There is a novel imaging method to solve the above two drawbacks. The effect it can be achieved is that the scanning mechanism rotates at a constant speed, and the optical aiming line can be kept still, which can avoid the smearing of the image and obtain a good imaging effect at any time. This is a feasible novel detection, which can realize a large field of view, while maintaining the high resolution of the optical imaging.
Imaging spectroscopy technology combines imaging technology with spectroscopy technology. The most common imaging spectrometers are dispersive imaging spectrometers and interferometric imaging spectrometers. The incident slit of dispersive imaging spectrometers is located on the front focal plane of the collimation system, and the incident light passes through the collimator. After the straight optical system is collimated, the light energy is imaged on different positions of the detector in the order of wavelength by the imaging system after dispersion by the prism or grating, and the target spectrum is directly obtained. The principle is simple and the technology is relatively mature, but the light flux will be affected by the incident slit. The interferometric imaging spectrometer forms an interferogram by introducing different optical path differences into the incident beam, and then uses the Fourier transform relationship between the interferogram and the spectrogram to obtain the spectral information of the object, with high luminous flux, multi-channel and high spectral resolution. The CUDA architecture was developed by NVIDIA and is mainly used in the field of parallel computing. Its core idea is to use the GPU as a co-processor of the CPU, which is responsible for the calculation of a large amount of data and greatly shortens the data calculation time. It has been widely used in finance. Simulation, biological computing, physical simulation, simulation computing and artificial intelligence and other fields. The spectral data processing of the infrared interference spectrometer system mainly includes steps of data rearrangement, de-DC, apodization and Fourier transform. Due to the large amount of calculation of Fourier transform and long calculation time, it seriously affects the real-time application capability of the system. Therefore, this paper proposes a method using base 4 FFT algorithm for implementing fast Fourier transform on GPU platform using CUDA in infrared interference spectrometer system. GPU and the base 4 FFT algorithm are used at the same time to greatly improve the degree of parallelism and shorten the calculation time. A spectral raw image of 640*480*256 band, using the traditional base 2 fast Fourier transform on the CPU takes about 20 minutes to invert into a pseudo-color image. With the algorithm of this paper, the time is shortened to less than 2 minutes.
In this paper, a homogeneous off-axis reflective infrared imaging system with an aperture of Φ300mm is designed according to the requirements. The calculation and optimization of structural parameters are completed in the optical software Code V. The system obscuration is eliminated by combining aperture off-axis with off-axis field of view. By introducing complex surface type to correct the residual aberrations, the off-axis optical system with good capability and structure size meeting the overall layout requirements is obtained. The system is composed by main reflector (F-1), secondary mirror (F-2), plane mirror (M) and the third mirror (F-3). The mirror M is a folding reflector; even aspheric surface is used for both F-1, F-2 and F-3 mirror. The uncooled thermal imager is used as the imaging device. The target plane of the detector is 10.88mm × 8.70mm, and the corresponding field of view is 0.6 °× 0.45 °. At 15lp / mm, MTF > 0.2 is close to the diffraction limit of the system, and the wavefront aberration of the full field of view is less than 0.01λ. The distortion is less than 1.2%.
Interference imaging spectroscopy is the advanced subject among the infrared remote sensing, and it has become an important technique to detect spatial information and spectral information of targets. It has the advantages of high flux, high spectral resolution and high spatial resolution that can be used for detecting more details of the spectral and spatial information. Based on a Michelson interferometer with its mirrors replaced by corner-cubes, principles of a hand-held, static, long-wave infrared Fourier Transform(FT) imaging spectrometer using an uncooled microbolometer array are introduced. Because in such FT-based spectral imager, the interferogram is acquired over the whole field of the camera while the scene of interest scans the path difference range, vignetting should be strongly limited while keep the size of the interferometer as small as possible. Interferometer size is given and interferential light path is verified through TracePro software. First results of field and laboratory measurements using the spectral imager are presented. Remotely obtained spectrums collected with this instrument and with those of high precise Michelson spectrometer are compared, and the measured values turned out to be closely corresponded. The results, in turn, verified the feasibility of the systematic working mode. The resulting system tested here provides datacubes of up to 640×480 pixels over the 7.7~13μm spectral range, this wavelength range reveals important information about scenes such as gas or landmine detection, and the instrument has a spectral resolution of about 8cm-1 that fulfils the requirement for most targeted applications. Examples of sky and buildings detection are shown.
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