An Area Array Multispectral Temperature Measurement System Based On Blackbody Radiance Approximation

China’s aviation and aerospace industry is developing towards larger airspace,higher speeds,and longer distances,which increasingly demands engine technology for hypersonic aircraft and cruise missiles that can operate at faster speeds and wider ranges.Real-time monitoring of aircraft engine temperatures is a necessary safety measure and a key factor in calculating engine performance and lifespan.The multispectral thermometry method is a highprecision temperature measurement technique that uses the relationship between the radiance of a target at different wavelengths and its temperature to determine the target’s temperature.Additionally,since this method does not require contact with the target,it can be used to measure temperatures in high-temperature,dangerous,or difficult-to-reach environments,making it highly practical in fields such as aviation,aerospace,defense,and industry.Currently,the measurement of turbine blade temperatures in aircraft engines is still unsatisfactory,mainly reflected in low accuracy of area-array thermometry and the inability to monitor temperatures in real-time.To address these issues and meet project requirements,this paper conducted relevant research combining multispectral thermometry theory with CMOS imaging theory,and constructed an area-array thermometry system.The main contents and innovations are as follows:1)Introducing several methods of spectral thermometry and existing spectral emissivity measurement methods,combining blackbody radiation theory with CMOS sensor imaging principles,deriving the theoretical formula for area-array multispectral thermometry,and introducing the multispectral data processing method based on blackbody radiance approximation.2)Building an area-array multispectral thermometry system and performing preprocessing,including non-uniformity correction of the sensor and normalization of the eight-channel spectral response.Using the system parameters for simulation calculation,the photoelectrons of the focal plane array were obtained.The theoretical analysis showed that the lower limit of the system’s temperature measurement could reach 700℃.3)Calibrating the system using a point source blackbody,the actual temperature measurement range of the system was determined to be 750℃ to 1500℃.Curve fitting was performed using a third-order polynomial method,giving the function relationships between grayscale,exposure time,and irradiance under eight channels.The fitting degree was evaluated based on the trend line and five random blackbody temperatures were set.The temperature data was inverted using the blackbody radiance approximation method,showing that the method can achieve a temperature measurement accuracy of ±1K for the target.The overall calibration fitting error did not exceed 2.6%.4)Designing a verification experiment of laser-heated graphite blocks,deriving the transmission model of radiation energy from the laser-heated material,and proving the validity of the method.Measuring with a tungsten-rhenium Type 325 thermocouple,a high-speed midwave infrared thermal imager,and the multispectral thermometry system,and using an optical fiber spectrometer to measure the intensity spectra of a variable temperature blackbody and high-temperature graphite blocks at five positions.The spectral emissivity from 720 nm to980nm was calculated using the energy method and compared the test results of five methods:thermocouples,infrared,monochromatic,colorimetric,and blackbody radiance approximation.The error of the blackbody radiance approximation method was calculated using the thermocouple data as a benchmark,and the calculated analysis error did not exceed 0.84%.The comprehensive uncertainty was 1.71%,confirming the reliability of the method.