2014 Vol. 43, No. 4

Infrared technology and application
Research of atmospheric transfer correction in radiance measurement: atmospheric transfer correction system
Wei Heli, Dai Congming
2014, 43(4): 1019-1024.
[Abstract](390) [PDF 1244KB](166)
Atmospheric transfer correction is impo rtant to the measurement of target's radiation characteristic. Following the former paper, an atmospheric transfer correction system and the moderate-spectral-resolution combined atmospheric radiative transfer (CART) code were introduced. The comparisons of atmospheric correction and horizontal measurement results were presented. The precision of the atmospheric correction system on middle and long wavelength infrared was evaluated.
Performance of DTDI technology based on IRFPA detector
Su Xiaofeng, Pan Shengda, Gong Xueyi, Yang Yuzhou, Chen Fansheng
2014, 43(4): 1025-1031.
[Abstract](363) [PDF 2223KB](145)
The CMOS TDI of infrared detector based on bucket-brigade device (BBD) structure, has been widely used in the field of space remote sensing, it can compatible with the general CMOS process, and improve the signal-to-noise ratio (SNR) of the system. Compare with the analog TDI, the Digital Time Delay and Integration (DTDI) based on the infrared focal plane array is still in the initial stage. In this paper, the 320256 MWIR FPA was used to do the DTDI research, and the electron transfer efficiency, the BBD noise and the dynamic range of the analog TDI was in a detail analysis to compare with DTDI. And the NU and blind pixel were also taken into consideration to analysis the DTDI performance. Finally in the experiment, the SNR can be increased to 2.5 times and the NU can be reached 1.68% after the 16-stage DTDI was used, which verify the improvement of the system performance by using DTDI technique.
MW 320×256 IRFPA detector under rapid cooling down
Zhu Yingfeng, Han Fuzhong, Li Dongsheng, Huang Yibin, Mao Jingxiang
2014, 43(4): 1032-1036.
[Abstract](307) [PDF 2340KB](200)
The rapid cooling down stress deformation is one of the key factors for the reliability of FPA. Combined with chemical corrosion, a mechanical grinding method was studied in this paper to reduce the thickness of FPA chip, and therefore improving its flexibility. The amount of bad pixel and crack owing to pixel damage generated by stress transfer was reduced obviously in the thinned chips. The cold head expansion matched to decrease the cool down stress of the chip was also optimized, without increasing the structural components of the Dewar cold head. After verified by reliability testing, the long-term reliability and stability of the 320256 IRFPA detector under a rapid cooling startup was improved obviously by these optimizations.
Calculation and analysis on infrared radiation characteristics of UAV
Sun Zhanjiu, Nie Hong, Huang Wei
2014, 43(4): 1037-1046.
[Abstract](457) [PDF 4013KB](199)
A numerical method was developed for predicting the infrared radiation characteristics of UAV by combining a high precision resolution Computational Fluid Dynamics (CFD) technology of Navier-Stokes equations and discrete transfer method of spectral radiation intensity equation. Firstly, the skin aerodynamic heating performance, engine exhausts temperature and species mole fraction distribution of UAV were calculated by CFD method. Then, combining with discrete transfer method, comprehensive analysis of infrared signal characteristics of main radiation source, such as skin, nozzle and plume, were performed under different infrared detecting sensitive bands. As a result, the effects of the UAV geometric features, the engine nozzle configurations and plume flow field distribution on infrared radiation with different parameters were analyzed. Finally, some valuable conclusions for infrared stealth design of UAV were obtained.
Band selection method of spectrum detection about medium wave infrared stealth target
Lin Tao, Liu Fei, Han Pingli, Shao Xiaopeng, Ren Meng, Lv Honpeng, Zhang Jianqi
2014, 43(4): 1047-1051.
[Abstract](422) [PDF 1194KB](168)
A study establishing the infrared radiation contrast in wave band of infrared spectrum detection, based on the great difference of radiation characteristics in the narrow wave band about target and background, was proposed to accurately detect the infrared stealth targets whose infrared radiation characteristics were similar with that of background. The optimum wave band, through analyzing the relative contrast and absolute contrast of target and background and considering the influence of atmospheric conditions in the whole transmission procession, was determined 2.86-3.30 m and 4.17-4.55 m. The results show that the narrow wave band which was selected by infrared contrast could eliminate radiation of background well, highlighting the target radiation and enhancing the detectability of target.
Spectral and bands radiation characteristics of water sprays in two infrared atmospheric windows
Du Yongcheng, Yang Li, Sun Fengrui
2014, 43(4): 1052-1056.
[Abstract](340) [PDF 1257KB](140)
The law of infrared spectral and bands radiation characteristics of water sprays in the atmospheric windows, 3-5 m and 8-14 m, was researched. Through the research on spectral radiation characteristics of water sprays, a kind of approximate symmetry relationship between spectral scattering coefficients and spectral absorption coefficients was discovered. The axis of symmetry is just the 1/2 of the spectral extinction coefficients. The symmetry relationship was found to be more obvious along with the increase of the average droplets radiuses. Though the research on the bands radiation characteristics in 3-5 m and 8-14 m of water sprays, a group of approximate formulas for calculating the bands attenuation coefficients including extinction, scattering and absorption were founded. It's proved by error analyzing that the method mentioned above can ensure the relative errors of the three bands attenuation coefficients be less than 5%.
Analysis of effective absorption for atmospheric aerosol
Shao Shiyong, Mei Haiping, Huang Yinbo, Rao Ruizhong
2014, 43(4): 1057-1061.
[Abstract](300) [PDF 1578KB](161)
The black carbon, which absorbs light intensively, was selected for analysis of relation between effective absorption and Junge index. With increase of Junge index, the absorption coefficient numbers of black carbon firstly descended then ascended, somewhat liked U. For aerosol from the same source, the saving heat capacity of small particles was stronger than large ones. When content of large particles increased gradually, delay time droped correspondingly. Based on optical fiber Michelson interference, transmitting light of reflected light by mirror interfered with reflected light by inner surface of collimator. Phase changed when the interfering light path was illuminated by 1.064 m parallel light. It was recorded that effective absorption of aerosol from sunshine, fog, thin and dense smoke from burned paper using relation between phase variation and effective absorption coefficient, and corresponding sensitivity was 10-6 m-1. The baseline of signal always drifted slowly since environment temperature nearly changed all the time. The foundation was shown for research of absorption process and measurement of absorption coefficient.
Gray scale modulation and synchronization of infrared scene projector based on DMD
Xu Jialin, Li Bingyu, Liu Yang, Sui Long, Wang Xiaodong
2014, 43(4): 1062-1067.
[Abstract](437) [PDF 1776KB](435)
The Dynamic Infrared Scene Projector based on Digital Micromirror Device (DMD) can be used in Scene Simulation System. The principle of displaying grayscale images on DMD which used in Scene Simulation System and its driving timing were discussed in this paper. An infrared scene projector based on 0.7XGA DMD chipset of Texas Instruments was designed. This projector can be synchronized by external trigger signal, and its max frame rate is greater than 250 Hz while the image mode is 8 bits of grayscale resolution. The synchronization between the projector and the image sampling equipment (Infrared Thermal Imager) has great influence on the sampled result. 3 kinds of synchronization relationship, including the projecting phase leading, equal to and lagging the image sampling system, were analyzed to illustrate the influence of the synchronization relationship between the projector and the image sampling equipment. Experiments show the results in detail.
Preparation of Mn-Co-Ni-O films by RF magnetron sputtering for IR thermal detectors
Ouyang Cheng, Wu Jing, Zhou Wei, Gao Yanqing, Hou Yun, Huang Zhiming
2014, 43(4): 1068-1072.
[Abstract](417) [PDF 1537KB](197)
Mn-Co-Ni-O spinel, owing to its low resistivity and large temperature dependent resistivity, is an attractive ternary system for thermistor applications and infrared detecting bolometers. Mn1.56Co0.96Ni0.48O4 (MCNO) polycrystalline films for infrared detection were successfully deposited on amorphous Al2O3 substrates by radio-frequency (RF) magnetron sputtering. Energy dispersive spectroscopy (EDS) indicates, for all the MCNO films, that the deviations of metallic element composition rank less than 5% comparing to the target. Structural, electrical, optical properties of MCNO films annealed at 750℃ were also investigated. X-ray diffraction shows the 750℃ annealed sample has a single cubic spinel phase, and the film is of favorable crystallization and compact density. The conduction mechanism of MCNO thin film follows the small-polaron hopping model, and the hopping type is variable-rangehopping (VRH) at 240-330 K. The TCR and the activation energy of MCNO films at room temperature (300 K) is 0.297 eV and-3.83%K-1, respectively. Also, the absorption coefficient has a relatively high value in the region of ultraviolet-visible and the indirect band gap is about 0.61 eV.
Investigation on preparation method and performance of Mn1.56Co0.96-xNi0.48CuxO4 thin film IR detector
Zhou Wei, Ouyang Cheng, Wu Jing, Gao Yanqing, Huang Zhiming
2014, 43(4): 1073-1079.
[Abstract](367) [PDF 1672KB](164)
The preparation procedure and performance of Mn1.56Co0.96-xNi0.48CuxO4 (MCNC, x=0, 0.08, 0.16, 0.24) IR detectors were reported. By varying the content of Cu ratio, a series of MCNC films and IR detectors were fabricated. The results show that the substitution of Cu element can significantly reduces the resistance and device noise for detectors with specific thickness and size. The typical time constant of the detector is 20-40 ms. The MCNC IR detector with x=0.24 shows a detectivity (D*) of about 0.83107 cmHz1/2W-1, which is enhanced by about 130% in comparing to the x=0.00 one. Additionally, the ageing phenomenon of MCNC detector is discussed in general.
Ground target detection method on rotating infrared detector
Xu Fuyuan, Gu Guohua, Chen Qian, Wang Changjiang, Yang Wei
2014, 43(4): 1080-1086.
[Abstract](461) [PDF 2490KB](175)
The ground remote motion target detection is one of key techniques in infrared imaging defense. The ground remote motion target detection is a method which can automatic detection and capture the remote motion target by Infrared detector. It is difficult to extract the target from the complex background, because the target is distance, imaged area is small on infrared detector and easily blocked. A method can realize detect the ground remote motion target by rolling the area array infrared detector was presented. First, the motion compensation parameters were calculated through the image information and target first detection result was obtained through background update, then background and target motion information were obtained through the optical flow and target final detection result was obtained through calculating the relationship between background and target motion information. Experiments validate the proposed algorithm using a variety of scenarios; the results show that this method can expand the target search area by the rotating infrared detectors. Using the relevance of the movement information between background and targets effectively overcome the problems of the target obscured, goals overlap and parallax.
Infrared target tracking based on template adaptive Mean Shift
Guo Jingming, He Xin, Yang Jie, Wei Zhonghui, Gong Junliang
2014, 43(4): 1087-1093.
[Abstract](347) [PDF 5650KB](143)
In order to solve the problem that the target template of standard Mean Shift tracking can only be built from a single image, and difficult to update, an algorithm combining improved Mean Shift with incremental Support Vector Machine for infrared target tracking was proposed. First, target was described using gray histogram of the target region. Then, in order to solve the problem of target lost in tracking caused by target size obviously changing, target localization was started using standard Mean Shift, and then image moment feature of the sub image for secondary search was combined to calculate the tracking window size for next frame. Meanwhile, according to the problem of target occlusion easily lead to tracking failure, machine learning theory was introduced and incremental support vector machine was used to update target template adaptively, thus target tracking problem was converted to a problem of classification between the target and the background. Experiments show that the improved algorithm proposed in this paper performs well even if greatly change occurs in target pose, size or partial occlusion happens.
Millimeter-wave propagation characteristics in SiO2 fundus materials
Liu Huasong, Yu Junhong, Leng Jian, Zhuang Kewen, Ji Yiqin
2014, 43(4): 1145-1149.
[Abstract](307) [PDF 1282KB](141)
IR/MMW frequency divider is one of the key devices of IR/MMW composite-detected system. The influence of dielectric material characteristic parameters on millimeter-wave transmission, reflection and absorption properties were analyzed and calculated, which was based on theory of electromagnetic interference. The dielectric material thickness design guidelines in 35 GHz was put forward, the influence of SiO2 material different physical thickness and physical thickness deviation on the millimeter-wave transmission properties was analyzed. The results indicate that with the increase of physical thickness, the physical thickness deviation has more influence on millimeter-wave transmission, reflection and absorption properties, the accuracy requirements for physical thickness deviation becomes higher. This article have a certain reference value about the design of IR/MMW frequency divider.
Laser and optoelectronic technology application
Simulation analysis of high power asymmetric 980 nm broad-waveguide diode lasers
Xu Zhengwen, Qu Yi, Wang Yuzhi, Gao Ting, Wang Xin
2014, 43(4): 1094-1098.
[Abstract](435) [PDF 1096KB](136)
The design of asymmetric 980 nm InGaAs/InGaAsP broad-waveguide diode lasers with current blocking layer was designed for high-power, which prevents carrier leakage and increases electro-optical conversion efficiency. The properties of the 980 nm asymmetric waveguide quantum well structure lasers were numerically studied with a commercial LASTIP simulation program. Compared to symmetric structure, the lasers with asymmetric waveguide have a smaller band offset between waveguide and QW. The simulation results show that the asymmetric waveguide has a lower threshold current and higher slope efficiency, lower series resistance than symmetric waveguide the structure, so laser performance of asymmetric 980 nm InGaAs/InGaAsP broad-waveguide diode lasers with current blocking layer has higher electro-optical conversion efficiency and laser output power.
Research and development for optically pumped far-infrared gas laser
Qu Yanchen, Chen Huiying, Geng Lijie, Zhao Weijiang
2014, 43(4): 1099-1105.
[Abstract](400) [PDF 1034KB](265)
Far infrared laser sources have many properties of strong penetration, low photon energy, wide bandwidth, large transmission capacity of communication, have been widely applications in public security, environmental monitoring, biomedical diagnostics, astronomical observation, military and communicational application, etc. The technological advantages of the optically pumped far infrared gas laser were gave by comparing a variety of ways to produce far infrared laser based on introducing their development. Summarized far-infrared laser mediums and their new lines of the recent years. At last, the research trends of optically pumped far infrared which were summarized by reviewing the continuous and pulsed optically pumped far-infrared gas laser development, combining with some of the key research directions in this field were indicated.
Intensity tuning curves in boot process and performance of full-inter-cavity He-Ne lasers
Zhu Shoushen, Liu Weixin, Zhang Shulian
2014, 43(4): 1106-1110.
[Abstract](351) [PDF 1416KB](144)
Solid and semiconductor lasers have many advantages, but in the field of precision measurement, He-Ne lasers are still the most commonly used lasers of manufacturing high precision instruments. At the beginning of the warming process, He-Ne lasers went through a instability time of the power, frequency, horizontal mode. This paper comprehensively and integrated report rich intensity tuning curves of He-Ne lasers (General and birefringence dual frequency lasers) covered long-term experiments. As basis for judgment of laser performance, it is used in studies on how to infer laser parameters from the curve. It infer something include: laser's longitudinal mode interval, single or two longitudinal mode bandwidth, the degree of etalon or interference effect, etc.
New designs and CFD numerical simulations for solid-state laser heat sink
Liu Gang, Tang Xiaojun, Zhao Hong, Liu Yang, Liu Lei, Xu Liujing, Wang Chao, Chen Sanbin, Liang Xingbo, Wang Wentao
2014, 43(4): 1111-1116.
[Abstract](449) [PDF 2529KB](458)
A new type of heat sink for solid-state laser, namely pin-fins heat sink, was presented. Three typical structure designs of water cooled pin-fins heat sink, as well as traditional cavity structure and invariable cross-section mini-channel heat sink, were simulated with Computational Fluid Dynamics (CFD) method. The influence of cooling water flow rate on the characteristics of these approaches, such as gain media maximum temperatures, cooling surface temperature profiles, and pressure losses of heat sinks were comparatively investigated. On the assumptions of equal heat transfer rate and equal flow rate, the heat transfer characteristics of pin-fins heat sink mini-channel heat sink were better than cavity structure heat sink remarkably. The heat transfer resistance of pin-fins heat sink is less than that of minichannel heat sink; meanwhile the flow pressure loss of pin-fins heat sink is greater. Numerical simulation results suggest that pin-fins heat sink has a better performance compared with traditional cavity structure and mini-channel heat sinks. The heat transfer performance of pin-fins heat sink is slightly better than that of invariable cross-section mini-channel heat sink at a higher flow rate, and remarkably better while at a lower flow rate.
Technology of missile-borne laser active imaging guidance
Li Jianzhong, Peng Qixian, Li Zeren, Li Jian, Wang Rongbo
2014, 43(4): 1117-1123.
[Abstract](707) [PDF 2647KB](743)
The laser guidance weapon is becoming one of the most important beating weapons and playing important roles in the modern war, with low cost, high effect-cost rate and high precision. The different types of laser guidance were introduced, and application perspectives of Missile-borne Laser Active Imaging Guidance (MBLAIG) in laser guidance was commented, its working principles, characteristics, factors affecting the detection capability, technical route and technical difficulty were introduced, scanning imaging and scannerless imaging are analyzed in detail. The recent advances and future development trends of MBLAIG were reviewed, and the typical scannerless imaging laser guidance system, low-cost autonomous attack system (LOCAAS), loitering attack missile (LAM), CLAS and Jigsaw were described in brief. A feasible solution and some valuable suggestions for development MBLAIG were presented, and the key technology for the new laser radar system was summarized also.
Inverse synthetic aperture ladar imaging algorithm for uniform motion targets
Ruan Hang, Wu Yanhong, Ye Wei
2014, 43(4): 1124-1129.
[Abstract](408) [PDF 1356KB](132)
The transmitting signal of inverse synthetic aperture Ladar (ISAL) has the characteristics of short wavelength and large bandwidth. When imaging an uniform motion target, dispersion in range direction and migration through resolution cells (MTRC) exist in the ISAL image. Therefore, the conventional range-Doppler imaging algorithm is inapplicable. The precise ISAL echo model was established for an uniform motion target, and the motion-induced range dispersion effect was analyzed in detail. In this paper, an ISAL imaging algorithm was proposed for uniform motion targets. The fractional Fourier transform(FRFT) was adopted to eliminate the range dispersion. By using the keystone formatting technique, the MTRC was compensated after a pre-coherent processing to the range-compressed signal. Finally, the high-resolution ISAL image was realized. Simulation results confirm the validity of the proposed imaging algorithm.
Algorithm for speckle reduction of laser radar polarization active image
Wen Donghai, Jiang Yuesong, Hua Houqiang, Yu Rong, Zhang Yanzhong
2014, 43(4): 1130-1134.
[Abstract](405) [PDF 1798KB](126)
In order to reduce speckle noise of laser active polarization image, a shock anisotropic denoising model was proposed. The model utilized Smallest Univalue Segment Assimilating Nucleus (SUSAN) algorithm to extract image edge which reduced the noise influence on edge detection influence. The approach adjusted coefficient of the shock filter automatically, which made new algorithm both retain the image edge, and restrain image speckle. The threshold of SUSAN was estimated by eight direction order difference, which maked the estimation more accuracy. Fully developed regional average absolute error was used as the standard of iterative termination conditions. Through comparing the equivalent numbers of looks (ENL) and edge preserve index (EPI), the proposed algorithm provides more effective speckle reduction as well as edge preservation.
Reliability analysis of Raman scattering lidar for measurement of atmospheric carbon dioxide profiles
Yuan Ke'e, Zhang Shiguo, Hu Shunxing, Lin Jinming, Shao Shisheng, Cao Kaifa, Huang Jian, Xu Zhihai, Xu Huiling
2014, 43(4): 1135-1139.
[Abstract](457) [PDF 1831KB](159)
Raman scattering lidar is an important technique, which has the high space-time resolution, can measure atmospheric carbon dioxide mixture ratio profiles in real time. It is based on the Raman scattering frequency shift caused by laser and atmospheric CO2 or N2 interaction. A Raman scattering lidar system developed by Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, was introduced. And the theory and method for atmospheric CO2 space-time measurement were expatiated on. Two CO2 analyzers prior calibrated by each other, which tested the lidar's results reliability, were placed in the sites of transmitting terminal and one kilometer distance along the laser path. Experiment results displayed the two analyzers have good consistency with the lidar's in near-end and far-end respectively, where there are 0.8 ppm and 3.51 ppm difference in whole night averaged values. It was explained that the difference of CO2 mixture ratio in near-end and far-end. Thus atmospheric CO2 profiles monitored by Raman scattering lidar have authenticity and reliability.
Microstructure and properties of laser cladding high entropy alloy MoFeCrTiWAlxSiy coating
An Xulong, Liu Qibin, Zheng bo
2014, 43(4): 1140-1144.
[Abstract](387) [PDF 2113KB](281)
To obtain high performance coating materials, the HEAs MoFeCrTiWAlxSiy coating was prepared on 45# steel by laser cladding. By means of OM, XRD and micro-hardness tester, the microstructure and properties of the high-entropy alloy layer with adding Al and Si element were investigated. The experimental results indicate that the addition of Si element will promote the formation of intermetallic compound, and Al in the coating exhibits obvious the grain refining. In addition, the hardness of the coating is significantly increased, and reaches a maximum (839.3 HV). Adding Al can inhibit the formation of intermetallic compound and induces the simple BCC phase structure of the coating, but the hardness of the coating decrease. Simultaneous addition of Si and Al, the excellent quality coating with detailed microstructure and relatively high hardness can be obtained.
Dispersion properties of chalcogenide glass photonic crystal fiber for mid-IR supercontinuum spectrum generation
Cao Fengzhen, Zhang Peiqing, Dai Shixun, Wang Xunsi, Xu Tiefeng, Nie Qiuhua
2014, 43(4): 1150-1155.
[Abstract](424) [PDF 1242KB](154)
Photonic crystal fibers own the properties of endless single-mode, adjustable mode area and controlled dispersion which make it particularly suitable to achieve supercontinuum spectrum generation. One necessary condition of supercontinuum spectrum generation is that the used media has high nonlinear coefficient. Chalcogenide glass pocesses the property of very high nonlinear, so using chalcogenide glass photonic crystal fiber to generate supercontinuum spectrum has attracted widespread attention. In this work, Ge23Sb12S65 chalcogenide glass was fabricated using melt-quenching method and measured to have high nonlinear refractive index. Chalcogenide glass photonic crystal fibers used for mid-IR supercontinuum spectrum generation was designed and studied with multi-polar method. By controlling the hole spacing and the aperture ratio d/, the dispersion, loss and mode area optimized. Finally, a flattened dispersion photonic crystal fiber in the range 2-4m was obtained, with =2m and d/=0.43.
Design and application of high-precision threshold circuit for laser proximity fuze
Yao Pingping, Tu Bihai, Wang Xiangjing, Zhang Yi, Zhao Pingjian
2014, 43(4): 1156-1161.
[Abstract](348) [PDF 3136KB](287)
A newly compact high-precision timing discrimination circuit based on constant fraction discrimination was designed, which was adapted extraordinarily to laser proximity fuze. A biased switch compensation technology was adopted to counteract the crossing zero walk error caused by charge accumulative action, which meant that the biased voltage was decided by the laser echo amplitude. The timing discrimination error of the improved constant fraction discrimination was analyzed with lots of detailed experiments, The experiment results indicated that the timing discrimination error caused by the amplitude variation and the noise variation of the received signal was less than 125 ps, when the SNR was more than 20 and the input signal is 0.2 V to 2.134 V (20.12 dB dynamic range). The error was less than 100 ps when the SNR more than 60. Furthermore, Detection on the whole system integrating the timing discrimination circuit verifies that, the laser repetition frequency can reach 20 kHz, the single shot standard deviation is about 1.45 cm over 20 m ranges, which improve greatly the fixed distance precision of laser proximity fuze.
T-type feedback network applied in resonance frequency locking of resonator fiber optic gyro
Li Shengkun, Zheng Yongqiu, An Panlong, Li Xiaofeng, Chen Hao, Jiao Xinquan, Liu Jun, Yan Shubin
2014, 43(4): 1162-1166.
[Abstract](464) [PDF 1229KB](243)
For resonator fiber optic gyro (R-FOG), resonance frequency locking is a key technique at detecting the gyro signal. The stability of resonance frequency locking determines the output performance of the gyro, especially in the long-term test. According to the transmission theory of fiber ring resonator (FRR), the resonance characteristics and the first harmonic were analyzed; the R-FOG system was set up. The first harmonic demodulation signal derive from the experiments using the sine wave phase modulation technique; the drift errors of traditional analog proportional-integral PI consisting of operational amplifiers were analyzed. On this basis, T-type feedback network was applied in resonance frequency locking of R-FOG. The drift error was suppressed effectively and better result was obtained. The stability of resonance frequency locking for 4 000 s is superior to 910-12 by Allan variance analysis.
Advanced optics
Design of high dynamic range imaging optical system based on DMD
Lv Weizhen, Liu Weiqi, Wei Zhonglun, Kang Yusi, Feng Rui, Yang Jianming
2014, 43(4): 1167-1171.
[Abstract](625) [PDF 1638KB](740)
In order to solve the high dynamic range requirement for photoelectric imaging device when it was used to observe the actual spatial scene, a newly high dynamic range imaging system whose light intensity was modulated in pixel level was designed. This system consisted of imaging lens, a fold mirror, secondary transpose imaging lens, using a DMD(Digital Micromirror Device) produced by TI Inc. as light intensity modulator, connecting the two systems perfectly through the principle of the pupil matching, and utilizing the secondary imaging system to realize one to one correspondence between DMD units and image sensor pixels. Full field of view of the MTF are higher than 0.55 at the Nyquist frequency of the image plane, and the RMS spot diameter is less than the pixel size of the CMOS image sensor in the focal plane, meanwhile such aberration of distortion is also corrected excellently. This method not only enhances detected dynamic range of the image senor, but also can detect bright and dark target simultaneously, meeting the requirements of spatial visual target imaging.
Advanced optical
Investigation and design for structure of high-precision reference mirror
Ding Ling, Wang Tao, Yang Hongbo, Jia Hongguang
2014, 43(4): 1172-1175.
[Abstract](535) [PDF 1697KB](288)
In order to ensure the measuring precision of high accuracy optical, the accuracy of the interferometer reference mirror must be controlled strictly. The influences of different number of adhered points and point distribution, and different support schemes on the shapes of reference mirror were investigated by means of finite element method under gravitational conditions. In order to achieve the peak to valley(PV) value of reference sphere mirror which is better than /40, a kind of support structure of 150 mm reference mirror was designed according to the results of research. The experimental results by means of finite element method indicate that the peak to valley (PV) value and root mean square (RMS) value of the reference surface are only 7.36 nm and 1.52 nm by support scheme with 123 distributed and six-points flexible support, and the thermal deformation is less than gravity deformation. These results demonstrate that all targets validate the rationality of structure and it can well satisfy the requirements.
Structure optimization design of small-sized integrated support bracket of secondary mirror
Long Bo, Xing Tingwen, Liao Sheng
2014, 43(4): 1176-1181.
[Abstract](441) [PDF 1756KB](142)
To enhance the structure stiffness, parametric model of small-sized integrated tri-vane support bracket of secondary mirror with a 95-mm outside diameter was built by APDL language of ANSYS, and vane section parameters of the beam and the connecting pole were optimized considering fundamental frequency as the objective function. Optimized result indicated that the angle of the beam and the connecting pole evidently influenced fundamental frequency and their juncture location was near the base seat but not just at the root at the highest fundamental frequency. Based on primitive structure, new type of support bracket of secondary mirror with 6 spiral surrounded supporting ribs was designed, and supporting ribs greatly improved total structure stiffness. After optimization design, this new structure with only a 14.7 g mass increase had excellent performance that fundamental frequency was increased by 33% and mounting interface deformation of secondary mirror was reduced by 37.5% under transverse acceleration, and thus it can be a good structure adapted to mechanics environment. Parametric optimization method may improve the efficiency of modeling and simulation with multiple design variables and also the design level. Optimized result can provide powerful support for structure design with limited weight, volume and obscuration area.
Optical system design of broadband astigmatism-free czerny-turner spectrometer
Zhao Yiyi, Yang Jianfeng, Xue Bin, Yan Xingtao
2014, 43(4): 1182-1187.
[Abstract](910) [PDF 1294KB](593)
For the development trend of miniaturization and high-resolution of spectrometer, an optical design with a simple structure, broadband, astigmatism-corrected micro spectrometer was designed. The principle and correction method of the aberration of crossed beam czerny-turner spectrometer were analyzed in detail. The broadband astigmatism-corrected theory equations using cylindrical lens were deduced. For example, a micro spectrometer operating in 300-900 nm with an object NA of 0.08 has been designed. This spectrometer adopted crossed beam structure to minish its volume and used a cylindrical lens to remove astigmatism over the full bandwidth. The analyzed results demonstrated that this spectrometer with compact configuration and small volume corrected the astigmatism in the wide spectral region. The resolution of the spectrometer was better than 0.5 nm in the whole spectral region.
Optical system design of multi-spectral camera for space debris
Wang Hu, Luo Jianjun
2014, 43(4): 1188-1193.
[Abstract](469) [PDF 1693KB](289)
In order to detect the Space debris, a multi-spectral camera for Space debris was proposed. The multi-spectral camera was consisted of visible camera, long-wave infrared (LWIR) camera and mid-wave infrared (MWIR) camera. Three cameras used the primary mirror and secondary mirror together, including correction lens in every camera in order to balance aberration. The focal length was 1 000 mm and field of view was 1.2 for visible camera, and the focal length was 250 mm and field of view was 2.75 for LWIR camera, and the focal length was 500 mm and field of view was 1.38 for MWIR camera. Some measures were taken to make sure the less degradation of MTF for thermal distortion, such as a kind of material with good thermal property as mirror substrate to reduce surface distortion. The modulation transfer function(MTF) of three cameras in condition of 205℃ was analyzed, which showed a good result for user's requirement.
Elimination of reference surface error on high-accuracy subaperture stitching
Deng Wantao, Wang Kaiwei, Bai Jian, Zhang Jinchun
2014, 43(4): 1194-1199.
[Abstract](522) [PDF 2630KB](181)
Sub-aperture stitching can be used to measure large optical aperture with a relatively smaller aperture interferometer. In the process of sub-aperture testing, if reference surface error is taken into consideration, the stitching result will deviate from truth. As a result, obtaining and compensating reference surface error is necessary. An approach was proposed to obtain and compensate reference surface error by fitting overlap data of each sub-aperture with Zernike terms. A series of Zernike terms were added into traditional stitching function, the form of reference surface that characterized by a Zernike polynomial was obtained by using the least-square method. Experiments had been done on flat and sphere sub-aperture stitching, which were then compared with QED's result. The deviation of PV and RMS of these two results are less than 5 nm and 0.2 nm respectively. At the same time, the mismatch of stitching aperture is less than 10 nm. Experimental result proves that reference surface error can be compensated in the process of sub-aperture stitching and stitching aperture is more accurate.
Aircraft’s large attitude angles’usage in image motion compensation calculation of space camera
Yan Dejie, Li Weixiong, Wu Weiping, Wang Dong
2014, 43(4): 1200-1205.
[Abstract](461) [PDF 1268KB](122)
In order to achieve image motion velocity accurate calculation, the method was put forward when using aerocraft attitude parameters in big attitude angle. According to the transition matrix that was from orbit coordinate to aerocraft coordinate, the relationship between coordinate system attitude angular in orbit and attitude angle, attitude angular velocity in vehicle coordinate system was derived in the big attitude angle. By calculation, when the scroll angle was 30, the maximum relative error of S1, S2 and S3 that were caused by scroll angle were 1.175%, 50% and 13.223%; when the pitch angle was 30, the maximum relative error of S1, S2 and S3 that were caused by pitch angle were 63.397%, 0.1745% and 63.397%.According to the high calculation precision of space camera image motion velocity, in a certain attitude angle, the method of using aerocraft attitude parameters was identified. This proposed method is simple and easy to implement, which is suitable for the research of image motion compensation of space camera.
Analysis and validation of large size focal-plane focusing device for space camera
Wang Zhongshan, He Xin, Cui Yongpeng, Fu Liangliang
2014, 43(4): 1206-1209.
[Abstract](918) [PDF 2517KB](224)
To compensate focusing offset of space camera, which was caused by environment difference between ground and on the track and maybe caused by shock when launching, a focal plane focusing device was designed to ensure image quality. First, for focal plane was so large, focusing frame was designed to enhance focal plane rigidity, self-lock was achieved through worm wheel driving screw. Second, fem model was established and mode analysis was achieved by patran/nastran, in which simulate guide rail by mpc. Finally, carried out dynamic environment testing and precision testing. Test results revealed that focusing device had dynamic frequency, first analysis characteristic frequency was 228.7 Hz, and first test characteristic frequency was 223.9 Hz, the relative error was 2%. Focusing resolution was 0.25 m, focusing precision was 6.3 m, synchronization error on focal plane was 4 m. It can meet high resolution, high precision, high reliability needs of space camera.
Application of micromirror array in beam shaping
Du Meng, Xing Tingwen, Yuan Jiahu
2014, 43(4): 1210-1214.
[Abstract](932) [PDF 2518KB](201)
In the application of laser, the technique of beam shaping was used to modulate the beam to expected intensity distribution. The development of micro electronic and mechanic system provided a solution. The beam shaping was realized by the using of micro mirror array. Based on the idea of randomization, an algorithm was proposed for the application,and the performance under different unit numbers and different noise levels was analyzed so as to present valuable reference in practical application. At the end, a practical optical system model was built and beam trace was performed, and the results under single-mode Gaussian beam and with-noise beam were given. The analysis on results show that beam shaping is achieved effectively using micromirror array under different inputs. And because of the independent addressing property of the micromirror array, the method has flexibility which can satisfy a variety of application requirement.
Optoelectronic devices and materials
GaN-based avalanche photodiodes and its recent development
Liu Fuhao, Xu Jintong, Wang Ling, Wang Rongyang, Li Xiangyang
2014, 43(4): 1215-1221.
[Abstract](1100) [PDF 1288KB](534)
The investigation of GaN-based avalanche photodiodes(APDs) was motivated by the demand of high sensitivity ultraviolet detectors in numerous civilian and military applications. APDs operate under high reverse bias voltage, and carriers in the device caused impact ionization under high electric fields, as a result, the avalanche multiplication could be obtained. In this paper, reviews were made on the development of GaN-based avalanche photodiodes, the largest value of gain in this work was nearly 3105. Relationship between width of the intrinsic layer and dark current has been studied. The measuring system based on phase sensitive detecting technique has been shown. Relationships between modulating frequencies and noise has also been investigated. It was found that in the range of low frequency(30-2 kHz), the excess noise behaved as 1/f noise. In the end, the recent developments and applications of the Geiger mode operations of GaN-based APDs are introduced.
Stability of GaAs photocathode activation
Liu Hui, Feng Liu, Zhang Liandong, Cheng Hongchang, Gao Xiang, Zhang Xiaohui
2014, 43(4): 1222-1225.
[Abstract](309) [PDF 1155KB](189)
In order to improve the stability of GaAs photocathodes after Cs-O activation and prolong the lifetime of image tubes, Cs-O activation was studied to find appropriate solutions. Combined changing the excess amount of Cs in activation with online monitoring of photocurrent in UHV, the factors influencing the stability of GaAs photocathode were investigated. Three groups of experiments were carried out, and same five kinds of Cs excess proportion were included in each group. After the photocurrent decreased to 90%, 70%, 50%, 30% and 10% of the Cs peak value, oxygen was introduced for alternate activation. It was found that the stability of photocathodes with Cs excess of 90%, 70% and 50% was better and the stability of 30% or 10% was worse by online monitoring of photocurrent during 30 min in UHV of less than 110-8 Pa. The results indicate that with more Cs amount in Cs-O activation the construction of surface barrier is more integrated and the stability of photocathode is better. These results are important for improving the stability of GaAs photocathodes and prolonging the lifetime of image tubes.
Impact on surface state of high temperature annealing to GaAs photocathode
Zhang Liandong, Feng Liu, Liu Hui, Cheng Hongchang, Gao Xiang, Zhang Xiaohui
2014, 43(4): 1226-1229.
[Abstract](951) [PDF 1377KB](183)
The change of GaAs photocathode surface composition was analyzed by XPS before and after the photocathode was annealed and activated, combined the pressure curve of CO2, H2O, O, As, Cs obtained through four mass spectrometer while the photocathode was annealing, the difference of the two annealing was compared and discussed. It was Proposed that for the purpose of the second heating was not only cleaning photocathode surface, it was more important to procure first activated in a photocathode formed on the surface of the dipole layer is transformed to the more stable structure at high temperatures, Cs2O dipoles reacted with GaAs and generated on the photocathode surface of the stable existence of the GaAs-O-Cs dipoles, formed dipoles layer mainly by bonding strong GaAs(Zn)--Cs+, GaAs-O-Cs dipoles and Cs2O dipoles which was attached to the photocathode surface by the Van der Waals force. Based on this conclusion, The differences of light current variation between the activation of the photocathode was explained. It was of great significance to understand the activation of the photocathode and photoelectric launch model.
Analysis of optical and damage properties for several ultraviolet thin film materials
Zhang Qian, Jiao Hongfei, Cheng Xinbin, Ma Bin, Ji Yiqin
2014, 43(4): 1230-1234.
[Abstract](423) [PDF 2494KB](239)
For further improvement of optical and laser induced damage properties of the thin films equipped on three harmonic of YAG laser system, different test methods were used to analysis the correlations between optical constant, crystalline structures, surface roughness, weak absorption and laser induced damage threshold of several thin films fabricated by reactive electron beam deposition process with different ultraviolet materials. The weak absorption and the bandgap limited the laser-induced damage threshold, rather than the surface roughness increased by the appearance of crystalline structures. Two laser damage processes were observed as that in higher weak absorption material, small damage expanded step by step when it absorbed the pulse laser energy, while in lower weak absorption material, a sudden damage occurred when the absorbed laser energy were higher enough.
Comparison of CdS thin films on different flexible substrates before and after annealing
Cong Jiaming, Pan Yongqiang, Wu Yunhua, Zhang Chuanjun, Wang Shanli
2014, 43(4): 1235-1239.
[Abstract](378) [PDF 3706KB](215)
The CdS thin films were prepared on Flexible PI、AZO and ITO substrates by r.f. magnetron sputtering technique,and annealed at 380℃ in CdCl2 and dry air. The morphology, structure and optical properties of all samples were characterized by the scanning electron microscopy, X-ray diffraction and ultraviolet-visible spectroscopy. The results show that the microstructures of all the CdS thin films dependent on the type of substrate by as-deposited and annealed CdS thin films on different substrates, grain recrystallizes, grain size increases significantly and no longer depend on the substrate type. The entire prepared CdS thin films show a mixed phase structure of cubic and hexagonal. After annealing, the proportion of hexagonal phase is increased, the crystallization quality of CdS thin film is improved. The optical transmittance changes obviously after annealing, among them, the optical transmittance of CdS thin film on flexible AZO substrate is over 80%.
Advanced optical imaging technology
Research on speed stability of moving mirror in FTIR spectrometer
Zhang Mingyue, Zhang Jiabao, Yang Hongbo
2014, 43(4): 1240-1246.
[Abstract](494) [PDF 1690KB](267)
In order to improve static and dynamic performance of moving mirror motion system in Fourier transform infrared spectrometer, nonlinear PID controller based on disturbance observer was designed. Firstly, mathematical model of moving mirror driven system was established, nonlinear factors in the system were analyzed. And then the theoretical basis designing this controller was given. At last, numeral simulation and physical experiment were carried on. The experimental results show that, when moving mirror is moving at 133 mm/s, the maximum overshoot of system is 0, rising time was 3 ms, steady-state variance is 0.039 2 using NPID with DOB, which is obviously better than traditional PID controller. Conclusion shows that NPID with DOB controller is feasible and usable and it meets the requirement uniform motion of moving mirror.
Volume and sparseness constrained algorithm for hyperspectral unmixing
Wei Yiwei, Huang Shiqi, Wang Yiting, Lu Yunlong, Liu Daizhi
2014, 43(4): 1247-1254.
[Abstract](787) [PDF 2223KB](255)
To solve the problem of large solution space and a mass of local minima in the traditional non-negative matrix factorization (NMF), a volume and sparseness constrained NMF (VSC-NMF) algorithm was proposed. Firstly, end-members extracted by vertex component analysis (VCA) in hyperspectral image were taken as initialization of end-member matrix so as to accelerate the convergence speed. Then, the traditional NMF was extended by incorporating the minimum volume constraint and abundance's sparseness constraint to achieve better separation of mixed pixels. The experimental results on synthetic and real data illustrate that the proposed algorithm can overcome the shortcomings of traditional NMF and obtain more accurate end-members and corresponding abundance, especially in sparser hyperspectral image.
Impact of integral scheme on narrow-band k-distribution
Zhu Xijuan, Li Xia, Wu Jie, Dong Yanbing
2014, 43(4): 1255-1259.
[Abstract](404) [PDF 1334KB](199)
One of the key factors for narrow-band k-distribution model is integral scheme, for studying of the impact of integral scheme on narrow-band k-distribution model, five high-accuracy Gaussian integral schemes were studied. The narrow-band average transmissivity data of CO2 for four different conditions were calculated by narrow-band k-distribution of Gauss-Lobatto 7, and the comparison results were in good agreement with those of testing ones. In addition, Four new integral schemes, Gauss-Lobatto 5, Gauss-Lobatto 4, Gauss-Legendre 4 and Gauss-Legendre 2, were used to calculate four cases of CO2, and the comparsions of the results calculated by the five integral schemes with the line by line ones were discussed. The results indicate that the accuracy of Gauss-Lobatto 7 is the highest, next are Gauss-Lobatto 5 and Gauss-Legendre 4, that is higher than Gauss-Legendre 5. Obviously, for the same scheme, the more the number of integral point, the higher the calculation precision and the longer the calculation time, but for two different schemes, Gauss-Legendre is better than Gauss-Lobatto. Considered comprehensively, Gauss-Legendre 4 is better than others.
Hyperspectral band reconstruction based on compressed sensing theory
Yin Jihao, Sun Jianying
2014, 43(4): 1260-1264.
[Abstract](463) [PDF 1867KB](256)
Hyperspectral image processing had attracted high attention in remote sensing fields. One of the main issues was to address the problem of huge data and hard transmission via sampling and reconstruction. Compressed sensing theory was investigated in this paper for band reconstruction. Based on compressed sensing theory, original signal could be reconstructed efficiently without satisfying the Nyquist-Shannon criterion. Adjacent spectral bands of hyperspectral images were highly correlated, resulting in strong sparse representation. This significant property made it possible to obtain the whole spectrum information from limited bands of original hyperspectral data via compressed sensing theory. Experimental results demonstrate the feasibility and reliability of applying compressed sensing theory for sampling and reconstruction on bands of hyperspectral images. The proposed band reconstruction method can perform high correlation coefficients and low relative errors between a pair of reconstructed and original hyperspectral bands. Simultaneously, high levels of reconstruction efficiency are achieved, and reconstructed spectral curve is in accordance with original data as well.
Feasibility of using successive projections algorithm in spectral monitoring of rice leaves nitrogen contents
Liu Mingbo, Tang Yanlin, Li Xiaoli, Lou Jia
2014, 43(4): 1265-1271.
[Abstract](408) [PDF 2515KB](247)
5 segments moving average, baseline correction, area normalization, and multiplicative scatter correction (MSC) was used to preprocess Visible-NIR reflective spectrum of rice leaf. Successive projection algorithm (SPA) was used in the selecting of effective wavelengths. Multiple linear regression (MLR) models were built based on spectral indexes of RVI, NDVI and effective wavelengths selected by SPA. Principal components regression (PCR) models and Partial least squares regression (PLS) models were built based on all wavelengths in the spectrum. Nitrogen contents of rice leaves were predicted by these models. From comparison, It was found that the predictive validity of models based on SPA effective wavelengths were obviously better than models based on spectral indexes of RVI and NDVI, and slightly worse than PCR and PLS models based on all wavelengths in the spectrum. Models based on MSC preprocessed spectrum and SPA effective wavelengths has the predictive validity of r=0.7943, RMSE=0.4558. It is feasible to use successive projections algorithm in spectral monitoring of rice leaves nitrogen contents.
Nondestructive inspect of apple quality with hyperspectral imaging
Sun Mei, Chen Xinghai, Zhang Heng, Chen Haixia
2014, 43(4): 1272-1277.
[Abstract](943) [PDF 4716KB](211)
Image cubes containing continuous spectral waveband information, in which the image information could be used for external attribute inspection while the spectral information could be applied to the internal attribute inspection,could be obtained from implementing a hyperspectral image technology which combines the advantages of computer vision and spectroscopy. Apples were adopted as the experimental object. A hyperspectral imaging system with the wavelength range of 400-1 000 nm was built for detecting bruises. The hyperspectral imaging system was used as a powerful tool to determine the effective wavelengths that could be used for the detection of bruises on apples. The optimal wavelength region 550-950 nm for bruise detection was selected by the Principal component analysis (PCA), which is a very effective method for data dimension reduction and feature extraction of the hyperspectral data cube. The effective wavelengths 714 nm with weighing coefficients at peaks was determined using the loading coefficients of the PC4 image of PCA on 400-1 000 nm.
Photoelectric measurement
Design and applications of novel separated type star tracker
Zhong Hongjun, Lu Xin, Li Chunjiang, Li Yuming, Li Xiao
2014, 43(4): 1278-1283.
[Abstract](856) [PDF 1336KB](293)
Star tracker is current widely used optical sensor in spacecraft attitude control system which produces the most accurate measurements. The overall design description, application and qualification results of a novel separated autonomous miniature star tracker were introduced. The novel separated type star tracker successfully operated in-orbit on a large variety of different satellite platforms such as scientific experiment, telecommunication and earth observation. The novel star tracker has applied in-orbit with a total of 21 sets of products up to now. According to the real time telemetry data packages under real in-orbit conditions, the main qualification features are sensitivity 5.7 Mv, update rate 8 Hz, accuracy 2.6, sun exclusion 28, tracking slew rate 1 ()/s. The novel separated type star tracker was the first APS based star tracker ever flown which was adopted in AOCS closed loop control. A full analysis on ground qualification campaign was carried out successfully on the novel star tracker and an in-flight qualification was also achieved, with more than two years information from 20 other star trackers on different satellites. In flight results are in accordance with results obtained from ground night sky tests. The analysis results allow an almost complete validation of star tracker major requirements: accuracy, robustness, availability and reliability.
Research on multiple nodes target repeatedly localization of pyroelectric infrared sensor
Zhao Di, Yang Wei, Liu Qianjin
2014, 43(4): 1284-1288.
[Abstract](390) [PDF 1445KB](132)
In order to make full use of the passive detection features of the PIR and broaden the scope that the PIR applied in the field of target localization, one method of using PIR for moving targets (human) location theory was proposed based on the pyroelectric signal peak-peak value time difference method which was used to achieve the target's distance. And for the shortage of a single node's localization in blind area, reasonable optical lenses and ingenious machinery structure have been selected with good design, so the moving target's multipoint repeatedly localization was easily realized. According to the multi-nodes optimal layout principles, the different nodes optimal layout model was obtained respectively through discussing the optimal arrangement double-nodes. Finally, an experiment was implemented to verify the effectiveness and accuracy about moving target more position points localization under the two nodes optimal layout model. This method breaks the pyroelectric sensor hardware routine use, improving the range of use for PIR.
PST research and measurement of lunar-based optical telescope stray light
Xu Liang, Zhao Jianke, Xue Xun, Zhou Yan, Liu Feng
2014, 43(4): 1289-1295.
[Abstract](955) [PDF 1887KB](313)
To verify suppression capability of the stray light of the lunar-based optical telescope (LOT), its stray light rejection ratio of glare shield out of field range by point source transmittance on ground was tested, and assessing its stray light rejection ratio with PST of optical system diversity angle of offaxis. The new test method of PST breaks through the tradition method of stray light, using a new method that is combining high degree of accuracy star simulator with EMCCD, guaranteeing that the detector has large dynamic region within its linear range, and the dynamic range is 1012. It could satisfy the indexing demand that the PST testing result is 10-7 (at 22angle of off-axis). This test method could objectively and directly reflect the stray light rejection ratio of glare shield. The testing uncertainty of PST is above 60%, it will exceed the testing precision of classical stray light testing method. Moreover, discussing the improving method,the target PST testing result will reach 10-12. Last it verify the PST of LOT catering design demand with the experiment that it test stray light rejection ratio of glare shield.
Sub-aperture stitching interferometry for large parabolic mirror
Yang Haoyu, Tian Ailing, Liu Bingcai
2014, 43(4): 1296-1300.
[Abstract](331) [PDF 1794KB](206)
Based on research of surface measurement method for large-diameter parabolic mirror, a new sub-aperture stitching measurement technology based on aberrationless theory was proposed. Firstly, the special method of sub-apertures'generation and the calculation form for sub-apertures'nominal motion path of this stitching program were analyzed. Secondly, a unified function between image plane coordinate system and the global coordinate system was established, together with coordinate transformation, the global coordinate of each sub-aperture data was solved. Finally, the full aperture surface was recovered by the objective function method. The simulation experiment was established for parabolic mirror, the stitching deviation of RMS is 0.001 4 . The experimental results show that this measurement method can achieve high precision measurement for large-diameter parabolic mirror.
In-plane micro-displacement measurement based on digital speckle correlation method in frequency domain
Yang Yuhang, Chen Yu, Li He, Wang Wensheng
2014, 43(4): 1301-1305.
[Abstract](356) [PDF 1543KB](280)
When using traditional digital speckle correlation method to measure in-place micro-displacement, the noise and algorithm defects will cause low accuracy or slow data processing. In order to solve these problems, digital speckle correlation method in frequency domain is applied. In-plane micro-displacement measurement has been realized by speckle recording and MATLAB software programming. This method is not only making up for the inadequacies of traditional digital speckle correlation method but also simplifying the repeated adjustment in general optical measurement. Theoretical analysis and experimental results show that digital speckle correlation method in frequency domain for measuring in-plane micro-displacement has many advantages: simple system construction, fast measurement and high accuracy, the measure accuracy can be up to micro level and relative error less than 1%.
Internal corner detection of chessboard image for camera calibration based on 12 pixels symmetrical template
Dai Shijie, Shao Meng, Wu Jianing, Ge Shengqiang
2014, 43(4): 1306-1311.
[Abstract](382) [PDF 2904KB](332)
The problem of chessboard image corner extraction always determined the three-dimensional measurement's accuracy of the camera calibration. By analyzing the defect for SUSAN (Smallest Univalue Segment Assimilating Nucleus) algorithm that could not effectively distinguish the chessboard internal corners and edge points, the authors made use of the symmetry of the pixels around the internal corners, and proposed a symmetrical 12 pixels gray template detection algorithm. Firstly, a symmetrical 12 pixels USAN template was designed for fast distinguishing the internal corners and edge points. Meanwhile, both of the chessboard internal corners and smooth region would be treated as the candidates. Then the less gray variance of smooth region could be used to abandon them. At the same time, the proposed algorithm abandoned the external corners of the chessboard, which were very sensitive to the external factors, ensuring the precision of the corner extraction process. Experimental results show that the new method detects the nine order chessboard image by 1.244 577s, and its reprojection error was just [0.3, 0.3] pixels in Zhang's camera calibration. Both of these two indicators are better than the traditional SUSAN algorithm.
Dynamic high temperature field measurement device
Yan Bing, Li Jianbin, Sun Hongsheng, Zhang Hu, Li Shiwei, Wei Jianqiang, Ren Xiaowan
2014, 43(4): 1312-1315.
[Abstract](296) [PDF 3940KB](253)
On thermal test of aerospace research filed, wind tunnel is usually used for heating the sample up to 1 700℃. It is very difficult to measure dynamic temperature filed without using the expensive and non-flexible temperature metrical IR-camera. Based on colorimetric model, two selected near-infrared wavelengths near 900 nm were used and a high dynamic response CCD device was hired. Mechanic and optical design guaranteed space synchronization of collected images of two measurement tunnel. The device achieved temperature filed measurement, frame rate is up to 40 Hz, and the measurement accuracy is less than 6%.
Information processing
Similarity analysis of three-dimensional point cloud based on eigenvector of subspace
Hu Xiaotong, Wang Jiandong
2014, 43(4): 1316-1321.
[Abstract](510) [PDF 1479KB](651)
This paper presents a method of similarity analysis algorithm of the three -dimensional point cloud,which is based on eigenvector of the subspace. First of all, the three-dimensional point cloud data of two objects were obtained and positions of them were standardized. And then, the two three - dimensional point clouds were divided into several subspace by using the minimal spatial segmentation algorithm. Thirdly, the eigenvector of subspace were calculated, which should be divided into two steps: the first step was to calculate distance and angle from the centroid to the subspace surface, the next step was to compute the new eigenvector on the basis of vector space, which was composed of the distance and angle in step one. This research method took the advantage of small data in quantity and high precision in calculation because the eigenvector of subspace, which can describe the three -dimensional characteristics as the basis of similarity measure. The experiment shows that the algorithm can quantitatively analyze the similarity of two three-dimensional objects.
Normal estimate method of point clouds based on adaptive neighbor size
Wang Zhaofeng, Yan Bin, Tong Li, Chen Jian, Li Jianxin
2014, 43(4): 1322-1326.
[Abstract](366) [PDF 1783KB](477)
Normal vector estimation in three-dimensional space is of great significance in the field of research in computer vision and surface reconstruction, the local surface fitting method is a classical estimation method of point cloud data. In order to improve the veracity of the normal vector which computed by the way of local surface fitting, a method based on optimal neighborhood size for normals estimation was described and analyzed in this paper. The distribution of the neighbor of every point was formulated on the basis of the projection of gradient. Then, the adaptive size was chosen based on the distribution of the neighbor, the normal vector was fitted by the adaptive size. Experimental results show that presented algorithm could avoid the radius of neighbor estimated too large or too small, improve the veracity of the normal vector which computed by the way of local surface fitting effectively.
Estimation of point spread function for long-exposure atmospheric turbulence-degraded images
Ge Qi, Wang Kedong, Zhang Hong, Li Guibin, Di Chao
2014, 43(4): 1327-1331.
[Abstract](509) [PDF 3630KB](280)
The image quality will be remarkably declined by the atmosphere turbulence in the optical system. The farther the distance, the longer exposure time, the more serious atmospheric disturbance, then the more blurred images. It is able to restore the blurred images by utilizing the spread function of the atmosphere-turbulence degradation, but it is hard to obtain its accurate form of the natural atmosphere turbulence. According to the research background, in this paper an approximate isosceles triangle model was proposed to approach the accurate point spread function of the long-exposure atmospheric turbulence-degraded image, then a Wiener filter was designed to restore the blurred images. Numerical experiments show that the restore method is validated tentatively for the long-exposure atmospheric turbulence-degraded natural images with the large field of view and long distance. The effectiveness of the method is proven further by evaluating the restored images with the gray mean grads and the Laplacian sum standards.
Automatic building segmentation from remote sensing images using multi-layer level set framework
Guo Jing, Jiang Jie, Cao Shixiang
2014, 43(4): 1332-1337.
[Abstract](390) [PDF 2469KB](111)
Towards high resolution remote sensing images, combining with features of buildings, a novel method to extract buildings based on multi-layer level set framework was proposed. Firstly, as far as the impact of shadow and vegetation was concerned, it should be removed on the basis of the separation of gray value thresh and the joint distribution of hue and saturation. Then, an improved C-V level set segmentation algorithm combining with building features of roof's gray and obvious boundaries was applied to extract building regions of similar gray-scales on each gray layer, and thus all building regions of different gray-scales could be extracted layer by layer, followed by layers of segmented regions integration. Finally, the non-building regions were excluded by using normal areas of buildings and related position between buildings and shadows. The experiment results demonstrate that, compared with the traditional level set methods, this one can detect each single building of gray heterogeneity and buildings of multiple shapes and different gray-scales. Meanwhile, compared to the traditional C-V method, it largely reduces the leakage segmentation ratio by 25% and over-segmentation by 22%.
Design and implementation of handheld night vision system based on parallel signal processing
Sun Bin, Zhang Junju, Chang Benkang, Yang Feng, Han Bo
2014, 43(4): 1338-1343.
[Abstract](276) [PDF 2579KB](187)
In the view of the gaps of night vision technology between abroad and domestic, a kind of handheld night vision system was designed and implementated, which displays with three channels, respectively. In the different occasions, this system can be chosen infrared display, visible display and fusion display to observe the targets. The ideal of parallel signal processing was proposed and achieved it using dual-DSP and a FPGA, which solves the problem of real time. Aiming at the problem of video muddledness, a kind of adaptive image mosaic method based on FPGA was proposed. According to the results of experiment, the system has good images quality and very strong practicability, meets the need of various occasions.
Grain seeds identification based on mean of combination coefficient of shape difference
Hong Liang
2014, 43(4): 1344-1351.
[Abstract](279) [PDF 1312KB](120)
A seed's graphic usually has a quasi-convex boundary and symmetry, the development of its simple and rapid identification methods have practical significance. Using the pseudo minimum bounding rectangle (PMBR) and centroid, 8 of a object's feature informations were extracted. Based on the coefficient of shape difference (COSD), the similarity between multi-feature objects were measured. Based on the COSD in a class couple, a multi-feature graphic object alternative identification method was developed. Based on the mean of combination coefficient of shape difference (MOCCOSD), a multifeature graphic object one of many identification method was proposed. Identifications of rice and other seeds validated the methods.
Extraction of small target based on local extreme convergence
Wang Enguo, Gao Yinhan, Su Chengzhi, Liu Yanyan
2014, 43(4): 1352-1358.
[Abstract](433) [PDF 2772KB](198)
Automatic detection of small targets in the complex context is still not perfect, an algorithm was proposed that used all paths converging to the same limit point to describe the small target area. The starting points of the path were screened based on the image gradient features. A path starting from the starting point along the gradient direction of steepest descent converged to a local minimum point, and all the paths that converge in the same path constituted an independent core region. The difference was analyzed in the target features between the focus independent core region and noise independent region, and the gray average ratio of the target features inside and outside was used for the independent core area filtering, the focus of the core area was obtained. The region of the target core was obtained by polymerizing the independent core region. The experiments show that the algorithm can automatically detect the focus target, and compared with existing algorithms, it increases the degree of automation of the small object extraction, have a strong robustness.