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.
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.
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.
The concept of high-throughput imaging Fourier transform spectrometer is introduced. Starting from the principle of the lateral shearing interferometer, it analyses the decline reason for the signal modulation efficiency and theoretically analyses the several aspects of the surface errors of the plane mirror, the beamsplitter properties change and the incident light angle influence the modulation efficiency. Based on analysis results, some expressions of modulation efficiency are provided. Furthermore, the relationship between modulation efficiency and performance parameters is pointed out. The reasons for the interferometer signal modulation efficiency decline can contain the following several aspects: (1) the influence of the surface errors of the plane mirror, (2) the polarization state change because of the influence of the reflection and the transmission in the light incident process makes the signal modulation efficiency decline, (3) the influence of the incident light angle. The results show that: this class of system is inherently optomechanics robust, no-moving part system, simple and compact structure, easy assembly and adjustment, strong vibration resistance as well as high resolution and high-throughput. Our results will provide a theoretical and practical guide for studying, developing and engineering Michelson lateral shearing interference imaging spectrometers. It can be widely used in the long-wave infrared (LWIR) imaging spectrometer system for thermal infrared remote sensing community.