基于Microfacet理论,当光线照射到粗糙表面时会发生显著的多次镜面反射现象,而传统偏振双向反射分布函数(Polarized Bidirectional Reflectance Distribution Function,pBRDF)未能很好地描述这种现象,为了得到更精确的pBRDF模型,更好地...基于Microfacet理论,当光线照射到粗糙表面时会发生显著的多次镜面反射现象,而传统偏振双向反射分布函数(Polarized Bidirectional Reflectance Distribution Function,pBRDF)未能很好地描述这种现象,为了得到更精确的pBRDF模型,更好地分析材料的偏振特性,本文在包含镜面反射、漫反射和定向漫反射的三分量pBRDF模型基础上,进一步定义了高阶微相位角与一阶相位角的关系。改进后的pBRDF模型不仅考虑了多次镜面反射的几何衰减因子,还引入了微相位角的定义,从而建立了一个更全面的高阶镜面反射pBRDF模型。通过比较不同的pBRDF模型,并结合偏振特性采集装置进行验证,实验结果表明,本文提出的模型优于其他模型,三阶模型效果普遍优于二阶。在偏振图像渲染中,峰值信噪比和结构相似性平均分别提升10.09%和2.97%,呈现更加真实的渲染效果。验证本文提出的高阶镜面反射pBRDF模型能够更准确地描述目标表面的偏振特性。展开更多
An expression of degree of polarization（DOP） for metallic material is presented based on the three-component polarized bidirectional reflectance distribution function（p BRDF） model with considering specular reflec...An expression of degree of polarization（DOP） for metallic material is presented based on the three-component polarized bidirectional reflectance distribution function（p BRDF） model with considering specular reflection, directional diffuse reflection and ideal diffuse reflection. The three-component p BRDF model with a detailed reflection assumption is validated by comparing simulations with measurements. The DOP expression presented in this paper is related to surface roughness, which makes it more reasonable in physics. Test results for two metallic samples show that the DOP based on the three-component p BRDF model accords well with the measurement and the error of existing DOP expression is significantly reduced by introducing the diffuse reflection. It indicates that our DOP expression describes the polarized reflection properties of metallic surfaces more accurately.展开更多
A polarized bidirectional reflectance distribution function(pBRDF)matrix is developed from two-scale roughness theory with the aim of providing more accurate simulations of microwave emissions and scattering required ...A polarized bidirectional reflectance distribution function(pBRDF)matrix is developed from two-scale roughness theory with the aim of providing more accurate simulations of microwave emissions and scattering required for ocean-atmosphere coupled radiative transfer models.The potential of the pBRDF matrix is explored for simu-lating the ocean backscatter at Ku-band.The effects of ocean wave spectra including the modified Durden and Vesecky(DV2),Elfouhaily,and Kudryavtsev spectra on the pBRDF matrix backscatter simulations are investi-gated.Additionally,the differences in backscattering normalized radar cross-section(NRCS)simulations between the Ku-band geophysical model function and pBRDF matrix are analyzed.The results show that the pBRDF matrix can reasonably reproduce the spatial distribution of ocean surface backscattering energy,but the distribution pat-tern and numerical values are influenced by ocean wave spectra.The DV2 spectrum is the best one for the pBRDF matrix to simulate horizontally polarized NRCSs,with the exception of scenarios where the incidence angle is below 35°,the wind speed is less than 10 m s^(−1),and in the cross-wind direction.Also,the DV2 spectrum effec-tively characterizes the wind speed and relative azimuth angle dependence for vertically polarized NRCSs.The Elfouhaily spectrum is suitable for simulating vertically polarized NRCSs under conditions of low wind speed(be-low 5 m s^(−1))and incidence angles under 40°.The Kudryavtsev spectrum excels in simulating vertically polarized NRCSs at high incidence angles(>40°)and horizontally polarized NRCSs at low incidence angles(<35°).展开更多
The ocean surface emissivity model plays a pivotal role in satellite data assimilation and the retrieval of ocean physical parameters.In our previous research,we developed a physical emissivity model featuring a polar...The ocean surface emissivity model plays a pivotal role in satellite data assimilation and the retrieval of ocean physical parameters.In our previous research,we developed a physical emissivity model featuring a polarized Bidirectional Reflectance Distribution Function(pBRDF-E).This model effectively ensures the consistency between surface emission and reflection parameters.However,it suffers from low computational efficiency.In this study,we introduce a fast ocean emissivity model,OceanEM.Leveraging the emissivity data output from the pBRDF-E model,OceanEM is developed by using a multilayer perceptron neural network.It can compute the polarization emissivity vector across a wide range of conditions:incidence angles from 0°to 80°,wind speeds from 2 to 50 m s^(-1),sea surface temperatures from-2°to 30℃,sea surface salinities from 0 to 40 psu,and frequencies from 1.4 to 410 GHz.Alongside the FAST Microwave Emissivity Model(FASTEM6)and SURface Fast Emissivity Model for Ocean(SURFEM-ocean),OceanEM is integrated into the Advanced Radiative Transfer Modeling System(ARMS)as a user-selectable option.To validate the accuracy of OceanEM,we compare it with FASTEM6 and SURFEM-ocean using data from WindSAT,a polarimetric radiometer onboard the Coriolis satellite.The results show that the three models generally yield consistent simulations of WindSAT brightness temperatures.Specifically,for channels at 6.8GHz,10.7 GHz(both horizontal and vertical polarization),and 18.7 GHz(vertical polarization),OceanEM demonstrates higher accuracy than FASTEM6 but lower than SURFEM-ocean.Conversely,for channels of 18.7 GHz(horizontal polarization),23.8 GHz,and 37.0 GHz(both horizontal and vertical polarization),OceanEM outperforms both FASTEM6 and SURFEM-ocean.展开更多
The reflection of ocean surface is often assumed azimuthally symmetric in the previous vector discrete ordinate radiative transfer(VDISORT)and many other radiative transfer solvers.This assumption can lead to obvious ...The reflection of ocean surface is often assumed azimuthally symmetric in the previous vector discrete ordinate radiative transfer(VDISORT)and many other radiative transfer solvers.This assumption can lead to obvious errors in the simulated radiances.In this study,the vector radiative transfer equation is solved with a polarized bidirectional reflection distribution function(pBRDF)for computing the surface-leaving radiation from the lower boundary.An azimuthally asymmetric pBRDF model at visible and infrared bands over oceans is fully coupled with the updated VDISORT model.The radiance at the ocean surface is combined with the contributions of atmospheric scattering and surface properties.It is shown that the radiance at the ocean surface also exhibits a strong angular dependence in the Stokes vector and the magnitudes of I.Q.and V increase for a larger azimuthal dependence of pBRDF.In addition,the solar position affects the peaks of sun glitter pattern,thus modulating the signal magnitudes and the angular distributions.As ocean wind increases,the reflection weakens with reduced magnitudes of Stokes parameters and lessvarying angular distributions.展开更多
文摘基于Microfacet理论,当光线照射到粗糙表面时会发生显著的多次镜面反射现象,而传统偏振双向反射分布函数(Polarized Bidirectional Reflectance Distribution Function,pBRDF)未能很好地描述这种现象,为了得到更精确的pBRDF模型,更好地分析材料的偏振特性,本文在包含镜面反射、漫反射和定向漫反射的三分量pBRDF模型基础上,进一步定义了高阶微相位角与一阶相位角的关系。改进后的pBRDF模型不仅考虑了多次镜面反射的几何衰减因子,还引入了微相位角的定义,从而建立了一个更全面的高阶镜面反射pBRDF模型。通过比较不同的pBRDF模型,并结合偏振特性采集装置进行验证,实验结果表明,本文提出的模型优于其他模型,三阶模型效果普遍优于二阶。在偏振图像渲染中,峰值信噪比和结构相似性平均分别提升10.09%和2.97%,呈现更加真实的渲染效果。验证本文提出的高阶镜面反射pBRDF模型能够更准确地描述目标表面的偏振特性。
文摘An expression of degree of polarization（DOP） for metallic material is presented based on the three-component polarized bidirectional reflectance distribution function（p BRDF） model with considering specular reflection, directional diffuse reflection and ideal diffuse reflection. The three-component p BRDF model with a detailed reflection assumption is validated by comparing simulations with measurements. The DOP expression presented in this paper is related to surface roughness, which makes it more reasonable in physics. Test results for two metallic samples show that the DOP based on the three-component p BRDF model accords well with the measurement and the error of existing DOP expression is significantly reduced by introducing the diffuse reflection. It indicates that our DOP expression describes the polarized reflection properties of metallic surfaces more accurately.
基金funded by the National Key Research and Development Program[grant number 2022YFC3004200]the National Natural Science Foundation of China[grant number U2142212]the Hunan Provincial Natural Science Foundation of China[grant number 2021JC0009]。
文摘A polarized bidirectional reflectance distribution function(pBRDF)matrix is developed from two-scale roughness theory with the aim of providing more accurate simulations of microwave emissions and scattering required for ocean-atmosphere coupled radiative transfer models.The potential of the pBRDF matrix is explored for simu-lating the ocean backscatter at Ku-band.The effects of ocean wave spectra including the modified Durden and Vesecky(DV2),Elfouhaily,and Kudryavtsev spectra on the pBRDF matrix backscatter simulations are investi-gated.Additionally,the differences in backscattering normalized radar cross-section(NRCS)simulations between the Ku-band geophysical model function and pBRDF matrix are analyzed.The results show that the pBRDF matrix can reasonably reproduce the spatial distribution of ocean surface backscattering energy,but the distribution pat-tern and numerical values are influenced by ocean wave spectra.The DV2 spectrum is the best one for the pBRDF matrix to simulate horizontally polarized NRCSs,with the exception of scenarios where the incidence angle is below 35°,the wind speed is less than 10 m s^(−1),and in the cross-wind direction.Also,the DV2 spectrum effec-tively characterizes the wind speed and relative azimuth angle dependence for vertically polarized NRCSs.The Elfouhaily spectrum is suitable for simulating vertically polarized NRCSs under conditions of low wind speed(be-low 5 m s^(−1))and incidence angles under 40°.The Kudryavtsev spectrum excels in simulating vertically polarized NRCSs at high incidence angles(>40°)and horizontally polarized NRCSs at low incidence angles(<35°).
基金Supported by the National Key Research and Development Program of China(2021YFB3900400)National Natural Science Foundation of China(U2142212)。
文摘The ocean surface emissivity model plays a pivotal role in satellite data assimilation and the retrieval of ocean physical parameters.In our previous research,we developed a physical emissivity model featuring a polarized Bidirectional Reflectance Distribution Function(pBRDF-E).This model effectively ensures the consistency between surface emission and reflection parameters.However,it suffers from low computational efficiency.In this study,we introduce a fast ocean emissivity model,OceanEM.Leveraging the emissivity data output from the pBRDF-E model,OceanEM is developed by using a multilayer perceptron neural network.It can compute the polarization emissivity vector across a wide range of conditions:incidence angles from 0°to 80°,wind speeds from 2 to 50 m s^(-1),sea surface temperatures from-2°to 30℃,sea surface salinities from 0 to 40 psu,and frequencies from 1.4 to 410 GHz.Alongside the FAST Microwave Emissivity Model(FASTEM6)and SURface Fast Emissivity Model for Ocean(SURFEM-ocean),OceanEM is integrated into the Advanced Radiative Transfer Modeling System(ARMS)as a user-selectable option.To validate the accuracy of OceanEM,we compare it with FASTEM6 and SURFEM-ocean using data from WindSAT,a polarimetric radiometer onboard the Coriolis satellite.The results show that the three models generally yield consistent simulations of WindSAT brightness temperatures.Specifically,for channels at 6.8GHz,10.7 GHz(both horizontal and vertical polarization),and 18.7 GHz(vertical polarization),OceanEM demonstrates higher accuracy than FASTEM6 but lower than SURFEM-ocean.Conversely,for channels of 18.7 GHz(horizontal polarization),23.8 GHz,and 37.0 GHz(both horizontal and vertical polarization),OceanEM outperforms both FASTEM6 and SURFEM-ocean.
基金Supported by the National Natural Science Foundation of China(U2142212 and U2242211),Hunan Provincial Natural Science Foundation of China(2021JC0009)National Key Research and Development Program of China[2019QZKK(Qinghai Tibet KeKao)].
文摘The reflection of ocean surface is often assumed azimuthally symmetric in the previous vector discrete ordinate radiative transfer(VDISORT)and many other radiative transfer solvers.This assumption can lead to obvious errors in the simulated radiances.In this study,the vector radiative transfer equation is solved with a polarized bidirectional reflection distribution function(pBRDF)for computing the surface-leaving radiation from the lower boundary.An azimuthally asymmetric pBRDF model at visible and infrared bands over oceans is fully coupled with the updated VDISORT model.The radiance at the ocean surface is combined with the contributions of atmospheric scattering and surface properties.It is shown that the radiance at the ocean surface also exhibits a strong angular dependence in the Stokes vector and the magnitudes of I.Q.and V increase for a larger azimuthal dependence of pBRDF.In addition,the solar position affects the peaks of sun glitter pattern,thus modulating the signal magnitudes and the angular distributions.As ocean wind increases,the reflection weakens with reduced magnitudes of Stokes parameters and lessvarying angular distributions.
