Research On BRDF Measurement Technology Of Material Surface

With the rapid development of aerospace science and technology,in such space weak light detection systems as satellite laser communication,gravitational wave detection,etc.,stricter requirements have been put forward for the suppression of stray light.The surface scattering characteristics of optomechanical components directly determine the stray light distribution in the system.Among them,the non-target stray light outside the field of view caused by the light scattering on the surface of the metal structure severely restricts the signal-to-noise ratio of the system and greatly affects the stability of the system.The research on the surface scattering characteristics of metal structural parts has always been a "stuck neck" problem in engineering.Under the traction of actual engineering requirements,this paper studies the reflection distribution measurement technology on the surface of metal structural parts based on the Bidirectional Reflection Distribution Function.This paper firstly studies and analyzes the surface scattering characteristics of metal structures and the transmission of stray light,Secondly,the advantages and disadvantages of the two BRDF measurement methods are compared.Based on the BRDF absolute measurement method,an experimental measurement system was built to measure and study the surface scattering distribution of aerospace metal materials,and the BRDF peak distribution law and scattering distribution characteristics under different conditions were analyzed.And a BRDF model with texture distribution properties on the surface of metal structural parts is established.At the same time,in order to meet the actual engineering needs,the ABg and Harvey scattering models were fitted to the experimental measurement results,and a scattering model database for metal structural parts was established,which provided essential data support for stray light tracing simulation analysis,system design and material selection.The main work of this paper has the following three aspects:（1）A set of BRDF experimental measurement system is designed.Based on the absolute measurement principle of bidirectional reflection distribution function,this paper independently designs and builds a BRDF measurement system.The measurement system consists of a laser light source system,a rotating scanning system,a signal detection system and a software control system,which realizes the automatic scanning of scattered light energy in the hemispherical space.The various factors of the measurement uncertainty of the system are analyzed,and the comprehensive results show that the measurement uncertainty of the built system is 4.61%.（2）The distribution of surface scattering characteristics of metal structural parts was measured and analyzed.Experiments were carried out to measure the scattering distribution characteristics of three typical aerospace metal materials including titanium alloy,aluminum alloy and aluminum-based silicon carbide under different influencing factors.The peak distribution and scattering distribution characteristics of BRDF under different laser wavelengths,incident angles,scattering angles,texture distribution and surface roughness were compared and analyzed.It is qualitatively shown that the stray light suppression effect of titanium alloy is better than that of aluminum alloy,and the measurement results also provide direct scattering distribution values for the establishment of surface scattering models.（3）A BRDF scattering model on the surface of metal structural parts is established.Based on the particularity of the texture distribution on the surface of metal structural parts,a BRDF model of the surface of metal structural parts was established under the influence of shadowing and masking effects.Using the simulated annealing algorithm to fit the measured values,the relative error between the model calculation results and the measured values is better than 7.26%,indicating that the model can completely and accurately characterize the surface scattering characteristics of metal structural parts.At the same time,the undetermined parameters of the Abg and Harvey models are solved by using the measured data,and the scattering model database is established.Through the analysis of the stray light suppression of each structural part,it is quantitatively demonstrated that the suppression of stray light of titanium alloy is one order of magnitude better than that of aluminum alloy.