2013 Vol. 42, No. 9
2013, 42(9): 2299-2304.
Compared with traditional infrared imaging, polarization imaging system can detect and identify the man-made or camouflaged target more effectively by using the differences of the degree of polarization between a target and its background. As the polarization transmission is a complex process, it's necessary to study polarization properties of different objects and atmospheric effects, including atmospheric absorption, atmospheric path radiation and scattering of suspended particles in the atmosphere. In this paper, a general expression of polarized radiation control equation was obtained firstly. Secondly, the atmospheric absorption coefficient and path radiation in NIR, MWIR and LWIR were modeled and calculated respectively by using MODTRAN software. The polarization contrast and intensity contrast between the target and background with increasing detection distance were calculated. The results show that in NIR waveband, the reflection intensity is in a dominant position and that in MWIR both intensity and radiation cannot be ignored. While in LWIR, the radiation is in a dominant position and therefore in general polarization imaging has more advantages than intensity imaging. The results are basically consistent with the theoretical analysis. All the work mentioned above provides a reference to the choice of the way in IR detection.
2013, 42(9): 2305-2312.
The boundary shape identification based on the surface temperature measurement is not only a key theoretical basis for quantitative development of thermographic nondestructive technique, but also an important and difficult issue in the research of inverse heat conduction problem. When identifying the boundary shape, for ordinary algorithms, the boundary shape continually changes during the iterative process, which increases the calculation complexity and restricts practical application of the algorithm. Based on previous algorithm researches, the identification problem of interfacial geometry has been transformed into that of the distribution of effective thermal conductivities. The distribution result obtained based on the modified one-dimensional correction method is then converted to the desired boundary shape. Numerical test cases have proved that the algorithm with the transform theory which greatly reduced the calculational complexity of the identification process, is an effective method in dealing with identification problem of interfacial geometry.
2013, 42(9): 2313-2318.
Infrared focal plane array(IRFPA) is an important component of the thermal imaging system. However, due to facts like technical limitations and material defects in production, the environmental influence, and too long time operation, etc., the drift of the IRFPA response during their working is unavoidable. It affects the image quality of the thermal imaging systems and has negative effects on the precision of the thermal imaging equipments. Aiming to solve the problems of traditional radiation calibration and correction methods, considering the nonlinear response of infrared detectors, and taking advantage of the infrared imaging integral platform based on U-shape blackbody, a three-point infrared calibration and correction technology was discussed. Furthermore, the previous tow-point calibration and correction method was used for comparison. The experimental results show that during the temperature range of 25-65 ℃, compared with the original calibration precision, the three-point calibration technology owns quite an effective consequence with the biggest absolute error of 0.126 6 K and average error of -0.048 8 K. However, the method proposed does not have quite abvious difference with the tow-point method, so generally the tow-point calibration and correction can adapt the normal radiometric calibration application.
2013, 42(9): 2319-2323.
Projection optical system is the key component of the infrared scene simulation system based on DMD. The projection optical collimating system was designed. The initial structure of the system was obtained by use of athermal optical design method for the complementary of different thermal properties. The one side was designed to the dual surfaces, the aberration was reducing, and the optical transmission properties was improved, system athermalized designs was achieved. The refractive structure was used by projection light path, working in 8-12 m long-wave infrared band, with focal length of 113 mm, half-field angle of 4.5 and F number of 1.3. Optical system using the software ZEMAX was optimized to meet the requirements for use of the simulation system.
2013, 42(9): 2324-2329.
The mid-infrared atmospheric transmittance and radiation were calculated with four different HITRAN databases using LBL software. Results show that atmospheric transmittance is increases with the transmission path decreases. Radiation decreases with the transmission path decreases. The transmittance average absolute deviation of HITRAN96, HITRAN2k and HITRAN04 is small in the three downlink propagation. But the transmittance absolute deviation is larger in some bands, such as the maximum absolute deviation of HITRAN2k up to 0.81 in transmission path from 100 to 10 km. The radiation average absolute deviation level of HITRAN96, HITRAN2k and HITRAN04 is 10-6 in the three downlink propagation. The deviation caused by old versions of the database should be considered for calculating infrared atmospheric transmittance and radiation. The difference caused by different versions of the database should be considered.
2013, 42(9): 2330-2335.
Infrared thermography is a nondestructive testing and evaluating technique that allows the non-contact inspection and quick monitor large area. There are different detection methods of infrared technology for nondestructive testing. In order to study the advantages and disadvantages of different detection methods, different detection methods of infrared technology for nondestructive testing were comparatively analyzed according to the theory of heat transfer. A two-dimensional heat conduction model was established. The temperature fields of the specimen under different heat source excitation conditions were simulated by using the established model, based on this, PT LT and PPT of infrared technology for nondestructive testing were numerically simulated, from the theoretical point of view, the merit and demerit of the three kinds of methods were compared, the best useful range of three infrared technology for nondestructive testing were obtained, a theoretical basis for the selection of detection method of infrared technology for nondestructive testing was provided.
2013, 42(9): 2336-2340.
Based on the infrared radiation theory,some factors such as self-radiation,reflection radiation and long wave radiation of the atmosphere were considered. The simulation method of infrared radiation characteristics of the target and the infrared radiation simulation software of object were studied. With a steel plate as an example, the simulation of the target was modeled, and the surface boundary conditions of object was determined. Through the surface temperature field of the target calculated, the temperature data of the steel plate calculated by simulation was compared with the data measured by test. The results show that the average error of simulating calculation is less than 1.5 ℃, it verifies the correctness of the simulation method. Based on the simulation software, the distribution of infrared radiation characteristics of the target in different time is calculated. The rationality of infrared simulation method is proved, and it lays the foundation of infrared simulation of vehicle and complex background.
2013, 42(9): 2341-2347.
In order to analyze effects of disturbance rejection rate on stability of guidance and control systems, a conception of seeker disturbance rejection rate transfer function was presented. Both models of disturbance rejection rate transfer function and parasitical loop of seeker disturbance rejection rate were established. Then the characteristic of disturbance rejection rate transfer function was analyzed using frequency domain methods, and with Routh criteria the effect of guidance parameter on the stability zone of the parasitical loop as well as the influence of guidance dynamics orders on crossover frequency were studied. With an infrared image seeker, the disturbance rejection rate transfer function and stability of parasitical loop were analyzed further. Finally, measures for improving the disturbance rejection rate were presented. The study shows that the parasitical loop may go unstable in the middle frequency region mostly. Improving the gain of the seeker's stability loop in this frequency region is crucial to the disturbance rejection rate level and the stability margins.
2013, 42(9): 2348-2352.
A depth estimation algorithm from monocular vehicle infrared image based on depth estimation model by supervised learning was proposed. Firstly, kernel-based principle component analysis(KPCA) was used to select infrared image features. Original features extracted from infrared image were project nonlinearly to a high dimensional and linear separable feature space using kernel function. Principle component analysis(PCA) was performed to get dimension reduction infrared image features. Then the infrared image features and depth values were trained using BP neural network. A depth estimation model was obtained which can estimate the depth distribution of monocular vehicle infrared image. The experimental results show that most of the depth estimated by the model is consistent with the original depth information of infrared image.
2013, 42(9): 2442-2448.
In order to make the high resolution space Time Delay and Integration(TDI) CCD camera adapt to the satellite pitch attitude angle and enhance real-time ability of space remote sensing, the influence of satellite's pitch angle on the imaging of high resolution space cameras was analyzed. The optical projection method was used to qualitatively analyze the differences of image motion velocities among different fields of view when imaging with pitch angles. Generating principle of image with traverse image motion was promoted according to the operation mode of TDI CCD. The model of recovering image with the traverse motion image was built, and the simulation experiment and its algorithm accuracy analysis were accomplished. The analysis result shows that the larger the pitch angle of satellite is, the more different the image motion velocity of various fields of view is. From the emulational experiment and accuracy analysis, it is seen that image without traverse image motion could be gotten by the method of image recovery with traverse image motion, and the higher the collection digit of image with traverse image motion is, the smaller the error of grew value is. The ability to adapt the pitch angle of satellites is enhanced by the method of recovery of image with traverse image motion, and the capability of agile imaging of TDI CCD space camera is greatly improved.
2013, 42(9): 2449-2452.
For the disadvantage of conventional three mirrors system to achieve wide field of view, a new-style unobscured three-mirror optical system with wide field of view was designed based on the retrofocus-type objective configuration. One powerful retrofocus design approach was the combination with a reversed Galilean Telescope, the expression of initial configuration parameters was obtained and the unobscured style was carried out by decenter the field. A system with effective focal length of 100 mm, field of view of 2020 and F-number of 5 was designed, the modulation transfer function value at spatial frequency of 50 lp/mm was over 0.6 and image qualities were excellent. Compared with traditional common three-mirror optical systems, the most prominent advantage of this new three-mirror system are that it can provide wide field of view and just use two aspheric mirrors and one spherical, so that the cost of this system will be reduced.
2013, 42(9): 2453-2456.
Refract optical system using in remote sensing usually has many elements, complicated structure, and diffraction limited image quality, which makes the assemble puzzled. The tradition way is to alignment each optical element piece by piece, through the device designed to measure the surface tilt error of spherical surfaces with respect to a reference axis. It is time consuming, and worse than all the result is uncertain of successful. In this paper, the method of computer aid alignment was introduced as an assistant to avoid strict process control and reduce the difficulty. A example releases that when a special sensitively variables like distance between two lens is chosen as compensator to reduce the primary aberration after optimization of the optical system, it is effective and convenient to raise the optical system wavefront error RMS from 0.084 (=632.8 nm) to 0.046.
2013, 42(9): 2457-2461.
In order to obtain high-stiffness and good thermal stability of main supporting structure in space remote sensor, a flexible support structure was proposed to solve the contradiction of force and thermal constraints availably, which are two key environmental constraints on the imaging of the grating spectrometer. Firstly, according to the optical design requirements, the structure of the grating blank was determined. Secondly, the sensitivity of the sizes of the flexible support was analyzed by theoretical calculation,and their effects on bend rigidity were obtained. Optimum design was utilized to determine the final sizes. Finally, the surface figure precision and dynamic stiffness of the grating component in the thermal-structural coupling state were analyzed with finite element analysis(FEA) software. Simulation results demonstrate that design of the grating blank and its flexible support structure is reasonable, which can meet the requirements of the space application and supply the reference for further study and application.
2013, 42(9): 2462-2466.
A method used to fabricate artificial compound eye was presented in this paper. The artificial compound eye is composed of ommatidia like that of an insect's compound eye. By studying the characteristic of different fabrication technique, analyzing the performance of materials and relationship between different materials, and composing the fabrication techniques and materials together, a method to manufacture micro array elements based on curvature substrate was proposed. In this method, microlens patterns used as ommatidia were fabricated by regular micro-fabrication. Soft-lithography was used to manufacture the deformed elastomer membrane to obtain opposite concave microlens patterns. Polymer replication was used to transfer the patterns onto the hemispherical dome substrate. Experiments were carried out and an artificial compound eye contain over 20 thousands ommatidias were fabricated.
2013, 42(9): 2467-2471.
On the basics of a cool 320240 detector with staring focal plane array, a large aperture off-axis catadioptric middle infrared continuous zoom system was designed. The system worked at 3.7-4.8 m which achieved the zoom of 250 mm to 2 000 mm and F number of 4. The optical system was divided into two segments. Firstly, an off-axis aspheric non-power system as the front system was designed. Then the continuous zoom lens which matched with the non-power system as the back system was designed. Because of the material constraint, the refractive zoom system could not realize large aperture. Coaxal catadioptric zoom system had great block ratio. And three mirrors zoom system could not achieve cold shield efficiency 100%. The off-axis catadioptric zoom system cold account for forenamed limitation. The system cold offer a high resolution and excellent images, and its cold shield efficiency is 100%. The system satisfies the design requirements.
2013, 42(9): 2472-2477.
A modified iterative algorithm based on phase mixture was put forward in designing diffractive optical elements, aiming at recovering diffractive patterns of the output beam precisely. Different from Gerchberg-Saxton algorithm, in this paper, the new phase initiation was set as the weighted sum of the two phase functions in the succeeding neighbor loops to be immune from trapping local minimum. The formulas for calculating phase factor were given, and the selection of phase factor was discussed. The beam transformations from Gaussian distribution to uniform and to annular distribution were exampled to investigate with Gerchberg-Saxton algorithm and the proposed algorithm. The numerical result demonstrates a nearly uniform and annular target profile, and the ultimate mean square error, top beam uniformity, and energy efficiency of the proposed algorithm were all more excellent than Gerchberg-Saxton algorithm. This work can obtain better output diffraction pattern, and has reference value for the design of diffractive optical elements.
2013, 42(9): 2478-2484.
LED chips locating is a key link in chips detection, dicing, wafer expansion, die bond and in telling whether the electrical characteristics of the chips and the chips pin can meet the requirements and in telling whether it can sort the LED chips quality successfully. To solve this problem, the coarse-to-fine locating method was put forward. Firstly, the low magnification and high coverage were used to conduct the coarse locating of LED chips' template matching. Then, based on the generated coordinates of coarse positioning, the high-precision locating of high magnification and low coverage template matching within the eight fields of the coordinates were conducted. In this way it could solve not only the fastness but also the precision of the positioning. The results of the experiment show that the image locating precision error is less than 1 m; the moving table locating precision error is 4 m; overall locating system locating precision is less than 5 m; locating speed is greater than 5 grains/second, thus providing a new way for chips high-precision locating system of equipment such as detection machines, sorters and die bonders.
2013, 42(9): 2485-2489.
The VO2/TiO2 films were fabricated by a sol-gel method on the(001) oriented cleavage surface of muscovite slices. The X-ray diffractometer(XRD), X-ray photoelectron spectroscopy(XPS) and atomic force microscopy(AFM) were used to investigate the microstructure and describe the morphology of the films. The infrared transmittance spectrums of the VO2/TiO2 films at different temperatures were determined by in-situ Fourier transform infrared spectroscopy(FTIR), and the spectrums were used to analyze the thermochromic properties of the VO2/TiO2 films. The results show that the composite films are preferred VO2(011)/TiO2(101) orientated on the muscovite substrate with compact structure and smooth surface. The VO2/TiO2 films exhibit a significant infrared optic switching of 75.5% at the wavelength of 4 m during the metal-semiconductor phase transition(MST) process. The phase transition process of the composite film is quite sharp with a dTr/dT of 15.7%/℃, and the hysteresis width of films decreases to 8 ℃.
2013, 42(9): 2490-2495.
ECR was employed to etch the surface of monocrystalline silicon(100), etching effects and optical properties of low energy Ar+ ion beams with different ion energies and fluxes under normal ion incidence were studied. The experiment results indicate that, when ion flux density was 88-310 A/cm2 with ion beam energy of 1 000 eV, self-organizing nano dot structure appeared on the sample surface, orderly arrangement of the micro-structure was along with the increase in ion flux density; RMS decreased until the flux density was near 160 A/cm2, and then increased rapidly; The average transmittance of etched sample, within the range of near-infrared bands, was improved from 53% to more than 57%, which enlarged with the increase in orderliness of self-organizing nano-structure. When ion beam energy was 500-1 000 eV with ion flux density of 270 A/cm2, the tiny nano dot structure gradually formed, which tended to be concentrated and orderly with the increase of ion beam energy. If ion energy was going up below 1 100 eV, RMS slowly increased but rapidly reduced over the number. The transmittance of etched sample was sharply improved, with the increasing orderliness of self-organizing nano-structure. Etching rate was directly proportional to the square of ion flux energy. The pattern transformation of self-organizing nano-structure results from the interaction of spurting roughening and relaxation mechanism.
2013, 42(9): 2496-2504.
Space-time coding transmission information by parallel channels of the multi-antenna array can further improving transmission rate while guarantee the quality of communication. The authors' work at orthogonal space-time block code, space-time trellis code, unitary space-time code, differential space-time code, hybrid space-time code and relevant aspects was introduced, by adopting various pulse position modulations defined negative, conjugate and complement operation, transform the coding matrix into real matrix expressed by pulse position. The relationship between system error rate and transmitting antenna/receiving antenna number, atmospheric turbulence intensity was analyzed. The error rate characteristics of differential space-time code and unitary space-time code under different atmospheric turbulence were discussed. Combination of layered space-time code and space-time block code, reasonable compromise the multiplexing gain and diversity gain, a hybrid space-time coding scheme suitable for IM/DD type optical communication was put forward.
2013, 42(9): 2505-2509.
A new intensity modulated optic microphone theory model was introduced. Single-mode optical fiber here was used to realize collimation of beam. The propagation law in collimation lens was discussed, and light intensity modulation using matrix optical principle and Gaussian coupling theory was realized. The system contains MEMS pressure vibration membrane to pick up vibration displacement. Through the analysis of membrane size and the change of pressure, the related parameters about the sensitivity of fiber optic displacement sensor could be acquired. Simulation results show that the proper choice of parameters can make the sensitivity of sensor improve in orders of 103 magnitude than traditional light intensity modulated methods in condition of no increasing the complexity of structure.
2013, 42(9): 2510-2514.
The coupling efficiency of received optical power into a single-mode fiber is degraded by atmospheric turbulence in a free space optical communication system. The expression of average coupling efficiency of a collimated Gaussian beam into a single-mode fiber was derived under Kolmogorov turbulence channel, according to the theory of weak turbulence statistics. The relations between average coupling efficiency and turbulence intensity under different received aperture in 1 km propagation path were also simulated. The results show that coupling efficiency decreases below 0.1 when refractive-index structure constant rises to 10-12, and coupling efficiency degrades when the received aperture increases. A 37-element adaptive optics system with H-S wavefront sensor was adopted to compensate the efficiency. Compared with long exposure imaging and centroid position offset in different status of AO system, it was found that the P-V value and standard deviation decreased, Strehl ratio and coupling efficiency increased in low-order aberration correction. And things became better when high-order aberration was corrected.
2013, 42(9): 2515-2518.
In order to realize the rotary object pose measurement, single-station measurement based on photoelectric theodolite with flexible station placement, without station geographical restrictions, and the stereo matching image has a high application value. The measuring method and the principle of attitude angle were introduced. Taking full advantage of the knowledge of space-objects figuration, on the basis of the photoelectric theodolite single station space cosine attitude measurement method to obtain the target attitude parameters, through the further development and improvement, the requirements of this algorithm on image quality was reduced and the applicability of the algorithm was increased. Compared with other methods of measurement, the simulation experiments demonstrate that the pose measuring method is less than 0.5 accuracy, the measuring result is stable. It can satisfy the need of high accurate measurement of spatial 3D pose measurement of rotary object with very good practicability.
2013, 42(9): 2519-2524.
Final optics play an important role in Inertial Confinement Fusion (ICF) system. In this paper, the online inspection technology for final optics damage was studied in order to build a final optics damage online inspection system for ShenGuang-Ⅲ(SG-Ⅲ) prototype device. According to the assignment of final optics in optical module, a zoom telescope optical system with high resolution was designed by CODEV to meet the testing requirement. Based on the assignment of optical modules in target chamber, the positioning mechanism was designed to focus and switch the beamlines and the optics accurately and rapidly. At last, an off-line simulation experiment based on SG-Ⅲ was carried out. The result shows that the MTF at the spatial frequency of 68 lp/mm is greater than 0.4, 80% of the energy is distributed within 22 CCD cells. Between 1.8 m to 2.8 m, the resolution of the optical detecting mechanism can reach 160 m. The defects can be tracked when their diameter is up to 60 m by image processing method. The precision of the positioning mechanism is better than 13 arc sec.
2013, 42(9): 2525-2530.
Sub-aperture stitching technology can be used for testing large aperture optical mirrors with low-cost and high-precision and without supporting components. Based on planes and high steepness asphere, the algorithm of sub-aperture stitching for shallow asphere was detected. The mathematical model, stitching algorithm as well as the detection process were analyzed and discussed. A shallow asphere was fitted by 37 Zernike polynomials and divided by circular sub-apertures. Then the simulation of the sub-aperture stitching was completed as well as the analysis of the effect of the sub-aperture translation, tilt and random errors on stitching accuracy.
2013, 42(9): 2531-2535.
In order to meet the demand for coated composite functional material, farinas were metallized by chemical plating copper method and their figure, infrared and microwave characteristics were tested. SEM pictures show that these metallic farinas' figures are not destroyed and their cupreous shells are symmetrical. These metallic farinas have special infrared and microwave characteristics for their shells. Because of farinas cores, these particles are lightweight. The results indicate that it is practicable to use these metallic farinas as infrared and microwave materials.
2013, 42(9): 2536-2539.
Traditional method is using a collimator and polyhedron for encoder accuracy detection with shortcomings of low efficiency, which requires experienced master. Encoder error detection adopts binary light bars, when rotated encoder forward, the light bars will carry normal. However, this method is inefficient, and also resulting in an error of judgment. The automatic detection system for photoelectrical encoder was designed. Motor fiducial encoder and certified encoder were coaxial. As position and speed feedback, fiducial encoder's resolving was 0.077. DSP was the control core, automatic detection system was working in speed and position mode. Precision demarcating was in position mode while error checking was in speed mode. The automatic detection system was used to detect two 14 Bits encoders, comparing with collimator detection system, experimental results show that the system works effectively and properly. The accuracy detection and error code checking can be performed simultaneously, improved the detection efficiency and shorten the design cycle of the encoder. Other models encoder debugging and testing can be extended.
2013, 42(9): 2540-2546.
A self-calibration method based on spatial high frequency energy was proposed in view of the geometric artifacts caused by misaligned geometry in cone-beam CT. An optimization model was constructed based on spatial high frequency energy of the reconstructed image. Part of the parameters were directly extracted from the projection image to diminish the search scope, and the optimal solution of geometry parameters was achieved by NM-simplex method that makes the spatial high frequency energy of CT image maximize. To improve the speed of the algorithm, GPU was used to accelerate the process of image reconstruction to reduce the reconstruction time. Without reprocessing the reconstructed image, the proposed method has less computing complexity compared with the existing ones. The experiment results show that the presented method has significant effect in geometric artifact calibration of the reconstructed images with high accuracy and the maximum relative error is less than 5%. It can notably reduce iterations without precision reduction, and algorithm execution efficiency has been raised 18.8%.
2013, 42(9): 2547-2552.
A novel fusion algorithm for multi-focus images was proposed using Uniform Discrete Curvelet Transform(UDCT) for its characteristics of multi-scale; multi-direction and low redundancy. First, the source images were decomposed into several subbands using UDCT. Then, according to the characteristics of multi-focus images, the coefficients of low-frequency subband were fused with a scheme based on the sum-modified-laplacian; the coefficients of high-frequency subbands were fused with the fusion rule based on local energy; and the consistency of the fused coefficients was verified. Finally, the subband coefficients were reconstructed, and the fused image was obtained. The experiment results indicate that the proposed method can effectively fuse the directional information and detailed features of source images, and suppress pseudo-Gibbs phenomena of fused image; compared with other fusion methods, such as those based on Laplacian pyramid transform, discrete wavelet transform and contourlet transform, this method obtains better fusion quality in terms of both visual and quantified measure.
2013, 42(9): 2553-2560.
To improve the recognition rate and speed of the multi-target detection and tracking in the complex background, a tracking method based on neural network Kalman filter with correction mean square error estimation was proposed. Multi-target detection and tracking of the video sequence were achieved. In this method, first of all, the background was extracted accurately through the inter-frame difference method and multi-target detection was achieved combined with background subtraction method,the detection results were optimized utilizing morphological filtering. Then, Kalman_BP neural network filter was used to predict the position of the moving target. The estimation error of the Kalman filter caused by model changing and noise was mainly reduced with BP neural network, which made the predictive results more accurate. Finally, the fast matching of target was achievid via labeling different targets. Target chain was established by using the characteristics that little change of same goal centroid position and the boundary rectangle between the adjacent frames, which brought about the multi-target tracking. Simulation results show that the algorithm can not only track different scenarios targets, but also count the number of targets and display target trajectory rapidly and stably. Compared with the particle filter and other metheds, tracking is more smooth, thus the reliability of the tracking is improved.
2013, 42(9): 2561-2565.
For infrared image which is characterized by low SNR and serious background and noise disturbance, according to the correlation of moving target frame-to-frame and the irrelevance of noise in sequential images, based on Open Source Computer Vision Library, a detection algorithm for small target was proposed and the detected target was tracked. By using energy accumulation method, background of image was got and then removed from original image, image SNR was improved. Noise was removed via the correlation of target frame-to-frame and the movement information. At last, the detected target was tracked by Kalman filter algorithm. The experimental results show that this detection algorithm can effectively find small moving target from sequential images, the tracking algorithm can track in real time and forecast the position accurately when target is covered.
2013, 42(9): 2566-2573.
In order to detect small targets with changing size in infrared scene, aiming at the problems in traditional filtering method with fixed size filter, a method for small and dim infrared targets detection based on scale-space theory was proposed. First, the target characteristic was analyzed and point spread function form was used to represent the target model. Then, in order to suppress background clutter and enhance the power of target, fixed adaptive neighborhood method was used in image preprocessing, on the basis of Laplace scale-space after scale standardization which has different filtering responses for different elements, the suspicious targets were obtained in the images, then with the gradient relationship between suspicious target point and its surrounding pixels, the coordinates of the suspicious targets centers and its size were got; Finally, each suspicious targets gained an adaptive window to obtain segmentation threshold and true targets. Experiments results show that, compared with traditional methods, the new method proposed in this paper has a better performance to detect small targets, and has a lower false alarm rate.
2013, 42(9): 2574-2578.
The detection range equation of cat-eye target was extended by modeling the detection process based on matrix optics, which can be applied to the situation that the cat-eye optical system had out-of-focus reflecting element and the detection beam was oblique incidence. The detection range equation was verified by field experiment. The results prove that there is small drift angle between the incidence beam and echo beam and the echo divergence angle is much larger than the echo drift angle, which makes the echo beam be large enough to cover the detection system. On conditions of the same detection parameters, the echo power is only related to the focal length and defocusing amount of the cat-eye optical system and has nothing to do with the incidence angel of detection beam and the receiving aperture of the cat-eye optical system.
2013, 42(9): 2579-2583.
The subspace constructing strategy of classic subspace-based tracking schemes is to select appropriate subspaces with maximum energy, in this strategy the discriminability between the target and background is neglected, so when the target and background have similar appearance the tracking system's performance may be degenerated. To solve the problems of IR image's low SNR and low contrast, a novel subspace selecting method was proposed based on analyzing the discriminability between the target and background. The IR object tracking process was realized by the particle filter with the provided subspace selecting strategy. In this case, based on the prior knowledge of the particles distributions and the target state, different subspace's tracking ability by considering both the feature difference and the particles' approximation level to the target was estimated firstly, then the optimal subspaces were selected to realized the IR target tracking. Experiments on several complex scenes indicate that the proposed algorithm has better performance than the classic one.
2013, 42(9): 2584-2588.
A seamless IR image sequence mosaic method based on feature points and principle of overlap transition Poisson image fusion was proposed. Firstly, a simplified SIFT was used to extract invariant feature points from images. In order to improve the accuracy of matching, bidirectional and complementary matching method was used. Then, random sample consensus(RANSAC) was used to perform reliable matching parameters of the transformation between images which were obtained from the matched feature points. Finally, Poisson image fusion was used to accomplish seamless image mosaic. The feature points were invariant to affine transformation, noise contamination, leading to robustness of the method. Experimental results show that the image mosaic method is simple and effective, and eliminate the mosaic seams while keeping good image definition.
2013, 42(9): 2589-2596.
The log-polar transform is a well known space variant image registration scheme. However, due to the phase cross-power spectrum showing the multi-peak distribution, the accuracy of image registration is greatly influenced. To deal with this problem, an infrared image registration method based on the optimal peak of phase-correlation criterion was proposed. First, the source image and the reference image were converted to the log polar domain respectively. Second, the adaptive Butterworth high-pass filter was adopted to weaken the low-frequency noise. Finally, combined normalized cross-correlation and phase correlation similarity measure, the optimal peak of the cross-power spectrum was acquired based on truncating the low value of the cross-power spectrum. Moreover, the influence of LPT-image size on the matching performance was discussed and the appropriate size ratio of LPT transformation was presented. The experimental results indicate that the proposed method has higher precision and better anti-noisy performance than those of the normal LPT matching algorithm and is suitable for rotated, scaled and translated infrared images registration.
2013, 42(9): 2353-2357.
The aerosol is an important ingredient of atmospheric electromagnetic environment, the aerosol particles affect on the transmission of 1.06 m laser seriously. The single scattering albedo and asymmetry factor is an important parameter for the research on the laser transmission characteristics in aerosol. Cluster-cluster aggregation(CCA) model was used to simulate four kinds of aerosol aggregation particles consisting of 64 spherical original particles. Combined with the discrete dipole approximation method, the value of single scattering albedo and asymmetry parameter under different incident angles with 1.06 m laser incident were numerically calculated, and the influence of the size parameters of the single scattering albedo and asymmetry factor was analyzed. The results show that the single scattering albedo and asymmetry factor are significantly dependent on the incident angle and shapes for the aerosol aggregation particles with same number of original particles. And for the aerosol aggregation particles with different size parameters, the single scattering albedo and asymmetry factor increases with increasing size parameter, when the size parameter is greater than 3, the scattering of aerosol aggregation particles is mainly concentrated in the forward scattering.
2013, 42(9): 2358-2363.
A tunable diode laser absorption sensor was developed to measure gas temperature, which exploited scanned-wavelength direct absorption spectroscopy and fixed-wavelength modulation spectroscopy with second harmonic detection on two water vapour spectral features near 7 454.4 cm-1 and 7 185.6 cm-1. The sensor was capable of making absolute measurement and could reach 10 kHz output bandwidth using fixed-wavelength modulation spectroscopy. Its performance and accuracy were validated and demonstrated in a static cell with known temperature and pressure. The measured temperature using two techniques agree to within 2% RMS of thermocouple reading for temperature from 600 to 1 000 K, which indicates the sensor is capable of making rapid and highly accurate temperature measurement for uniform flow.
2013, 42(9): 2364-2369.
The precision optical system is included in laser fuze, among them, an important role is played by the optical receiver system, when it is used in conventional ammunition, high emission overload environment has a serious impact on the quality of weak echo focusing, system reliability can not be guaranteed. The receiver focusing lens and integrated program of narrow band filters are proposed, a new type of receiver system optical buffer structure was designed, a mathematical model of tradition receiver system and a mathematical model of new structure were established by using finite element analysis software ANSYS, nonlinear dynamics simulation and optical simulation were did by ZEMAX to the receive focusing lens; finally, the air gun impact experiment was did. The results show that in the experience of the 70 000 g impact acceleration, buffer structure of the new optical system can alleviate the receiver focusing lens plastic deformation effectively, the quality of pulse laser beam focusing plastic can be improved, the laser echo energy is enhanced significantly. A new method and theoretical basis are provided to the anti-overload design for conventional weapons of laser fuse receiving optical system.
2013, 42(9): 2370-2374.
In order to effectively control the quality of laser milling layer, BP neural network model was established between the laser milling quality of layer(the milling layer width, milling depth) and the milling layer parameters(laser power, scanning speed and defocus amount). Using particle swarm optimization (PSO)BP neural network weights and thresholds, quality prediction model based on particle swarm neural network was built. The proposed PSO-BP algorithm solve the problem that the general BP algorithm iteration speed was slow, and prone to local optimum. Al2O3 ceramics laser milling quality prediction model was taben to realize the algorithm.The simulation results show that the number of iterations of proposed PSO-BP algorithm, and the prediction error are greatly reduced. The built quality prediction model has high prediction accuracy and practical value.
2013, 42(9): 2375-2379.
In view of severe vibration in the operational environment of ballistic missiles and rockets, the error propagation characteristics of the laser gyro strapdown inertial navigation system(SINS) in linear vibration environment were studied and it was noted that the square error of accelerator had a significant impact on the navigation accuracy. Then, a 31-order error model was established including the square error. In order to evaluate the accuracy of the model, the static and linear vibration simulations were designed to compare with the 28-order error model without considering the square error. The simulation results indicate that the two models have equivalent accuracy in the static state but the accuracy of 31-order error model is five times higher than the 28-order model in the vibration state.
2013, 42(9): 2380-2385.
In order to study the influence of TEA CO2 laser repetition frequency on far-field beam quality, the temperature field and thermal deformation distribution of the mirror were calculated firstly by the finite element analysis of thermodynamics instantaneous method with TEA CO2 laser irradiation of different repetition frequencies. Then, mirror thermal distortion was fitted by Zernike polynomials. Finally, far-field characteristics of different repetition frequencies TEA CO2 laser were obtained by the angular spectrum propagation theory of diffraction. The theory and simulation results show that with the increasing of laser repetition frequency, the mirror temperature and thermal deformation are gradually increasing. After thermal deformation effect, Sr and the average energy density Ed decrease, and parameter gradually increases in the far field. Comparing with 10 Hz, Ed of 300 Hz decreases 40%, peak power in the far field decreases 43% and beam waist broadens 60%. When the laser repetition frequency is greater than 100 Hz,due to the appearance of peaks and valleys on the mirror, the far-field beam quality decreases significantly. The results of this paper can provide the reference to TEA CO2 laser launch system.
2013, 42(9): 2386-2391.
Based on the rate-equation model of end-pumped alkali vapor laser, the performance of diode-pumped Cs vapor laser was researched. By adjusting the parameters of pump source and vapor cell, the effects of each parameter on the absorption and output performances were analyzed. Results show that the power absorbed by Cs vapor and output laser power become saturated when pump power and ethane pressure increases. The powers also have a Gaussian dependence on the deviation between pump light wavelength and transition wavelength. Besides, the powers increase initially and then begin to decrease when adding more helium into the vapor cell. Furthermore, there exist a critical line-width of pump light and a temperature range to maintain the operation of laser. The simulated results are in line with reported experiments well, which will supply significant reference for further experimental research.
2013, 42(9): 2392-2396.
The image quality of laser active imaging system degraded dramatically in fog. The obtained infrared image had the features of low contrast and serious noise. Thus an image process method combining dark channel prior and bilateral filter was proposed. The dark channel prior was adopted to remove fog from the image. Then the image was denoised using the bilateral filter. So the contrast of the image was improved and the noise was reduced. Both subjective and objective evaluation of the processed image by different methods show that the proposed method could obtain better visual effect. The standard deviation is more than doubled. The information entropy and information capacity have about a twenty percent improvement. Thus, it's an effective way to improve the quality of infrared image in fog.
2013, 42(9): 2397-2402.
According to the characteristics of laser active imaging and practical application,a new image denoising algorithm based on homomorphic filtering and dual tree complex wavelet transform (DTCWT) was proposed. Firstly, speckle noise was converted from multiplicative noise to additive noise by homomorphic transform. Secondly, the noise image was decomposed with the Q-shift DTCWT, then wavelet coefficients were revised by Bayes adaptive threshold method. Finally, inverse transforms were carried out and the denoised intensity image was obtained. The algorithm proposed had approximate shift- invariant, good directional selectivity and perfect reconstruction. The image signal to noise ratio (SNR), peak signal to noise ratio (PSNR) and the run time were applied to estimate the denoising effect. Experimental results show that the proposed algorithm has advanced denoising performance in laser active imaging and great efficiency in computation. Meanwhile, the detail of image is well protected.
2013, 42(9): 2403-2408.
The parabolic point focusing thruster model was adopted as research object. The development process of flow field of air-breathing nanosecond laser propulsion with pulse repetition frequency of 2-50 Hz was numerically simulated, and the Effect of nanosecond laser pulse number and pulse repetition frequency on performance of laser propulsion was analyzed. The results indicate that with the increase of pulse number, the average impulse coupling coefficient decreased due to the reducing air density and increasing temperature. The average impulse coupling coefficient with nanosecond laser is significantly higher than that with microsecond laser, though. With the same pulse number, when the pulse repetition frequency increased, the flow field had less time to recover, leading to the decreasing average impulse coupling coefficient, and the decreasing trend is much more clear in pulse repetition frequency of f10 Hz than in f10 Hz.
2013, 42(9): 2409-2413.
A kind of porous fiber for low-loss Terahertz wave guiding was designed based on Topas cyclic olefin copolymer(Topas COC). Topas COC is a kind of novel Terahertz low-loss material. Terahertz wave was well confined in a series of subwavelength air holes, which were arranged in base material with triangular lattice. Propagation properties of the designed porous fiber were investigated by using the full-vector finite element method. The results indicated that the designed Topas porous fiber had low loss and low dispersion properties within Terahertz frequency. The loss was less than 0.2 cm-1 from 0.4 THz to 1.5 THz, and the dispersion was 1.80.3 ps/THz/cm within 0.48-1.5 THz. The designed fiber structure was relatively simple and feasible for fabrication. It can be fabricated by the thermo-drawing techniques of polymer preforms invented by our group. The results provided theoretical references for fabrication of Topas Terahertz low-loss and flexible fiber waveguides.
2013, 42(9): 2414-2420.
Duo to including the ground control points that choosed by manual geometric precision correction were not precise, and the existing methods ignorded the spectrum consistency of hyperspectral data, an automatic geometric precision correction method based on SIFT feature was proposed to solve the problems. SIFT feature was extracted from the image and the geographic coordinate of the hyperspectral data was used to accomplish local feature matching. In order to extract high-precision and uniformly distributed ground control points, a sub-regional Random Sample Consensus(RANSAC) algorithm was proposed. The airborne hyperspectral data collected by HyMap in Dongtianshang, Xinjiang Autonomous Region, was used to analyze and validate the performance of the algorithm. The CE90/CE95 and root mean square error were calculated to evaluate the geopositional accuracy. The results show that the automatic geometric correction method based on SIFT feature can achieve 0.8 pixel geopositional accuracy, and the spectrum of the spectrum angle between warp image and corrected image is less than 0.01 radian.
2013, 42(9): 2421-2425.
The main study on spectral unmixing is to develop a regression between mixed spectral features of main land-cover types and their responding fractional cover. Studying on in situ spectral reflectance data, based on one of the best known algorithms of manifold learning, locally linear embedding (LLE), a new modeling method named constrained least squares locally linear weighted regression(CLS-LLWR) was proposed. Spectral reflectance of four kinds of the mixed land-cover types in different percentages was measured and preliminarily analyzed. The model CLS-LLWR was verified by predicting fractional cover of main land- cover types. Compared with principal component regression (PCR) and partial least squares regression(PLSR), through comparison and analysis of the standard error of prediction(SE), the result shows that the CLS-LLWR has better predictability. This study indicates that manifold study has the potential for the information extraction of mixed land cover types in hyperspectral image.
2013, 42(9): 2426-2430.
Glass formulation design is particularly important in laser glass preparation processes according to predetermined qualification. Traditional calculation systems of physical properties of inorganic oxide glass were outstanding representatives, but those systems usually do not involve glass spectral characteristics. The absorption properties of glass were calculated by considering the intrinsic vibration frequency and amplitude of doped laser glass and considering the Sellmeier equation and dispersion curve together. If the formulation design is changed based on the calculated glass spectrum performance, it could greatly shorten the development cycle and ensure quickly to find an optimal formulation in experiments. It is proved in the experiments that these formulations could be used to generate favorable glass states after the cooling process.
2013, 42(9): 2431-2436.
Through theory modeling, the mathematics model of the discharge intensity distribution in high voltage apparatus was studied in this paper, and the relationship of spectral line light intensity and detection distance was constructed. Then the intensity measurement of corona discharge ultraviolet spectrum in high voltage electric equipment experiment was studied. The whole detection system included needle discharge device and ICCD detector. Through the optical fiber transmission, the solar-blind ultraviolet spectrum was detected. In the experiment, optical fiber probe position was adjusted, the vertical distance of optical fiber probe and optical fiber probe about distance from the center of migration was changed respectively. Acquisition corresponding ultraviolet spectrum, and the relationship between intensity and location at 262.773 nm, 265.456 nm and 274.435 nm with different offset position wavelength, and the track of the interaction between is an exponential curve. This discovery is consistent with the theoretical analysis. Using Burg recursion algorithm for power spectrum estimation to collect ultraviolet spectrum data, it is found that the power spectral density of 350 Hz can be used as characteristic parameter. It shows that the corona discharge point identification is feasible.
2013, 42(9): 2437-2441.
Hyperspectral images of five corn varieties were acquired using Field Imaging Spectrometer System(FISS). After reflectance retrieved, noise removal and first-order differential, stepwise discrimination analysis based on the minimization of Wilks' lambda was employed to select the feature bands of corn spectral, and then discrimination model was built. The results of Least-one-out Cross-validation(loocv) show that:(1) average discrimination accuracy is 91.6%, in which, discrimination accuracy of High-oil corn No.115 is 87%, and discrimination accuracy of the other varieties is over 90%;(2) if discrimination method, band number and the size of samples of each variety are fixed, discrimination accuracy is effected by variety number and separable;(3) the effect of selected band number on discrimination accuracy is analysed and result shows that discrimination accuracy increases with the increasing of band number. Therefore, FISS has an important application value in corn-variety discrimination and quality examination.
