| Laser detection has the advantages of high precision,good directionality,short detection time and strong anti-electromagnetic interference ability.It is widely used in military fields such as lidar,laser communication,laser fuse and laser guidance.However,laser detection is easily affected by discrete media such as smoke and dust,cloud and fog,rain and snow or other media in the environment.During laser transmission,it will scatter and absorb with media particles in the environment,resulting in laser energy attenuation and change of transmission direction.At the same time,it will produce backscattered echo interference,which will cause laser detection system to respond incorrectly and seriously affect the working performance of laser detection system.Taking the pulsed laser proximity fuze as the research object,this paper studies the characteristics of pulsed laser interfered by the smoke and dust environment of the complex battlefield near the ground in the process of detecting targets.Firstly,it introduces the current research status of the scattering characteristics of particles,the transmission characteristics of pulsed laser in smoke and dust environment and the pulsed laser anti smoke and dust interference at home and abroad,and summarizes the main research contents of this paper.Secondly,the physical characteristics of the smoke and dust environment and the scattering characteristics of smoke and dust particles are studied,and the physical characteristics such as the composition of the near ground smoke and dust environment,the shape,refractive index and particle size distribution of smoke and dust particles are analyzed.Through the measurement of the collected soot samples,its micro appearance shape and particle size distribution are obtained,and confirm that the particle size distribution is log-normal distribution.The calculation methods of Mie scattering of spherical particles and T matrix scattering of non-spherical particles are described,and the scattering characteristics of single soot particles and polydisperse particle swarm are compared and analyzed.The effects of different effective radius,ratios of long and short axes,wavelength of incident light and refractive index on the scattering of smoke and dust particles are studied,and the relationship between the mass concentration of smoke and dust and the extinction coefficient of the polydisperse particle swarm is deduced.Then the multiple scattering process of the pulsed laser when detecting the target in the smoke and dust environment is analyzed,and the echo receiving model in the inhomogeneous smoke and dust environment is established.The traditional Monte Carlo method is improved to deal with the smoke and dust field in layers,the photon random walk step,the photon scattering direction,the target reflection direction are sampled with random numbers.The laser emission pulse is divided into photon packets,the receiving probability of each time series of photons is calculated by the semi-analytical receiving method to obtain the echo impulse response function,which is convoluted with the transmitted signal to obtain the echo signal.The simulation analyzes the difference between the backscattered echo signal of smoke and the target echo signal,the effects of different laser parameters such as different transmitting pulse width,the distance between transmitting and receiving system,receiving field angle and laser wavelengths on the echo signal without target and the effects of different transmitting pulse width,target distance and reflectivity of target on the received echo signal with target are compared and analyzed.It is obtained that when the transmitting pulse width is narrow,the smoke and dust backscattering echo signal has obvious broadening in time domain,When the target is detected by narrow emission pulse width laser,two peak signals can be observed obviously.The amplitude of smoke backscattering echo decreases with the increase of the distance between transmitting and receiving system and receiving direction angle.Through the simulation results,the anti smoke and dust backscattering interference methods of pulse laser fuze are summarized: using narrow pulse width and collimated laser or using dual wavelengths laser detection,increasing the distance between transmitting and receiving system or receiving direction angle to increase the short-range blind area and reduce the field of view angle.Then the laser transmitting and receiving system is designed,and the smoke and dust environment simulation test field with real-time monitoring of smoke and dust concentration is built.The measured smoke and dust concentration data shows that the simulated smoke and dust environment tends to be stable after about nine hundred seconds by many experiments,which verified the consistency of the simulated smoke and dust environment in the closed smoke and dust field.Finally,the influence experiment of smoke environment on pulsed laser echo is carried out to obtain the relationship between smoke concentration and echo peak value with or without target in soot environment.The experiment is carried out by adjusting the the distance between transmitting and receiving system and receiving direction angle.When there is no target in the detection field of view,the echo amplitude increases with the increase of the smoke concentration,and decreases with the increase of the the distance between transmitting and receiving system and the receiving direction angle.When there is a target in the detection field of view,two echo peak signals are receiving by using the narrow pulse width laser.According to the results of experiment,the simulation conclusion of the multiple scattering echo simulation is verified.It is concluded that using narrow pulse width to emit laser,increasing the distance between transmitting and receiving system or receiving direction angle can effectively reduce smoke and dust backscattering interference,which provides theory support and experimental reference for improving the anti smoke and dust interference ability of pulsed laser fuze. |
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