Infrared Polarized BRDF Rapid Measurement System at Variable
Temperatures
HUANG Ang1, WANG Jing-hui1*, DONG Wei1, MENG Fan-shan1, 2, HUANG Shuai1, LI Yi-wen3, FENG Guo-jin4
1. Division of Thermo-physics Metrology, National Institute of Metrology, Beijing 100029, China
2. College of Mechanical and Transportation Engineering, China University of Petroleum, Beijing, Beijing 102249, China
3. Science and Technology on Plasma Dynamic Laboratory, Airforce Engineering University, Xi'an 710038, China
4. Division of Optical Metrology, National Institute of Metrology, Beijing 100029, China
Abstract：Infrared-polarized BRDF at variable temperatures can accurately reflect the radiation characteristics of the material surface, provide basic data for studying the optical properties of the surface, and have a wide range of applications in thermal imaging and infrared target detection. However, existing polarized BRDF measurement systems mainly use a discrete point-by-point scanning strategy, with a single-angle scanning time of more than 5 minutes and a complete BRDF measurement time of several hours, and the resolution is relatively low. When BRDF systems are applied to variable temperature measurements, high temperatures must be maintained on the sample surface for a long time, which leads to increased energy consumption and is difficult to implement. Therefore, there is an urgent need to investigate fast measurement methods. In this work, an infrared polarization BRDF measurement system with a portable sample heater from room temperature to 1 000 ℃ was developed, and the mechanical arm's load and temperature resistance problems were overcome. A continuous scanning method of polarized BRDF based on a robotic arm was proposed. Fast and continuous 3D BRDF measurements in different polarization states were realized in two ways: discrete rotation of the robotic arm with continuous scanning of the rotary table and discrete rotation of the rotary table with continuous scanning of the robotic arm, improving the measurement speed and resolution. The single-angle scanning time was less than 1 minute, and the complete BRDF measurement time was shortened to about 1 hour, which is more suitable for variable-temperature BRDF measurements. The developed system was applied to measure the BRDF of a frosted stainless steel sample with a high specular reflection surface at variable temperatures. The area of strong reflections was finely scanned continuously, and three-dimensional distributions of polarized BRDF at three solid angles of 6.1×10-6, 1.37×10-5, and 3.81×10-5 were obtained. The larger the solid angle, the stronger the spatial filtering effect, revealing smaller measurement peaks, which was consistent with the physical model of BRDF. Therefore, it is necessary to use a small solid angle to minimize the spatial filtering effect for measurements of highly specular materials. The stainless steel sample in this work was measured with a solid angle of 6.1×10-6 sr. In variable temperature experiments, the oxidation reaction occurred on the stainless steel surface with increasing temperature, and the S- and P-polarized BRDF peaks both decreased. The maximum standard deviations of the measurements in the two polarization states were 0.56% and 0.24%, respectively, compared to the average BRDF value. The repeatability of BRDF measurements was good at different temperatures and the changes of the two polarization states converge to be consistent, indicating that the developed polarized BRDF measurement system was effective.
Key words：Bidirectional reflectance distribution function;Polarization measurement;Variable temperature;Infrared reflection
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