In order to achieve infrared imaging spectrometers for environmental gas monitoring in the medium-wave infrared and long-wave infrared spectra, meanwhile detecting the characteristic spectra of a variety of ambient gas molecules, it is necessary to do research on the design of the infrared wide spectrum (3.2μm～14μm) imaging spectrometers optical system with a large relative aperture. First of all, the lens power of reasonable distribution will be available by solving of the wide spectrum correcting chromatic aberrations equation and athermalization equation. Secondly, the list compares the common infrared optical material in the infrared wide spectrum dispersion characteristics and thermal characteristics differences, optimizes the three infrared optical materials of the Germanium single crystal, wide spectral Zinc sulfide, and Chalcogenide glass for transmission optical system design. Thirdly, using CODE V optical design software to optimize the optical parameters, the system uses four lenses, introduces four aspherical faces, the rest are spherical. Finally, the modeling gives the 3D layout of the system, and the image evaluation and tolerance analysis of the optical system are carried out. The results show that the modulation transfer function (MTF) value of the optical system at the spatial frequency 30lp/mm is greater than 0.5. The average square root (RMS) value of the diffused spot diameter is less than 17μm; The working band is 3.2μm ~14μm, F number 1, the optical system in the temperature range of -40°C ~+60 °C has a good imaging quality. The optical system has the characteristics of large relative aperture, wide working band, good process and compact structure, and can be used for 640×480 the infrared wide-spectral segment focal plane detector.
For spatial-modulation imaging spectrometers, the conventional non-uniformity correction method cannot efficiently reduce the pattern noise caused by stationary interference fringes on the imaging plane. In this study, we apply optical the defocus method to realize scene-based non-uniformity correction. By applying severe defocusing, the diffraction effects can be neglected, and the point spread function of the system is equivalent to the geometric projection at the exit pupil. When the light of each spot is within the field of view, it illuminates the entire detector, and the detector obtains uniform irradiance. We can implement a single-point calibration or single-plus-two calibration using the uniform irradiance.
During the transmission of the thermal radiation in the atmosphere, the radiant energy is attenuated due to physical processes such as refraction, absorption, and scattering, which causes a change in the detection capabilities of the thermal imaging system. As a key performance of thermal imaging system, the inspection of the operating range is of great significance to the theoretical research and practical application of thermal imaging systems. Actually, the environmental condition that does not match the specified test condition when testing the operating range which are not encountered. It's complex to judge whether the thermal imaging system meets the index requirements by the test result directly. By modeling the target, analyzing and comparing the spectral transmittance under different atmospheric conditions, the paper introduces a method for judging the operating range of the infrared thermal imaging system when inspecting environmental deviates from the specified environment proposed.
The new progress of ground-based long-wave infrared remote sensing is presented. The LWIR hyperspectral imaging by
using the windowing spatial and temporal modulation Fourier spectroscopy, and the results of outdoor ether gas detection,
verify the features of LWIR hyperspectral imaging remote sensing and technical approach. It provides a new technical
means for ground-based gas remote sensing.
A LWIR Fourier-transform imaging spectrometer based on the static Michelson interferometer with high throughput is presented. Advantages and disadvantages of some common structures of imaging spectrometer are analyzed. Some selection of optimum configurations for imaging spectrometer is proceeded. The interferogram is acquired over the whole field of the camera while the scene of interest scans the path difference range, and vignetting should be strongly limited while keeping the size of the interferometer as small as possible for manufacturability and practicability reasons. The key point is to put the entrance pupil of the imaging lens inside the interferometer. The design of optical system is proposed. The field of view(FOV) is 10°.The operating wavelength range is from 8 to 12μm, F number is 2 and the working temperature range is -20°C～40°C. Optical system with 100% cold shield efficiency is good adaptability to wide environment temperature change. The spectrometer system has low utilization of solar energy in the infrared band, so to ensure its transmittance, and it is necessary to use a small amount of lenses as possible, so here the method of the active electromechanical athermalisation just uses four lenses in the system. Modulation transfer function (MTF), aberrant and distortion etc of optical system are analyzed. The results show that an excellent performance and image performance are obtained despite the simple structure.
Signal-to-noise Ratio of hyper-spectral imaging FTIR interferometer system plays a decisive role on the performance of the instrument. It is necessary to analyze them in the development process. Based on the simplified target/background model, the energy transfer model of the LWIR hyper-spectral imaging interferometer has been discussed. The noise equivalent spectral radiance (NESR) and its influencing factors of the interferometer system was analyzed, and the signal-to-noise（SNR） was calculated by using the properties of NESR and incident radiance. In a typical application environment, using standard atmospheric model of USA(1976 COESA) as a background, and set a reasonable target/background temperature difference, and take Michelson spatial modulation Fourier Transform interferometer as an example, the paper had calculated the NESR and the SNR of the interferometer system which using the commercially LWIR cooled FPA and UFPA detector. The system noise sources of the instrument were also analyzed in the paper. The results of those analyses can be used to optimize and pre-estimate the performance of the interferometer system, and analysis the applicable conditions of use different detectors. It has important guiding significance for the LWIR interferometer spectrometer design.