2013 Vol. 42, No. 11

Articles
Mathematical model of operating range for ground-based distributed aperture infrared system
Zhu Bin, Fan Xiang, Cheng Zhengdong
2013, 42(11): 2871-2875.
[Abstract](238) [PDF 282KB](212)
Distributed Aperture Infrared System(DAIRS) is the trend of infrared search and track system of military powers. Operation range is one of the most important parameters of DAIRS, which is decided by system parameters, features of target and background, etc. The operation range based on the characteristics of imaging and information processing of DAIRS was studied in this paper. A mathematical model of operating range for ground-based DAIRS was established, and the influences of target orientation, detector integration time, and instantaneous field of view(IFOV) on operation range of DAIRS and traditional scanning imaging infrared system were analyzed. The mathematical model is helpful to the design of DAIRS.
Experimental study on infrared characteristics of terminal-sensitive projectile at steady-state scanning stage
Zhang Jun, Liu Rongzhong, Guo Rui, Ma Xiaodong, Zhao Bobo, Bang Zhihui, Zhang Peng
2013, 42(11): 2876-2881.
[Abstract](355) [PDF 428KB](133)
Taking the infrared early warning system for detecting and identifying the terminal-sensitive projectile (TSP) as application background, thermal camera was used to capture and track the TSP which was thrown from a hot air balloon in real time, and the infrared image sequences in complex cloud layer background of TSP in steady-state falling were obtained. Since infrared images had the features of fuzzy, low SNR et al, a detection algorithm of combination spatial filter was introduced. In this method, the wavelet threshold and median filter algorithm were combined to denoise, the Top-Hat transform was presented to restrain the background, and target feature was extracted and the grayscale contrast between the target and the background was enhanced with the morphological filter. The multi-frame detection results show that the combined filter algorithm can effectively detect the TSP from the experimental image sequences, thus providing basis for further technology research of target tracking.
Dual-band infrared optical system design and image quality evaluation
Li Peimao, Wang Xia, Jin Weiqi, Li Jiakun, Dun Xiong
2013, 42(11): 2882-2888.
[Abstract](480) [PDF 502KB](270)
The dual-band/multi-band imaging technology get more and more attention. As a key part, the dual-band optical systems, especially medium-wave infrared/long-wave infrared (MWIR/LWIR) imaging systems, becomes one of hot issues research subjects. Catadioptric optical system, off-axis three-reflection optical system and all-refractive optical system were designed, three dual-band imaging optical systems and theirs imaging performance were analyzed. The sensor which can response MWIR and LWIR at the same time was adopted. The main technical indicators are as follows: working waveband are 3-5 m(MWIR) and 8-12 m(LWIR), F/#=2, 2=5.74, f'=100 mm, distortion of the whole field of view is less than 2%, MTF is higher than 0.4 at 16.7 lp/mm in the all field of view. The construction features of the three dual-band imaging optical systems were analyzed and researched, the aberration curves and MTF curves of this three optical systems were presented, the advantages and disadvantages of this three optical systems were summarized.
Optical design of dual aperture infrared zoom optical system
Zhao Kun, Li Shenghui
2013, 42(11): 2889-2893.
[Abstract](379) [PDF 450KB](180)
In this paper, the narcissus of short focal length system was analyzed. A method of dual aperture zoom system was propounded, and a dual aperture infrared optical system was designed. The focal length of this zoom system at 3.7-4.8 m was 30 mm、150 mm and 300 mm with a zoom ranger of 10:1, F-number of 4 and 100% cold efficiency. The narcissus between dual aperture and normal single aperture was analyzed and compared,and the narcissus of dual aperture can be controlled preferably. The dual aperture zoom system has good image quality, big zoom range, low narcissus of small focal lens and compact configuration, so it can be used in the high thermal imager widely.
Design and testing of high contrast ratio MW/LW infrared dual-bands scene simulation system
Zhang Jianzhong, Guo Banghui, Tan Xiangquan, Sun Qiang
2013, 42(11): 2894-2900.
[Abstract](294) [PDF 563KB](176)
For the requirements of performance testing and evaluation of IR guidence system which works in dual-bands of MW/LW, a DMD based dual-bands infrared scene simulation system was designed, including a projection lens and illumination optical system. The aberration characteristics of the aspherical surface and the projection system with long exit pupil relief and infinity projection was taken into account. Using common infrared materials with reasonable distribution of power and ashperical surface, it balanced the coma, astigmatism, distortion and chromatic aberration, introduced by the dual-bands and long exit pupil relief. In the design of the illumination system, directly irradiation combined with the Abbe illumination principle was adopted to achieve an uniform illumination in the case of oblique incidence, also the improvement of light energy utilization and suppression of the stray light as well. The design result shows that IR MW/LW scene simulator has a full field of view of 2, exit pupil relief of 190 mm, and exit pupil dimeter of 70 mm. The distortion of the lens is less than 0.2%, the modulation transfer function(MTF) is close to the diffraction limination at all the field of view in both the MWIR and LWIR; meanwhile, the relative illumination is higher than 95%. The test result shows, when blackbody temperature is 300 ℃, the lowest simulated temperature is 31.6 ℃, the highest temperature is 250 ℃, and the temperature difference reaches to 215.4 ℃, the system contrast ratio is higher than 0.98, and the relative illumination is higher than 98.1%. The simulation system has the characteristics of high contrast, wide temperature difference and realistic image.
Application of infrared star catalog in ground-based infrared radiation measurement system
Huang Chen, Wang Jianjun, Gao Xin, Li Jianting
2013, 42(11): 2901-2906.
[Abstract](411) [PDF 509KB](233)
The known infrared catalog has limited available quantity, limited coverage of waveband and irradiance, low intensity distribution. This can not meet the need for astronomy calibration of existing ground-based infrared radiation measurement system. According to the system detection waveband, IRAS, WISE, 2MASS, AKARI four all sky surveys and their infrared star catalogs were selected. Considering the impact of atmospheric dispersion and attenuation, the limiting detection capability of system in 1-3 m, 3-5 m, 8-10 m and the limiting magnitude in corresponding point source catalog was calculated. Searching in catalogs and selected stars which can be observed by system, results show that 4 599 stars in 1-3 m, 125 stars in 3-5 m, 1 stars in 8-10 m were found. This work also provides a theoretical basis for astronomical calibration and infrared star catalog application for domestic ground-based infrared radiation measurement system.
Fast capture of appointed infrared targets based on estimation of rotation angle
Xue Song, Han Guangliang
2013, 42(11): 2907-2912.
[Abstract](272) [PDF 549KB](154)
For the problem of recognizing infrared targets, a method based on estimation of rotation angle was proposed. The method first segmented the image by local adaptive threshold and mark connected areas. Integral image was used to accelerate the computation of the local threshold. The connected areas were resized to the same size. The pixel values of the resized images were used as features. Then the rotation angle of the target was estimated by a neural network. Some areas were filtered during the estimation. At last, the area was recognized by another neural network. For some applications, the number of sample was not sufficient and a little difference existed between the samples and targets. For this problem, a method based on random growth and erosion was proposed to generate samples. Experiments show the method is effective and has a high recognizing rate even when the shape of samples is not exact.
Infrared variable resolution dim target detection with multi-scale matching
Zhao Xiao, Zhang Wei, Hou Qingyu, Gong Jinnan
2013, 42(11): 2913-2918.
[Abstract](256) [PDF 610KB](192)
According to the imaging characteristics of infrared variable resolution dim target in cloudy background, a method for small target detection based on scale space theory was proposed in this paper. Firstly, a Gaussian parameter model was established for small target, and then the scale space of the detected image was generated by using Gaussian kernel. Next, with optimal scale matching for scale space, the target region of interest (ROI) was extracted. Finally, the scale adaptive contrast (SAC) of ROI was calculated as detection criterion to remove the false alarms, achieving small target detection. The results of experiments show that the method proposed in this paper can not only accurately detect the target, but also estimate the size of target, and has high detection rate and efficiency.
Infrared dim-small target image simulation based on nonlinear mapping model
Gao Chenqiang, Yan Bingzao, Li Qiang
2013, 42(11): 2919-2924.
[Abstract](259) [PDF 604KB](123)
As the study and evaluation of the long distance infrared dim-small target detection algorithm requires a large amount of test images, a method of the IR dim-small target image simulation was proposed based on nonlinear mapping model. First, the irradiance and imaging gray value were got by theoretical calculation and actual shooting. By taking advantages of the data the various alternative mapping models so as to get the best mapping model were evaluated. Then, the mapping model was applied to the simulation process of actual target image and the target simulation image was got which reflected the real brightness variations. Finally, considering the effect of atmospheric transmission and so on, the target simulation image was combined with real background image to get final infrared dim-small simulation image. By comparison with the traditional simulation method, this proposed simulation method has more sense of reality.
Thermal effect on inner-shield in main optical telescope of solar space telescope
Li Rong, Wang Sen, Shi Huli
2013, 42(11): 2974-2978.
[Abstract](390) [PDF 777KB](143)
The SST (Space Solar Telescope) is designed to obtain its diffraction limit quality with aperture over 1 m. It observes the sun with a small view field of 2.8'1.5' to obtain its high spatial resolution imaging of 0.1-0.15. SST observing the sun directly can receive huge heat flow more than 1 000 W that will lead to unacceptable thermal distortion of the optical components. The sunlight enters into the telescope, which is an intense source of both heat and stray light. Based on the special thermal effect and stray light in the solar telescope, a compatibility analysis of the thermal effect of inner-shield in SST was performed. The relationship between the thermal control design and scatting elimination plan on the inner-shield structures in SST was presented. The objective and method of the compatibility analysis were determined. With the thermal analysis software, the temperature fields were calculated for a series of heights of inner-shield structure. A design of the inner-shield structure was put forward in thermal control terms and the suggestion was put out synchronously, which restrained the inner-shield with the height less than 400 mm. The aims of the optimal design of the inner-shield structure of SST are reached. The thoughts and methods of the optimal analysis are also useful for similar optical telescopes designed for solar observation.
Thermal design of light and small high resolution camera on Mars orbit
Zhang Yue, Zhou Feng
2013, 42(11): 2979-2983.
[Abstract](304) [PDF 757KB](145)
Light and small high resolution camera on Mars orbit takes high requirements for thermal control system mass and power dissipation. Considering thermal design details to the whole camera, the thermal control system was designed with light and good thermal performance structure material, advanced temperature controlled data transfer system, and many thermal controlled measures. Finally, it met the design requirements. In this paper, some thermal analysis and thermal design work about this advanced thermal control system were introduced. Based on the analysis about camera's external heat flux, two hot working conditions: =70, R=0and =-70, R=0, and one cold working condition: =0, R=-30 were determined. Considering with the interior heat flux and interface condition, detailed integrated thermal control schemes were established, and simulation results show the correctness of the thermal control schemes. This work will offer some technique supports to research about light and small high resolution camera on Mars orbit.
Design of controlling software for force actuator group of thin-mirror active optics
Wang Liang, Chen Tao, Zhang Bin, Liu Xinyue, Li Hongzhuang, Zhang Zhenduo
2013, 42(11): 2984-2989.
[Abstract](235) [PDF 794KB](144)
A software was designed for controlling experiments of an force actuator group, which was intended to be used in thin-mirror active optics. In the beginning, requirements of the controlling experiments on the software were analyzed, from both function angle and performance angle. Also, five working modes, such as correcting mode, testing mode, installing mode, stopping mode and restoring mode, were designed for the software according to practical requirements, and transition conditions between different working modes were discussed. Afterwards, the software was divided into three modules, such as data-transmission module, data-procession module and user-interface module, and design of each module was explained. Finally, the software was tested with each working mode, and a correcting experiment with an aluminum mirror was conducted in the correcting mode. Results of the test and the correcting experiment show that this software can meet almost all the anticipative requirements of the force actuator group experiments.
Data simulation and experimental analysis on anti-vibration performance of simple optical system
Shao Jun, Ye Jingfeng, Hu Zhiyun, Zhang Zhenrong, Huang Meisheng
2013, 42(11): 2990-2995.
[Abstract](306) [PDF 785KB](107)
With ANSYS software, the finite element anasysis of the integrated optical system based on tunable diode laser absorption spectroscopic technology(TDLAS) was built, numerical modal and harmonic response were analyzed. Based on the shaking table test result, the system structural dynamic properties, the amplitude-frequency curves under different dynamic loadings were measured in experiments. Then, combined with calculation results and test results, anti-vibration performance of optical system was analyzed, and frequency swing of environment vibration in which system can work was got. Result shows that system can work within 900 Hz environment vibration. It has the capability of testing and diagnosis outside the lab.
Calibration of star simulator based on LCOS splicing technology with wide-field
Zhang Xiaojuan, Zhang Guoyu, Sun Gaofei, Liu Shi, Zheng Ru, Gao Yujun
2013, 42(11): 2996-3001.
[Abstract](264) [PDF 758KB](147)
A calibration method of a large field LCOS splicing star simulator as well as the structure and principle of the calibration system were introduced. In order to make the star simulator to obtain a larger width of the field of view, proposing the connection technique of two LCOS was proposed. A variety of splicing errors were analyzed and then the calibration method was gave out. The focal length measurement error, distortion error and the imaging relationship error brought by the spliced LCOS were analyzed, a mathematical model of the angular distance between stars was established. Moreover, the various parameters of the model under the optimal accuracy were calculated by using a large number of the measurement data. Experimental result shows that, after calibration, the accuracy of angular distance between stars from the star simulator is significantly improved and the measurement error is better than 20.
TMT third-mirror shafting system alignment based on maximum likelihood estimation
An Qichang, Zhang Jingxu, Sun Jingwei
2013, 42(11): 3002-3007.
[Abstract](220) [PDF 817KB](160)
In order to complete the testing and alignment of TMT third mirror shafting, the maximum likelihood estimation was introduced. Firstly, two intersecting planes were used to identify a space line. Then, considering the noise of the measured data, maximum likelihood estimation was made use of to estimate TMT third mirror shafting parameters. And in MATLAB, which produced a training set with Gaussian white noise, the angle of collection axis and ideal axis from 6.29 to the optimized 5.24 was reduced, with optimization of 17%. Lastly, Vantage Laser Tracker was made the testing tool for TMT large shafting. Using optimization before, the TMT third mirror shafting residuals error was drawn to 2.9, which was less than the TMT indicator of 4. This paper will do good to TMT third mirror shafting alignment, and raise a real-time method to other large diameter optical system shafting alignment.
Analysis of transmission modes and its transmission precision of photoelectric encoder
Li Yonggang, Ding Jinwei, Liu Zhongyu, Han Pengpeng, Zhang Bao
2013, 42(11): 3008-3012.
[Abstract](237) [PDF 794KB](116)
In order to increase the payload's space of electro-optical platform, inner frame dispositions need to be optimized reasonably. The photoelectric encoder is mounted next to the spindle and using the parallel shaft transmission, which can expand axial space of inner frame effectively. The advantages and disadvantages of the concentric shaft transmission and parallel shaft transmission were analyzed, and applicability and limitations of parallel shaft transmission such as single gear transmission, elimination clearance gear transmission and steel belt transmission were expounded. The influence of elimination clearance gear transmission and steel belt transmission to angle measuring precision of photoelectric encoder were analyzed through experiment. Experimental results show that the angle measurement error of elimination clearance gear transmissionis is greater than 3' in a limited angle range, and the angle measurement error of steel belt transmissionis is less than 1' within a limited angle range. It provides a method for increasing payload's space of electro-optical platform.
Real-time compensation of subdivision error for Moire fringe photoelectric signal
Gao Xu, Li Junfeng, Zhang Shumei, Wan Qiuhua
2013, 42(11): 3013-3018.
[Abstract](262) [PDF 868KB](308)
In order to ensure the interpolation precision of the high precision photoelectric rotary encoder in the harsh working conditions, the real-time compensation processing system based on digital potentiometer was designed. On the basis of Moire fringe photoelectric signal mathematical model, the spatial distribution of the subdivision error due to signal amplitude deviation and DC drift was revealed. Error discipline and calculation formula was obtained. From several production aspects, such as encoder opto-mechanical alignment, uniformity of the code disk and photosensitive element debugging, fundamental characteristic of the encoder photoelectric signal subdivision error was pointed out. The resolution of high precision photoelectric encoder was constrained. From the Moire fringe signal form outputted by encoder photosensitive element, digital potentiometer look-up table with 0.1 resolution was constructed and key algorithm of real-time compensation was designed. A 23 bit encoder was selected as the experimental object and the compensation processing system was tested at -40-60 ℃. The experimental results showed that the DC drift was less than 1.2% and amplitude difference was less than 2% and the automatic compensation time was about 3 s. It can meet the encoder resolution(0.154) and real-time requirements. The method can be applied in the encoder system and improve the environmental adaptability and angle measurement reliability.
Online predicting of line-of-sight angular rate based on LS-SVM method
Hu Qiang, Song Shenmin
2013, 42(11): 3019-3023.
[Abstract](300) [PDF 810KB](104)
Firstly, the least squares support vector machine(LS-SVM) algorithm was improved by a time-weighted and last-elimination mechanism. Secondly, the improved LS-SVM algorithm was used for line-of-sight angular rate online prediction when the target was unlocked by the seeker due to the line-of -sight of the seeker which was blocked by the clouds(clouds-crossing) or other interferences. On one hand, if the target was locked by the seeker the improved LS-SVM should be used for online training. On the other hand, if the target was unlocked the decision function(result of the online training) should be used for predicting the line-of-sight angular rate. Lastly, by adding up the miss-distances of the numerical simulations in which the seeker was unlocked in the terminal part of the trajectory, the results demostrated the effectiveness of LS-SVM method to the typical line-of-sight angular rate signal predicting and the application prospects in increasing the capacity of clouds-crossing and anti- interference of the small air to surface tactical missles.
Stability of constant current source for SLD in variable temperature environment
Yang Mingwei, Wang Lei, Yang Yuanhong, Wu Changxin
2013, 42(11): 3024-3028.
[Abstract](302) [PDF 779KB](159)
The stability of superluminescent diode(SLD) characteristics in the temperature of -45-70℃ directly affects the performance of fiber optic gyroscope, therefore, the stability of the constant current mode in the temperature of -45 -70 ℃ has become one of the key issues of system design and optimization. In this paper, the circuit model was presented and the analytic form of the temperature stability of constant-current source was given, and some design rules were also presented according to the formula. Meanwhile, using the analytical formula, the theoretical analysis and calculation of the temperature stability of the constant current source under several different conditions were done, consistent with theoretical calculations and experimental results. The performance of SLD constant current source can be effectively assessed with this formula, and it is of important guiding significance for the SLD driver design.
Method of real-time pose location based on structural feature of dynamic target
Wang Kun, You Anqing, He Xi, Wang Lei
2013, 42(11): 3029-3034.
[Abstract](222) [PDF 851KB](108)
As to the change of 3D pose of dynamic target without tags, how to locate the target's pose on single camera mode rapidly and accurately was researched. On the premise of the knowledge of target's structure, the method of real-time pose location based on structural feature was proposed. On the basis of tracking steadily, the 2D feature of target in image which was caputured by optical camera was extracted. Corresponding the 3D features of the target with its 2D features in image, the mathmatics mode could be cancluted, and then the pose of dynamic target was located. The simulated experiment was developed with the imitation of airplane's flight. Applying this method on the imitation flight, the aveage time of processing was less than 0.02 s and the frequency of location was upper than 50 Hz. The experiment results show that this method is effective for pose real-time location of dynamic target.
Novel solar-blind photodetector using AlGaN in combination with a PVDF film
Liu Xiujuan, Li Chao, Wang Jianlu, Zhang Yan, Sun Jinglan, Li Xiangyang
2013, 42(11): 3035-3039.
[Abstract](400) [PDF 825KB](152)
A novel solar-blind detector which combined a AlGaN-based structure and a Poly(vinylidene fluoride)(PVDF) -based pyroelectric detector structure in one chip was fabricated. The pyroelectric response spectra of the PVDF-based pyroelectric structure was measured when the UV light illuminated from the side of the AlGaN-based structure. The peak response voltage was measured as high as 129.6 mV when the light's wavelength was 260 nm and the radiation power was 39.8 nW. The response mechanism was assumed as followed: the light at 260 nm was absorbed by i-Al0.35Ga0.65N layer and the heat energy was generated through the direct recombination of photoexcited-carriers, then the heat transferred to the PVDF layer and a response voltage was got through the pyroelectric effect of the PVDF. To confirm this assumption, another sample which added a porous SiO2 layer between the AlGaN-based structure and the PVDF-based structure was fabricated. Its response spectra showed two peaks, one was at 260 nm and the other was at 300 nm. A large decrease of the peak responsivity at 260 nm was observed, and it's in accordance with the assumed response process as the porous SiO2 layer acted as a heat-isolated layer. At last, the response voltage at different chopping frequency was measured for the device without porous SiO2 layer and had the measured data fitted by utilizing the conventional pyroelectric detector's responsivity equation.
Research development of nano optical waveguide smoothing technology
Shi Qiang, Sang Shengbo, Zhang Wendong, Li Pengwei, Hu Jie, Li Gang
2013, 42(11): 3040-3046.
[Abstract](477) [PDF 863KB](153)
With the development of semiconductor industry,the critical dimension of integrated optoelectronic devices are becoming smaller and smaller, the technology of smoothing nano optical waveguide surface are facing new challengs. Reducing the nano optical waveguide surface roughness, manufacturing ultra-low loss nano optical waveguide and achieving the efficient optical interconnection and inside coupling between chips are the key to optoelectronic devices integration and especially the development of high sensitive micro gyro, biochemical sensors, optical communication devices and so on. In this review, the relationship between surface roughness and scattering loss were analyzed while the emphasis was the technological approaches of smoothing nano optical waveguide surface, including the research status and the latest achievements of thermal oxidation method, hydrogen annealing method and laser reformation method. Additionally, the technical difficulties and development prospects of various technologies were summarized together with their application prospects in the fields of MEMS, large-scale photonic integrated circuits.
Self-assembled Au nanoparticles arrays by porous anodic alumina oxide and optical properties
Wang Yingwei, Wang Fei, Fu Liping, Fang Jingyue, Wang Guang, Chang Shengli, Zhang Xueao
2013, 42(11): 3047-3052.
[Abstract](348) [PDF 788KB](160)
Using vacuum deposition and subsequent thermal dewetting, Au nanoparticles ordered array were fabricated on the conventional ordered porous alumina template. Here, a self-assembled two-dimensional Au nanoparticles arrays was demonstrated, which consisted of several gold nanoparticles around every hole on the surface of porous alumina template. Furthermore, second anodized and widen diameter time influence on templates formed were investigated. During the fabrication of template, first anodization played guiding role for second anodization, and the diameter of hole direct was proportion with the widen diameter time. It also found that the form of Au nanoparticles arrays depend on the thickness of Au film. At last, optical properties for the material was test. Strong absorption peaks of the UV-visible absorption spectrum due to the surface plasmon resonance of Au nanoparticles were observed.
Turning of DOE Ge single crystal with micro-circle diamond tool
Li Junqi, Zhang Yunlong, Su Jun, Wang Zhibin, Guo Xiaogang, Zong Wenjun, Zhang Lei
2013, 42(11): 3053-3058.
[Abstract](334) [PDF 877KB](247)
Single crystal germanium material diffractive optical element (DOE), which possesses unique negative chromatic dispersion and thermal expansion coefficient, has been widely used in the IR optical field. DOE requires optical surface and transition of phase profile well. Micro-circle single point diamond turning is one of the ways to solve it. Actually it's difficult to have the proper cutting tool parameters to fit the surface roughness and the transition of phase profile. So there is great sense to study the micro-circle single point diamond turning of DOE. This paper studied the roughness of single crystal Germanium materials affections on the turning parameters and the tool parameters by using the DEFORM 3D software. Then the test was done according to the optimization results of the simulation. The results show that the surface roughness is 4 nm when the micro-circle radius of single point diamond turning is 0.1 mm.
Effects of design parameters of diffractive optical element on stray light
Yin Kewei, Huang Zhiqiang, Lin Wumei, Xing Tingwen
2013, 42(11): 3059-3064.
[Abstract](435) [PDF 688KB](210)
Diffractive optical elements (DOEs) have been widely applied to acquire different beam shapes in illumination systems. However, the experimental values of diffraction efficiency are greatly different from the ideal values because of stray light of high diffractive orders around the targeted spot. The reasons were theoretically discussed for the stray light and many DOEs with different design parameters were simulated. Through the simulation analysis, a new parameter, named relative period, was defined. It was proportional to the wavelength and inversely proportional to the far-field diffraction angle and the size of DOE cells. It is suggested that the diffraction efficiency, which is independent from the beam shapes, could be improved by increasing relative period. As a result, the stray light of high diffractive orders could be suppressed effectively by regulating the parameters of the far-field diffraction angle and the size of DOE cells. The new parameter has an important role in the design of DOE.
Advance on data relay technology for inter-satellite laser links
Zhao Jing, Zhao Shanghong, Li Yongjun, Zhao Weihu, Han Lei, Li Xuan
2013, 42(11): 3103-3110.
[Abstract](336) [PDF 933KB](575)
High speed and secure data relay satellite system based on high power inter-satellite laser links can provide high capacity and seamless relay services for earth observation satellite and user spacecraft with different functions in different orbits, it has a broad prospect of application both in military and civil fields. The European countries have studied the data relay satellite with laser links, the theoretical research and technology demonstration on-broad is launched, and so is the corresponding engineering verification program. In this paper, the research progress was demonstrated and reviewed; typical data relay satellite system based on inter-satellite laser links was introduced, especially in the system structure, the hardware and experimental foundations. The prospect of the inter-satellite laser links networking toward advanced applications was expected.
Performance analysis on atmosphere laser communication system based on circular polarization shift keying
Liu Dan, Liu Yan, Liu Zhi, Wang Puyao, Zhou Xin
2013, 42(11): 3111-3115.
[Abstract](309) [PDF 876KB](121)
In order to effectively suppress the impact factors of space laser communication performance, such as atmospheric disturbances and so on. An atmospheric laser communication system was described that took a new modulation method that was Circle Polarization Shift Keying(CPolSK). The working principle was introduced. The system model of CPolSK was given, and the factors that affeced the performance of communication in the system were analyzed. The four parameters of the detector noise, the sensitivity, the atmospheric channel attenuation and the transmission power which impacted on communication performance were considered. The experimental study of polarization shift keying system communication process was done by the OptiSystem software. The results indicate that the communication performance of the based CPolSK atmospheric laser communication system is obvious better than OOK system under identical communication conditions.
Characteristics of film sensor based on tilted long-period fiber gratings
Chen Haiyun, Gu Zhengtian, Chen Xin
2013, 42(11): 3116-3121.
[Abstract](411) [PDF 986KB](194)
In order to design a high-sensitive fiber-grating-based film sensor, the coupling features and sensing characteristics to the film refractive index of tilted long-period fiber gratings (TLPFG) coated with high-refractive-index sensitive films were studied, based on the coupled-mode theory. TLPFGs can couple the core mode to higher-order(azimuthal number l1) cladding modes whose coupling coefficients increased with the tilt angle and were much less than that of the first-order cladding mode for 80. It is confirmed that the tilt angle plays a role in determining the spectral transmittance rather than the resonant wavelength of the cladding-mode coupling. The response of spectral transmittance related to the 1-order and 5-number cladding mode of TLPFG to the variation of film refractive index were investigated under 80. The dependence of sensitivity of coated TLPFGs on the grating structural parameters(L,,) and film optical parameters(h3,n3) were analyzed. Result shows the sensitivity is greater than that of the non-tilted LPFGs by one order and the resolution of film refractive index is available to be 10-9.
Effect of high altitude platforms position instability on performance of PPM on inter-platforms optical links
Wang Xiang, Zhao Shanghong, Li Yongjun, Shi Lei, Zhao Guhao, Zhu Zihang
2013, 42(11): 3122-3126.
[Abstract](253) [PDF 964KB](186)
Based on the model of high altitude platforms position instability, the symbol error probability of PPM on inter-platforms optical links was derived. Based on the symbol error probability, the effect of three moving modes due to high altitude platforms position instability on the performance of inter-platforms was analyzed. The simulation results show that platforms rotation has the greatest influence on inter-platforms optical links, and the changing of inter-platforms distance has the lowest influence on inter-platforms optical links. A wide optical beam waist has better adaptability in platform instability. But when beam waist is more than 20 rad, the improvement of system performance is insignificant.
Application of optical fiber sensors in measurement of belt transmission parameters
Guan Xiangyi, Zhao Lili, Zhu Lin, Zheng Dayu, Sun Jianming
2013, 42(11): 3127-3131.
[Abstract](377) [PDF 900KB](119)
A new method of using optical fiber sensors to measure tiny displacement of high-speed rotating component was proposed to realize the non-contact high speed and high precision displacement measurement. On the base of measurement principle of optical fiber sensors, relation between light intensive and range was calculated in this paper. Voltage fitting formula between business value and range was established by turning a light intensity into a voltage signal. Test bench for measuring the parameters of V belt was designed to measure the radial displacement of V belt when stable operating in race to get the knowledge of track of V belt in belt pulley and the slide angles. New sliding angle formula was drawn by continuous optimizing the original V belt sliding angle. Comparative results from two experiments show that the new formula is more accordance with experiment with less error and can provide theoretical basis for the accurate design for V belt.
Image definition evaluation algorithm based on color relativity
Guo Huinan, Cao Jianzhong, Zhou Zuofeng, Tang Linao, Wang Hua, Ma Nan
2013, 42(11): 3132-3136.
[Abstract](321) [PDF 950KB](247)
Definition evaluation function of digital image plays an important role in digital camera auto-focus. Due to the existing definition evaluation functions are of some marked disadvantages, a spatial domain evaluation algorithm for digital color image was proposed. The colorful property of each pixel was judged and definition chromatic difference parameters was created by using chromatic difference between their tri-stimulus values. Besides,nonlinear function was used to improve the gradient coefficient of each pixel which made the evaluation function be more sensitive to some images in extreme cases. Experimental results show the superiority of our algorithm over the most of existing evaluation algorithms in dealing with natural images. And our method also is of a good ability of robustness as well as reducing calculation complexity and it can be easily achieved on hardware.
Application in compressed sensing ISAR imaging based on sparse banded measurement matrices
Tan Xin, Feng Xiaoyi, Wang Baoping
2013, 42(11): 3137-3143.
[Abstract](387) [PDF 1008KB](167)
The application of compressed sensing(CS) theory to inversed synthetic aperture radar(ISAR) can make effective use of the data of defective radar echo, and solve the lower quality of imaging, which is caused by the defective data. By analyzing the present situation, it was found that the number of independent random elements in the commonly used Gauss and Bernoulli random measurement matrices was too huge, and the storage space was too large, which led to the high hardware implementation cost. Sparse banded measurement matrices were constructed in this paper, which significantly reduced the number of nonzero elements in measurement matrix and the requirement of system sampling, and saved the hardware implementation cost, by sparsifying measurement matrices banded cyclic shift zero. Finally, the data of simulation and anechoic chamber experiment verify the feasibility and effectiveness of the application of sparse banded measurement matrices into ISAR imaging through the point target model.
Global translational motion parameters estimation based on pre-selection algorithm
Xi Zhihong, Chu Shouyan, Xiao Yihan
2013, 42(11): 3144-3149.
[Abstract](354) [PDF 944KB](104)
In order to estimate the camera's small amplitude translational dither motion, various mismatching factors were analyzed, such as self-moving objects, unstable edge details and smooth areas. After summarizing the characteristics of various factors and the existing related basic theories, and the same time on the basis of the improved C-1BT transformation, the fast global translational motion parameters estimation based on the pre-selection process algorithm were proposed. Firstly, before the local motion vector estimation, the pre-selection process was used to keep some special sub-blocks, because they can better represent the global motion nature. Secondly, according to the characteristic of the pre-selection algorithm, the initial arm-length predictive part of the traditional adaptive rood pattern search method was improved to reduce the risk of falling into local optimum. At last, the optimum global motion parameters were obtained, with the translational motion model and the statistical principles. MATLAB simulation results show that the proposed method fast and robustness.
Research of EMCCD image filtering method based on adaptive fuzzy median filter
Qi Lei, Zhang Wenwen, Chen Qian, Gu Guohua
2013, 42(11): 3150-3155.
[Abstract](232) [PDF 921KB](112)
The noise density of Electron Multiplying CCD(EMCCD) image varies with the gain, a noise detection based on adaptive fuzzy median filter(AFMF) algorithm was proposed. The algorithm consisted of fuzzy filtering module and adaptive module. First, the noise pixels in the center of the filter window was identified. Second, the double thresholds were introduced for these detected noise points, basing on the thresholds and median of the filtering window, the fuzzy membership function of noise points was put forward, and the fuzzy membership function was utilized to filter the noise points. Finally, the adaptive module was used to adjust the pixel in the image. Simulation and experimental results indicate that the new algorithm is able to remove noise pixels effectively and protect the details well in the image. Compared with the adaptive median filtering, the average PSNR improves at least 15 dB. The performance is better than the other median filters under the condition of low noise density and relatively stable under the condition of high noise density.
Calculating probability of objectness likelihood model based on superpixels
Ji Chao, Liu Huiying, Sun Jingfeng, He Sheng, Huang Minzhu
2013, 42(11): 3156-3162.
[Abstract](329) [PDF 981KB](115)
Establishing calculation model on the probability of saliency objectness likelihood based on superpixels was introduced to dectect image saliency. At first, factors which affected the size of saliency were analyzed according to the principle of saliency and natural characteristics; And then the SLIC algorithm was used to divide image into K superpixels; Next, according to the texture, color and gradient feature information, calculation models were established on probability saliency object under different rules: including compactness in class, color spatial distribution estimation and edge continuity; Moreover,integrating the probability of saliency object under each rule to get the probability of objectness likelihood according to the characteristics of combining with activity in cells responding to stimuli and exponential function; Finally some experiments extracting regions of interest from complex scenes prove that the proposed algorithm is more efficient than other algorithms.
Laser and optoelectronic technology application
Simulations and experiments on optical inner-channel thermal deformation for high-power laser system
Guo Ruhai, Chen Ning, Shi Kui, Wang Bing, Shi Long
2013, 42(11): 2925-2930.
[Abstract](551) [PDF 621KB](155)
In order to research the influence on the beam quality due to cumulative effect of the inner channel thermal deformation in the high energy laser system, the theoretical simulation and experimental study were performed. Firstly, three typical laser power 10 kW, 50 kW and 100 kW with the unstable resonator were selected to analyze thermal deformation of mirror through the finite element analyze of thermodynamics instantaneous method. Then the wave front aberration could be calculated by ray-tracing theory. Finally, Strehl ratio, parameter of far-filed beam can be calculated and comparably analyzed by Fresnel diffraction integration. The simulation results show that due to the effect of inner channel thermal deformation, eccentric phenomenon and astigmatism of far-filed beam emerge, and peak power and the focused ability decrease. With the increasing of reflection times, Strehl ratio decreases and parameter increases, and tilt, astigmatism and coma of x direction gradually increase, which become the main aberration. Comparing with above theoretical simulation study, the thermal deformation experimental platform was built to measure the single copper mirror of 99% reflectivity with the 10 kW TEA CO2 laser. Through the equivalent scale rule, the experimental results can also represent the 50 kW and 100kW power level. The measurement precision of thermal deformation of mirror is smaller than /15 and agree well with the simulation results. The results show that the thermal deformation of mirror cannot be neglected when the laser power great than 10 kW and has a great influence on the far-field transmission properties with the power increasing and reflection times. These results can also provide the reference to the thermal aberration analyze for high power laser system and can be applied to the field of laser nuclear fusion and laser weapon etc.
Laser diode-end-pumped Nd:YAG/LBO laser operating at 946 nm/473 nm
Mayilamu Musideke, Yao Jianquan, Wang Peng
2013, 42(11): 2931-2934.
[Abstract](343) [PDF 591KB](147)
The properties of Nd:YAG 946 nm and 473 nm laser were studied. By using Nd:YAG composite as laser gain medium, 11 W continuous-wave(CW) laser output at 946 nm was obtained under the incident pump power of 31.8 W, corresponding optical efficiency and slope efficiency were 34.6% and 35.4%, respectively. The M2 factor was 7.53 and the power stability was better than 0.4% with 0.5 h. After intra-cavity frequency-doubled by an LBO crystal which was cut for critical type Ⅰ phase matching, 0.887 W CW output power at 473 nm was obtained, corresponding to an optical efficiency of 5.87%. Experimental results prove that the end pumped CW laser has important practical value.
Grazing incidence laser scattering characteristics of anisotropic rough sea surface
Wang Xintao, Qu Huiming, Qu Hongxing, Gong Jingtang, Wang Lin
2013, 42(11): 2935-2939.
[Abstract](384) [PDF 649KB](165)
In light of the laser scattering field model of the rough sea surface is not suitable for laser beam grazing incidence and ignores the influence of wind speed, based on the Cox-Munk and kirchhoff approximation(KA) simulation model of anisotropic rough sea, directional reflectance ratio distribution model for grazing incidence laser beam was set up, change law of directional reflectance ratio vs wind speed, wind direction, incident angle, incident position angle, reflection angle, reflection position angle was simulated, and the result was verified by pool experiments. Results show that the laser energy scattering of rough sea surface mainly distributes in the conical space angular which in order to irradiated surface for a vertex, this space angular direction locates near the specular reflection direction, as the wind speed increases, space angular becomes larger, for grazing incidence laser beam, due to the shielding effect, the direction of space angular away from the specular direction. The model can provide certain theoretical basis for the research of semi-active laser guided missile shooting small targets at sea and layout of laser decoy in rough sea.
Simulation and analysis of Gauss laser beam TEM00-mode scattering signal
Wang Lianfen, Zhao Xuanke, Zuo Xiang, Wang Jinjin, Sun Honghui
2013, 42(11): 2940-2943.
[Abstract](457) [PDF 644KB](167)
The scattering characteristics of off-axis spherical particles to Gaussian laser beam of TEM00-mode were studied based on the general Mie scattering theory in this paper. According to the expanding form of Gaussian beam in the spherical coordinate system, the limited series solution forms of the expansion coefficient were programmed and calculated. In the case of the scattering of off-axis spherical particles to Gaussian laser beam, the relationship of scattered light intensity with the particle size parameter, refraction rate, scattering angle and relative location of scattering particles were simulated, then the simulation results were discussed and analyzed contrasting with the plane wave scattering patterns. The results show that the scattered light intensity distribution pattern of Gaussian beam is different from the plane wave scattering pattern, but in the case of big beam-waist radius, it has a lot of characteristics in common with the scattering pattern of plane wave.
Single solid F-P etalon-based dual-frequency Doppler lidar
Shen Fahua, Sun Dongsong, Liu Chenglin, Qiu Chengqun
2013, 42(11): 2944-2950.
[Abstract](244) [PDF 723KB](173)
The single solid Fabry-Perot (FP) etalon-based dual-frequency Doppler lidar technology was proposed. Its structure is introduced, and the principle of wind field measurement with that Doppler lidar system is analyzed. According to the detection requirements, each unit of system parameters, especially the F-P etalon parameters are carefully optimized. Furthermore, the detection performance of the lidar system with optimized parameters is simulated. The simulation results show that the radial velocity errors is less than 0.75 m/s at 3 km altitude on sunny days and less than 0.58 m/s at 1.5 km altitude on hazy days for 60 elevation angle, 60 m range resolution and 1min temporal resolution, and is less than 1m/s at 4 km range under different visibility conditions for 8 elevation angle, 60 m range resolution and 10 s temporal resolution with a 100 mm diameter telescope and a 50 J pulse energy, 6 kHz repetition rate semiconductor laser.
Effect of ethanol molecules on change of water hydrogen bonding with laser Raman spectra
Wu Bin, Chen Kunfeng, Wang Hengfei, Ying Chengping, Shi Xueshun, Liu Hongyuan, Luo Xiaosen
2013, 42(11): 2951-2956.
[Abstract](446) [PDF 696KB](240)
In order to study the molecular interactions involved in dilute ethanol-water solutions, the OH stretching vibration spectra of ethanol-water solutions with the concentration range of 0-10 vol.% were measured, and the difference spectra of the samples were calculated. The hydration of ethanol molecule in the solutions of low concentration was analyzed based on the difference spectra. The result shows a very small amount of ethanol in the solution can enlarge the hydrogen bonding network in pure water, and the hydrogen bonding degree of water molecules around hydrophobic groups of ethanol molecules was also enforced. Ethanol molecules tend to aggregate together with increasing concentration, which was caused by hydrophobic hydration, and the hydrogen bonding network of water molecules become loosen due to this. As a result, some of the water molecules break away from the hydrogen bonding network, and transfer to small clusters of different size; at the same time, the hydrophilic groups of ethanol molecules associate with free water molecules through hydrogen bond.
Application of artificial neural network in Al2O3 ceramics laser milling
Xu Zhaomei, Zhou Jianzhong, Huang Shu, Sun Quanping
2013, 42(11): 2957-2961.
[Abstract](370) [PDF 682KB](133)
In order to control the quality of Al2O3 ceramics, based on the artificial neural network (ANN), a model was established to describe the relation between the laser milling quality of Al2O3 ceramics with the ceramics parameters. The milling quality of Al2O3 ceramics were predicted with the model in which the input parameters consisted of laser power, scanning speed and defocus amount and the output parameters included the milling depth and width. The results show that the mean error is small, and the model has good verifying precision and excellent ability of predicting. Five group process parameters were chosen to test the reliability of the neural network model out of the train samples. The maximum relative error of the output test value and the experiment sample value was 7.06%. The laser process parameters can be chosen easily and accurately to improve the processing quality of Al2O3 ceramics.
Preliminary study on effects of laser irradiation on thin aluminum alloy sheet in tangential flow
Li Junshen, Zhao Guomin, Jiao Luguang, Yuan Chun, Chen Minsun
2013, 42(11): 2962-2966.
[Abstract](208) [PDF 727KB](126)
Experiments and simulations were performed to study the laser irradiation effects on thin aluminum alloy sheet in different tangential flow. The temperature traces of the aluminum alloy sheet in the nitrogen flow and air flow were consistent, which indicated that the combustion effect could hardly progress. The temperature of aluminum alloy sheet without flow was higher than those in the nitrogen flow and air flow at the same time. The center displacements traces of the aluminum alloy sheet in three different gas flows kept same shape with corresponding temperature traces, which implied that the tangential flow did not play a dominant role compared with the heat distortion induced by laser heating. Moreover, a numerical model was developed, with finite element analysis software ANSYS, to simulate the process of temperature and displacement of the aluminum alloy sheet in different gas flow and analysis how the power distribution and convection heat transfer impact the results was performed. The computed results present good agreements with experiment data. The results show that the tangential flow mainly take on cooling effect when the power density of laser is not high, especially in the cooling period when the laser irradiation ends.
Strapdown optical seeker characteristics and multi-dimension optimal guidance law
Zhang Yue, Chu Hairong
2013, 42(11): 2967-2973.
[Abstract](331) [PDF 785KB](125)
In order to realize strapdown optical imaging seeker and guidance system integrated design, strapdown guidance and control system were established. According to the characteristics of strapdown seeker, guidance and control principle were studied. The models of strapdown seeker and gyro were established. For the problem of strapdown seeker can't extract the line-of-sight angular rate precisely, the control and guidance scheme of combining of attitude autopilot and LOS integral proportional navigation was proposed, and the relationship between body line of sight(BLOS), scale factor, navigation ratio and system stability region were analyzed. In order to improve system response speed, strapdown guidance system optimal guidance law was deduced. In the end, flight simulation were done, and the results show that strapdown guidance and control systems can attack on stationary and moving(60 km/h) targets effectively. The maximum firing errors were 1.49 m and 2.62 m respectively. System errors, gyro bias and bias stability play a very important part in the guidance system accuracy. Strapdown seeker guidance and control systems can meet the requirements of air-to-ground system for attacking stationary and low speed moving target.
Advanced optical imaging technology
New hyperspectral imaging system based on AOTF
Liu Jifan, Ma Yanhua, Zhang Lei, Shu Rong
2013, 42(11): 3065-3069.
[Abstract](389) [PDF 874KB](180)
AOTF (Acousto-optic Tunable Filter) is a new kind of electronically controlled optical filter. It has many advantages such as random wavelength access, fast spectral scanning speed, small size, no moving parts, good environmental adaptability, and so on. The working principles of AOTF and the method for spectral resolution programmability based on multi-frequencies mode were analyzed, the new hyperspectral imager based on AOTF was proposed, and the original experimental results were presented. The system works in the visible-near-infrared spectral range, and the outstanding feature is that both the wavelengths and the spectral resolution can be configured via software. So it has better flexibility and higher data efficiency compared to traditional hyperspectral imagers.
Hyperspectral remote sensing image parallel processing based on cluster and GPU
Wang Maozhi, Guo Ke, Xu Wenxi
2013, 42(11): 3070-3075.
[Abstract](440) [PDF 845KB](306)
The parallel algorithms design and implementation of covariance matrix, related to PCA and MNF, and SCM used in hyperspectral remote sensing image data process was discussed in this paper. The covariance matrix parallel algorithm was designed and implemented under cluster circumstance based on MPI. On the other hand, parallel algorithm of SCM was designed and implemented based on GPU. Both of these two parallel algorithms were verified during the application on hyperspectral remote sensing data processing. The experiment results prove that high performance computing is effective during the data process of hyperspectral remote sensing image, and it should be an important technique for generalization of hyperspectral remote sensing to engineering quick application. The results also prove the correctness of the parallel algorithms proposed in this paper.
Supervised method for hyperspectral image camouflage target detection
Liu Zhigang, Lu Yunlong, Wei Yiwei
2013, 42(11): 3076-3081.
[Abstract](498) [PDF 905KB](222)
Aiming at camouflage target detection problem, a supervised method for hyperspectral image camouflage target detection was proposed. The plant camouflage targets were taken as study objects, and then based on the spectral characteristics analysis of camouflage materials and plants, camouflage materials and plant's spectral differences were magnified through spectrum rearrangement, spectral derivative and spectrum difference enhancement. Then, principal components analysis(PCA) was used for dimensionality reduction, thus a detection method for big camouflage target in hyperspectral image was realized. The experimental result shows that the method outperforms weighted correlation matric-constrained energy minimization(WCM-CEM) and unsupervised target generation process-orthogonal subspace projection(UTGP-OSP) both in the detection time and detection result.
Noise-improvement of complementary S matrix uesd in DMD spectrometer
Gao Lingxiao, Zhang Zhihai, Zhang Wenkai
2013, 42(11): 3082-3086.
[Abstract](279) [PDF 895KB](127)
A complementary S-matrix code modulation scheme was designed for digital micromirror spectrometer. The theoretical analysis proved that the complementary S matrix itself had good properties: it could improve for abouttimes of S matrix in respect of noise improvement. It was proved that this scheme could reduce the noise of stray light and dark current in implementing process by detailed deduction and analysis on noise-improvement theory of complementary S matrix through modeling on spectral signatures. When this scheme was applied in DMD spectrometer for experimental verification. The results demonstrate that the 63 order complementary S matrix coding scheme improved for 1.69 times compared with same-order S-matrix coding scheme in signal-to-noise ratio, which is identical with the theoretical analysis.
Experimental measurement of spectral BRDF and research of chromaticity characteristics of silicon solar cell panel
Wang Anxiang, Wu Zhensen, Cao Yunhua
2013, 42(11): 3087-3095.
[Abstract](402) [PDF 995KB](138)
The spectral bidirectional reflectance distribution function(spectral BRDF) of silicon solar cell panel was measured in the visible spectrum(380-780 nm). The variation of spectral BRDF with wavelength and scattering angle was analyzed. The relationship between the bidirectional reflectance factor in the theory of light scattering and the spectral reflectance factor of colorimetry was obtained by combining the theories of colorimetry and light scattering, a method was developed for characterizing chromaticity characteristics of object using the spectral BRDF. Using the lightness index and chromatic indexes and in CIELAB color system, chromaticity characteristics of target samples was described under the condition of several incident and scattering directions. The application of spectral BRDF of target samples in color optics possesses important values in the detection, identification and color reproduction of target samples.
Fusion method of multispectral and panchromatic images based on improved PCNN and region energy in NSCT domain
Li Xin'e, Ren Jianyue, Lv Zengming, Sha Wei, Zhang Liguo, He Bin
2013, 42(11): 3096-3102.
[Abstract](352) [PDF 914KB](223)
A fusion method of multispectral(MS) and panchromatic(PAN) images based on improved Pulse-Coupled Neural Network(PCNN) and region energy in Nonsubsampled Contourlet Transform(NSCT) domain was proposed. Firstly, the two original images were decomposed into a low frequency subband and more bandpass directional subbands by NSCT. Then, for the low frequency subband coefficients, an adaptive regional energy weighting image fusion algorithm was presented; while for the bandpass directional subband coefficients, based on improved PCNN, the bandpass directional subband coefficients was used as the linking strength. After processing PCNN with the linking strength, new fire mapping images were obtained. The fire mapping image region energy was calculated, and the fusion coefficients were decided by the compare-selection operator with the fire mapping image region energy. Finally, the fusion images were reconstructed by NSCT inverse transform. The experimental results show that, when the numbers of iterations are 100 times, respectively as comparing with that of improved wavelet method, Contourlet method and NSCT method: the standard deviation increases by 9.48%, 9.73% and 3.84%; the entropy by 0.95%, 0.94% and 3.34%; the correlation coefficient by 21.56%, 11.27% and 7.89%, and the deviation index reduces by 29.66%, 9.45% and 7.42%.