In order to overcome the problems of low diffraction efficiency, large aberrations and stray light of traditional ruled gratings in reflective Raman spectrometers, combined with the characteristics of the Raman signals of lunar surface minerals, a volume phase holographic (VPH) grating Raman spectrometer system for lunar surface detection was designed. The spectral range of the spectrometer is 140~3073cm-1, and the field of view is 3°. According to the Kogelnik coupled wave theory, the diffractive efficiency of the designed VPH grating is more than 95% at the central wavelength, and the average efficiency is more than 80% in the whole spectral range. After optimizing with zemax, the MTF of the entire spectrometer system at the Nyquist frequency is greater than 0.45, and a spectral resolution of 10 cm-1 can be achieved.
This paper proposes a method for extracting the solar centroid based on a multi-color model. The method is based on the three-color models (Lab, HIS, RGB) to segment and extract the color features of the image at the same time, coarsely locate the existence area of the sun target, and filter the obtained results through shape features, etc. We should try our best to optimize algorithm, for which can obtain a precise sun image. It is very important to combine circle center fitting with edge extraction to obtain the coordinate of edge point. What’s more, we need to select the edge points to form a sample set of edge points. It is helpful to fit the center of the circle by the least square method. The algorithm is improved to find the center of mass of the sun. By subjective judgment and error analysis evaluation of a large number of results, this method is useful as we expecting for the segmentation and extraction of solar targets. But due to the interference of the shooting angle, light, exposure, weather and other factors when the image was taken, which makes the result of target segmentation not ideal. However, it has little effect on the final centroid extraction result.
The explosives detection has been a hot and difficult issue in the field of security,it is particularly important to detect explosives quickly and reliably. There are many methods to detect explosives currently, stand-off Raman spectroscopy is one of the most promising and practical technologies, this technique can be used for non-contact and nondestructive detection, ensure the safety of attendants, at the same time the precision and speed of detection are also very high and be characterized by rapid response. This paper mainly gives an account of the fundamental principle of Raman spectroscopy, as well as recount major challenges of Standoff Laser Raman Spectroscopy applied in explosives detection and corresponding solutions. From the perspective of the system, this paper sums up related theories and techniques of the excitation laser and telescopic system etc.. Ultimately, a brief analysis and summary of the development trend of this technology is given.
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