Method to identify defective detectors of thermal focal plane array based on its frequency domain characteristicsHuang, Xiaoxian; Xu, Feifei; Fu, Yutian
doi: 10.1117/12.2665554pmid: N/A
The targets on the earth can be detected by its radiation in thermal band from the remote sensing satellite day and night. The State-of-the-art infrared detector technology makes it possible to use thermal focal plane array (FPA) to probe interested target in the boundless sea. Unfortunately due to accidental and uncontrollable factors during detector production, there always are defective detectors in the thermal focal plane array, more or less. We can call it dark element if it has no or weaker response, or can call it hot element if it has abnormal stronger response. These two kinds of defective response cannot be mitigated by linearity correcting, contrarily it will be harmful to the target detecting. Method to identify these defective detectors by analyzing their frequency domain characteristics is stated here. The recognition rate of defective detectors is greater than 98% by using such method.
A space-time downscaling approach of Fengyun-4A satellite based on deep learningYang, Chunlei; Xie, Meng; Gu, Mingjian; Liu, Lili
doi: 10.1117/12.2664546pmid: N/A
Fengyun-4A (FY-4A) is the second-generation geostationary orbit meteorological satellite series with higher observation frequency and resolution compared with the first-generation in China. While, the spatial resolution (4km) of the infrared channel and water vapor channel is lower than that of the visible light channel (1km), which limits the application of FY- 4A in extreme weather monitoring. At the same time, in order to adapt to the characteristics of the rapid time change of small and medium-scale meteorological disasters, this study based on the deep learning method to downscale the FY-4A satellite data in space and time. The approach consists of two main steps: first, FY-4A data is downscaled using a ESRGAN model transfer learning, which can extract spatially relevant information and reconstruct image resolutions such as infrared channels from 4km to 1km; second, based on the Super SloMo model, the time-related information can be extracted to effectively downscale the FY-4A data, and the temporal resolution of the FY-4A is reconstructed from 15min to 6min , making it comparable to the time resolution of weather radar. The spatial resolution evaluation based on the visible light channel shows that the method used in this study is superior to the spatial downscaling method of bicubic interpolation and Papoulis-Gerchberg in Peak Signal to Noise Ratio (PSNR), Structural Similarity (SSIM), Root Mean Square Error (RMSE), and Correlation Coefficient (CC), and can more effectively convert low-resolution FY-4A satellite data to the corresponding high-resolution satellite data. At the same time, the time-related information can be extracted based on the time downscaling model, the time resolution is converted from 15min to 6min, and the movement direction of the cloud remains the same. Compared with traditional methods, this downscaling approach is a postprocessing method of satellite data with higher precision, which can improve the application value of FY-4A in disaster weather warning.
Visualization of radiation intensity sequences for space infrared target recognitionZhang, Shenghao; Chen, Xin; Rao, Peng; Zhang, Hao
doi: 10.1117/12.2665173pmid: N/A
Infrared target recognition is an important task in space-situational awareness. In the space target detection process, due to the small energy of the point target, it is easy to make the target disappear from the detection field of view under the interference of dense noise, resulting in a decline in recognition system performance. Reasonable representation of the infrared characteristics of a target is an effective means of improving the stability of recognition systems. In this study, a one-dimensional radiation intensity sequence was mapped to a two-dimensional space based on the Gramian angle field, Markov transition field, and recurrence plots to visualize the structural mode of the target radiation intensity sequence and the dynamic properties of the system generating the sequence. On this basis, a recognition framework based on convolutional neural networks was proposed to train and recognize three types of visualized signals and raw data. The experimental results showed that the proposed recognition method based on visualized signals can effectively identify the target and is robust against noise interference and missing data.
Design of cooled infrared bionic compound eye optical system with large field-of-viewYu, Yang; Chi, Ying-hao; Li, Lin-han; Wang, Xiao-yu; Chen, Jun; Yue, Juan; Gu, Yu-zhang; Su, Hai-feng; Gao, Si-li
doi: 10.1117/12.2664573pmid: N/A
A multi-aperture compound eye infrared optical system is designed for the imaging of cooled medium wave infrared detector. The optical system includes an infrared lenslet array arranged on the front spherical surface, and a relay infrared optical system matched with a cooled infrared detector. The problem of matching and connection between the infrared lenslet array arranged on a spherical surface and the relay infrared optical system matching with a cooled infrared detector is solved, and a set of multi aperture infrared bionic compound eye optical system that can match the cooled infrared detector is designed. Through the relay optical system, the focal surface imaged by the curved infrared lenslet array of compound eye is re-imaged on the focal plane of the cooled infrared detector. The waveband of the designed compound eye infrared optical system is 3.7-4.8m. The total focal length is 3.5mm, the total field of view of the multi aperture compound eye optical system is 108, the distortion of the full field of view is less than 6%. The design result shows that the image quality of the system with different aperture approaches the diffraction limit, and has the advantages of multi-aperture, large field-of-view, low distortion and ideal image quality.
Evaluation of rice freshness based on a modified VGG network and terahertz imagingWang, Qian; Zhang, Yuan; Ge, Hongyi; Jiang, Yuying; Qin, Yifei
doi: 10.1117/12.2665257pmid: N/A
The freshness of rice reflects the time that has elapsed since it was harvested and the extent of deterioration in the quality of the rice that has occurred during storage. Therefore, it is crucial to detect the freshness of rice samples; here, we undertake that task using terahertz images and a modified VGG network. Terahertz imaging is non-destructive, permits molecular fingerprinting, and is low in energy consumption. Terahertz imaging technology uses terahertz rays to irradiate the sample and obtains a terahertz image of the sample by processing and analyzing the transmission and reflection spectra of the sample. Terahertz imaging technology has been widely used in applications related to material identification, medical diagnoses, quality detection of agricultural products, and safety inspections. In this paper, terahertz images of rice stored for various lengths of time were analyzed using a terahertz imaging system. Due to a large amount of data and inconspicuous features of the terahertz image, the traditional 1D-VGG network is relatively insufficient in computing power. Thus, it is not well suited to the extraction of features from within the images. To resolve this issue, the Inception-ResNet-A asymmetric convolution module in the Inception-ResNet-V2 network has great computing power,which is introduced into the VGG19 network structure. This proposed network is found to increase identification accuracy up to 99.8%. This work indicates that terahertz images combined with the modified 1D-VGG network represent an efficient and practical method for identifying rice freshness; this work thus has great potential for use as a tool for ensuring food quality and safety.
Helium Joule-Thomson cryocooler below 4.5 K for infrared detectorsChen, Zhichao; Liu, Shaoshuai; Jiang, Zhenhua; Ding, Lei; Huang, Zheng; Wu, Yinong
doi: 10.1117/12.2665290pmid: N/A
Mechanical cryocooler technology are one of the significant technologies for earth and space scientific exploration. To meet the needs of future applications of infrared and millimeter wave detectors, Shanghai Institute of Technology Physics, Chinese Academy of Sciences (SITP, CAS) has developed a helium Joule-Thomson cryocooler (JTC) below 4.5 K for space applications. As the two most important components of the helium JT cryocooler, the precooler and the JT compressor are both developed by SITP. The precooler is a two-stage pulse tube cryocooler, and the JT compressor is an oil-free linear compressor, all of which can achieve long-life operation. First, a 4 K JTC was developed, experimental results show that after about 11 hours of cooling, the 4 K JTC successfully reached the liquid helium temperature and has a cooling performance of at least 110 mW@4 K.
In-situ ellipsometric study on composition-dependent short-wave HgCdTe in the process of molecular beam epitaxy growthYang, Liao; Shen, Chuan; Chen, Lu; He, Li
doi: 10.1117/12.2664815pmid: N/A
Hg1-xCdxTe is considered as the preferred material for high performance infrared photodetectors and imaging focal plane array (FPA) detectors. One of the technical challenges of multi-dimensional integrated HgCdTe epitaxy by molecular beam epitaxy (MBE) lies in the in-situ extraction, characterization and precisely control of a series of parameters such as alloy composition, surface roughness, substrate temperature and film thickness at a relatively low substrate temperature of about 180C. Therefore, an in-situ, nondestructive spectroscopic ellipsometry (SE) method is needed to characterize the performance of HgCdTe films. In this paper, real time optical property characterization of short-wave Hg1-xCdxTe epitaxial grown by MBE is reported. Run to run feasibility and stability of in-situ SE is confirmed by buffer layer thickness verification in multiple growth runs. Lorentz oscillator parametric model provides a new approach to describe optical dispersion property of HgCdTe over spectral range of 1.5-4.1 eV. The absorption peaks show blue shift with the increase of HgCdTe Cd composition (x). Under this circumstance, the longitudinal x value for HgCdTe during epitaxy process can be obtained in real time without any surface damage by successfully building a composition-dependent optical constant library, with routine run-to-run reproducibility measurement accuracy Δx of ~ 0.0015. This work will facilitate the fabrication of HgCdTe heterojunctions with complex component distribution and doping profiles.
Study on immersion grating for methane detection spectrometerNenghua, Zhou; Liu, Quan; Huang, Bing
doi: 10.1117/12.2665330pmid: N/A
Methane is the second largest greenhouse gas after carbon dioxide, and the measurement and monitoring of methane is essential for regional and city-scale emission reduction strategies. Atmospheric methane concentration observations are also important for predicting regional emission trends. Spectrometers are important optical instruments for monitoring the content of greenhouse gases in the atmosphere, and most spectrometers choose a grating as the spectroscopic element. Due to the higher resolution of the immersion grating, it reduces its volume while improving the performance of the spectrometer and reducing the weight of the whole machine, so it is of great significance to study the immersion grating for the practical application of the spectrometer. In this paper, the quartz immersed grating was designed for weak CH4 band. The rectangular groove structure with high refractive index dielectric film was designed in consideration of possible fabrication errors. In the 2.275-2.325μm band, the duty cycle of the rectangular groove is 0.3~0.45, the thickness of TiO2 is 165~170nm and the groove depth is in the 800~980nm region, the diffraction efficiency of the grating is higher than 70%. When the thickness of TiO2 is 170nm and the groove depth is in the 800~950 nm region, the diffraction efficiency of the grating is higher than 80%. When the TiO2 thickness is 175~180 nm, the overall polarization degree is less than 0.1. For trapezoidal grooves, when the duty cycle is 0.3~0.35, the bottom angle of the trapezoid is 80°~86°, the thickness of TiO2 is 195 nm, the depth of the grating groove is 820~900nm, and the diffraction efficiency can be above 80%. When the thickness of TiO2 is 177~195nm, the polarization degree is less than 0.1. The TiO2 film will be deposited by atomic layer deposition.
Study on small spacing total internal reflection quantum well infrared focal plane array deviceShao, Enshan; Li, Xiangyang; Huang, Hong; Yang, Fucheng
doi: 10.1117/12.2665339pmid: N/A
Since infrared detection was proposed, infrared detectors have been to the 3rd generation . Both of the small size and large scale are the requirements for the development of infrared detectors. At present, the focal plane array devices on the market have a relatively high difference between the response wavelength and the size of pixel and therefore, when dealing with long wavelength detection, there will be a large size FPA. The quantum well infrared focal plane array devices fabricated by GaAs/AlGaAs have been widely used due to high uniformity and mature technology, but in the field of long-wave and very-long-wave detection, if the traditional grating coupling structure is used, because the wavelength and the size of the pixel are close, a strong diffraction effect will occur before the infrared radiation reaches the active region. This will lead to significant crosstalk and errors. Therefore, using grating diffraction as the quantum well coupling mechanism limits the size of the pixel and as a coupling mechanism, it is difficult to achieve due to small pixel size. Therefore, this paper adopts the total internal reflection type coupling structure proposed by K.K.Choi, and compare it with the traditional grating coupling structure to study how this structure improves the performance when detecting long-wavelength and reducing the size of pixels. In this paper, a quantum well infrared focal plane array with a pixel size of 640×512, a center-to-center distance of 15 μm and a response wavelength of 10.55 μm is fabricated by using GaAs/AlGaAs and melting photoresist technology which is different with the method proposed by K.K.Choi to fabricate this structure. The FDTD-based open source field simulation software MEEP is used to simulate the field distribution of the devices and evaluate its performance about fighting against optical crosstalk of this structure and compare its performance with the grating coupling structure. In this paper, we also use MEEP to explore the influence of the reflection angle, the position of the active region, and the period of the quantum well on the distribution of the field inside the device, and calculate the electromagnetic wave’s energy of the active region as the evaluation factor. These results shows that these geometrical factors restrict each other, therefore, to produce a good QWIP FPA based on the total internal reflective structure, one need to take these factors into account to tune these parameters to maximize the optimized performance. The main content of the research is to fabricate a 640×512 total internal reflection quantum well infrared focal plane array device, and use the MEEP to study the electrical field distribution inside the device with related geometric factors.