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Atmospheric and Oceanic Optics|34 Article(s)
Inversion Method for Turbulence Profile Based upon Multi-aperture Scintillation Sensor
NI Zhi-bo, HUANG Hong-hua, HUANG Yin-bo, YUAN Ke-e, and RAO Rui-zhong
Based on the theory of multi-aperture scintillation sensor,the contribution of aperture filter function and spectral response function to weighting function are discussed,respectively.According to simulation results of scintillation with Hufnagel-Valley 5/7 model included bounding layer,vertical turbulence profile is inversed with the method of singular value decomposition.The magnitudes of the vertical inversion results are between and ，and decreases with height increased,which are all in accord with academic model.Using the measuring results of Shack-Hartman,horizontal turbulence profile is inversed,the transmission distance of which is 1 km.The magnitudes of horizontal inversion results are between 10-14 and 10-15，and the tendency accords the practice condition of experimental site depending on propagation distance,and accords the ensemble average depending on time. Based on the theory of multi-aperture scintillation sensor,the contribution of aperture filter function and spectral response function to weighting function are discussed,respectively.According to simulation results of scintillation with Hufnagel-Valley 5/7 model included bounding layer,vertical turbulence profile is inversed with the method of singular value decomposition.The magnitudes of the vertical inversion results are between and ，and decreases with height increased,which are all in accord with academic model.Using the measuring results of Shack-Hartman,horizontal turbulence profile is inversed,the transmission distance of which is 1 km.The magnitudes of horizontal inversion results are between 10-14 and 10-15，and the tendency accords the practice condition of experimental site depending on propagation distance,and accords the ensemble average depending on time.
Acta Photonica Sinica
- Publication Date: Dec. 01, 2009
- Vol. 38, Issue 12, 3269 (2009)
Influence of Fog on Atmospheric Laser Communication System and the Relevant Methods
WANG Yong, YU Lei, ZHANG Ya-bin, and CAO Jia-nian
The causes of fog,the relevant mathematical models and its influence on atmospheric laser communication system are analyzed.In order to overcome the influence of fog on wireless optical communication link,the LDPC codes as channel coding are applied into atmospheric laser communication system,and it is simulated in the foggy atmospheric channel with combination of BP iterative decoding algorithm and sub-carrier PSK intensity modulation.The simulation results show that LDPC codes have excellent error correction capabilities and access to a larger coding gain,and the proposed scheme can satisfy the need of atmospheric laser communication system. The causes of fog,the relevant mathematical models and its influence on atmospheric laser communication system are analyzed.In order to overcome the influence of fog on wireless optical communication link,the LDPC codes as channel coding are applied into atmospheric laser communication system,and it is simulated in the foggy atmospheric channel with combination of BP iterative decoding algorithm and sub-carrier PSK intensity modulation.The simulation results show that LDPC codes have excellent error correction capabilities and access to a larger coding gain,and the proposed scheme can satisfy the need of atmospheric laser communication system.
Acta Photonica Sinica
- Publication Date: Dec. 01, 2009
- Vol. 38, Issue 12, 3275 (2009)
Estimation of Random Errors for Backscatter Lidar Observations
TAO Zong-ming, ZHANG Qing-ze, FANG Xin, WANG Shao-lin, CAO Kai-fa, HU Shun-xing, JI Yu-feng, and HU Huan-ling
Based on the analysis of random errors and characteristic of lidar data,a new method of estimating random errors is introduced,which is called noise scale factor method.Using background signals in far range in one measurement,the noise scale factor is obtained,and the uncertainty of lidar signals at any distances can be estimated.The experiment results show that this method is reliable and feasible. Based on the analysis of random errors and characteristic of lidar data,a new method of estimating random errors is introduced,which is called noise scale factor method.Using background signals in far range in one measurement,the noise scale factor is obtained,and the uncertainty of lidar signals at any distances can be estimated.The experiment results show that this method is reliable and feasible.
Acta Photonica Sinica
- Publication Date: Dec. 01, 2009
- Vol. 38, Issue 12, 3279 (2009)
Method of Retrieving Refractive Index of Aerosol Particles
LI Xue-bin, GONG Chun-wen, HUANG Yin-bo, WEI He-li, and HU Huan-ling
A new method was proposed to retrieve imaginary part of aerosol refractive index by using two kinds of particle counters.One measured the optical size of aerosol particle,which was greatly effected by the refractive imaginary part,and the other one measured aerodynamic of aerosol particle size,which was not effected by refractive imaginary part.The aerosol refractive index was retrieved by combining the measurement of these two kinds of particle counters. A new method was proposed to retrieve imaginary part of aerosol refractive index by using two kinds of particle counters.One measured the optical size of aerosol particle,which was greatly effected by the refractive imaginary part,and the other one measured aerodynamic of aerosol particle size,which was not effected by refractive imaginary part.The aerosol refractive index was retrieved by combining the measurement of these two kinds of particle counters.
Acta Photonica Sinica
- Publication Date: Feb. 01, 2009
- Vol. 38, Issue 2, 401 (2009)
Belief Propagation Decoding of Low-density Parity-check Codes for Atmospheric Turbulent Optical PPM Communication Systems
CHEN Jia-jie, and LI Xiao-feng
BP decoding of LDPC code for weak atmospheric turbulent optical PPM systems was studied, and corresponding decoding algorithm was introduced according to the system model. Through theoretical analysis and extensive computer simulations, the result shows that the LDPC coded weak atmospheric turbulent optical PPM system has better BER than the uncoded weak atmospheric turbulent optical PPM system, but the BER performance of the system increases with the increase of slot. BP decoding of LDPC code for weak atmospheric turbulent optical PPM systems was studied, and corresponding decoding algorithm was introduced according to the system model. Through theoretical analysis and extensive computer simulations, the result shows that the LDPC coded weak atmospheric turbulent optical PPM system has better BER than the uncoded weak atmospheric turbulent optical PPM system, but the BER performance of the system increases with the increase of slot.
Acta Photonica Sinica
- Publication Date: Feb. 01, 2009
- Vol. 38, Issue 2, 405 (2009)
Density of Phase Branch Points for a Light Wave Propagation in Atmospheric Turbulence
YUAN Ke-e, ZHU Wen-yue, and RAO Rui-zhong
Under Rytov approximation and geometrical optics approximation, a formula of the variance of the log-amplitude derivative was deduced for the case of a plane wave propagating through turbulence. It was clarified that the main factors, which determined the variance, were the Rytov variance, the turbulence inner scale and the Fresnel size. And, based on the formulae deduced by Voitsekhovich, the expression for density of phase branch points was modified. The relationship between the density and the above mentioned parameters was analyzed thoroughly, which indicates that the density increases with Rytov variance increasing and decreases with turbulence inner scale and Fresnel size increasing under the condition of Rytov variance less than 1. Under Rytov approximation and geometrical optics approximation, a formula of the variance of the log-amplitude derivative was deduced for the case of a plane wave propagating through turbulence. It was clarified that the main factors, which determined the variance, were the Rytov variance, the turbulence inner scale and the Fresnel size. And, based on the formulae deduced by Voitsekhovich, the expression for density of phase branch points was modified. The relationship between the density and the above mentioned parameters was analyzed thoroughly, which indicates that the density increases with Rytov variance increasing and decreases with turbulence inner scale and Fresnel size increasing under the condition of Rytov variance less than 1.
Acta Photonica Sinica
- Publication Date: Feb. 01, 2009
- Vol. 38, Issue 2, 410 (2009)
Method of Laser Radar Cross Section Measuring with Atmosphere Condition Changing
BAO Xue-zhi, and GAO Wei
Using two-channel detection,influences on laser radar cross section measure accuracy caused by atmosphere condition changing were studied.The new formula of comparing measure was deduced.An experiment was carried out on the new formula,and its using qualification was discussed.Through measuring the diffuse reflection board′s LRCS in the outfield,the result indicates that the new formula can correct the measure error because of the atmosphere condition changing and help to improve measure accuracy,and its calculation is very brief and carried out easily. Using two-channel detection,influences on laser radar cross section measure accuracy caused by atmosphere condition changing were studied.The new formula of comparing measure was deduced.An experiment was carried out on the new formula,and its using qualification was discussed.Through measuring the diffuse reflection board′s LRCS in the outfield,the result indicates that the new formula can correct the measure error because of the atmosphere condition changing and help to improve measure accuracy,and its calculation is very brief and carried out easily.
Acta Photonica Sinica
- Publication Date: Feb. 01, 2009
- Vol. 38, Issue 2, 414 (2009)
Aero-Optic Effects Induced by the Fluctuation Flowfield Surrounding Hypersonic Aircrafts
YANG Wen-xia, CAI Chao, DING Ming-yue, and ZHOU Cheng-ping
Computational analysis was carried out regarding the aero-optical effect induced by the turbulence field surrounding the hyper-speed aircraft.The transport equation of the variance of the index of refraction fluctuations was derived based on the scalar transport governing equations of the turbulence model. The refraction fluctuation variances and the fluctuations correlation and phase covariance function along the line-of sight were obtained. Using statistical methods, the turbulent modulation transfer function(MTF) and the refraction correlation function induced in the transmission direction for the refraction fluctuation was computed, which characterized the aero-optical effect in different aspects. Experimental results show that the amplitude response of the transmission function of the aero-optical effect can be characterized as a low-pass filter, which results blurring in the obtained image; while its irregular phase response results nonlinear shifts of the target in the image.And, the higher the Mach number, the more severe the distortion in the image. The correctness of the theoretical MTF was evaluated by wind tunnel experiment. Computational analysis was carried out regarding the aero-optical effect induced by the turbulence field surrounding the hyper-speed aircraft.The transport equation of the variance of the index of refraction fluctuations was derived based on the scalar transport governing equations of the turbulence model. The refraction fluctuation variances and the fluctuations correlation and phase covariance function along the line-of sight were obtained. Using statistical methods, the turbulent modulation transfer function(MTF) and the refraction correlation function induced in the transmission direction for the refraction fluctuation was computed, which characterized the aero-optical effect in different aspects. Experimental results show that the amplitude response of the transmission function of the aero-optical effect can be characterized as a low-pass filter, which results blurring in the obtained image; while its irregular phase response results nonlinear shifts of the target in the image.And, the higher the Mach number, the more severe the distortion in the image. The correctness of the theoretical MTF was evaluated by wind tunnel experiment.
Acta Photonica Sinica
- Publication Date: Aug. 01, 2009
- Vol. 38, Issue 8, 2117 (2009)
Intensity Distribution of Focused Hollow Vortex Beams with a Gaussian Background in Turbulent Atmosphere
CANG Ji, ZHANG Yi-xin, and XU JIAN-cai
Based on the extended Huygens-Fresnel principle and the quadratic approximation of phase structure function, the theoretical modal of optical intensity distribution on the focal plane for focused hollow vortex beams with a Gaussian background propagating in turbulent atmosphere was investigated and obtained.The effects of atmospheric index structure constant C2n, topological charge, focal length and beam wavelength on optical intensity distribution on the focal plane were analyzed. The results indicate that with the increase of focal length, the intensity distribution on the focal plane varies from central-dip form to Gaussian distribution. The effects of weak turbulence on intensity distribution are negligible. The maintenance of singularity of vortex beams with larger topological charge in turbulent atmosphere is better than that for vortex beams with smaller topological charge. The central-dip form of the intensity distribution becomes shallow and the intensity distribution becomes smooth with the turbulence outer scale increasing. Based on the extended Huygens-Fresnel principle and the quadratic approximation of phase structure function, the theoretical modal of optical intensity distribution on the focal plane for focused hollow vortex beams with a Gaussian background propagating in turbulent atmosphere was investigated and obtained.The effects of atmospheric index structure constant C2n, topological charge, focal length and beam wavelength on optical intensity distribution on the focal plane were analyzed. The results indicate that with the increase of focal length, the intensity distribution on the focal plane varies from central-dip form to Gaussian distribution. The effects of weak turbulence on intensity distribution are negligible. The maintenance of singularity of vortex beams with larger topological charge in turbulent atmosphere is better than that for vortex beams with smaller topological charge. The central-dip form of the intensity distribution becomes shallow and the intensity distribution becomes smooth with the turbulence outer scale increasing.
Acta Photonica Sinica
- Publication Date: Aug. 01, 2009
- Vol. 38, Issue 8, 2122 (2009)
Research of Numerical Simulation and Comparison of Experiment from Differential Image Motion Monitor
CHEN Hua-lin, PEI Chong, YUAN Xiang-yan, and CUI Xiang-qun
Differential image motion monitor is widely used to obtain real-time seeing. Differential image motion was numerical simulated by random phase screen and optical defocus aberration, and the measurement accuracy of differential image motion monitor was analyzed, which showed that differential image motion monitor can reliably measure the near-ground turbulence. Comparision of experiment of two differential image motion monitors with the same hardwares was carried out at Xinglong Station of National Astronomical Observatory of China. The correlation between exposure time and measuring results was analyzed. The results show that the limited exposue time will reduce differential image motion and underestimate seeing value, and the trends over time and statistics of measurement results have good consistency. Differential image motion monitor is widely used to obtain real-time seeing. Differential image motion was numerical simulated by random phase screen and optical defocus aberration, and the measurement accuracy of differential image motion monitor was analyzed, which showed that differential image motion monitor can reliably measure the near-ground turbulence. Comparision of experiment of two differential image motion monitors with the same hardwares was carried out at Xinglong Station of National Astronomical Observatory of China. The correlation between exposure time and measuring results was analyzed. The results show that the limited exposue time will reduce differential image motion and underestimate seeing value, and the trends over time and statistics of measurement results have good consistency.
Acta Photonica Sinica
- Publication Date: Dec. 01, 2014
- Vol. 43, Issue 12, 1201001 (2014)
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