Measurement Technology And Experimental System Of Bidirectional Reflectance Distribution Function

The Bidirectional Reflectance Distribution Function(BRDF)is a physical quantity that characterizes the spatial reflection characteristics of the target surface and can effectively describe the spatial reflection characteristics of the target surface.Hence BRDF has been widely used in target light scattering calculations,stray light analysis,computer image processing,remote sensing,target recognition,and research on the optical properties of materials.BRDF is affected by many factors such as surface morphology,wavelength,and temperature,which brings great difficulties for its measurement.However,most of the BRDF measurements focus on visible light and cannot meet the requirements of the research field such as target recognition and aerospace.Supported by the National Natural Science Foundation of China,an absolute measurement method is proposed and a BRDF experimental system is built based on this method.The device is capable of measuring BRDF in wavelength coverage of 380?2500 nm band.The main research work includes the following aspects:1.The advantages and disadvantages of the absolute measurement and relative measurement methods are analyzed comprehensively.It is pointed out that the absolute measurement method should be adoptted in the design of high-performance BRDF measurement devices.In this paper,a BRDF absolute measurement method is proposed based on the relevant definition of radiometer,and the derivation process of the measurement principle is presented.In derivation process,the relation between the effective detection area and the incident light illumination area is discussed.The approximation of "area equal" is eliminated during the transition from the measurement of the incident irradiance to the measurement of the reflection radiance.Finally,the main factors affecting the reliability of BRDF measurement are analyzed according to the derivation process of the principle.2.A BRDF experimental system was built based on the proposed absolute measurement method.1)considering the design goals,the experimental is equipped with three light sources,including a laser light source,a high-pressure ignition xenon lamp and a laser-driven white light source;2)The geometric dimensions of the components of the corner device are optimized according to the occlusion angle,geometric error and integration error and other factors,and the rotation scheme of the corner device is described in detail.3)The measurement light path,detector and signal processing system of the detection system have been described in detail.4)The design of the heater and temperature control system was presented elaborated,and the maximum measured zenith angle at high temperature was calculated according to the design parameters.3.The Uncertainty analysis and reliability verification of the experimental system were performed.1)The factors affecting the uncertainty of experimental system are analyzed.All the factors are discussed and calculated in detail.The combined uncertainty of the experimental system is 3.79%.2)The noise problem in the measurement is discussed in detail,and the reasonable solution was proposed according to different situations;3)BRDF of polytetrafluoroethylene and the spectral reflectances of commercial protective metal film mirrors in the near-infrared band are measured.The reliability of the experimental system was verified by comparison with the reference values.4.The spectral polarization BRDF of the low carbon steel E235 B in the visible and near infrared bands were measured.The measurement results of spectral BRDF show that the trend of polarization BRDF with reflection zenith angle is not affected by wavelength,and the curve of BRDF versus wavelength is not affected by the reflection zenith angle.In this chapter,the factors affecting the measurement of BRDF are analyzed by separating spectral and spatial properties,i.e.,the spatial reflection characteristics are analyzed at a single wavelength,and the spectral reflection characteristics of the surface are analyzed at the direction of the mirror reflection.5.The color of industrial pure titanium during the heating process was studied,and the color mechanism was analyzed.The BRDF of sample surfaces with different color was measured,and the measurement results were compared with the characteristics of structural color and pigment color.The results indicate that the color of industrial pure titanium in the heating process belongs to the pigment color.The measurement method and the experimental system proposed in this paper can realize the measurement of spectral BRDF under different conditions.The components of the experimental system are independent and can be improved according to research needs.The work of this article will play an important role in the measurement and application of BRDF.