Journals > > Topics > Atmospheric and oceanic optics
Atmospheric and oceanic optics|55 Article(s)
Influence of space between atmospheric channels and beams' number on scintillation
Weihui Liu, and Jian Wu
On the basis of Kolmogorov's theorem, the physical meanings of beams' correlation function on received plane are extended. Approximate formula of channels' across correlation coefficient is deduced from multiple beams through atmosphere. And the scintillation variance of multiple beams is also induced. The result shows along with the channels close to one another, the correlation coefficient increases, and so does the scintillation variance. When the channels completely combine, the scintillation variance of multiple channels is with no difference from that of one channel. On the basis of Kolmogorov's theorem, the physical meanings of beams' correlation function on received plane are extended. Approximate formula of channels' across correlation coefficient is deduced from multiple beams through atmosphere. And the scintillation variance of multiple beams is also induced. The result shows along with the channels close to one another, the correlation coefficient increases, and so does the scintillation variance. When the channels completely combine, the scintillation variance of multiple channels is with no difference from that of one channel.
Chinese Optics Letters
- Publication Date: Jan. 01, 2003
- Vol. 1, Issue 11, 11621 (2003)
Compensating laser wave-front aberration in atmosphere 1.27 km away with SBS
Youlun Ju, Qi Wang, Deying Chen, Xin Yu, and Yuezhu Wang
It is reported that the wave-front aberration produced by atmosphere disturbance can be compensated with nonlinear optics phase conjugate technology. The distance of laser propagating in atmosphere is up to 1.27 km away. The result shows that SBS phase conjugating beam energy can be focus in a little area on target. And the biggest energy of phase conjugating beam on target is up to 142 mJ. It is reported that the wave-front aberration produced by atmosphere disturbance can be compensated with nonlinear optics phase conjugate technology. The distance of laser propagating in atmosphere is up to 1.27 km away. The result shows that SBS phase conjugating beam energy can be focus in a little area on target. And the biggest energy of phase conjugating beam on target is up to 142 mJ.
Chinese Optics Letters
- Publication Date: Jan. 01, 2003
- Vol. 1, Issue 12, 12683 (2003)
Strong intensity variations of laser feedback interferometer caused by atmospheric turbulence
Yiyi Sun, and Zhiping Li
The significant variation of the laser output can be caused by feedback of a small part of laser beam, which is reflected or backscattered by a target at a long distance from laser source, into the laser cavity. This paper describes and analyzes theoretically and experimentally the influence of atmospheric turbulence on interference caused by laser feedback. The influence depends upon both the energy of feedback into the laser cavity and the strength of turbulence over a laser propagation path in the atmosphere. In the case of stronger energy of feedback and weak turbulence variance of fluctuation of the laser output can be enhanced by hundreds to thousands times. From our measurements and theoretical analysis it shows thatthese significant enhancements can result from the change of laser-cavity-modes which can be stimulated simultaneously and from beat oscillations between a variety of frequencies of laser modes. This also can result from optical chaos inside the laser resonator because a non-separable distorted external cavity can become a prerequisite for optical chaos. The significant variation of the laser output can be caused by feedback of a small part of laser beam, which is reflected or backscattered by a target at a long distance from laser source, into the laser cavity. This paper describes and analyzes theoretically and experimentally the influence of atmospheric turbulence on interference caused by laser feedback. The influence depends upon both the energy of feedback into the laser cavity and the strength of turbulence over a laser propagation path in the atmosphere. In the case of stronger energy of feedback and weak turbulence variance of fluctuation of the laser output can be enhanced by hundreds to thousands times. From our measurements and theoretical analysis it shows thatthese significant enhancements can result from the change of laser-cavity-modes which can be stimulated simultaneously and from beat oscillations between a variety of frequencies of laser modes. This also can result from optical chaos inside the laser resonator because a non-separable distorted external cavity can become a prerequisite for optical chaos.
Chinese Optics Letters
- Publication Date: Jan. 01, 2003
- Vol. 1, Issue 5, 05249 (2003)
Raman lidar measurements of tropospheric water vapor over Hefei
Yonghua Wu, Huanling Hu, Shunxing Hu, and Jun Zhou
L625 Raman lidar has been developed for water vapor measurements over Hefei, China since September 2000. By transmitting laser beam of frequency-tripled Nd:YAG laser, Raman scattering signals of water vapor and nitrogen molecules are simultaneously detected by the cooled photomultipliers with photon counting mode. Water vapor mixing ratios measured by Raman lidar show the good agreements with radiosonde observations, which indicates this Raman lidar is reliable. Many observation cases show that aerosol optical parameters have the good correlation with water vapor distribution in the lower troposphere. L625 Raman lidar has been developed for water vapor measurements over Hefei, China since September 2000. By transmitting laser beam of frequency-tripled Nd:YAG laser, Raman scattering signals of water vapor and nitrogen molecules are simultaneously detected by the cooled photomultipliers with photon counting mode. Water vapor mixing ratios measured by Raman lidar show the good agreements with radiosonde observations, which indicates this Raman lidar is reliable. Many observation cases show that aerosol optical parameters have the good correlation with water vapor distribution in the lower troposphere.
Chinese Optics Letters
- Publication Date: Jan. 01, 2003
- Vol. 1, Issue 7, 07373 (2003)
A new differential absorption lidar for NO2 measurements using Raman-shifted technique
Shunxing Hu, Huanling Hu, Yinchao Zhang, Jun Zhou, Guming Yue, Kun Tan, Yufeng Ji, and Ben Xu
Based on Raman-shifted wavelengths of D2 and CH4 pumped by third harmonic of Nd:YAG laser, a differential absorption lidar was presented in this paper and had been constructed for probing environmental NO2 concentration. NO2 experimental measurements were carried out at Anhui Institute of Optics and Fine Mechanics in Hefei. Some NO2 measurement results were given and discussed. Based on Raman-shifted wavelengths of D2 and CH4 pumped by third harmonic of Nd:YAG laser, a differential absorption lidar was presented in this paper and had been constructed for probing environmental NO2 concentration. NO2 experimental measurements were carried out at Anhui Institute of Optics and Fine Mechanics in Hefei. Some NO2 measurement results were given and discussed.
Chinese Optics Letters
- Publication Date: Jan. 01, 2003
- Vol. 1, Issue 8, 08435 (2003)
Lidar signal de-noising based on wavelet trimmed thresholding technique
Haitao Fang, and Deshuang Huang
Lidar is an efficienttool for remote monitoring, but the effective range is often limited by signal-to-noise ratio (SNR). By the power spectralestimation, we find that digital filters are not fit for processing lidar signals buried in noise. In this paper, we present a new method of the lidar signal acquisition based on the wavelet trimmed thresholding technique to increase the effective range of lidar measurements. The performance of our method is investigated by detecting the real signals in noise. Theexperiment results show that our approach is superior to the traditional methods such as Butterworth filter. Lidar is an efficienttool for remote monitoring, but the effective range is often limited by signal-to-noise ratio (SNR). By the power spectralestimation, we find that digital filters are not fit for processing lidar signals buried in noise. In this paper, we present a new method of the lidar signal acquisition based on the wavelet trimmed thresholding technique to increase the effective range of lidar measurements. The performance of our method is investigated by detecting the real signals in noise. Theexperiment results show that our approach is superior to the traditional methods such as Butterworth filter.
Chinese Optics Letters
- Publication Date: Jan. 01, 2004
- Vol. 2, Issue 1, 0101 (2004)
Exo-atmospheric target discrimination using probabilistic neural network
Jianlai Wang, and Chunling Yang
Exo-atmospheric targets are especially difficult to distinguish using currently available techniques, because all target parts follow the same spatial trajectory. The feasibility of distinguishing multiple type components of exo-atmospheric targets is demonstrated by applying the probabilistic neural network. Differences in thermal behavior and time-varying signals of space-objects are analyzed during the selection of features used as inputs of the neural network. A novel multi-colorimetric technology is introduced to measure precisely the temporal evolutional characteristics of temperature and emissivity-area products. To test the effectiveness of the recognition algorithm, the results obtained from a set of synthetic multispectral data set are presented and discussed. These results indicate that the discrimination algorithm can obtain a remarkable success rate. Exo-atmospheric targets are especially difficult to distinguish using currently available techniques, because all target parts follow the same spatial trajectory. The feasibility of distinguishing multiple type components of exo-atmospheric targets is demonstrated by applying the probabilistic neural network. Differences in thermal behavior and time-varying signals of space-objects are analyzed during the selection of features used as inputs of the neural network. A novel multi-colorimetric technology is introduced to measure precisely the temporal evolutional characteristics of temperature and emissivity-area products. To test the effectiveness of the recognition algorithm, the results obtained from a set of synthetic multispectral data set are presented and discussed. These results indicate that the discrimination algorithm can obtain a remarkable success rate.
Chinese Optics Letters
- Publication Date: May. 26, 2011
- Vol. 9, Issue 7, 070101 (2011)
Real-time measurement of atmospheric parameters for the 127-element adaptive optics system of 1.8-m telescope
Jie Mu, Wenjia Zheng, Mei Li, and Changhui Rao
A real-time method for measuring atmospheric parameters based on co-processor field-programmable gate array (FPGA) and main processor digital signal processing (DSP) is proposed for ground-based telescopes with adaptive optics (AO) systems. Coherence length, outer scale, average wind speed, and coherence time are estimated according to closed-loop data on the residual slopes and the corrected voltages of AO systems. This letter introduces the principle and architecture design of the proposed method, which is successfully applied in the 127-element AO system of the 1.8-m telescope of Yunnan Astronomical Observatory. The method enables real-time atmospheric observations with the same object and path of the AO system. This method is also applicable to extended objects. A real-time method for measuring atmospheric parameters based on co-processor field-programmable gate array (FPGA) and main processor digital signal processing (DSP) is proposed for ground-based telescopes with adaptive optics (AO) systems. Coherence length, outer scale, average wind speed, and coherence time are estimated according to closed-loop data on the residual slopes and the corrected voltages of AO systems. This letter introduces the principle and architecture design of the proposed method, which is successfully applied in the 127-element AO system of the 1.8-m telescope of Yunnan Astronomical Observatory. The method enables real-time atmospheric observations with the same object and path of the AO system. This method is also applicable to extended objects.
Chinese Optics Letters
- Publication Date: Sep. 14, 2012
- Vol. 10, Issue 12, 120101 (2012)
Composition of Airy disc
Guoquan Zhou, Xiuxiang Chu, and Jun Zheng
The description of a plane wave diffracted by a circular aperture is directly started from the Maxwell's equations. Based on the vector angular spectrum representation of Maxwell's equations, the diffracted plane wave is decomposed into the TE and TM terms. The analytical TE and TM terms in the far field are presented by stationary phase. As the TE and TM terms are orthogonal to each other in the far field, their sum constitutes the so-called Airy disc pattern. Therefore, this research reveals the composition of Airy disc, which is beneficial to deepen and enhance the recognition of the classical diffraction problem. The description of a plane wave diffracted by a circular aperture is directly started from the Maxwell's equations. Based on the vector angular spectrum representation of Maxwell's equations, the diffracted plane wave is decomposed into the TE and TM terms. The analytical TE and TM terms in the far field are presented by stationary phase. As the TE and TM terms are orthogonal to each other in the far field, their sum constitutes the so-called Airy disc pattern. Therefore, this research reveals the composition of Airy disc, which is beneficial to deepen and enhance the recognition of the classical diffraction problem.
Chinese Optics Letters
- Publication Date: Jul. 24, 2019
- Vol. 6, Issue 6, 06395 (2008)
Direct inversion of shallow-water bathymetry from EO-1 hyperspectral remote sensing data
Zhishen Liu, and Yan Zhou
Using the US National Aeronautics and space Administration (NASA) Earth Observing-1 Mission (EO-1) hyperion hyperspectral remote sensing data, we study the shallow-water bathymetry inversion in Smith Island Bay. The fast line-of-sight atmospheric analysis of spectral hypercubes module is applied for atmo-spheric correction, and principal component analysis method combined with scatter diagram and maximum likelihood classification is used for seabed classification. The diffuse attenuation coefficient Kd is derived using quasi-analytical algorithm (QAA), which performs well in optically deep water. Kd obtained from QAA requires correction, particularly those derived in some coastal areas with optically shallow water and calculated by direct inversion based on radiative transfer theory to obtain the bathymetry. The direct inversion method derives the water depth quickly, and matches the results from optimized algorithm. Using the US National Aeronautics and space Administration (NASA) Earth Observing-1 Mission (EO-1) hyperion hyperspectral remote sensing data, we study the shallow-water bathymetry inversion in Smith Island Bay. The fast line-of-sight atmospheric analysis of spectral hypercubes module is applied for atmo-spheric correction, and principal component analysis method combined with scatter diagram and maximum likelihood classification is used for seabed classification. The diffuse attenuation coefficient Kd is derived using quasi-analytical algorithm (QAA), which performs well in optically deep water. Kd obtained from QAA requires correction, particularly those derived in some coastal areas with optically shallow water and calculated by direct inversion based on radiative transfer theory to obtain the bathymetry. The direct inversion method derives the water depth quickly, and matches the results from optimized algorithm.
Chinese Optics Letters
- Publication Date: May. 12, 2011
- Vol. 9, Issue 6, 060102 (2011)
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