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Xianyang, China

Wang L.-G.,Xidian University | Wu Z.-S.,Xidian University | Wang M.-J.,Xianyang Normal College
Wuli Xuebao/Acta Physica Sinica

Rytov theory combined with the ABCD ray matrix is used to analyzes the statistical property of a reflected wave from a retro-reflector caused by atmospheric turbulence. The covariance function and the scintillation index of the receiving field caused by the combined effect of the turbulence and the random shaking of the reflector array are deduced on the basis of the mutual statistical independence of the two kinds of effects. The aperture factor and the scintillation of a receiving aperture with a finite size are calculated, and those of the retro-reflector and the array are compared to prove that the array does not change distribution of the intensity fluctuation but amplifies the fluctuation by a factor of 2. © 2013 Chinese Physical Society. Source

Wang R.,Xidian University | Wu Z.,Xidian University | Zhang Y.,Xidian University | Wang M.,Xianyang Normal College
Hongwai yu Jiguang Gongcheng/Infrared and Laser Engineering

The terahertz wave provided greater communication bandwidth and capacity than millimeter. Compared with the visible light and the infrared light, THz pulses had longer wavelength propagating in the random medium, not only caused the temporal and spatial deformation, but also affected on the incident particle scattering, then the pulse signal attenuation occurred. Based on the Mie theory, using the discrete distribution of particles with the random wave transmission and scattering theory, the extinction coefficient of fog droplet in the terahertz wave was calculated. And the extinction coefficients of different wavelengths of terahertz wave change with the particle size were analyzed. Considered the droplet particle size distribution, the average albedo and phase function were obtained under different wavelengths. Finally, propagation characteristics of terahertz signals in fog particles by different visibilities were analyzed. The result shows that in the atmospheric environment, the absorption and attenuation of fog in terahertz wavelength can not be ignored, the imaginary part of the refractive index changes greatly with different wavelengths, and the transmission of the THz wavelength in fog is seriously impacted. Source

Li Y.-Q.,Xidian University | Wu Z.-S.,Xidian University | Zhang Y.-Y.,Xidian University | Wang M.-J.,Xianyang Normal College
Chinese Physics B

Based on the modified Rytov theory and the international telecommunication union-radio (ITU-R) slant atmospheric structure constant model, the uniform scintillation index of partially coherent Gaussian - Schell model (GSM) beam propagation in the slant path is derived from weak- to strong-turbulence regions considering inner- and outer-scale effects. The effects of wavelength of beams and inner- and outer-scale of turbulence on scintillation are analyzed numerically. Comparison between the scintillation of GSM beams under the von Karman spectrum and that of beams under the modified Hill spectrum is made. The results obtained show that the scintillation index obtained under the von Karman spectrum is smaller than that under the modified Hill spectrum. This study can find theory bases for the experiments of the partially coherent GSM beam propagation through atmospheric turbulence. © 2014 Chinese Physical Society and IOP Publishing Ltd. Source

Liu W.,Northwest University, China | Chang Q.-R.,Northwest University, China | Guo M.,Northwest University, China | Xing D.-X.,Northwest University, China | And 2 more authors.
Guang Pu Xue Yu Guang Pu Fen Xi/Spectroscopy and Spectral Analysis

The hyperspectral reflectance of soil was measured by a ASD FieldSpec within 400~1000 nm. Next, its first derivative of spectra were acquired and de-noised by the threshold de-noising method based on wavelet transform. From the de-noised derivative spectra, absorption areas used as indicatoresas for soil organic matter content were acquired by numerical integration. Results show that: (1) Because of much noise, it is difficult to identify spectra contour and features in the first derivative of soil spectra resulting from different organic content levels. (2) When the scale of wavelet decomposition was 3, the threshold de-noising method based on wavelet transform can keep the balance between smoothing curve and holding spectra features. (3) Absorption area S(538, 586) is extracted from de-noised first derivative of soil spectra, and the coefficient of correlation between it and organic matter content is 0.8963. Source

Xiang N.,Xidian University | Wu Z.,Xidian University | Wang M.,Xianyang Normal College
Hongwai yu Jiguang Gongcheng/Infrared and Laser Engineering

Based on the extended Huygens-Fresnel integral, the cross-spectral density and Rytov's phase structure function, average intensity was derived by a formula for the Fourier transform of Gaussian function. Then mean squared root beam width, beam wander of a partially coherent Gaussian-Schell-model (GSM) beam in turbulent atmosphere were found out. It shows that beam spread and beam wander have relation with initial beam radius, initial coherence width, wavelength and transmitter hight in the atmospheric turbulence. At last, some measures were brought to decrease the effect of atmospheric turbulence. Source

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