M8激光雷达回波的非接触式发射率三维分布测量方法

Non-contact three-dimensional emissivity distribution measurement method of M8 LiDAR echo

针对目前发射率测量方法只是对某一单一物质进行接触式测量,难以获得复杂目标的发射率三维分布问题,提出一种基于M8激光雷达回波的非接触式发射率三维分布测量方法。首先基于激光雷达传输距离方程分析回波强度特性,通过M8激光雷达对95%标准漫反射板进行扫描,叠加多帧单线点云,得到具有反射光谱特性的雷达强度三维点云像;运用分段多项式模型拟合距离-强度及入射角-强度之间的关系,基于得到的分段多项式模型校正距离和入射角度影响下的回波强度,使不同距离与入射角情况下所测回波强度能够真实地反映目标的反射光谱特性,校正结果显示,标准漫反射板回波强度变异系数分别从0.2676和0.3438降低到了0.0420和0.0412,回波强度一致性分别提高了84.31%和88.02%,使雷达所测得强度值能直接反映目标材料的反射光谱特性,验证了强度校正模型的有效性;最后基于得到的分段多项式校正模型对带有反射率真值贴片的缩比卫星模型雷达强度三维点云像进行强度校正,利用校正后的回波强度的反射光谱特性,计算出目标表面的反射率,运用反射法进一步推导其发射率,得到缩比卫星模型发射率的三维分布,三组卫星模型表面贴片的发射率平均偏差均分别能控制在3.33%、4.84%和4.44%。为目标识别、低空可探测技术等提供技术支持。

Objective Emissivity is an important physical quantity to characterize the radiation ability of material surface.It is an important thermal physical parameter and has very important applications in many fields.Emissivity is not the intrinsic property of an object.It is a physical quantity that is difficult to measure accurately.It is related to temperature,wavelength,angle and so on.Its measurement is more complicated.At present,most of the emissivity measurement methods are only contact measurement of a single substance.It is impossible to measure the three-dimensional distribution of emissivity of complex targets.Combined with the characteristics of LiDAR,a non-contact three-dimensional distribution measurement method of emissivity is proposed based on LiDAR echo.Methods Firstly,the echo intensity characteristics are analyzed based on the LiDAR transmission distance equation,the main factors affecting the LiDAR echo intensity are explored,and the target point cloud data with intensity information by line array scanning of 95%reflectivity standard diffuse reflector plate are obtained by line array LiDAR(Fig.4).The stacked multi-frame single line point cloud(Fig.5)and the three-dimensional point cloud image of radar intensity with reflective spectral characteristics is obtained(Fig.8).Secondly,the piecewise polynomial model is used to fit the relationship between distance-intensity and incident angle-intensity(Tab.4).Based on the obtained piecewise polynomial model,the echo intensity under the influence of distance and incident angle is corrected,so that the measured echo intensity under different distance and incident angle can truly reflect the reflection spectrum characteristics of the target,and the validity of the correction model is verified(Fig.15-16).Finally,based on the obtained piecewise polynomial correction model,the intensity correction of the three-dimensional point cloud image of the radar intensity of the scaled satellite model with the reflectivity true value patch is carried out.The reflectivity of the target surface is calculated by using the reflectance spectral characteristics of the corrected echo intensity.The emissivity is further deduced by the reflection method,and the three-dimensional distribution of the emissivity of the scaled satellite model is obtained(Fig.21).Results and Discussions The correction results show that the standard deviation of echo intensity STD under the influence of distance before and after standard diffuse reflection correction is reduced from 50.58 to 3.49(Tab.5),and the standard deviation of echo intensity STD under the influence of incident angle is reduced from 19.25 to 3.17(Tab.5).The coefficient of variation of echo intensity under the influence of standard diffuse reflection plate distance effect and incident angle effect is reduced from 0.2676 and 0.3438 to 0.0420 and 0.0412(Tab.5)respectively.And the consistency of echo intensity is increased by 84.31%and 88.02%respectively(Tab.6).The average emissivity deviations of the surface patches of the three satellite models can be controlled at 3.33%,4.84%and 4.44%,respectively(Tab.7).Conclusions In view of the fact that most of the current emissivity measurement methods are only contact measurement of a single substance,it is impossible to measure the three-dimensional distribution of emissivity of complex targets.Combined with the characteristics of LiDAR,a non-contact emissivity three-dimensional distribution measurement method is proposed based on M8 LiDAR echo.The band of the M8 linear array LiDAR used in this paper is 905 nm,which belongs to the near-infrared band in the infrared band,and the emissivity measurement in the medium and long infrared band cannot be involved.The reflectivity of the materials used in this paper is the true value at room temperature,and the influence of temperature on emissivity measurement is not involved.In addition,due to the differences in physical factors of different LiDARs and the inconsistent expression of the unit and numerical scale of the echo intensity,the current measurement method is only applicable to specific scanning instruments.The robustness and universality of the emissivity measurement method are worthy of further discussion.Therefore,the next step will further improve the universality of the method and introduce the influence of temperature on the emissivity measurement.