2013 Vol. 42, No. 10
2013, 42(10): 2599-2602.
The tracking convergent property is an important guideline for a reticle seeker. The tracking of the reticle seeker is driven by the period mean torque which is generated by the tracking signal. In this paper, the convergent property of the reticle seeker was analyzed and some significant conclusions were attained using series theory. The convergence of the tracking procession was affected by both the tracking coefficient and the phase bias between the target location and the tracking signal. The convergent conditions and the convergent step function were also obtained. These conclusions are important for the design of the convergent tracking algorithm of the reticle seeker.
2013, 42(10): 2603-2607.
Infrared imaging guidance weapon countermeasure was the important fields of opto-electronic countermeasures. The detector of IR imaging seeker was replaced by image emulation and injection computer in the hardware-in-the-loop simulation test of digital image injection, it was necessary to consider the equivalence of control capability for the servo system under the simulation test and actual conditions by means of building the accurate transfer function of servo system for the IR imaging seeker. Based on this, the entire servo system of the seeker was divided into seven different function module according to the configuration of the seeker, and the total design method about the modeling of the servo system was proposed. Then the integrated mathematic model of the servo system was set up by adopting the mechanism modeling combined with the experimental test method. Light axis of the seeker remained in a state of stabilization with 5 amplitude and 2 Hz disturbing of bomb. Line of sight and line of sight velocity between target and bomb of simulation output could precisely track the actual line of sight and line of sight velocity by testing the model. Simulation analysis validates the correctness of the model of the servo control system. The results of research provide theoretical method support for the modeling of the servo control system for the same type device, and also give the model for the feasibility of the new digital image injection simulation test on the infrared imaging guidance weapon.
2013, 42(10): 2608-2613.
According to the problem of the terminal guidance with a strapdown seeker, the main reason of the disturbance rejection rate was analyzed. The proportional navigation guidance system (PNGs) with the disturbance rejection rate parasitical loop(DRRPL) was established, the uniformly asymptotical stability of PNGs was put forward based on Lyapunov stability theory for the time varying system, restrictions of stabilizing PNGs were analyzed with the passivity approach, and the effect of the disturbance rejection rate on the stability of PNGs was studied. The results show that the uniformly asymptotical stability of PNGs is stricter to realize than DRRPL, while the disturbance rejection rate caused by the imperfect decoupling is uncertain, and the positive feedback of DRRPL is more likely to make PNGs unstable in advance and cause a larger miss distance.
2013, 42(10): 2614-2619.
Focusing on the adaptability testing of IR seeker in complicated battlefield environment, a new closed-loop simulation test method of using digital image injection was proposed, the composing and principle of closed-loop simulation test system were analyzed. The detector of IR seeker was replaced by image simulation computer and injection device in the simulation condition, thus the performance of servo system was likely to differ from that under the actual conditions due to the image generation delay and miss distance error, which affected the precision and reliability of simulation test result. The influence of time delay and miss distance error on seeker's servo system by building servo system model was studied. The research result indicates that the influence of miss distance error on track precision is only 1.33%, the closed-loop simulation is feasible if time delay is less than 56.5 ms. The results of research provide theoretical support for actualizing closed-loop injection simulation test of IR imaging seeker.
2013, 42(10): 2620-2624.
The traditional infrared focal plane adaptive correction algorithm has target degradation problem and its convergence time is too long. Aiming at this problem, infrared focal plane adaptive non-uniformity correction algorithm based on bilateral filter histogram equalization was proposed. By analyzing infrared focal plane response characteristics, a statistical model of the infrared focal plane array response was created. According to the model, a single pixel time-domain statistical histogram was calculated firstly, then bilateral filter was fused to get the mean of the neighborhood histogram, and non-uniformity correction was completed using the mean histogram equalization. According to the practical application, this algorithm has the advantage of the strong ability to eliminate the image degradation, fast convergence speed and high precision.
2013, 42(10): 2625-2629.
The ability to search in accordance with standard graphics is one of the key capabilities of IR seeker, which can make up small filed of view and improve the ability of target acquisition. For roll-pitch infrared platform, the searching graphic distortion was analyzed by using the common method that the two orthogonal axes scan in turn. The standard mouth searching was carried out by a new proposed segmented scan method, which a recursively solving spherical arc line constraint equation based on quaternion was used. This segmented method was constrained less and the algorithm was small amount of calculation. It was a more efficient solution to solve the approximation search problem. A virtual simulation system was built using the MATLAB ToolBox and the validity of the segmented scanning method was also proved. This method can not only implement the standard mouth searching pattern at any position in the front hemisphere scene, but also be used for any arbitrary shape search pattern for the analogous seeker.
2013, 42(10): 2630-2635.
A four-spectral infrared radiometer, which can automatically measure the temperature of sea surface, was designed to calibration and test the satellite on ground. The electronics system of the infrared radiometer was designed in detail using the spectral modulation, the wave length of 3.5-4 m, 8-13 m, 10.3-11.3 m, 11.5-12.3 m infrared band was used to acquire and process the data. The temperature of the sea surface was computed by double blackbody standard source real-time automatic correction system parameters and corresponding algorithm. The designed infrared system could also display the temperature and save the data synchronously on PC. In addition, the requirement of sampling precision of 0.1K was guaranteed by the design of A/D sampling. Finally, by analying the data acquired in south China sea, the measure precision of the system was verified in 0.5 K, which can satisfy the technical requirement.
2013, 42(10): 2636-2641.
In this paper, a new method was presented for spatiotemporal segmentation of moving-object using boundary evaluation in infrared video. At first, the ideal seeds of every moving object were extracted based on the holes effect of temporal difference, respectively. The wok focus was spatial segmentation. On the basis of the relationship between the global and local standard deviation of seeds, the segmented masks could be grown form the ideal seeds by using different growing thresholds. For determination of the best growing threshold, a criterion was constructed for evaluating the boundary of the segmented mask of infrared moving-object without prior knowledge. According to the proposed criterion, an iterative model which was segmentation-evaluation-segmentation-evaluation and the search method called as coarse to fine were applied to find the best growing threshold. Meanwhile the best segmented mask was obtained too. The experiment results show that the proposed method is superior and effective on segmentation of moving object in infrared video.
2013, 42(10): 2724-2731.
Particle swarm optimization (PSO) technique is applied to design a five-lens system.The optical merit function composed of spherical aberrations, an image distance, distortions, field curvatures, comas and light dispersion values, were employed as fitness functions of the particle swarm algorithm. By using this function automatic searching for the optimal design, a simple five-lens system was carried out. Comparisons in terms of spherical aberrations, distortions, field curvatures, comas and light dispersion values were performed between a five-lens system designed with PSO and a five-lens system from ZEBASE. The result shows that spherical aberrations, distortions, meridional field curvatures, sagittal field curvatures, sagittal light dispersion values of a five-lens system designed with PSO are smaller, and meridional light dispersion values, meridional comas, sagittal comas of a five-lens system from ZEBASE are smaller. The example for a five-lens system design using particle swarm algorithm indicates that PSO can overcome the shortcomings of the modern optical design software which highly depends on an initial structure input by the user and can create arbitrarily search ranges of structure parameters, which is an important step towards automatic design with artificial intelligence.
2013, 42(10): 2732-2736.
With the rapid development of precision guidance technology, simultaneous detection of both bands has become very important, the demand of the corresponding optical system and its design increase rapidly. According to the harmonic diffraction element with the characteristic of achromatism, athermalization, same focus on each low diffractive level and high diffractive efficiency, using the CODEV optical design program, a coaxial dual-band IR optical system was designed that worked at-45~ +71℃ in the existing processing conditions of diamond cutting. The modulation transfer function(MTF) approached to the diffraction limit in the whole range of temperature and no need to focus, there was no vignetting in optical system and the efficiency of cold shield reached 100%. The dual band infrared optical system has the advantages of compact structure, fewer elements and high transmittance, it is a qualitative leap for improving detection accuracy and recognition ability of the seeker.
2013, 42(10): 2737-2741.
Subsurface damage (SSD) of optical material is a focal point of research in laser optical field. The existence of SSD of substrates would change the properties of thin film, and the influence of the surface damage in substrates is essential to ansider during the design, manufacture of high precision low loss laser antireflection coating. Physical properties of SSD were studied. And the physical thickness and refractive index gradient of SSD could be retrieved by the spectroscopic ellipsometry of substrate surface. Then the effect of them on reflection spectrum of antireflection coating was obtained by calculation. The depth of SSD affects the reflection spectrum periodically. At last, with depth and gradient of SSD taken into account, the design of laser antireflection coating was revised theoretically, and the numerical experiment shows that the design is possible to realize zero-reflection at 633 nm.
2013, 42(10): 2742-2747.
For advanced 640 512 cooled staring focal plane array (FPA) detector, a mechanical compensation continuous zoom optical system with greater than 30zoom range was presented based on the requirements of infrared thermal imager. The zoom system provided continuous changed in the field of view from the narrow field of view to the wide field of view. The largest constraint that used to exist developed a strategy that would allow the zoom focus to be continuous. The large zoom range created the condition of the zoom groups moving through the 1magnification case. Discontinuities about this 1magnification point was well documented in the paper. The spectral band of the system was 3.7-4.8 m, and F number was 4.0. It realized 15-550 mm continuous zoom with a smooth zoom path and provided high image quality within the whole zoom range. Moreover, detailed design and image quality were given by CODE V optical design software. By the virtue of secondary imaging structure and tow reflectors, it has 100% cold shield efficiency and can reduce the transverse and radial size of system. The design results prove that the zoom system has high resolution, large zoom range, small size and excellent image quality and has also been found to be capable of accommodating advanced infrared thermal imager.
2013, 42(10): 2748-2752.
The fast steering mirror (FSM) was widely used in beam stabilization controlling systems. In order to ensure the FSM work more stably and precisely, the transfer function model of the FSM was deduced using giant magnetostrictive material as the displacement generator based on the material's physical properties and the dynamic characteristics of the FSM. With the actual measured result of the FSM's amplitude frequency response characteristics and phase frequency response characteristics, the accurate transfer function of the FSM was identified using the levy identification algorithm in the matlab software. Compared with the actual measured result, we concluded that the error of the transfer function obtained by identification is under 0.5 dB in magnitude and 5 in phase in the low and intermediate frequency range. The result shows that the transfer function model deduced is reasonable and supplied theoretic reference of how to improve FSM's performance in its application system.
2013, 42(10): 2753-2759.
The primary mirror handing device with 12 axial supporting bars was designed in this paper, according to the structure and material characteristic of 4m SiC primary mirror. Firstly, it was determined that the handing device consisted of main body frame, axial supports, radial supports and upper compaction. Secondly, with method of finite element model building, analysis and optimization, the design of main body frame, the optimization of application area of force and projected dimension were studied. Thirdly, the mirror deformation plot and stress state and the primary mirror supported by 3 points and tilted caused by the installation error were analyzed. Finally, the final project of handing device was determined, and it was machined, assembled and applied according to the results of the analysis and optimization. The analysis result and practical application indicate that the design requirement of the handing device is achieved, and the direction for similar structure is provided here.
2013, 42(10): 2760-2764.
To achieve LED digital projectors project in a short distance with the bigger picture projection, according to the structural characteristics of such projectors, a short focal digital projection lens for 0.7 inch DLP projectors was designed and a design example of a lens, whose operating wavelength was 462-625 nm,full field of view angle was 84, relative aperture was 1:2.4, focal length was 10 mm and back focal length was greater than 20 mm was given on the basis of the theoretical calculation and the optimization of optical design software ZEMAX. Its MTF in all fields less than 30 is higher than 0.5 at the limiting spatial frequency of 40 lp/mm. The absolute value of the full field of view distortion of the lens was less than 1.5% ,the image quality is very good. Analytical results show that the design can decrease the production costs of the projecting system and promote the technological industrialization.
2013, 42(10): 2765-2771.
Concatenated space-time code is one of the efficient encoding that can improve the error correction capability and approaching the Shannon limit. The performance will be greatly enhanced when channel coding and space-time coding combination used, thus the concatenated space-time code becomes one of the important direction in space-time coding research. In this paper, the RS code and LDPC code concatenate scheme with space-time code were introduced, and the bit error rate characteristics under different atmospheric turbulence condition were analyzed. The results show that the concatenated spacetime code can significantly improve the performance of the MIMO system, inhibit atmospheric turbulence effects, conducive to obtain coding gain and further more improve the system BER performance.
2013, 42(10): 2772-2777.
Chaotic sequence, which is more secure and diverse in form, can be used as spreading code in spread spectrum systems. A new random sequence for spectrum spreading was introduced by piecewise conjugate augment of Skew Tent map into a new construction method which could greatly improve the weak chaotic property of traditional Skew Tent map random sequence, especially in the aspects of randomness and correlation. Simulation results show the new map construction method has better sequence chaotic property and achieved lower BER (Bit Error Rate) than traditional one. Improved piecewise Skew Tent map, as the encryption algorithm for image communication system, has improved the quality and safety of the image information effectively. Piecewise conjugate augment of Chaos Map which can improve the weak chaotic property, is an effective construction method, and the better chaotic property Chaos Map will broaden the application of spreading communication in military and civil field.
2013, 42(10): 2778-2783.
Based on a power spectrum of non-Kolmogorov turbulence developed by A S Gurvich et al, the variance of angle-of-arrival (AOA) fluctuations was derived. The concise closed-form expression was obtained and used to analyze the joint influence of Kolmogorov tropospheric turbulence and non-Kolmogorov stratospheric one on the fluctuations in the angle of arrival (AOA) of starlight. It is shown that the AOA fluctuations of starlight were mainly determined by Kolmogorov tropospheric turbulence. And the non-Kolmogorov stratospheric turbulence was responsible for 5-14 percent of the total of AOA fluctuations for different receiver apertures in weak fluctuations regime. In addition, the AOA fluctuations induced by non-Kolmogorov turbulence depended on the receiver aperture and the outer scale and the intensity of non-Kolmogorov turbulence.
2013, 42(10): 2784-2789.
Demodulation system is the core sensing technology of optical fiber Bragg grating (FBG). De-noising and seeking the peak wavelength are the two important factors that influence the demodulation accuracy. In order to obtain the precise wavelength drift, aiming at the defects of the traditional demodulation methods, a new wavelength detection scheme for optical fiber Bragg grating (FBG) was put forward, which was composed of an improved de-noising method and the Gaussian fitting peak searching algorithm. The translation invariant wavelet combined with the new threshold value and the proposed new threshold function method to deal with noisy FBG sensor signal; then the Gaussian fitting peak searching algorithm was adopted to find the peak wavelength of the de-noised signal for further analysis. The experiment result shows that the improved invariant wavelet can deal with noisy FBG sensor signal with different SNR and get a higher SNR value and a lower mean square error value than the other wavelet de-noising methods mentioned; this kind of wavelength detection technique can get the measurement maximum peak error of less than 1 pm, which means a much higher accuracy than general wavelength detection methods.
2013, 42(10): 2790-2795.
Fast-steering mirrors is the core component of fine tracking system in the electro-optical tracking system. In order to meet the requirements of electro-optical tracking system, the fast-steering mirrors close-loop control system must has high disturbance rejection ability, fast tracking ability and high tracking accuracy. A fourth-order model structure by the approach of theoretical modeling and the needed third-order model structure by the approach of experimental modeling were obtained. After confirming the needed third-order model, an ideal third-order model was chosen which responses fast and precisely to be a reference model in the adaptive control algorithm. For simulating interference, two sinusoidal signals were put in front of the FSM. A large number of simulations explained that, interference could be suppressed efficiently by use of the adaptive control algorithm, and that the third-order reference model could be followed precisely. Since the reference model responses fast and precisely, the FSM control system based on the adaptive control algorithm has the ability of responsing fast and precisely.
2013, 42(10): 2796-2799,2852.
Terahertz (THz) technology has attracted a great deal of interest for its unique features and potential applications in many areas. Along with the increasing demand of high bit rate for wireless data transmission and the improvement of material growth and device fabrication, THz communication has become one of the most important fields in the development of future high speed wireless communication systems. The characteristics and the state of the art in THz wireless communication were introduced in this paper. A digital communication link based on terahertz quantum cascade laser (THz QCL) and terahertz quantum well photodetector (THz QWP) was demonstrated. Using direct On-Off-Key (OOK) modulation and direct detection, a pseudorandom non-return-to-zero (NRZ) signal with a bit rate of 1 Mbps was transmitted through the link. The carrier frequency was 3.9 THz, and the link distance was 2.2 m. The limitation and potentiality of the transmission speed for such a system was discussed.
2013, 42(10): 2800-2804.
Accurate measurement of the vertex radius of off-axis aspheric mirrors is the key to guarantee the assembly and adjustment quality. During the tests of off-axis aspheric mirrors, the influence of coordinates deviation was analyzed in order to improve the precision of fitted results. A fitting model with the corresponding processing method was proposed so that the impact of coordinates deviation could be eliminated. Besides, the parameter fitting procedures were also presented. Compared with the classical direct fitting, presented method can achieve smaller Sum of Square Error and Root of Mean Squared Error while the coefficient of determination is much closer to 1. The experiment verifies the the proposed method's validity. Furthermore, this method is available to coordinates deviation analysis and parameter fitting process in all off-axis aspheric mirror tests.
2013, 42(10): 2805-2811.
A paths planning algorithm was proposed to solve the problem of dual-aircraft cooperative tracking and locating a maneuvering target with bearings-only measurements (BOMs) in 3-dimension situation. Its purpose was to improve the passive target tracking and localization performances. After the passive tracking extended Kalman filter(EKF) was set up, the mutual information metric function and the covariance control metric function were given. The target position geometrical dilution of precision (GDOP) was deduced by introducing the vector theory. Details of the paths' planning algorithm were put forward. Computer simulation studies indicate that the EKF-based method has a worse performance when the target has maneuvers. The GDOP-based method has a good adaptation to the maneuvering target.
2013, 42(10): 2812-2816.
For the shortcomings of the traditional flat glass thickness measurement, one method which was based on the principle of light refraction, with the dual laser symmetrical transmission method was proposed, and the whole measured system of on-line measurement of flat glass thickness was designed, in which line laser was the light source and the symmetry plane of mirrors were the optical path switching device to modulate the symmetrically distributed optical paths into two parallel line lasers, and a linear array CCD sensor was set as a visual exploration tool, meanwhile, the grey level of the transition area of the background and target was selected as the boundary threshold value of the single beam line's light band image according to the characteristics of captured image, the algorithm for obtaining light band center pixel was made modified gray gravity. After the experiment of the measurement on the sample glass thickness, the results show that the accuracy of these measurement methods can reach to 0.1 mm. The measuring accuracy is correspond with the requirements of the testing standards. Therefore the feasibility is verified, that have a good practical value.
2013, 42(10): 2817-2821.
Sea-sky-line is important reference information for long-range ship detection. At present, the sea-sky-line detection algorithms, such as liner fitting algorithm, weighted information entropy and Hough line detection methods all need large amount of computation to detect the sea-sky-line. A novel sea-sky-line detection method based on Seam Carving was first proposed in this article. Firstly, the gradient amplitude image was calculated, and then dynamic programming searching for the highest energy line was used to extract the sea-sky-line. The experimental results show that the proposed algorithm have the characteristics of high detection accuracy, wide range of applications, low computational complexity and strong real-time.
2013, 42(10): 2822-2827.
In order to realize the ground calibration tests of star sensors, a ground calibration system of large field of view and high angular distance between stars' simulation accuracy was designed, the composition of calibration system, optical system design and simulation precision were studied. According star sensors ground calibration requirements the system components was introduced, a method to realize the angular distance between stars' simulation precision better than that of 20 was put forward. Using the new display LCOS as star chart display, the image plane field by splicing methods was expanded, and Zemax software was used to design the optical system accordingly. On the basis of the original measuring method, the evaluation method of ground calibration equipment precision was given. And a way was proposed to improve the angular distance between stars' simulation accuracy by the method of star correction. The experimental results show that the star sensor ground calibration equipment of the angular distance between stars'simulation precision is less than 20, meet the star sensor for ground calibration test requirements.
2013, 42(10): 2828-2835.
Feature point tracking is an important technology to implement the visual odometry for navigation. Aiming at the problem of feature tracking with big errors caused by large motion of the video fixed on UAV, a multi-constraint KLT tracking strategy based on time-reversibility and bi-directional displacement constraint was proposed and the pyramid model was used for the hierarchical displacement computation of the tracking points. The new objective function was set up according to the fusion of forward and backward tracking. A new bi-directional displacement was constructed based on the displacements of forward and backward tracking, and the optimal estimation of the displacements was implemented in the structure of pyramid model. The experiment results demonstrate that the proposed algorithm improves the performance of precise tracking effectively and outperforms the similar tracker.
2013, 42(10): 2836-2841.
In order to achieve high-accuracy measurement of the long focal length, a method of measuring long focal length based on Talbot-Moireffect was studied in this paper, a long focal length test device was established, it included a collimated wavefront generator, a Talbot interferometer and a imaging system. The effect of wavefront aberration on accuracy of focal length was analyzed. Then the distance s from the sample to the grating G1, the space d between grating G1 and grating G2,and angle of two grating lines as influencing factors on accuracy of focal length were analysed. The alignment method to improve the accuracy was proposed. Pentaprism method for the detection of wavefront was introduced, to ensure that the collimated wavefront quality better than a wavelength. The linear grating encoder was used to measure s and calibrate d, to make the accuracy of the distance better than 0.1 mm. A reference reflective concave sphere was used for angle calibration, to make the accuracy of angle better than 0.001. The experimental results show that the relative error is less than 0.35% when measured focal length is 5436mm.
2013, 42(10): 2842-2845.
The uniformity of optical thin films has become quite vital because large diameter optical devices are used widely. In this paper, according to the basic theory of photothermal detuning technique, with Visual Basic 6.0 to write control program, the experiment system for measuring the absorption uniformity of optical films was designed and built for the first time. Absorptions at the different points on the sample surface were measured, and the surface absorption image of the sample was made. The result shows that the designed experimental system which is stable and accurate can be used to absorption uniformity measurement of optical thin films, and the automated measurement in the whole system is achieved. The designed system which provides experimental foundation for the advancing application of the photothermal detuning technique is feasible.
2013, 42(10): 2846-2852.
By analyzing the major image registration techniques at present, a new image registration method based on image entropy on account of the distribution issue of feature point and the registration of corresponding points was introduced. First, the image was divided into blocks to a certain extent and the image entropy of each block, which reflected the texture transformation within the block, was computed according to the information theory. The rough-match was then made on the basis of the computed image entropy. After that, a certain number of feather points were extracted from each block. The more information content the block had, the more abundant the texture became and so the larger extraction number we got. The precise match was made with these typical corresponding points. To demonstrate the validity of the proposed method, the improved image registration technique was compared to conventional methods on same images.
2013, 42(10): 2853-2857,2870.
D-S evidence theory cannot combine highly conflict evidence and brings counterintuitive results. In order to solve this issue, a new conflict evidence combination approach was proposed from clustering analysis. Firstly, cosine similarity space in which evidence was regarded as space vecter was built up, and cosine between evidence vectors was calculated to define conflict evidence detection coefficient. Based on the space and coefficient, conflict evidence criterion was presented to judge the conflict evidence, and the evidence was classified into similar evidence and conflict evidecne. Secondly, conflict proportion coefficient was introduced to decide the modified method in which conflict evidence was modified by use of the absolute similarity and all the evidence was modified by use of the relative similarity. Finally, the modified evidence was put into D-S combination formula to combine. Application examples prove that this new method can judge conflict evidence and combine them effectively, and processes good classification precision, convergence speed and stability.
2013, 42(10): 2858-2864.
In order to determine the stability of the NAND Flash image recorder and the peak recording speed, reducing the amount of manual testing, a new load test system was designed. To solve the problem of stability test, speed load model based on exponential regression and test time control model based on the lognormal distribution were proposed. To test the peak recording speed, the test methods combining hardware with software based on climbing search algorithm and speed dichotomy was praser. The hardware data generator was designed, whose speed was software adjustable according to valid data duty cycle mechanism. Climbing search algorithm rough determined the peak recording speed range, and then the speed dichotomy approached the peak recording speed; the test report was transferred to PC for display through the serial port and Gigabit Ethernet. Experimental results show that the speed load regulation accuracy is up to 0.1MB/s; the speed load range is from 0 to 1 600 MB/s; verification of read back data using hardware has no clock delay; the tested NAND Flash recorder connecting with 8 SLC NAND Flash chips has the peak recording speed of 240.12 MB/s; under the speed load 200 MB/s, the NAND Flash record controller can work well continuously for more than 24 h. The load test system can be used for load test of other transmission and recording system because of its universal architecture.
2013, 42(10): 2865-2870.
Terahertz waves can be used as a tool of non-destruction detection and imaging for certain kinds of materials because of unique characteristics. Improvement of imaging quality is of great significance to the application of terahertz imaging system. Digital image processing is a very important solution to the enhancement of imaging quality. Based on terahertz transmission imaging experiments, investigation was made on the use of image de-noising and enhancement techniques in order to suppress the influence of experimental noise of the imaging system and ultra-short laser power jitter. The methods included spatial domain filtering, Gaussian smoothing, frequency-domain filtering and edge detection. Analysis on the choice of methods and the comparison of effects was also given. Results show that, through an integrated use of image de-noising and enhancement techniques, the definition and identifiability of terahertz images are improved enormously.
2013, 42(10): 2642-2645,2650.
Based on the theoretical model of photocarrier radiometry (PCR) testing solar cells, numerical simulation analysis was proceeded to study the influence of different circuit states in frequency domain response signal, and amplitude response curves were achieved with different external load resistors. Experiments were carried out with built set-up for photocarrier radiometry diagnostic approach for Si solar cells. The feature of amplitude diagram and phase diagram were stated. The effect of different circuit states on test results was discussed. At last the fitting life time was compared in different circuit states to study whether circuit states affect the carrier parameter measurement. The results shows that open circuit state gives the highest amplitude in amplitude diagram, and the smaller the load resistance is, the lower amplitude becomes. However, phase didn't change clearly. The fitting life time is nearly consistent, not changed with circuit states, which shows the results of PCR testing solar cells in open circuit states can forecast frequency domain response results and carrier parameters fitting calculation in other circuit states.
2013, 42(10): 2646-2650.
Multi-beam combining is an effective method for improving the power and far-field beam uniformity of pulsed laser diode. It can also increase the imaging range, and the laser active imaging system can be miniaturized. First, the combining beams distribution was derivated using Exponent-Gaussian model. Then the influence of some parameters such as the angle of the laser diodes away from horizontal line, the spacing between laser diodes and the lasing delay times were simulated with Matlab. Finally, the range-gated imaging beyond 1.5 km was obtained. It can be concluded that multi-beam combining can improve the performance of the range-gated imaging by comparing the imaging of different numbers of the laser diode.
2013, 42(10): 2651-2657.
NiCrBSi+TiC composite coating was fabricated by mechanical vibration assisted laser remelting hybrid modification process on 45 steel substrate surface. The morphology, microstructure and phase constitution of the composite coating were characterized by scanning electron microscopy (SEM), energy dispersive spectroscope(EDS) and X-ray diffraction(XRD), respectively. Microhardness distribution of the composite coating was also analyzed. Results indicate that the matrix is changed from dendrites to cellular dendrite. The TiC particles and other reinforced phase shows an increasing trend, the area fraction in the field of view increases by 18.2%. The diffusion of Ti element exhibits a decreasing trend. The crystallization strength and dispersion strengthening are improved due to the influence of the combination of laser rescanning and vibrating force. The microhardness fluctuations trend of the mechanical vibration assisted laser remelting coating slows down in the interface. Mechanical vibration can improve effectively the transverse microhardness fluctuations of the bonding interface zone.
2013, 42(10): 2658-2662.
In the configuration of the fiber laser/amplifier, the characteristics of the fiber pump combiner influence directly on the output power of the laser/amplifier. According the basic structure of the fiber pump combiner, the origin of the loss was analysed, the characteristics of power and temperature in some series of domestic combiner were studied in different conditions. The influence on the working temperature of pump combiner at the factor of the loss of pump energy, the return of pump energy, the ambient temperature and the brightness of pump light was pointed out. Some new type high power combiner was tested and the result demonstrates one input fiber of the combiner can stand up over 100W pump power, which make it possible to create the kilowatt fiber laser based on all-domestic appliances. Some correlative results of this research can provide the reference of the design and the heat management for the fiber combiner.
2013, 42(10): 2663-2668.
In order to obtain HgCdTe crystal thermal damage threshold irradiated by high repetition frequency laser, firstly, irradiation effect experiment was conducted on the Hg0.826Cd0.174Te crystal by high repetition frequency CO2 laser with a pulse width of 300 ns. Then the theoretical model of Hg0.826Cd0.174Tecrystal irradiated by high repetition frequency CO2 laser was developed to calculate thermal damage process of Hg0.826Cd0.174Te crystal. Finally,the impact of irradiation time and repetition frequency on damage threshold was analyzed. The research results show that when the irradiation time is longer than 10s, damage threshold of the crystal does not depend on the irradiation time, and the value is 1.4214103W/cm2. Damage threshold mainly depends on average power density,and doesn't depend on repetition frequency. Damage results of SEM show the crystal damage is thermal damage, and the obvious crack is not found on the surface. The model prediction agrees well with the experiment data, and the conclusions have a reference value for laser application and laser protection on high repetition frequency CO2 laser.
2013, 42(10): 2669-2671.
The transmission characteristics of Gaussian pulses in optical fiber has been solved by analytical solutions, but that of hyperbolic secant pulses emitted by mode-locked laser only depend on numerical methods. In order to study the transmission characteristics of hyperbolic secant pulse with high-power in a single-mode optical fiber, the split-step Fourier method was used to analysis the transmission procedure of the hyperbolic secant pulse in single mode fiber with initial chirp 1.7 rad/s, dispersion length 0.64 m, nonlinear length 1.53m and length 1 m. The results indicate that the dispersion inductive spread of the hyperbolic secant pulse is consistent with the Gauss pulse, but its dispersion inductive frequency chirp is not vary linearly. It will also arouse the spectral oscillation if the input power is too high.
2013, 42(10): 2672-2676.
Analysis of laser damage quadrant detector(QD) for laser guided weapon was presented in this paper. Firstly, the principle of laser damage photoelectrical detectors and QD detection theory were shown, detection bias and normalized detection curve were calculated based on the quadrant detector model. Then, Laser guided bomb trajectory simulated by weapon control model in different laser damage level were studied. Finally, undershoot value of laser guided bomb was discussed in different QD's laser damage distance. The research indicates that QD's laser damage level and damage distance influencing the laser guided weapon, and the result will be helpful for the effect evaluation of blanket jamming to laser guided weapon.
2013, 42(10): 2677-2681.
The target searching method based on the equal energy of water backscattering light in range-gated underwater imaging system was studied. Computing model of water backscattering light energy received by ICCD was built, and the formula of water backscattering light power received by ICCD was deduced in a single imaging. The energy of water backscattering light received by ICCD at any imaging could be equal by controlling the moment and the time of ICCD opening gate. And then, the searching strategy based on the equal energy of water backscattering light could be established, the simulation result of the searching strategy was given. The judgment rule of target existence was given which the signal energy received by ICCD would be enhanced at a certain imaging if the target existed. The simulation result proves the right of the judgment function rule.
2013, 42(10): 2682-2686,2696.
A fuzzy C-means algorithm based on spatial positioning was proposed to do the segmentation for range-gated image, which had the feature of low contrast, uneven illumination, and blurring. Object extraction is essential in image processing, providing the basic and necessary information for other methods. Traditional FCM algorithm needs the number of classes to cluster the data, which limits its adaptability. It also lacks in sensitivity of spatial information, resulting in misclassification as well as incomplete extraction of objects. For the above defects, the traditional algorithm was improved by pre-positioning. Firstly, median filter, Otsu method, and mathematical morphology method were applied to do the initial segmentation, obtaining the centroid and grayscale information of all targets, which took very short time. Then both of the centroid and grayscale information were used in clustering process, accomplishing the classification with fewer iterations and less time consuming than traditional FCM. Experiments indicate that the the Spatial Positioning FCM (SPFCM) is effective in segmentation of range-gated image, the targets can be extracted more completely and faster than traditional FCM algorithm. This new method can be applied to navigation, tracking and surveillance with range-gated imaging system.
2013, 42(10): 2687-2691.
The influence of atmospheric turbulence on aim precision of ground-to-satellite was theoretically investigated in this paper. First of all, the definition of aim precision of ground-to-satellite laser was proposed in the atmospheric turbulence. Secondly, the aim precision of ground-to-satellite laser under the different launch parameters was numerically simulated by solving the parabolic equation of laser atmospheric propagation with multi-phase screen method. The results show that the aim precision of ground-to-satellite laser is proportional to the launch aperture of laser, but inversely proportional to the divergence angle of laser. The power and power density at the satellite's pupil were lastly calculated under the different aim precisions. The research conclusion can provide the theoretical basis and data reference for carrying out the countermeasure experiment of ground-to-satellite.
2013, 42(10): 2692-2696.
The discrete dipole approximation method was used to compute the radiative characteristic parameters including the optical cross-sections, single-scattering albedo and asymmetrical parameter for a variety of mixed agglomerates in different mixing states at a visible wavelength 0.55 m. It is shown that the influence of the mixing states on the asymmetrical parameter is very great, and that on the scattering cross section and single-scattering albedo is heavy, while that on the absorption and extinction cross sections is not obvious. The influence of mixing patterns on the asymmetrical parameter, scattering cross section and single-scattering albedo is becoming more obvious with the increase of the size of agglomerates. The mixture ratios has an obvious effect on the radiative characteristic quantities of agglomerates in internal and external mixing states, and the effect varies with the monomer diameters, and number of monomers in the agglomerates. The scattering cross-sections of external mixture of agglomerates are larger than those of their internally mixed counterparts, but the single-scattering albedo decreases accordingly at the same mixture ratios.
2013, 42(10): 2697-2701.
A novel transversely excited atmospheric (TEA) CO2 laser with high repetition-rate was reported. The size of laser is 300 mm300 mm300 mm. The discharge volume is 12103 mm3, the length of cavity is 310 mm. The ultraviolet preionization makes the discharge even and stable, the output energy can be as high as 15 mJ under the circumstance of free oscillation, and the full width at half maximum of the light pulse is 70 ns.To acquire the high wind velocity, a turbocharger was used in the system of the fast-gas flow cycle. When the pressure in the cavity is 100 kPa, the wind speed is 100 m/s, and the repetition rate of the TEA CO2 laser is up to 1.5 kHz. On the basis of preliminary experiment, the system of the grating tuning line selection can be applied to the high repetition-rate pulse laser to abtain the output of grating line selection accurately and fast.
2013, 42(10): 2702-2706.
The IR/MMW terminal combined guidance missile, such as terminal-sensitive submunition, has been used widely on the war field. It is difficult to evaluate operational effectiveness with ball firing of terminal-sensitive submunition attacking armored forces. The movement model of terminal-sensitive submunition operate, such as ballistic model etc. was established. The attack state of terminal-sensitive submunition aiming at armored forces was constructed. The simulation test was used to evaluate hitting probability of terminal-sensitive submunition to armored forces. The operational effectiveness of terminal-sensitive submunition was evaluated also by simulation test. The simulation result demonstrates that the terminal-sensitive submunition has been the severe threat for armored forces.
2013, 42(10): 2707-2711.
In order to address intrinsic nonlinearities of hyperspectral remote sensing data, isometric feature mapping (ISOMAP) is the most widely utilized global manifold learning approach for nonlinear dimensionality reduction. In this paper, it was employed to extract the inherent manifold of hyperspectral data and the experimental results show that ISOMAP provides a significantly more compact feature representation of hyperspectral data than the minimum noise fraction (MNF) transform. Considering the spectral information of hyperspectral data, spectral angle (SA) was applied to derive the neighborhood distances in ISOMAP algorithm, and the result was better. Extracted subspace features via ISOMAP algorithm were also implemented in conjunction with k Nearest Neighbor (kNN) classifier for classification. Experimental results show ISOMAP achieves higher classification accuracies than MNF transform, but with much smaller dimensionality. Especially, ISOMAP provides better discrimination for spectrally similar classes.
2013, 42(10): 2712-2717.
In allusion to the specific structural characters of Offner imaging spectrometer, the fundamental design principles of its fore telescope were analyzed. A novel method to design the wide FOV, long focal length and telecentric off-axis three-mirror anastigmatic (TMA) optical system was presented. For the projective demand, a fore telescope system for Offner imaging spectrometer was designed. Its focal length was 800 mm. Its FOV was 8.60.148, and the operation spectrum band was from 0.9 m to 5 m. The evaluation results of its imaging quality demonstrate that the MTF of each spectrum band is higher than 0.65 at the Nyquist frequency 16.7 lp/mm. The imaging quality has reached the diffraction-limitation, which satisfies the pre-designed requirement. Therefore, the design method is feasible. The designed telescope system is compact, easy to be fabricated and suitable for space borne Offner imaging spectrometer.
2013, 42(10): 2718-2723.
The fusion of hyperspectral image (HSI) and panchromatic image (PI) is a crucial and useful technique. The fused image possesses good spatial and spectral quality, and it is very helpful for the follow-up image processing. By using spectral constrained express, the traditional NMF (nonnegative matrix factorization) was improved, and used it in the hyperspectral image fusion. Firstly, the hyperspectral image was decomposed into basis and weight, then the details of hyperspectral image were sharpened by enhancing the details of the basis with high resolution image. Meanwhile, a spectral constraint function was added in the model to preserve the spectral information. Therefore, the fused image obtained by the proposed fusion model possesses good spatial and spectral information at the same time. At last, the experiments on simulated and real data were done with conventional and the proposed methods. The proposed method behaves better both in visual and objective indices, indicating it is a better choice for HSI fusion.
