Optical Design And Analysis Of Uncooled Double-band Thermal Imaging Spectroment

Uncooled Thermal Infrared Imaging Spectrometer has become one of the important and low-cost tools for humans to observe the earth and explore the universe,based on the development of micro-bolometers arrays.There are also advantages such as small size,simple structure and small mass.However,the instrument's own thermal radiation is large in the uncooled environment,which seriously affects the imaging quality.Therefore,studying the design of its optical system and the method of effectively suppressing stray radiation is the key to the successfully development of an uncooled thermal infrared imaging spectrometer.This paper is dedicated to researching and designing an uncooled high performance thermal infrared imaging spectrometer.First,the domestic and foreign development status of thermal infrared multi-spectrometer and hyper-spectrometer are introduced.Most infrared thermal sensors currently used to monitor forest fires are refrigerated multi-spectrometers,which are costly.Their dynamic range of the temperature measurement and spatial resolution are also difficult to meet the needs of fire detection.Based on the needs of forest fire detection and the successful launch of the uncooled Mercury detector MERTIS developed by ESA the year before,we have further expanded its working wavelength range from long-wave thermal infrared to the mid-wave thermal infrared band,making this technology suitable for satellite forest fire monitoring.Based on the forest fire remote sensing detection principle,the feasibility of this novel spaceborne forest fire detection technology was studied,and the technical indicators of this thermal infrared imaging spectrometer were analyzed and determined.Based on the off-axis three-reflector telescope and Offner-type convex diffraction grating spectroscopic imaging device,an all-aluminum imaging spectrometer optical system with a working wavelength covering the mid-wave and long-wave infrared bands was designed,which has the advantages of no blocking,no thermal difference,no distortion and good image quality.In order to effectively suppress stray radiation,a specular reflection baffle and an optical-mechanical structure are used to suppress stray radiation outside the field of view while reducing the stray radiation caused by the instrument's own radiation.Based on the analysis of the optical and mechanical system's radiation performance and its suppression ability,a method of double-exposure background noise detection is proposed to improve the signal-to-noise ratio.The feasibility of monitoring forest fires by uncooled thermal infrared imaging spectrometer was verified by model simulation,which laid the foundation for the further development of uncooled high-performance thermal infrared remote sensor.