Wu Zhensen

The Study of MMW and MW Attenuation Considering Multiple Scattering Effect in Sand and Dust Storms at Slant Paths

The influence of sand and dust storms on modern MMW and satellite communication systems reliability have been paid more attention to. The attenuations induced by sand and dust storms are estimated by means of Mie-theory and Rayleigh approximation, in the case of the tenuous distribution of particles. With the particle density increasing, however, these method become inadequate, the multiple scattering effects then become dominant for attenuation estimation. The attenuations considering multiple scattering effects are estimated by Monte-Carlo and four fluxes method at horizontal paths. At slant paths, based on multi-layer media model, the attenuations considering multiple scattering effects are calculated by layered Monte-Carlo method at 100, 37, 24, and 14GHz. It is shown that the multiple scattering effects should be considered at the attenuation prediction in the sand and dust storm, which the visibility is about 0.5km and smaller than 0.5km and frequency is about 20GHz. Above 30GHz, the multiple scattering effects due to sand and dust particles should be considered, as visibility is about 1km and smaller than 1km at slant paths.

Bistatic scattering by arbitrarily shaped objects with rough surface at optical and infrared frequencies

The scattering cross sections for arbitrarily shaped dielectric objects with rough surface are determined for optical and infrared frequencies using the Kirchhoff approximation. The formula of the coherent scattering cross section is derived, and numerical method of incoherent scattering cross section is given. As a specific example, the infrared laser scattering cross sections of rough spheres are calculated at 1.06 μm.

Millimeter-wave attenuation due to fog and clouds

Millimeter wave applications are becoming increasingly considered and exploited in order to satisfy the demand for new communications systems, active and passive remote sensing, etc. Fog may be one of the dominant factors in determining the reliability of millimeter wave systems, especially in coastal areas where dense moist fog with high liquid water content and larger drop size happen frequently. Clouds are similar to fog, the attenuation due to clouds may be a factor of importance especially for microwave systems well above 10 GHz or low-availability systems.The parameters of gamma drop size distribution model of fog and clouds are derived based on the liquid water content and optical visibility, the attenuation are calculated and discussed with this model and empirical relations of the liquid water content and the visibility or other parameters of fog and clouds. A new empirical formula to estimate fog and clouds attenuation is presented based on the Reyleigh absorption approximation, which is more accurate in general and can be used in wider frequency and temperature range than other empirical formulas.

Analytical model of a laser range profile from rough convex quadric bodies of revolution.

Profile information about a three-dimensional target can be obtained directly by analyzing two-dimensional data of the pulse laser range profile (LRP). The profile, shape, and posture of the target can be detected using LRPs. An analytical LRP model from rough convex quadric bodies of revolution is presented. This model can be used to analyze the effects of geometric parameters, surface material, and orientation on LRPs. The numerical results of the effects on LRPs of four typical targets are given. Based on the results of the simulated model and theoretical analysis, the rough convex quadric bodies of revolution can be identified. The analytical expressions of this model are significant in the application of LiDAR imaging.

Steady-state bright-dark vector spatial solitons in biased photorefractive-photovoltaic crystals

We show that bright–dark vector solitons are possible in biased photorefractive–photovoltaic crystals under steady-state conditions, which result from both the bulk photovoltaic effect and the spatially nonuniform screening of the external bias field. The analytical solutions of these vector solitons can be obtained in the case of |σ|≪1, where σ is the parameter controlling the intensities of the two optical beams. In the limit of −1<σ⩽1, these vector solitons can also be determined by use of simple numerical integration procedures. When the bulk photovoltaic effect is neglectable, these vector solitons are bright–dark vector screening solitons studied previously in the |σ|≪1 regime, and predict bright–dark vector screening solitons in the −1<σ⩽1 regime. When the external bias field is absent, these vector solitons predict bright–dark vector photovoltaic solitons in closed and open circuits.

An analytic model of specific attenuation due to rain

Rain attenuation is one of the dominant factors in determining the reliability of microwave and millimeter systems; the specific rain attenuation is a fundamental quantity in calculation of rain attenuation statistics for terrestrial and earth-space paths. The power-law relationship of specific rain attenuation y/sub R/ (dB/km) and rain rate R (mm/h), y/sub R/ = kR/sup a/ is widely used and the values of k and a are usually tabulated for specific frequencies. The values tabulated are particularly convenient for estimation of specific attenuation in experimental applications or link designs at specific frequency, and the interpolated values should be used for other frequencies. However, It would be quite useful for system studies requiring calculations at many frequencies to have simple analytic expressions which give results in good agreement with the values tabulated. Regression to determine the relationships between the parameters, k and a, and frequency has been done and the regressed expressions given.

Polarimetric scattering from a two-dimensional improved sea fractal surface

This paper studies the influence of wind parameters and fractal dimension from an improved two-dimensional sea fractal surface on the polarimetric scattering by using facet integration. A two-dimensional improved sea surface simulated is discretized into three matrices of sea surface facets including a height matrix and two slope matrices on orthogonal directions. Based on the Kirchhoff approximation, the polarimetric scattered field is derived in the Cartesian coordinate system by integration of three matrices mentioned above. Finally, the fully polarised radar cross section is numerically simulated and the dependence of the polarimetric scattering on the sea fractal surface, such as the wind speed, the wind direction, as well as the fractal dimension, is discussed in detail.

Debye Series of Scattering by a Multi-Layered Cylinder in an Off-Axis 2D Gaussian Beam

The Debye series of light scattering by an infinite multi-layered cylinder in an off-axis 2D Gaussian beam is studied. A simplified but rigorous iterative formula for scattering coefficients is presented. The numerical calculations of scattering intensity by a cylinder in on-axis and off-axis beams are developed. It is indicated that the results of Debye series reach an agreement with those of generalized Lorenz–Mie theory and the off-axis distances vary the results to a great extent. The Debye series components of a two-layered cylinder are further discussed. The relations between them with rainbow phenomena are analysed.

Temporal Skewness of Electromagnetic Pulsed Waves Propagating Through Random Media with Embedded Irregularity Slab

Electromagnetic pulsed waves can be distorted in the propagation through random media, and their energy distributions change along the leading and trailing edge of the waveform, which can be presented by the temporal skewness. The skewness presents asymmetry and is treated by the third-order temporal moment, in which an analytic solution for the two-frequency mutual coherence function is obtained recently. Then, transionospheric pulses are discussed in details. Both theoretical analysis and numerical computation indicate that the contributions from scattering and dispersion of irregularities dominate over those of background, so the latter can be neglected in most cases. Also, the temporal skewness of a transionospheric pulse is negative and energy is shifted to the leading edge.

Propagation modeling of ocean-scattered low-elevation GPS signals for maritime tropospheric duct inversion

The maritime tropospheric duct is a low-altitude anomalous refractivity structure over the ocean surface, and it can significantly affect the performance of many shore-based/shipboard radar and communication systems. We propose the idea that maritime tropospheric ducts can be retrieved from ocean forward-scattered low-elevation global positioning system (GPS) signals. Retrieval is accomplished by matching the measured power patterns of the signals to those predicted by the forward propagation model as a function of the modified refractivity profile. On the basis of a parabolic equation method and bistatic radar equation, we develop such a forward model for computing the trapped propagation characteristics of an ocean forward-scattered GPS signal within a tropospheric duct. A new GPS scattering initial field is defined for this model to start the propagation modeling. A preliminary test on the performance of this model is conducted using measured data obtained from a 2009-experiment in the South China Sea. Results demonstrate that this model can predict GPS propagation characteristics within maritime tropospheric ducts and serve as a forward model for duct inversion.