For expanding the amplitude-frequency response range of the differential cross-phase multiply(DCM)algorithm in theφ-OTDR system,a temporal spline interpolation(TSI)method is proposed to pre-process Rayleigh backscatt...For expanding the amplitude-frequency response range of the differential cross-phase multiply(DCM)algorithm in theφ-OTDR system,a temporal spline interpolation(TSI)method is proposed to pre-process Rayleigh backscattering(RBS)signals.Through the TSI method,the discrete temporal signals characterizing RBS traces are subjected to interpolation,facilitating a reduction in differential approximation errors.This,in turn,establishes a heightened level of precision in phase demodulation,especially relevant across extensive sensing distances.By comparing the recovered time-domain waveforms and the corresponding power spectral densities without and with the TSI,the above improvement effect has been experimentally validated by utilizing the TSI.The results show that,with the TSI,the amplitude-frequency response range of the DCM algorithm is enlarged by 2.78 times,and the new relationship among f_(pulse),f,and D under the root mean square error(RMSE)tolerance less than 0.1 can be expressed as 1.9(D+1)f≤f_(pulse).This contribution underscores a substantial advancement in the capabilities of the DCM algorithm,holding promise for refined performance in optical fiber sensing applications.展开更多
Background: Monitoring forest health and biomass for changes over time in the global environment requires the provision of continuous satellite images. However, optical images of land surfaces are generally contaminat...Background: Monitoring forest health and biomass for changes over time in the global environment requires the provision of continuous satellite images. However, optical images of land surfaces are generally contaminated when clouds are present or rain occurs.Methods: To estimate the actual reflectance of land surfaces masked by clouds and potential rain, 3D simulations by the RAPID radiative transfer model were proposed and conducted on a forest farm dominated by birch and larch in Genhe City, Da Xing’An Ling Mountain in Inner Mongolia, China. The canopy height model(CHM) from lidar data were used to extract individual tree structures(location, height, crown width). Field measurements related tree height to diameter of breast height(DBH), lowest branch height and leaf area index(LAI). Series of Landsat images were used to classify tree species and land cover. MODIS LAI products were used to estimate the LAI of individual trees. Combining all these input variables to drive RAPID, high-resolution optical remote sensing images were simulated and validated with available satellite images.Results: Evaluations on spatial texture, spectral values and directional reflectance were conducted to show comparable results.Conclusions: The study provides a proof-of-concept approach to link lidar and MODIS data in the parameterization of RAPID models for high temporal and spatial resolutions of image reconstruction in forest dominated areas.展开更多
The finite-difference time-domain(FDTD)method is used effectively to solve electromagnetic(EM)scattering and radiation problems using a 3D sub-gridding algorithm.For accuracy and stability of the FDTD method,the compu...The finite-difference time-domain(FDTD)method is used effectively to solve electromagnetic(EM)scattering and radiation problems using a 3D sub-gridding algorithm.For accuracy and stability of the FDTD method,the computational domain of EM problems with locally fine structures or electrically small objects is discretized with finer grids.This sub-gridding algorithm for different regions of the computational domain was implemented to increase the accuracy and reduce the computational time and memory requirements compared to those of the traditional FDTD method.In the sub-gridding algorithm,the FDTD computational domain is divided into separate regions:coarse grid and fine grid regions.Since the cell sizes and time steps are different in the coarse and fine grid regions,interpolations in both time and space are used to evaluate the electric and magnetic fields on the boundaries between different regions.The accuracy of the developed 3D sub-gridding algorithm has been verified for radiation and scattering problems,including multiple fine grid regions.Excellent performance is obtained even for higher and different contrast ratios in fine grid regions.展开更多
基金supported in part by the National Natural Science Foundation of China(Grant Nos.62075153,62075151,and 62205237)in part by the Shanxi Provincial Key Research and Development Project(Grant No.202102150101004)+2 种基金in part by the Shanxi Provincial Central Guiding Local Science and Technology Development Fund Project(Grant No.YDZJSX20231A019)in part by National Key Research and Development Program of China(Grant No.2023YFF0715700)in part by Natural Science Foundation for Young Scientists of Shanxi Province(Grant No.20210302124396).
文摘For expanding the amplitude-frequency response range of the differential cross-phase multiply(DCM)algorithm in theφ-OTDR system,a temporal spline interpolation(TSI)method is proposed to pre-process Rayleigh backscattering(RBS)signals.Through the TSI method,the discrete temporal signals characterizing RBS traces are subjected to interpolation,facilitating a reduction in differential approximation errors.This,in turn,establishes a heightened level of precision in phase demodulation,especially relevant across extensive sensing distances.By comparing the recovered time-domain waveforms and the corresponding power spectral densities without and with the TSI,the above improvement effect has been experimentally validated by utilizing the TSI.The results show that,with the TSI,the amplitude-frequency response range of the DCM algorithm is enlarged by 2.78 times,and the new relationship among f_(pulse),f,and D under the root mean square error(RMSE)tolerance less than 0.1 can be expressed as 1.9(D+1)f≤f_(pulse).This contribution underscores a substantial advancement in the capabilities of the DCM algorithm,holding promise for refined performance in optical fiber sensing applications.
基金the Chinese National Basic Research Program (2013CB733401)the Chinese Natural Science Foundation Project (41171278)
文摘Background: Monitoring forest health and biomass for changes over time in the global environment requires the provision of continuous satellite images. However, optical images of land surfaces are generally contaminated when clouds are present or rain occurs.Methods: To estimate the actual reflectance of land surfaces masked by clouds and potential rain, 3D simulations by the RAPID radiative transfer model were proposed and conducted on a forest farm dominated by birch and larch in Genhe City, Da Xing’An Ling Mountain in Inner Mongolia, China. The canopy height model(CHM) from lidar data were used to extract individual tree structures(location, height, crown width). Field measurements related tree height to diameter of breast height(DBH), lowest branch height and leaf area index(LAI). Series of Landsat images were used to classify tree species and land cover. MODIS LAI products were used to estimate the LAI of individual trees. Combining all these input variables to drive RAPID, high-resolution optical remote sensing images were simulated and validated with available satellite images.Results: Evaluations on spatial texture, spectral values and directional reflectance were conducted to show comparable results.Conclusions: The study provides a proof-of-concept approach to link lidar and MODIS data in the parameterization of RAPID models for high temporal and spatial resolutions of image reconstruction in forest dominated areas.
文摘The finite-difference time-domain(FDTD)method is used effectively to solve electromagnetic(EM)scattering and radiation problems using a 3D sub-gridding algorithm.For accuracy and stability of the FDTD method,the computational domain of EM problems with locally fine structures or electrically small objects is discretized with finer grids.This sub-gridding algorithm for different regions of the computational domain was implemented to increase the accuracy and reduce the computational time and memory requirements compared to those of the traditional FDTD method.In the sub-gridding algorithm,the FDTD computational domain is divided into separate regions:coarse grid and fine grid regions.Since the cell sizes and time steps are different in the coarse and fine grid regions,interpolations in both time and space are used to evaluate the electric and magnetic fields on the boundaries between different regions.The accuracy of the developed 3D sub-gridding algorithm has been verified for radiation and scattering problems,including multiple fine grid regions.Excellent performance is obtained even for higher and different contrast ratios in fine grid regions.
