random distributions. The results show phase-only optical waveguide arrays control, without the reconstruction of devices, has fine side-lobes compression effects with -9.89[dB] side-lobes intensity ratio. So the performance of scanning beams gets well improved.

The Three-Dimensional Analysis of Light Scattering Characters for Rayleigh Particles On/Below the Wafer

Laser light scattering is a powerful tool for its noncontract nature and its convenience to nondestructive examination in the semiconductor industry. Taking the advantage of the scattering matrixes, the models of particulate contaminants on the wafer and subsurface defects are established, respectively. And the bidirectional reflectance distribution functions are derived. The results show that when the Rayleigh particle is on the wafer, the variation of BRDFpp is smooth without gulch for a definite incident angle. However, there is a gulch with the increment of scattering angle and the position of gulch is reduced with the increment of incident angle. When the Rayleigh particle is below the wafer, with an identical incident angle, there is a gulch with the variation of scattering azimuth angle. In addition, BRDFpp becomes larger and larger with the incident angle of p polarization light increment. The conclusions provide theoretical basis for quality evaluation and identify the information of contaminants detected in the semiconductor industry.

Path Loss of Non-Line-of-Sight Single-Scatter Model

Based on the single-scatter model of the Non-Line-of-Sight(NLOS), we analyze the effect of the geometric parameter of the transceiver on path loss, such as the receiver field of view(FOV), the transmitter apex angle and so on. And path loss in different visibility and weather conditions are simulated. The simulation results show that increasing the receiver FOV, or reducing the transmitter apex angle or the receiver apex angle can reduce path loss. And visibility and weather have an important effect on path loss.

Study of Aperture-Averaged Scintillation for a Partially Coherent Gaussian Schell-Model Beam Propagation in Slant Atmospheric Turbulence

Based on the extended Huygens-Fresnel principle, scintillation of a partially coherent Gaussian Schell-model (GSM) beam propagation in weakly slant atmospheric turbulence is studied. The expression of aperture-averaging factor of the system receiver is derived. We analyzed the aperture-averaged scintillation index numerically. A comparison of the aperture-averaged scintillation of the beam propagation in slant path with that of the beam propagation in horizontal path is made. Results obtained show using partially coherent beams and considering aperture-averaging effect can decrease the scintillation and improve the optical communication system performance.

Study of Electromagnetic Scattering Characteristics from Typical Land Surface with Integral Equation Method

Based on the equivalent dielectric model, the permittivity of the soil and simple plants which are assumed to satisfy exponential rough surface model is calculated. The electromagnetic scattering coefficients for the two types of rough surfaces are investigated by the Integral Equation Method (IEM) with the changing dielectric constant. The detailed analysis and discussions are made. And the results obtained are in good agreement with the experimental results.