2018 Vol. 39, No. 2

Oe System and Engineering
Research on vehicle 360° situational awareness system
Chen Wei, Liu Fei, Liang Qingqian, Wang Jing, Chen Jing
2018, 39(2): 165-168. doi: 10.5768/JAO201839.0201001
In order to adapt to the complex battlefield space and improve the armored vehicle's short distance protection ability and battlefield survivability, a vehicle 360° situational awareness system was proposed. The framework of the system was given, and the key technologies such as general design, high throughput of embedded image processing platform, real-time panoramic mosaicing, target recognition and threat estimation were analyzed. Then the solutions were put forward. Results show that this system realizes the high-definition image mosaic in multi-channel. The delay time is better than 190 ms, and the detection distance to the vehicle is up to 1 km. It has the abilities of detection and threat prompting for human and vehicle targets, and can improve the situation awareness of armored vehicles in near range significantly.
Design of universal digital fish-eye lens testing system
Li Weishan, Shan Hong, Gao Jinzhao, Yan Jihua, Yang Gang, Wang Hongda, Zhang Wensheng, Wang Hongwei, Yu Meixia
2018, 39(2): 169-173. doi: 10.5768/JAO201839.0201002
A universal digital fish-eye lens testing system was designed.The system is composed of illumination system, testing plate, equivalent parallel plate system and ball screen, and the illumination system is configured of plane reflector, cylindrical fly-eye lens array and alignment lens. In this way, the volume of system is reduced, the utilization rate of light energy and uniformity of illumination are improved, and the size of the illumination spot can be adjusted. An angle dividing ruler is carved on the inner wall of ball screen for testing the field of view(FOV) of lens.The range of illumination FOV for testing system is φ8.1 mm~φ36.3 mm, the illumination uniformity is 91%, and the luminous flux of testing system is above 5 000 lm which is adjustable. The testing system can test the performance of various types of fish-eye lenses with 1DLP, 3DLP, 3LCD and 3LCOS in 0.55″~1.55″chip size, such as FOV angle, resolution, color rendition, chromatic aberration, and the projection effect. It has strong general availability, and can reduces the cost of testing.
Research on missile-borne common aperture laser micro-Doppler target recognition system
Chen Wenjian, Gao Wei, Sun Weiping, Duan Yuanyuan, Li Gang, Ma Shiwei, Liu Xiaoying, Lei Junjie
2018, 39(2): 174-179. doi: 10.5768/JAO201839.0201003
In order to realize the extraction of vibration features at 100 Hz from a distance of 4 km, a method of using laser micro-Doppler to enhance the capacity of missile target identification was proposed, and a laser transmitting/receiving/video common aperture system based on polarization splitting was designed.This compact two-stage stable system is adapted to the missile-borne environment, and the optical path is compensated automatically by optical fiber selection, the coherent light matching can be realized. Using the coherence method of local oscillator/echo signal, the detection pulse light is formed by the modulation of local oscillator light with a line width of 300 Hz, so the detection range can be improved, also the false peak caused by the attenuation of atmosphere can be avoided. The Fourier transform circuit constructed by FPGA/DSP can obtain the time-frequency curve signal, the identification of the target can be achieved when the frequency is 36 kHz.
Directional error analysis of 2D galvanometer scanning system
Chen Zhibin, Fan Lei, Xiao Wenjian, Qin Mengze, Xiao Cheng, Zhang Dongxiao
2018, 39(2): 180-186. doi: 10.5768/JAO201839.0201004
The advantages and disadvantages of existing beam scanning system were compared and analyzed.A 2D galvanometer scanning system was used as the optical axis alignment device of the multispectral integrated target.The alignment precision of the optical axis alignment device can affect the calibration accuracy of the multispectral integrated target. The directional error of 2D galvanometer scanning system was analyzed, the directional model of 2D galvanometer scanning system was established, and the measurement experiment of alignment error of 2D galvanometer scanning system was carried out. The results show that the azimuth error and pitch angle error of the 2D galvanometer scanning system are less than 8″, the alignment angle error is less than 9″, and the alignment error is less than 10″, which demonstrates that the optical axis alignment accuracy of multispectral integrated target can be satisfied.
Design and realization of on-line testing device of portable photoelectric tracking system
Zhang Baoyi, Mu Wei, Wang Hu, Yao Linhai, Liu Tong
2018, 39(2): 187-191. doi: 10.5768/JAO201839.0201005
The on-line detection of a certain photoelectric tracking system was realized through the computer simulation platform, however, the simulation platform is large in volume, inconvenient in carrying and complex in installation. In order to solve the problem of using in field, a portable photoelectric tracking system on-line detection device was designed and implemented.The device adopts the ARM embedded platform based on WinCE operating system and divides the working state detection into one system-level module and multiple component-level modules, which can conduct testing through module according to actual needs, thereby the CPU load and detecting device consumption can be reduces. Actual verification show that, the device can realize real-time on-line detection of the detailed state of photoelectric tracking system and accurately locate the fault site to achieve the purpose of quickly repairing the fault.
Design of continuous zoom optical system for periscope
Wu Xuepeng, Hu Jixian
2018, 39(2): 192-195. doi: 10.5768/JAO201839.0201006
A continuous zoom optical system with working focal length of 252 mm~504 mm was designed based on the basic principle of periscope.Instead of traditional flip zooming which is a discontinuous zoom mode, the system adopts the mechanical-compensated optical configuration in which the given variable lenses groups move along the optical axis driven by a cam to achieve the continuous change of effective focal length (EFL). Through simulating and imaging quality analysis, it is proved that all the performance indicators meet the design requirements. Test results show that spatial resolving ability of the optical system is below 2′.
Fresnel diffraction calculation with virtual light wave field and its application
Liu Zhiqiang, Song Qinghe, Liu Chao, Gui Jinbin, Li Junchang
2018, 39(2): 196-199. doi: 10.5768/JAO201839.0201007
In order to satisfy the high spatial resolution requirements of light wave field in specific observation areas, a diffraction calculation method was presented. Through introducing a virtual optical wave field, it can use the sampling number of original light wave field to represent the diffraction field of arbitrary areas in the observation plane. Simulation experiments were carried out using the proposed method. The calculation results indicate that the method can increase the amount of effective information in the observation areas, and the spatial resolution of the diffraction field obtained by the method of virtual optical wave field can reach 5.2×10-3 mm/pixel. However, the spatial resolution of the diffraction field obtained by S-FFT is 26.6×10-3 mm/pixel. Moreover, the experimental results show that the proposed method can achieve better reconstruction performance in color digital holography wavefront reconstruction.
Oe Information Acquisition and Processing
Depth image enhancement algorithm for preserving boundary
Zhou Zigu, Cao Jie, Hao Qun, Gao Zedong, Xiao Yuqing
2018, 39(2): 200-206. doi: 10.5768/JAO201839.0202001
The drawback of current depth image enhancement algorithms is poor performance of edge preserving. To solve this drawback, the gradient mask guided joint filtering(GMGJF)algorithm is proposed. The Sobel gradient transform is used to obtain the boundary direction information, and the hole region of the depth images was utilized to generate the hole mask.Furthermore, taking the boundary direction and the cavity mask as the guidance, the color image was jointed to perform iterative Gaussian filtering and hole filling on the depth image. Experimental results show that the peak signal to noise ratio(PSNR)and the structural similarity index measure(SSIM) of GMGJF algorithm are improved by at least 3.50% and 1.07% respectively, compared with the iterative median filter(IMF), guided filter (GF) and joint bilateral filter(JBF) algorithms, it has both the strongest ability of denoising and hole filling, and can remain the boundary features best, which is good for feature extraction and target recognition of depth image.
Fluorescence lifetime representation method based on impulse delay estimation
Wang Yue, Meng Xiaochen, Zhu Lianqing
2018, 39(2): 207-211. doi: 10.5768/JAO201839.0202002
The precise measurement of fluorescence lifetime is of great significance in the fluorescence detection and analysis techniques. Aiming at the problem that the nanosecond fluorescence lifetime cannot be measured directly in the flow cytometry system, a fluorescence lifetime characterization method based on the cross correlation algorithm was proposed, which combined the chirp Z transform (modified chirp Z-transform, MCZT) algorithm with the correlation peak interpolation (fine interpolation of correlation peak, FICP) algorithm.The comparison with the standard fast Fourier transformation (FFT) algorithm was conducted, the fluorescence lifetime of mammalian cells was measured, the obtained data was processed, and the performances of MCZT and FICP algorithms were verified. The experimental results show that the algorithm reduces the fence effect caused by FFT calculation effectively, the resolution ability of the cross-correlation function is improved, and the relative error in measuring fluorescence lifetimes was increased by 4.344 3%.
Optical Metrology and Measurement
Research on critical method of large objects three-dimensional measurement based on monocular structured light
Fu Yanjun, Weng Lingxiao, Hu ming
2018, 39(2): 212-219. doi: 10.5768/JAO201839.0203001
In three-dimensional measurement system based on structured light, the grating fringe cycle is broadened on the reference surface with the reason of the oblique-angle, which brings errors to the measurement and reduces the accuracy. At the same time, because of large objects' geometry and morphology and other factors, as well as the limit of the intersecting axis projection system, the single shape measuring range is limited. It is difficult to measure large objects' complete shape in one time. And when measuring large objects, camera lens' nonlinear distortion also affects the measurement accuracy. According to the periodic pattern of grating stripes on the reference plane, a well-fitted, convenient and quick stripe cycle correction method was proposed. Based on the cycle correction method, a theoretical model of four-step phase shift method was put up, and then a theoretical model of time phase unwrapping based on fringe period correction was proposed. After that, the lens distortion correction model was used to improve the measurement accuracy. With the mark points pasted on the surface of objects, the three-dimensional coordinates of them were got, as well as the transformation matrix by using the singular value decomposition (SVD) and Levenberg-Marquardt (L-M) optimization algorithm, and three-dimensional image mosaic was realized under the global coordinate system. Finally, the linear weighting algorithm was used to realize the image fusion of overlapping areas. Experimental results show that the registration errors in x, y, z axes are 0.14 mm, 0.16 mm, and 0.19 mm respectively, which all meet the requirements.
Three-dimensional profile measurement for lens by full-field interferometry
Liu Jiajian, Dong Bo, Lu Ziliang, Zhang Wei, Wu Weizeng, Zhou Yanzhou
2018, 39(2): 220-224. doi: 10.5768/JAO201839.0203002
A method for measuring the three-dimensional (3D) profile of lens by full-field interferometry was proposed to meet the requirement of high accuracy processing technology. A distribution feedback(DFB)diode laser of calibrated 3D profile measurement system was used to perform the wavenumber-scanning interferometric measurement for the lens. The interference image random sampling Fourier transform(RSFT) and unwrapping algorithm were used to process interference image acquired by CCD, and finally the 3D lens profile was obtained after had been calculated. Experimental results indicate that the horizontal and vertical resolution of the system are both 0.011 3 mm / pixels, and the root mean square error of measurement in the depth direction is ±19.8 nm. The system is characterized by simple structure, high stability, no contact with the lens, no damage to the lens surface, and high-precision contour measurement suitable for the lens.
Calibration method for structured light 3D measurement systemhaving single camera and single projector
Geng Kaizhen, Gao Zhihua
2018, 39(2): 225-229. doi: 10.5768/JAO201839.0203003
Calibration of the system parameters is the basis of three-dimensional measurement system of the structured light, and accuracy of parameter calibration directly affects accuracy of the measurement, in which the projector still has the problems of complex calibration process and low precision. In order to solve this problem, a calibration method is put forward, which is done by projecting circles pattern to a flat with circular signalized points. Based on projective transformation theory, projective corresponding relation is established between projector image coordinates and camera image coordinates through error compensation method, and accurate projector image coordinates of calibration points is obtained. Taking two groups of image coordinates and world coordinates as initial value, nonlinear algorithm is used to optimize the whole system parameters. Experimental results show that the maximum error of the system is less than 0.05 mm and the error root mean square is less than 0.03 mm. The results show that the calibration process is simple and can improve the calibration accuracy and has wide applicability.
High-precision displacement measurement method based on laser modulation
Zhai Yusheng, Jiang Liujie, Wang Xinjie, Zhang Zhifeng, Liu Jiaming
2018, 39(2): 230-234. doi: 10.5768/JAO201839.0203004
The displacement measurement system based on laser collimation technology has been used in many fields. The core device of measurement system is the position sensitive detector. Such as stray light, power fluctuation and noise of photoelectric signal processing circuit, these factors can affect the measurement accuracy. To solve these problems, a high-precision displacement measurement method based on laser modulation was presented. Laser was operated in a modulation mode, instead of continuous laser mode. A photoelectric signal processing circuit was designed and optimized, and a program based on Labview was designed to implement the functions such as spectrum analysis, bandpass filtering and mean processing. Through the experiments and analysis, the measurement stability of two methods was compared. The experimental results show that the fluctuation of measurement results decreases from 7 μm to 2.6 μm, The effectiveness of laser modulation was verified, which can reduce the noise effectively by filtering and improve the measurement accuracy within 3 μm.
Study on axial thermal disturbance imaging in vision measurement
Wu Jun, Wang Zhijun, Xu Haitao, Yu Zhijing, Xing Shujian
2018, 39(2): 235-239. doi: 10.5768/JAO201839.0203005
In order to study the image distortion and blurring caused by the heat source interference, the level of distortion, blurring and total similarity for the heat source axial displacement imaging were evaluated through using the feature points' average distortion displacement, peak signal to noise ratio, mean squared error and cross correlation coefficient. Furthermore, the correlative discipline between thermal disturbance imaging changes and heat source axial position was gained. Experiment shows that for the heat source axially moving between imaging system and imaging target, the level of distortion, blurring and imaging fault will be worse as the heat source comes closer to the imaging system, and the maximum average distortion displacement is 2.765 3 mm at D=300 mm; as the heat source comes closer to the imaging target, the level of distortion, blurring and imaging fault will be better, and the average distortion displacement decreases to 0.810 2 mm at D=0 mm.
Optical Element and Fabrication
Error analysis on measuring system of vertical target with single-linear array CCD camera and dual-laser
Dong Tao, Du Wangqiang, Li Hai
2018, 39(2): 240-245. doi: 10.5768/JAO201839.0205001
In order to improve the measuring accuracy of single-linear array CCD camera and dual-laser vertical target system, theoretical and experimental basis is provided for the system design. Theoretical analysis is carried out on the measuring error and the system measuring error formula is derived based on the establishment of system's mathematic model. Measurement error is simulated by Matlab software. The influence of error factors on measurement error of target coordinates is obtained, and error distribution in 1 m×1 m target surface is obtained. Error analysis is carried out by simulating the live ammunition experiment. Experimental results show that standard deviation σx and σy for measuring error of the x-coordinate and y-coorcinate are 4.1 mm and 10.2 mm respectively, and the error of the simulated live ammunition coordinate is consistent with the theoretical analysis.
Modified long-range surface plasmon wave sensor based on planar waveguide excitation
Liu Jin, Yang Haima
2018, 39(2): 246-251. doi: 10.5768/JAO201839.0205002
Sensitivity of the waveguide surface plasmon resonance sensor based on intensity detection method should be improved. Modified long range surface plasmon wave, which is excited by the planar waveguide in the dielectric film-metal film-testing dielectric structure, is studied.Method of ion exchange is used to prepare the planar waveguide whose refractive index can be fitted by the FERMI function.Influences of ion exchange time on the modulus and equivalence refractive index are studied, thus the effective basis for the optimization design of the waveguide is provided. An asymmetry structure of dielectric film-metal film-testing film is excited by planar waveguide, and influences of metal material, the thickness of dielectric film and metal film on the characteristic of long range surface plasmon wave are researched.Experiments are realized to detect the refractive index of solutions.Results show that sensitivity of this method is about 6 times that of traditional surface plasmon resonance sensor's, and has a good linear relationship.
Precise axis centering calibration technology for optical lens
Guan Wei, Wang Zhangli, Wang Zhongqiang, Yang Haicheng
2018, 39(2): 252-256. doi: 10.5768/JAO201839.0205003
At present, with the structural complexity and performance requirements of military optical lenses increasing, the defects of great errors and inconsistency in the conventional adjustment methods become more and more obvious. Therefore, a precise axis centering calibration technology for optical lens was proposed, in order to providing support for advanced optical systems. First of all, the error sources affecting the quality of optical lens were analyzed. Second, the manufacturing chain principle with data feedback closed-loop was proposed, and the entire optical system development links were combined together into a closed loop. Then, aiming at the shortcomings of the existing adjustment methods, a precise calibration method of lens group axis taken centering process as the core was put forward through ensuring both the center deviation and the optical spacing. Its optical-mechanical axis consistency reaches the second level and the dimensional accuracy reaches the micron level. Finally, a set of optical lens was designed and developed using this technique. Compared with the traditional lens, the focal length error increases from 1% to 0.1% and the resolution from 2.3" to 2.04".
Design of optical system of wide angle infrared earth sensor and study on distortion correction
Zhou Hao, Deng Loulou, Lyu Zhengxin, Tian Xinling, Zuo Fuchang, Wang Weihua, Li Liansheng, Gai Fangqin
2018, 39(2): 257-261. doi: 10.5768/JAO201839.0206001
In order to meet the requirements of low orbit spacecraft guidance, navigation and control (GNC) system for light small infrared earth sensor, the design on wide angle long-waveband infrared (LWIR) optical system and its distortion correction were studied. The wide angle LWIR optical system consists of 3 germanium lenses, using the form of retro-focus imaging, its full field of view could be 140°. The operating wavelength range is 14μm~16.25μm, and F number is 0.8. The optical system is characterized by small volume, simple structure and high image quality, the miniaturization and high-precision design of the infrared globe sensor optical system can be realized. Different distortion correction formulas were established for different field ranges, and the correction error is less than 1/5 pixel size. The distortion correction method can meet the requirement for attitude measurement of sensor products.
Stray light analysis on infrared channel of dual-band imaging system
Wang Weili, Lyu Yong, Li Xiaoying, Niu Chunhui
2018, 39(2): 262-267. doi: 10.5768/JAO201839.0206002
To analyze the effect of stray light on infrared imaging system comprehensively, a common aperture imaging optical system was designed for both visible band(0.4 μm~0.7 μm) and infrared band(3 μm~5 μm) while the field of view is 2.27°×2.27°. By analyzing the stray light source, the effect of in-band stray light and off-band stray light on imaging quality of infrared channel was studied respectively. The structure of the hybrid light was designed for in-band stray light and the suppression capability was simulated and analyzed by FRED optical software. According to the result, the in-band stray light can be suppressed well, the ghost impact is negligible, and the point sources transmittance (PST) of solar stray light suppression level reaches the set threshold level of 10-8. For off-band stray light, the influence of 1.064 μm and 2.6 μm infrared laser on infrared imaging system was mainly studied by finite element method. Results show that the in-band infrared radiation can be generated strong when the temperature of system mirror rises to 703 K and the radiation power to the image plane reaches 0.069 mW, which can cause strong noise interference on the infrared imaging surface.
Research on de-orbiting characteristic of small scale space debris removal using space-based laser
Yang Liwei, Wen Quan, Zhao Shanghong, Fang Yingwu, Wang Yi, Zhang Jian, Guo Wenjuan
2018, 39(2): 268-273. doi: 10.5768/JAO201839.0207001
The models of the spinning and non-spinning space debris were established, the velocity variation of the space debris ablating by space-based laser was analyzed, and the orbit maneuver of the space debris irradiating by laser was modeled and investigated. The variations of the perigee and apogee altitudes in different locations of the space debris orbit under the irradiation of high-energy pulse laser were simulated and analyzed, and the debris removal efficiency by using laser in different irradiation angles was analyzed relatively. The simulation results show that, there is an optimal action area of removal of space debris using space-based laser. The initial true anomaly of debris for most effective de-orbiting effect is around 120° and 240°. The angle of laser irradiating debris has a great influence on removal efficiency. The removal efficiency of laser irradiating debris in different angles has the symmetry relative to the elliptical axis of debris orbit.
LD pumped folded electro-optic Q-switched laser
Yan Xuejing, Pang Yu, Ye Yidong, Jiang Jianfeng, Sun Shujuan, Zhang Xuguang, Ruan Xu
2018, 39(2): 274-278. doi: 10.5768/JAO201839.0207002
Aiming at the applying demand of airborne laser ranging and laser indication, a compact and reliable electro-optical Q-switched laser was designed.Based on the rate equation with Q-switched, the relationship that the laser output energy increased with the increasing optimization parameter z and the pulse width decreases with increasing z was analyzed. The Nd:YAG laser crystal of ø6.5mm×56 mm, LD side pump, u model of folded cavity which applied cube-corner prism for folding the light, was used as the resonator cavity. The anti-misalignment ability of resonator cavity can be improved under the premise of gain satisfaction. Under the condition of 1.2 J implanted electrical pulse, the energy output of laser single pulse is 108 mJ, the pulse width is 11.8 ns, the energy instability is less than 0.8% and the light efficiency is 18%, which can be stably operated for a long time.
Pulse lasers based on WS2 saturable absorber
Yao Jie, Wang Yonggang, Li Yongfang
2018, 39(2): 279-283. doi: 10.5768/JAO201839.0207003
Based on the saturable absorption characteristics of WS2, passively Q-switching and passively Q-switched mode locking operations of a side-pumped Nd:YAG solid-state laser were experimentally demonstrated in a self-designed Z-type four-mirror cavity structure. The Q-switching operation started under the pump current of 9.5 A and turned into a stable operation under more than 9.8 A. When the pump current was 12.8 A, the maximum average output power was 466 mW, the narrowest pulse width was 3.205 μs, the repetition frequency was 71.70 KHz, corresponding to the maximum pulse energy of 6.5 μJ.When the pump current was 13.4 A, a passively Q-switched mode locking operation was obtained. The maximum output power of passively Q-switched mode locking was 590 mW, the repetition rate of Q-switched pulse was 71.98 KHz, and the corresponding repetition rate of pulse train under single Q-switched pulse envelope was 123.1 MHz, and each Q-switched envelope contained 369 pulses with the single pulse energy of 22.2 n.The results show that the WS2 material can act as the absorber for solid-state lasers.
Design of optical fiber transmission system for high speed Cameralink video signal
Wu Qi, Xue Haidong, Liu Zhaoqing, Yin Hongbo, Yin Hailin, Yang Dong
2018, 39(2): 284-289. doi: 10.5768/JAO201839.0208001
Aiming at the problem that the system structure of optical fiber transmission scheme of commonly used Cameralink video signal is too complicated, an optical fiber transmission scheme of the Cameralink video signal based on MAX9249 / MAX9268 was proposed.At the transmitting end, the Cameralink video signal was deserialized, encoded and serialized by using MAX9249 to obtain the optical module driving signal CML. At the receiving end, the CML signal was deserialized, decoded and serialized by using MAX9268 to obtain the Cameralink video signal, and the design and selection of optical transceiver module were detailed described.Finally, the oscilloscope was used to capture the eye diagrams of high-speed serial signals at transmitting end and receiving end. The eye diagrams of high-speed serial signals at transmitting end and receiving end are relatively clear and the eye opening degree is large. The Q factor at the transmitting end is 24.46, meeting the requirement of greater than 12 at transmitting end, while it is 8.13 at the receiving end, meeting the requirement of greater than 6. In addition, the real-time pictures acquired by the computer acquisition end has no obvious visible pixel noises after 10 minutes transmission, which proves the feasibility and effectiveness of the transmission scheme.
Research on backscatter noise suppression for resonator fiber optic gyro
Lan Shiqi, Lei Xing, Wang Ke, Hu Qiang, Han Zonghu
2018, 39(2): 290-294. doi: 10.5768/JAO201839.0208002
Backscatter noise is one of the main noises in resonator fiber optic gyro(RFOG). Based on the principle for reducing the backscatter noise by carrier suppression method, the mathematical model was established for the influence of temperature and voltage on the gyro bias. It is theoretically proved that this method is largely affected by temperature and has higher circuit requirements. A new scheme of RFOG based on three-mode differential technology was put forward. In this scheme, the backscatter noise is decreased by operating three beams with large frequency intervals in the resonant cavity. A comparative experiment was conducted with traditional two-mode closed-loop gyro. The results show that the new scheme can effectively minimize the gyro noise, and both the maximum gyro bias and bias stability are improved by around 4 times.
Monitoring and experimental analysis of distributed optical fiber pipeline leakage based on wavelet packet energy spectrum
Zhao Ya, Wang Qiang, Zhai Yongjun, Hu Dong, Ding Wuji, Liao Xiaoling
2018, 39(2): 295-300. doi: 10.5768/JAO201839.0208003
Based on the principle of Mach-Zehnder and Sagnac hybrid interferometer, the simulated experiment of urban gas pipeline leakage monitoring was carried out using distributed optical fiber sensor. Firstly, the method of wavelet packet energy spectrum extraction and the absolute distance method were combined to process the interference signals caused by pipeline leakage when measuring optic fiber length are 4 km and 6 km. Then the gas pipeline leakage was located according with the frequency spectrograms. Finally, the false alarm rate(FAR) of the distributed optical fiber system was analyzed.The results show that the FAR of proposed method reduces by 8.475%, compared with the traditional zero frequency spectrum localization method, it can more accurately identify the gas pipeline leak or not, thereby enhancing the reliability of system monitoring and positioning.