Study On Ground Measurement Method Of Longwave Infrared Radiation Of Airplane's Skin At High Atltitude

The research on infrared radiation characteristics of aircraft is of great significance in both civil and military fields,from theoretical and technical point of view.The main radiation sources of the aircraft are divided into three parts: the tail nozzle,the plume and the skin.The research on the infrared radiation characteristics of skin has great application value.At present,most of the researches on infrared radiation characteristics of aircraft were of theoretical modeling and data simulation,or of radiation measurement of aircraft skin or plume under the ground test condition,but fewer studies were focused on radiometric measurements of airplanes flying at high altitudes.Skin temperature is a key infrared radiation characteristic of aircraft target,so it is very important to measure and invert the skin temperature of aircraft.This thesis will focus on the research on the method of radiation measurement for civil aviation aircraft in flight.Effective infrared radiation data of aircraft target will be acquired through the information acquisition system based on long-wave infrared,and the temperature of aircraft skin will be inverted.First,a brief description is made of the infrared radiation characteristics of aircraft target,and the main research technical route is put forward.A set of aircraft skin temperature measurement system is designed and developed based on long-wave infrared imager,with main effort focused on modularization,low noise and high sensitivity.The system is divided into two parts: the long-wave infrared imager and the matched host computer software.The long-wave infrared imager consists of an imaging system and an electronic system,which is the core of the whole system.The imaging system is used to convert infrared radiation into electrical signals,and its design focuses on the selection of lenses and detectors.The electronic system is used to convert the electrical signals of detectors into digital signals for transmission to the host computer.Its design focuses on modular design and low noise performance.The host computer software is divided into communication software and collection and storage software.The communication software is used to complete the parameter setting and parameter feedback function to ensure the appropriate working state of the system under different conditions.The acquisition and storage software is used to complete the acquisition,real-time display and storage of image data to obtain the data information of the target.Second,this thesis introduces the theoretical model of aircraft skin temperature measurement,and proposes a successive approximation temperature inversion method.The radiation model of aircraft skin is established,the composition of skin radiation is analyzed in detail,and all the radiation of skin is approximated to the heat radiation of skin itself according to the calculation.By establishing the model of atmospheric transmission and attenuation,a more accurate method for calculating the radiance of the target signal entering the pupil is obtained.By establishing the radiometric calibration model,the correspondence between the radiance of the target signal entering the pupil and the DN value is obtained.The successive approximation temperature inversion method is proposed by integrating several models.Finally,several error sources of the temperature inversion model are analyzed.At last,a comprehensive imaging test is performed,and the experimental data are calculated and analyzed.The linear relationship between the radiance of the entrance pupil and the DN value is obtained through the radiation calibration test.The target radiation measurement test of Boeing 787 and Airbus 350 large-scale civil aviation aircraft at 5km and 10 km flight altitude was completed through test planning and implementation,and the radiation response data of long wave infrared camera to aircraft skin was obtained.Then according to the experimental results,it is divided into two modules: the skin radiation atmospheric transmission module and the absolute radiation calibration module to calculation and analysis the experimental data.Finally,the uncertainty of inversion temperature is calculated and modified.The reshaping result of the skin temperature of civil aircraft with 5 km flight height is 268 K,the reshaping uncertainty is 4K and the reshaping relative uncertainty is 1.49%.The reshaping result of skin temperature modification of civil aircraft with 10 km flight height is 232 K,t the reshaping uncertainty is 3K and the reshaping relative uncertainty is 1.29%.The results indicate that the infrared radiation measurement method proposed can achieve a high accuracy inversion of aircraft skin temperature,provide data support for the study of aircraft infrared radiation characteristics,for the observation,monitoring and identification of aircraft targets,and is hence meaningful for improving the management level of aircraft.