Measurement And Modeling Of Brdf On Brass Surface Under Variable Temperature

The material in reality is between the ideal Lambert body and the smooth mirror.To study its optical scattering properties,it is necessary to introduce a physical quantity that can combine the ideal diffuse reflection and specular reflection-the Bidirectional Reflectance Distribution Function.BRDF can describe the space reflection characteristics of all kinds of material surface well,and has a wide range of applications in scientific research,industrial production,aerospace and other fields.The bidirectional reflection distribution function will change when factors change.Temperature is one of the important influencing factors,and temperature changes in BRDF measurements can cause large errors in measurements.However,there is little work on BRDF measurement in near-infrared band under variable temperature at this stage.The spectral BRDF at variable temperature in the near-infrared band can reflect the optical properties of materials and provide data for qualitative and quantitative analysis of material components,design of stealth materials,and evaluation methods for camouflage effects.Therefore,the measurement and application of BRDF in the near-infrared band under variable temperature are of great significance.Focusing on the study of BRDF on material surface under variable temperature,the optical properties of rough brass surface are measured and studied in near-infrared band.The main work includes the following aspects:(1)In this thesis,a set of traditional BRDF measurement devices is improved.The voltmeter and ammeter of the detection system in the original device were replaced by a phase-locked amplifier and a chopper,which reduces the error caused by the increase of the background noise in the original device and the random change of the measurement time in the measurement times,and improves the measurement accuracy of the faint light in the infrared band.(2)Based on the improved measuring device and the absolute measurement method,the spectral BRDF of brass surfaces with four different roughness are measured in the near infrared band.The effects of roughness,thermal radiation,temperature,heating time and wavelength on BRDF are analyzed in detail,and the measurement uncertainty is evaluated.(3)The relationship between roughness and temperature is established through measurement and numerical fitting,and a six parameter BRDF model is established on this basis.The model is used to fit the measured data of this experiment,and the results show that the fitting results of the model are in good agreement with the experimental measurement results,which fully shows that the six-parameter model established in this thesis can simulate the BRDF of brass surface under variable temperature well.