At present, there are few studies on nondestructive testing of aircraft surface based on hyperspectral imaging at home and abroad. Therefore, an indoor near infrared (NIR) hyperspectral damage detection system with a spectral resolution of 5nm was established, and the paint damage on the sample surface was identified. The reflectance calibration, average reflectance calculation and principal component analysis (PCA) dimensionality reduction were performed on the collected hyperspectral data. On this basis, the unsupervised classification iterative self-organizing Data analysis algorithm (ISODATA) is used to identify the damaged samples. The results show that the spectral curves of the damaged and undamaged pixels of the sample are significantly different at about 910nm. The first 10 principal components selected can contain 97% of the sample data information, which can realize the effective identification of damage samples based on ISODATA. In this study, paint damage was taken as an experimental sample to verify the feasibility of using near-infrared hyperspectral imaging technology for damage identification. In addition, preliminary outfield experiment results also show that it is feasible to apply this technology to aircraft surface damage detection.
Monitoring the formation process and occurrence state of methane in abyssal gas-liquid-hydrate coexistent system is the premise for gas hydrate research and exploitation, and the key lies in real time, synchronous and in-situ acquisition of multi state parameters, like concentration, temperature, pressure of methane. In this paper, we propose a novel multi parameter in situ methane sensor (Submarine Methane Imaging Interference Spectrometer, SMIIS) that can simultaneously measure concentration, temperature and pressure information of submarine methane. Then to evaluate SMIIS’s feasibility and performance, we build SMIIS’s simulation model and analyze its forward interferogram. The signal-to-noise ratios (SNRs) of the simulation interference fringes for the six spectral lines of methane are in the range of (3 - 618). The detection sensitivities for concentration, temperature and pressure measurements can reach to 0.5 nmol/L, 0.5 K, and 0.05 MPa, respectively. The results indicate that the preliminary design of SMIIS is feasible. After further testing and improvement, this system will have the potential to be applied to the seabed methane detection.
In this paper, nanocones array is introduced into bottom silicon cells design. By finite-difference time-domain methods, the absorption efficiency in the range of 300-1100nm has been analyzed, and the structural parameters have been also optimized. Our calculations show that with the increase of the height of the nanocones, the spectra of the top cell and the bottom cell have significant interference effects, and the short wave photons and long wave photons can achieve the maximum light absorption through strict optical management.The absorption enhancement modes of photons at different wavelengths have been analyzed intuitively by the distribution of electric field. These results enable a viable and convenient route toward high efficiency design of perovskite/Si tandem solar cells.
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