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Atmospheric Optics and Oceanic Optics|224 Article(s)
Numerical Simulation of Gaussian Laser Beam Propagation Characteristics in Seawater Based on Mie Scattering Model
Dian Gui, Haoran Meng, Hao Yang, Xinyue Liu, and Feng Yan
To further study the application of Gaussian laser beams in underwater communication and information detection and the characteristics of the transmission process in different seawater environments, in this study, the most-common terrestrial suspended sediment particles in seawater were taken as an example. First, Mie scattering theory was combined with the Monte Carlo method to establish a 520-nm Gaussian laser transmission model in seawater containing suspended solids, and the effects of particle groups with specific diameters and densities on laser transmission were studied. Second, the variation in the normalized received power with the initial divergence angle of the laser at different detection distances was analyzed. The research results indicate the following. 1) When the diameter and density of suspended sediment particles in the Mie scattering model are changed, thereby changing the extinction coefficient, scattering coefficient, and asymmetry factor set in the simulation, the received power of the detection target decreases exponentially with increases in scatterer diameter, density, and transmission distance. 2) Within a certain range, the change in the initial divergence angle does not affect the power of the receiving surface, and this range decreases with increases in the scattering coefficient and transmission distance. The research method used lays a theoretical foundation for further analyzing the changes in Gaussian laser transmission characteristics in seawater containing complex particle groups (suspended bubbles, planktonic algae, and suspended sediment) and provides reference for related engineering estimates. To further study the application of Gaussian laser beams in underwater communication and information detection and the characteristics of the transmission process in different seawater environments, in this study, the most-common terrestrial suspended sediment particles in seawater were taken as an example. First, Mie scattering theory was combined with the Monte Carlo method to establish a 520-nm Gaussian laser transmission model in seawater containing suspended solids, and the effects of particle groups with specific diameters and densities on laser transmission were studied. Second, the variation in the normalized received power with the initial divergence angle of the laser at different detection distances was analyzed. The research results indicate the following. 1) When the diameter and density of suspended sediment particles in the Mie scattering model are changed, thereby changing the extinction coefficient, scattering coefficient, and asymmetry factor set in the simulation, the received power of the detection target decreases exponentially with increases in scatterer diameter, density, and transmission distance. 2) Within a certain range, the change in the initial divergence angle does not affect the power of the receiving surface, and this range decreases with increases in the scattering coefficient and transmission distance. The research method used lays a theoretical foundation for further analyzing the changes in Gaussian laser transmission characteristics in seawater containing complex particle groups (suspended bubbles, planktonic algae, and suspended sediment) and provides reference for related engineering estimates.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2024
- Vol. 61, Issue 9, 0901001 (2024)
An Algorithm of Aerosol Extinction Coefficient Retrieval from Dual-Wavelength Mie Lidar Observations
Rongrong Qin, Weiyuan Yao, Ning Wang, Beibei Zhang, and Lingling Ma
Space-borne Mie lidar is the most widely used instrument to profile aerosols in the global scale. However, due to the variation of atmospheric aerosol types, the retrieval model for aerosol extinction coefficients from lidar signals assumes a prior aerosol model, which impedes the further improvement of retrieval accuracy. As such, an iteration algorithm for aerosol extinction coefficient profiling from space-board dual-wavelength lidar observation is proposed. First, the initial extinction-to-backscatter ratio (i.e., lidar ratio) is obtained based on a prior aerosol mode and the aerosol extinction coefficient and optical depth at two channels are then retrieved. Moreover, with the relationship built between aerosol optical depth and aerosol mass column, the total aerosol mass columns at two channels are estimated. Finally, by applying the constraints that the two-channel observations correspond to the same aerosol mass column, the lidar ratio and the optical parameters are optimized iteratively based on lidar observation extensively. Due to the limitation of the channel number of the dual-wavelength lidar, the method is only applicable to the two-type mixed aerosol model. The accuracy and the applicability of the method are evaluated based on the background information of aerosol profiles in Baotou, Inner Mongolia, China. The retrieval results from the empirically estimated lidar ratio are taken as the control group. The results show that the proposed method yields mean accuracy improvement of extinction coefficient at 532 nm and 1064 nm channels by 21.16% and 3.00%, respectively. The method is also applied to CALIOP data to further validate the application potential of the proposed retrieval model. Space-borne Mie lidar is the most widely used instrument to profile aerosols in the global scale. However, due to the variation of atmospheric aerosol types, the retrieval model for aerosol extinction coefficients from lidar signals assumes a prior aerosol model, which impedes the further improvement of retrieval accuracy. As such, an iteration algorithm for aerosol extinction coefficient profiling from space-board dual-wavelength lidar observation is proposed. First, the initial extinction-to-backscatter ratio (i.e., lidar ratio) is obtained based on a prior aerosol mode and the aerosol extinction coefficient and optical depth at two channels are then retrieved. Moreover, with the relationship built between aerosol optical depth and aerosol mass column, the total aerosol mass columns at two channels are estimated. Finally, by applying the constraints that the two-channel observations correspond to the same aerosol mass column, the lidar ratio and the optical parameters are optimized iteratively based on lidar observation extensively. Due to the limitation of the channel number of the dual-wavelength lidar, the method is only applicable to the two-type mixed aerosol model. The accuracy and the applicability of the method are evaluated based on the background information of aerosol profiles in Baotou, Inner Mongolia, China. The retrieval results from the empirically estimated lidar ratio are taken as the control group. The results show that the proposed method yields mean accuracy improvement of extinction coefficient at 532 nm and 1064 nm channels by 21.16% and 3.00%, respectively. The method is also applied to CALIOP data to further validate the application potential of the proposed retrieval model.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2024
- Vol. 61, Issue 5, 0501004 (2024)
Underwater Neighborhood Sound Field Reconstruction Method Based on Laser Deflection Effect
Yifan Zhen, and Bin Xue
The high-precision reconstruction of an underwater neighborhood sound field is crucial for studying and analyzing the structural characteristics of neighborhood sound field and improving the underwater acoustic sensing performance. The deflection effect of the laser beam passing through the acoustic field carries the gradient and pressure information of the acoustic field when the laser beam width is much smaller than the acoustic wave wavelength. This study provides a data sensing basis for sound field reconstruction by employing the Kirchhoff integral theorem. The calculation method of a virtual extended acoustic field aperture is presented herein by using the density of the laser sensing acoustic field, which further approaches the theoretical requirement of the infinite integral interval in the Kirchhoff integral theorem. The results of the proposed sound field reconstruction ideas and methods are verified in an underwater neighborhood space. The results show that, compared with direct acoustic holography, the proposed acoustic field reconstruction method improves the peak signal-to-noise ratio by 5.5 dB, thereby providing a new feasible idea for developing high-precision neighborhood acoustic field sensors. The high-precision reconstruction of an underwater neighborhood sound field is crucial for studying and analyzing the structural characteristics of neighborhood sound field and improving the underwater acoustic sensing performance. The deflection effect of the laser beam passing through the acoustic field carries the gradient and pressure information of the acoustic field when the laser beam width is much smaller than the acoustic wave wavelength. This study provides a data sensing basis for sound field reconstruction by employing the Kirchhoff integral theorem. The calculation method of a virtual extended acoustic field aperture is presented herein by using the density of the laser sensing acoustic field, which further approaches the theoretical requirement of the infinite integral interval in the Kirchhoff integral theorem. The results of the proposed sound field reconstruction ideas and methods are verified in an underwater neighborhood space. The results show that, compared with direct acoustic holography, the proposed acoustic field reconstruction method improves the peak signal-to-noise ratio by 5.5 dB, thereby providing a new feasible idea for developing high-precision neighborhood acoustic field sensors.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2024
- Vol. 61, Issue 5, 0501003 (2024)
Skylight Polarization Patterns Modelling Method Under Influence of Dawn and Twilight
Kun Wei, Zhiguo Fan, Haihong Jin, Ceding Gui, and Wanjuan Dong
Existing theoretical models of skylight polarization patterns have problems that only consider the influence of the sun or the moon alone and could not adequately describe the polarization patterns of the sky during the transition between dawn and dusk in clear weather. Therefore, a modelling method of skylight polarization patterns under the influence of dawn and twilight is proposed. The method introduces the influence of the sun and the moon and calculates the Stokes vectors using the position of the sun and the moon. Considering the factors of multiple scattering of atmospheric particles in the actual sky, the influence weights of the sun and the moon are determined by Stokes vector optimization. In addition, the obtained angle of polarization is used to characterize the skylight polarization patterns. The experimental results show that the simulation results of the proposed model and the measured angle of polarization have the same distribution and variation characteristics, and maintain a high degree of similarity, which can effectively characterize the skylight polarization patterns influenced by dawn and twilight. Existing theoretical models of skylight polarization patterns have problems that only consider the influence of the sun or the moon alone and could not adequately describe the polarization patterns of the sky during the transition between dawn and dusk in clear weather. Therefore, a modelling method of skylight polarization patterns under the influence of dawn and twilight is proposed. The method introduces the influence of the sun and the moon and calculates the Stokes vectors using the position of the sun and the moon. Considering the factors of multiple scattering of atmospheric particles in the actual sky, the influence weights of the sun and the moon are determined by Stokes vector optimization. In addition, the obtained angle of polarization is used to characterize the skylight polarization patterns. The experimental results show that the simulation results of the proposed model and the measured angle of polarization have the same distribution and variation characteristics, and maintain a high degree of similarity, which can effectively characterize the skylight polarization patterns influenced by dawn and twilight.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2024
- Vol. 61, Issue 5, 0501002 (2024)
Spatial Distribution of Bromine and its Influencing Factors Near the Eastern Shore of Leizhou Peninsula
Weiyi Liu, Zhengye Xiong, Jingyuan Guo, Xiaoting Liao, and Guo Yu
The content of Bromine was measured by X-ray fluorescence approach in order to study the spatial distribution characteristics of Bromine in seawater and analyze the reasons that affect the distribution of Bromine near the Eastern shore of Leizhou Peninsula. First, the calibration curve of standard solution is obtained by small-focus X-ray fluorescence spectrometer and direct injection method, and the linear fitting equation is derived from the relationship between the fluorescence intensity and the mass concentration of Bromine, to detect the mass concentration of Bromine in coastal waters. Then, we further analyze the influences of the land runoff, tide and the structure of circulation on the distribution of Bromine in seawater in the east of Leizhou Peninsula based on the spatial variation of Bromine mass concentration in water, the spatial distribution of land runoff, tide and the structure of circulation. The Bromine mass concentration of 18 stations in the east of Leizhou Peninsula is in the range of 50.79?62.11 mg/L derived by the X-ray fluorescence spectrometry approach, and the results indicate that the content of Bromine in this area is less than that in the ocean and varies greatly with space. In this area, the Bromine content almost increases with the distance between the sampling site and two-bays-one-island (Zhanjiang bay, Leizhou bay and Naozhou island) increasing. In addition, in the south of this area and the entrance of Qiongzhou Strait, for the complex influences of currents, the Bromine content increases along the flow direction of Qiongzhou Strait. The variation of Bromine mass concentration in coastal waters demonstrates that the distribution of Bromine is uneven, and the uneven distribution fact of Bromine is mainly caused by the land runoff, tide, alongshore current near Western Guangdong, Qiongzhou Strait current, and cyclonic circulation. The content of Bromine was measured by X-ray fluorescence approach in order to study the spatial distribution characteristics of Bromine in seawater and analyze the reasons that affect the distribution of Bromine near the Eastern shore of Leizhou Peninsula. First, the calibration curve of standard solution is obtained by small-focus X-ray fluorescence spectrometer and direct injection method, and the linear fitting equation is derived from the relationship between the fluorescence intensity and the mass concentration of Bromine, to detect the mass concentration of Bromine in coastal waters. Then, we further analyze the influences of the land runoff, tide and the structure of circulation on the distribution of Bromine in seawater in the east of Leizhou Peninsula based on the spatial variation of Bromine mass concentration in water, the spatial distribution of land runoff, tide and the structure of circulation. The Bromine mass concentration of 18 stations in the east of Leizhou Peninsula is in the range of 50.79?62.11 mg/L derived by the X-ray fluorescence spectrometry approach, and the results indicate that the content of Bromine in this area is less than that in the ocean and varies greatly with space. In this area, the Bromine content almost increases with the distance between the sampling site and two-bays-one-island (Zhanjiang bay, Leizhou bay and Naozhou island) increasing. In addition, in the south of this area and the entrance of Qiongzhou Strait, for the complex influences of currents, the Bromine content increases along the flow direction of Qiongzhou Strait. The variation of Bromine mass concentration in coastal waters demonstrates that the distribution of Bromine is uneven, and the uneven distribution fact of Bromine is mainly caused by the land runoff, tide, alongshore current near Western Guangdong, Qiongzhou Strait current, and cyclonic circulation.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2024
- Vol. 61, Issue 5, 0501001 (2024)
Parallel Multi Scale Attention Mapping Image Dehazing Algorithm
Heng Yuan, and Tinghao Yan
Problems such as image color distortion, blurred image details, and image artifacts are prone to occur in the current dehazing algorithm. In order to solve the above problems, an image dehazing algorithm with parallel multi scale attention mapping is proposed. The algorithm achieves image defogging through an end-to-end encoder decoder structure. In the encoder stage, the continuous downsampling layer is used to reduce feature dimension and avoid over-fitting. In the feature transformation stage, a parallel multi scale attention mapping block with a parallel branch structure is designed, so that the model can make full use of multi scale features while focusing on important features of the image, and effective collection of image spatial structure information by connecting selective feature fusion block in parallel. In the decoding stage, the upsampling layer is used to reconstruct the image, and through skip connections of up and down sampling to better preserve image edge information. Experimental results show that the algorithm has better dehazing effects on both synthetic hazy datasets and real hazy images. Compared with traditional dehazing methods, this algorithm better preserves image details and has better color retention. Problems such as image color distortion, blurred image details, and image artifacts are prone to occur in the current dehazing algorithm. In order to solve the above problems, an image dehazing algorithm with parallel multi scale attention mapping is proposed. The algorithm achieves image defogging through an end-to-end encoder decoder structure. In the encoder stage, the continuous downsampling layer is used to reduce feature dimension and avoid over-fitting. In the feature transformation stage, a parallel multi scale attention mapping block with a parallel branch structure is designed, so that the model can make full use of multi scale features while focusing on important features of the image, and effective collection of image spatial structure information by connecting selective feature fusion block in parallel. In the decoding stage, the upsampling layer is used to reconstruct the image, and through skip connections of up and down sampling to better preserve image edge information. Experimental results show that the algorithm has better dehazing effects on both synthetic hazy datasets and real hazy images. Compared with traditional dehazing methods, this algorithm better preserves image details and has better color retention.
Laser & Optoelectronics Progress
- Publication Date: Feb. 25, 2024
- Vol. 61, Issue 4, 0401002 (2024)
Application of Piecewise Intensity Transformation in Aerosol Flow Field Detection Based on Planar Laser-Induced Fluorescence
Siying Chen, Wei Hao, He Chen, Pan Guo, Qingyue Xu, and Fan Xue
Real-time detection of aerosol flow field using planar laser-induced fluorescence (PLIF) technology is crucial for studying the motion of aerosol. To enhance the visibility of weak signals in real-time PLIF aerosol signal detection, we propose a method of piecewise intensity transformation in this paper. This method sets constraints based on the characteristics of signal intensity, iteratively divides the signal into several intensity ranges, and then replans the signal intensity in each range. The proposed piecewise intensity transformation is applied to the signal processing of PLIF aerosol flow field detection,compared with the processing results of limited contrast adaptive histogram equalization (CLAHE), this method has good results in weak signal enhancement and noise suppression of large dynamic range fluorescent signals, with an improvement of over 20% in the signal-to-background ratio of weak signals. The proposed method achieves real-time detection at 25 frames per second for different stages of aerosol flow field, meeting the requirements for real-time detection of aerosol flow field fluorescence signal. Real-time detection of aerosol flow field using planar laser-induced fluorescence (PLIF) technology is crucial for studying the motion of aerosol. To enhance the visibility of weak signals in real-time PLIF aerosol signal detection, we propose a method of piecewise intensity transformation in this paper. This method sets constraints based on the characteristics of signal intensity, iteratively divides the signal into several intensity ranges, and then replans the signal intensity in each range. The proposed piecewise intensity transformation is applied to the signal processing of PLIF aerosol flow field detection,compared with the processing results of limited contrast adaptive histogram equalization (CLAHE), this method has good results in weak signal enhancement and noise suppression of large dynamic range fluorescent signals, with an improvement of over 20% in the signal-to-background ratio of weak signals. The proposed method achieves real-time detection at 25 frames per second for different stages of aerosol flow field, meeting the requirements for real-time detection of aerosol flow field fluorescence signal.
Laser & Optoelectronics Progress
- Publication Date: Feb. 25, 2024
- Vol. 61, Issue 4, 0401001 (2024)
Empirical Orthogonal Function Aerosol Fine Particle Optical Depth Inversion Algorithm Based on Directional Polarimetric Camera
Wenjie Li, Shurong Wang, Changxiang Yan, and Ning Ding
Aiming at the problem that the semi-empirical model in the aerosol fine particle retrieval algorithm on the directional polarimetric camera(DPC) platform carried by the GF-5 satellite is not suitable for the estimation of urban surface polarization reflectance. In this paper, based on the empirical orthogonal function method of DPC, the inversion of the optical thickness of aerosol fine particles is carried out. The aerosol radiative contribution is calculated based on Mie scattering, the surface contribution is calculated by the empirical orthogonal function method, and the optical thickness of aerosol fine particles is inverted by using the multi-angle polarization data and the vector radiative transfer equation. The inversion results of this study are consistent with the moderate-resolution imaging spectroradiometer distribution trend of aerosol fine particle optical depth products, quantitatively compared with the measurement results of AERONET Beijing, Xianghe, and Hong Kong stations, the correlation coefficients are 0.97, 0.96, and 0.9, the mean absolute error is 0.08, 0.07, and 0.12, and the root mean square error is 0.12, 0.11, and 0.17, which verifies the high precision and rationality of the algorithm. Finally, the monthly average data of aerosol fine particle optical thickness in some areas of China in 2019 are presented, and the changes of aerosol fine particle optical thickness in Shandong are analyzed. It is found that June is the highest period of the year, with an average value of 0.7. The above results verify the reliability of the algorithm and provide technical support for DPC to effectively monitor the spatiotemporal distribution of aerosols Aiming at the problem that the semi-empirical model in the aerosol fine particle retrieval algorithm on the directional polarimetric camera(DPC) platform carried by the GF-5 satellite is not suitable for the estimation of urban surface polarization reflectance. In this paper, based on the empirical orthogonal function method of DPC, the inversion of the optical thickness of aerosol fine particles is carried out. The aerosol radiative contribution is calculated based on Mie scattering, the surface contribution is calculated by the empirical orthogonal function method, and the optical thickness of aerosol fine particles is inverted by using the multi-angle polarization data and the vector radiative transfer equation. The inversion results of this study are consistent with the moderate-resolution imaging spectroradiometer distribution trend of aerosol fine particle optical depth products, quantitatively compared with the measurement results of AERONET Beijing, Xianghe, and Hong Kong stations, the correlation coefficients are 0.97, 0.96, and 0.9, the mean absolute error is 0.08, 0.07, and 0.12, and the root mean square error is 0.12, 0.11, and 0.17, which verifies the high precision and rationality of the algorithm. Finally, the monthly average data of aerosol fine particle optical thickness in some areas of China in 2019 are presented, and the changes of aerosol fine particle optical thickness in Shandong are analyzed. It is found that June is the highest period of the year, with an average value of 0.7. The above results verify the reliability of the algorithm and provide technical support for DPC to effectively monitor the spatiotemporal distribution of aerosols
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2023
- Vol. 60, Issue 9, 0901003 (2023)
Influence of Dispersed Oil on Diffuse Attenuation Coefficient of Downwelling Irradiance
Junjie Yang, Miaofen Huang, Xufeng Xing, and Zhonglin Wang
The diffuse attenuation coefficient of downwelling irradiance (kd) is one of the most critical optical parameters in oceanic optics. The optical parameters of waters around the Dalian port polluted by dispersed oil (oil in water) were measured, and the underwater light field was simulated using the radiative transfer model (Hydrolight) to analyze the influence of oil in water on kd and to establish a semi-analytical model for kd. The simulation results show that the kd spectra of various water depths increase with increasing oil concentrations. Moreover, kd increases with increasing depth, particularly for the waters containing high concentrations of dispersed oil, and the faster it approaches its steady asymptotic value. In addition, this study also shows that the contributions of the absorption coefficient (a) and backscattering coefficient (bb) to kd of water polluted by dispersed oil differ from those of a and bb to kd of natural water body, so that the parameter values of the kd semi-analytical models of water polluted by dispersed oil and natural water body are significantly different. Therefore, the existing kd semi-analytical model for natural water body is unsuitable for accurate calculations of kd of water polluted by dispersed oil. Hence, a semi-analytical model of kd was developed based on the simulation results of Hydrolight. The accurate downwelling irradiance can be further calculated using kd obtained with this developed semi-analytical model to provide a rapid and reliable solution for the underwater light field simulation of waters polluted by dispersed oil. The diffuse attenuation coefficient of downwelling irradiance (kd) is one of the most critical optical parameters in oceanic optics. The optical parameters of waters around the Dalian port polluted by dispersed oil (oil in water) were measured, and the underwater light field was simulated using the radiative transfer model (Hydrolight) to analyze the influence of oil in water on kd and to establish a semi-analytical model for kd. The simulation results show that the kd spectra of various water depths increase with increasing oil concentrations. Moreover, kd increases with increasing depth, particularly for the waters containing high concentrations of dispersed oil, and the faster it approaches its steady asymptotic value. In addition, this study also shows that the contributions of the absorption coefficient (a) and backscattering coefficient (bb) to kd of water polluted by dispersed oil differ from those of a and bb to kd of natural water body, so that the parameter values of the kd semi-analytical models of water polluted by dispersed oil and natural water body are significantly different. Therefore, the existing kd semi-analytical model for natural water body is unsuitable for accurate calculations of kd of water polluted by dispersed oil. Hence, a semi-analytical model of kd was developed based on the simulation results of Hydrolight. The accurate downwelling irradiance can be further calculated using kd obtained with this developed semi-analytical model to provide a rapid and reliable solution for the underwater light field simulation of waters polluted by dispersed oil.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2023
- Vol. 60, Issue 9, 0901002 (2023)
Orbital Angular Momentum in a Superposition State for High-Dimensional Modulation and Demodulation in Underwater Optical Communication
Haida Liu, Xiaobing Hei, Yang Yang, Yuanhao Xie, Lei Gai, Yongjian Gu, Ya Xiao, and Wendong Li
This paper presents a method for high-dimensional information modulation and demodulation using a vortex beam for underwater wireless optical communication by identifying the superposition state of orbital angular momentum in the vortex beam. The method and process of identifying the superposition states of two vortex beams are described. The topological charge numbers in the superposition states are obtained based on the light intensity distribution diagram of the superposition states after water channel transmission. Based on the results, it is experimentally demonstrated that the superposition state of orbital angular momentum can achieve the modulation and demodulation of 16-dimensional information under low-topological-charge conditions. Thus, this study provides a feasible scheme for applying vortex beams in underwater wireless optical communication. This paper presents a method for high-dimensional information modulation and demodulation using a vortex beam for underwater wireless optical communication by identifying the superposition state of orbital angular momentum in the vortex beam. The method and process of identifying the superposition states of two vortex beams are described. The topological charge numbers in the superposition states are obtained based on the light intensity distribution diagram of the superposition states after water channel transmission. Based on the results, it is experimentally demonstrated that the superposition state of orbital angular momentum can achieve the modulation and demodulation of 16-dimensional information under low-topological-charge conditions. Thus, this study provides a feasible scheme for applying vortex beams in underwater wireless optical communication.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2023
- Vol. 60, Issue 9, 0901001 (2023)
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