Propagating Characteristics of Pulsed Laser in Rain

International Journal of Antennas and Propagation, Sep 2015

To understand the performance of laser ranging system under the rain weather condition, we need to know the propagating characteristics of laser pulse in rain. In this paper, the absorption and attenuation coefficients were calculated based on the scattering theories in discrete stochastic media, and the propagating characteristics of laser pulse in rain were simulated and analyzed using Monte-Carlo method. Some simulation results were verified by experiments, and the simulation results are well matched with the experimental data, with the maximal deviation not less than 7.5%. The results indicated that the propagating laser beam would be attenuated and distorted due to the scattering and absorption of raindrops, and the energy attenuation and pulse shape distortion strongly depended on the laser pulse widths.

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Propagating Characteristics of Pulsed Laser in Rain

Propagating Characteristics of Pulsed Laser in Rain Jing Guo,1 He Zhang,2 and Xiang-jin Zhang2 1School of IOT, Nanjing University of Posts and Telecommunications, Nanjing 210003, China 2ZNDY of Ministerial Key Laboratory, Nanjing University of Science and Technology, Nanjing 210094, China Received 28 March 2015; Revised 10 August 2015; Accepted 12 August 2015 Academic Editor: Ikmo Park Copyright © 2015 Jing Guo et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract To understand the performance of laser ranging system under the rain weather condition, we need to know the propagating characteristics of laser pulse in rain. In this paper, the absorption and attenuation coefficients were calculated based on the scattering theories in discrete stochastic media, and the propagating characteristics of laser pulse in rain were simulated and analyzed using Monte-Carlo method. Some simulation results were verified by experiments, and the simulation results are well matched with the experimental data, with the maximal deviation not less than 7.5%. The results indicated that the propagating laser beam would be attenuated and distorted due to the scattering and absorption of raindrops, and the energy attenuation and pulse shape distortion strongly depended on the laser pulse widths. 1. Introduction Laser detection becomes more and more important in remote measurement, for its highly monochromatic and coherent, high energy density and fine time resolution [1]. Meanwhile, it is also well known that light propagating in atmosphere is highly scattered by atmospheric hydrometeors and aerosols, occasionally causing an extreme high attenuation of the received power [2–6]. Rainfall is one of the most common types of precipitation. As pulsed laser propagates in rain, the interaction of light with raindrops, such as absorption and scattering, will take place, so the received signal is attenuated and distorted which leads to the degradation of laser ranging performance. Therefore, the investigation of light propagation in rain is an indispensable part of the design of the laser ranging system. Some pertinent propagation models are developed in the past researches. Wojtanowski et al. [7] analyzed the propagating characteristics of pulsed laser with wavelengths of 905 nm and 1550 nm in rain and fog. Lakshmi et al. [8] studied rain attenuation at 11 GHz based on the measured Drop Size Distribution (DSD). Choi [9] presented the measurement results of rain-induced attenuation at 12.25 GHz during some rain events; their measured results are in good agreement with the ITU-R prediction. Wang et al. [10] calculated the scattering phase functions for droplets and raindrops based on the Mie theory and compared the extinction measurements from Forward Scattering Visibility Meter (FVM) with those from manual observations during fog and rain. Dhawan and Singh [11] investigated the effect of the various atmospheric conditions including fog, snow, and rain on the FSO link. Some other studies combined the empirical relationships with the knowledge based on the theoretical analysis of light scattering in rain and fog [12–14]. While being sufficient for practical purposes, the available research results do not present the whole characteristics of the laser propagation in rain and these characteristics are very important to the design of laser ranging system. As a result, the propagating characteristics and energy attenuation of pulse laser in rain are comprehensively studied in this paper. The Monte-Carlo (MC) method is utilized to study the relationship of optical attenuation and the physical parameters of rain, and the controlled experiments are carried out to verify the theoretical simulation. 2. Propagation and Attenuation of Pulsed Laser in Rain The performance of laser ranging system can be demonstrated by a laser ranging equation, which is commonly used to estimate the maximum detection range and influence factors of ranging system. The optical echo power reflected by the target is provided by a classical ranging equation [15]:where is the peak power of emitting laser pulse, is the spectral transmission of emitting optics, is the spectral transmission of receiving optics, is the transmission of narrow band filter, is the target’s reflectivity coefficient, is the receiving aperture area, is the angle between the normal of target surface and the optical axis, is the target distance, and is the atmospheric extinction coefficient at distance . From (1), pulse echo characteristics are related to the process of laser propagation in atmosphere and reflection on the target surface. In order to track the target and measure its range in the complex atmospheric conditions (such as rain, dust storms, and fog), the influence of atmosphere must be consider (...truncated)


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Jing Guo, He Zhang, Xiang-jin Zhang. Propagating Characteristics of Pulsed Laser in Rain, International Journal of Antennas and Propagation, 2015, 2015, DOI: 10.1155/2015/292905