2013 Vol. 42, No. 8
2013, 42(8): 1951-1955.
In order to assess the impact of aerodynamic heating effect of infrared imaging missile, through theoretical analysis of the variation of the missile during flight by aerodynamic heating, and research laboratories and large-scale pilot test data, pneumatic thermal effects modeling process and the normaldistribution method was first introduced to create a virtual prototype simulation model. Using the normal distribution, missile during flight rectifierhood by pneumatic thermal radiation and infrared images from the change process was simulated. Through digital simulation loop simulation and large-scale experimental verification, the method to establish the model was proved to be consistent with the actual situation. It can be used to assess the impact of aerodynamic heating effect on product performance information processing algorithms improvement.
2013, 42(8): 1956-1961.
The silicon aerogel substrate was prepared by a two-step base/acid catalyzed sol-gel process using tetraethoxysilane(TEOS) as silicon source and by freeze drying. By adding different content of triethylamine hydrochloride(TEAHCl) to the substrate during the aging process, composite aerogels with broadband absorption in mid-and far-infrared windows was prepared. The structure and property of composity aerogels were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), N2 physisorption at 77 K and Fourier-transform infrared spectroscopy(FT-IR). Results show that the triethylamine hydrochloride is crystallized adhering to the whole three-dimensional network of silicon aerogel. The silicon aerogel substrate has the specific surface area about 524.5 m2/g, total pore volume about 1.2 cm3/g and average pore diameter about 9.2 nm. The composite aerogels have the specific surface area about 37.93-138.7 m2/g, total pore volume about 0.08-0.28 cm3/g and average pore diameter about 7.1-8.8 nm. The apparent density of silicon aerogel substrate and composite aerogels are 0.25 g/cm3 and 0.35-0.51 g/cm3 respectively. The composite aerogels have the characteristic of broadband absorption in mid-and far-infrared windows. The relative absorption intensity in mid-infrared window increased in proportion with the increase of TEAHCl.
2013, 42(8): 1962-1966.
The present literatures have not analyzed the influence of satellite's physical parameters changing with the temperature on its infrared feature. First, the theoretical calculation models of the satellite's temperature field were established. Second, the calculation method of the satellite's temperature field was deduced with the use of the finite element method (FEM) when physical parameters of solar panels changed with the temperature. Third, the calculation models of the satellite's infrared radiant emittance and its infrared radiant intensity were established. Finally, the influence of physical parameters of solar panels changing with the temperature on the surface temperature, infrared feature and the spatial distributions of infrared radiation intensities in 3-6 m band and in 6-16 m band of the satellite were calculated and analyzed. The research results of this paper have referential value on the improving calculation precision of infrared feature and infrared detecting of spatial targets.
2013, 42(8): 1967-1972.
For strongly attenuating the heat radiation through scattering and absorbing effect, fine water sprays are used in military object infrared stealth. The 8-14 m infrared radiation attenuation model by water sprays was established, in which water sprays were treated as absorbing, emitting, and anisotropic scattering medium and non-grey properties were dealt with bands discretion method. The average optical parameters in the discrete spectral bands were got by Mie theory and the radiation transfer process was carried out with finite volume method. It is found that there would be some errors when the polydisperse sprays are treated as monodispersion. The errors resulting from Sauter radius is minimum, where as that from the linear average radius is maximum. The inner radiation and scatter of the sprays have biggest influence on the transmission, so it should be considered during calculations. For restraining the radiative transmission effectively, the measures of increasing the sprays concentration and decreasing the geometry average radiuses should be done.
2013, 42(8): 1973-1978,2007.
Based on the full study for the under-sampling aliased response of focal plane thermal imaging systems, the Aliasing As Noise(AAN) method and the optical imaging system under-sampling evaluation method on the basis of information theory were analyzed. The under-sampling aliased response was regarded as a system noise and put into MRTD model like other system noise. The new MRTD model containing the under-sampling noise was obtained. By contrasting the data which got from the simulation of the new MRTD model and references, the change between the simulation and data in references is basically same. So the new model can be used to evaluate the impact of under-sampling on the performance of thermal imaging systems, however it needs further amendment for more accurate. The next step, the new MRTD model with aliasing response will be amended by measured MRTD data of focal plane thermal imaging systems.
2013, 42(8): 1979-1986.
In view of the urgent need for domestic decoys loop simulation technology and infrared guidance technology research, a finite element modeling method interference characteristics for decoys was proposed in this paper. The mechanism and the operating status of the decoys were analyzed, the flow field of the decoys were solved accurately based on finite element theory. Then the changes of air resistance in the process of decoys sports movement and the distribution of temperature field were studied in the paper, and the decoys movement characteristics and radiative properties of the finite element model were set up, which provides a theoretical basis for the hardware-in-loop simulation. And simulation verify the validity and correctness of the proposed model. The method can not only provide the basis for the infrared decoys design and infrared-guided algorithm research, but also have important guiding significance of infrared decoy HIL simulation system.
2013, 42(8): 1987-1990.
Stripe nonuniformity is a very typical fixed pattern noise in line infrared focal plane arrays (IR-FPA) and uncooled staring IR-FPA. In this paper a model was put forward based on the separation between stripe nonuniformity and real scene, and the correction could be achieved in a single frame. The estimated nonuniformity correction parameter was obtained by traversing the error function of adjacent column pixels in local template window. Through the succession of two adjacent columns' correlation, the stripe nonuniformity correction was achieved. By analyzing the experiment results of the simulated imagery and the real infrared image sequence, it is obvious that the proposed method can significantly enhance the performance of stripe nonuniformity correction.
2013, 42(8): 1991-1996.
In order to quickly and accurately understand the impact on performance requirements by a number of parameters, the operating range, which is an important parameter in IR detection system, was studied in this paper. Firstly, considering the spectral transmittance characteristics of the filter and the encircled energy affected by the relative position between point spread function and the pixel, the number of electrons produced by contrast radiation intensity between target and background in the image plane was presented. Secondly, irradiance produced by both temporal and spatial noise in the image plane based on end-to-end physics performance model of IR imaging system was studied quantitatively. Considering variety of noise conditions, the operating range calculation equation was given based on the target image's signal-to-noise ratio (SNR) detection criterion. Finally, a set of MWIR staring sensor was used as an instance to calculate and analyze the operating range. By this example, it is verified that the distance calculation equation is simple and feasible. Besides, it could predict operating range of IR imaging system for different weather conditions and regions. This performance model will help the user to refine the various parameters of the IR sensor at the early design stage.
2013, 42(8): 2085-2091.
To achieve a high signal-to-noise ratio, high spectral resolution spectroscopy detection performance, it needs to control the mirror reciprocating precision swing to complete uniformity scan modulation of the interference optical path difference in time modulation type Fourier transform spectrometer. Firstly, the relationship between the spectral detection performance and the scanning control performance requirements was analyzed. On this basis, according to the high performance requirements, a controller design method based on the pole assignment was proposed. Referencing the state feedback design results, the forward and the feed-forward link was used to realize effectively. The controller design and the difficulty of the realization was simplified. The simulation results show that the proposed method is effective.
2013, 42(8): 2092-2096.
With the development of IR technology, more and more IR instruments were used on large telescopes. A cryogenic circumstance was necessary for IR instruments operation, this sets many technical challenges for opto-mechanical design. Optical parts need accurate mounting and positioning, meanwhile they must not be cracked or breaked by thermal stresses during cryogenic. In order to solve this problem, the kinematic mount theory was presented, detailed mechanical design for all reflecting mirrors, lens, filter wheels used in optical systems were proceeded and kinematic mount was realized by these designs. The conflict between firmly fixing the optics and preventing stresses within the optics during cooling was well settled via these kinematic mount designs. Optical system security and imaging quality during cooling were well ensured by these kinematic mount designs. The research results have important referential valve for mechanical and thermal design for IR optics system.
2013, 42(8): 2097-2102.
A scan-retrace optical scanner model without rotating direction change of the driving motor, was proposed. The scanner's fly-back angular velocity doubled its scan trip. By utilizing partially-cut gear transmission and spring-damper element, the system could realize stable scanner rotating direction change without the shift of driving motor current direction. Because the energy was mainly provided by the resilient member in the scanner rotating direction changing phase, it meant the driving motor was less demanding in the system than that in the traditional one. The scanner was subject to motor's driving torque and resilient member spring-back torque in scan and retrace trip. This design helped to eliminate gear clearance efficiently and could assure transmission accuracy of the system. Compared with traditional motor directly driving scanning system, rotational driving motor doesn't need current direction shift in this system, thus control system design is simplified, performance of driving motor is decreased and scan rate is improvd. This model plays a good potential solution for the compact, large trip, high precision optical scanning system development.
2013, 42(8): 2103-2107.
Aiming at structure characteristics of camera developing in some project and the complexity of space environment, the camera thermal vacuum optical experiments are fulfilled prior to launch, in order to obtain the law of the thermal optical focusing, to check the correctness of the integrated simulation model, test input and boundary conditions. Space thermal vacuum environment is so simulated on the ground. As the environmental conditions of the vacuum tank for the camera is not conducive to staff to operate. The development of vacuum thermal optical bench is very important, to achieve the convenient adjustment of the camera posture in a vacuum tank. Some parameters of bench were calculated. The grating scale or encoder was adopted to achieve closed-loop control. The vacuum grease for lubrication of low volatile was adopted. The bench rotation accuracy is 6. Mobile accuracy is 0.02 mm. The bench accuracy can meet camera experiment adjustment requirements. Thermal optical vacuum test platform is not only able to complete the requirements of the camera thermal optical experiments, but also to save experimental time in significantly and improve the experimental efficiency, favorable to ensure the successful completion of the camera experiment.
2013, 42(8): 2108-2114.
Spectrum method is one of the important testing technique by which the optical properties (reflectance, transmittance and absorptance) of the thin film-substrate system could be obtained directly. The expressions for reflectance, transmittance and absorptance in case of weak absorption existing in substrate were derived by researching the optical transport characteristics of thin film-substrate system. The optical properties of thin film could be calculated by testing the properties of thin films deposited on single sided polishing substrate and double sided polishing substrate indirectly. HfO2 thin film deposited on fused silica substrate was measured by Lambda-900 spectrophotometer. And the error analysis shows that the error of single side reflectance is 1.00%, however, the error of single side transmittance is about 0.601%. It can be concluded that the characterization and evaluation of various types of single side thin film could be obtained by the method in this paper.
2013, 42(8): 2115-2119.
In order to increase the large aperture telescope third mirror supporting structure first order natural frequency, eight pre-stressing cables was used to replace the four wing beams structure. Firstly, according to the Bernoulli-Euler beam theory, the mirror supporting structure was simplified as a model composed of quality point and beam and the system natural frequency expressions was got as well as the first order natural frequency. Then, in 1.23 m telescope, with pre-stressing force at 20 000 N, the first order natural frequency comes to 18.9 Hz, comparing with the finite element software ANSYS, 17.8 Hz, with error of 6%. Finally, through the analysis of the condition that the second mirror room quality maintain invariable, relations for pre-stressing force under different primary mirror diameter and secondary mirror supporting structure of the first order modal was got. For 1.23 m telescope, pre-stressing force of 70 000 N can make the first order modal frequency reached 34 Hz. For 2 m 4 m telescope, by adjusting the pre-stressing force, the first frequency can be controlled in more than 20 Hz. The method can be used for similar structure dynamics calculation. Meanwhile, this structure can have high torsional rigidity, and can effectively reduce the weight of the secondary mirror supporting structure, the design of the optical system in the large diameter has very good guidance.
2013, 42(8): 2120-2125.
In order to detect the performance of infrared lens accurately and rapidly, an auto focus measurement system with rapid infrared CCD was put forward, based on image processing. In this system, mid-wave cooled infrared CCD was used, whose wave length ranges from 3.7-4.8 m. The infrared CCD received the radiation which came through the detecting infrared lens, auto focus and image processing. By using the technology of auto-focus and image processing, the performance of the lens such as symmetry or focus and so on would be test. In this article, the modern auto-focus methods were emphasized, and the auto focus method suit for this detection system was put forward. A new image clarity evaluation organically combined grey entropy with statistics function was described, and was verified by a lot of testing results. The experimental results show that the position precision of the system resetting is up to 10 m.
2013, 42(8): 2126-2131.
Axial support system plays an important role in axial position and deformation of primary mirror. In order to profoundly develop such study, axial hydraulic Whiffle-tree support was introduced in the foundation of structure Whiffle-tree. First, according to the principle of kinematic constraint and support based on three axial points, the characteristic and category of Whiffle-tree system were introduced. Especially, the difference between structure Whiffle-tree and hydraulic Whiffle-tree was compared in detail. Then the model building method was elaborated, and an axial hydraulic Whiffle-tree support system for a large aperture primary mirror was selected to be calculated and optimized in statics. As a result, the mirror deformation is 18.6 nm which satisfies the design requirement and the rationality and accuracy of such modeling method are also certificated according to comparison between two different modeling methods.
2013, 42(8): 2132-2136.
Mirror is an important part of catadioptric omnidirectional imaging system. Aiming at different application, several kinds of mirror such as hyperboloid surface, ellipsoidal surface, parabolic surface and some others were designed for the system. However, the image of these systems has large distortion and low resolution on the edge of picture. In order to make the system suitable for pavement survey, based on front projection model, concave hyperboloid mirror was designed. Imaging features of horizontal scene was analyzed for new system. The simulation results show that by optimization of distance between omnidirectional viewpoint and focus of mirror, new system attains low distorted imaging features compared with systems consist of hyperboloidal mirror or horizontal distortionless mirror.
2013, 42(8): 2137-2145.
The wireless optical MIMO technology which combined antenna transmit diversity, receive diversity and channel coding diversity, significantly improved the channel capacity. The auther's research progress at layered space-time code was introduced, the relationship between error rate characteristics and transmitting/receiving antenna number, detection algorithm was analyzed, this paper compared the different coding scheme that including horizontally-layered space-time codes (H-BLSTC), threaded-layered space-time codes (T-BLSTC), diagonally-layered space-time codes (D-BLSTC) and vertical-layered space-time codes (V-BLSTC). Then, it's also analyse turbulence intensity inhibits effects due to different coding scheme and detection algorithm. Through the analysis of three kinds of layered space-time coding to get diagonally-layered space-time codes is own the best performance, followed by threaded-layered space-time codes, and at last is the horizontally-layered space-time codes.
2013, 42(8): 2146-2149.
Considering the determination of mode effective refractive index in the free propagation region of AWG, a new method using weighted equivalent mode refractive index as the mode effective refractive index in the free propagation region was proposed. The vector wave equation of magnetic field in the free propagation region of AWG was demonstrated using Galerkin finite element method with absorbing boundary condition under the slowly-vary-envelope approximation. On this basis, the mode of free propagation region was analyzed based on 3D full-vector beam propagation method, and the equation of weighted equivalent mode refractive index was deduced with guided-mode propagation analysis method. This method provides a useful theoretical tool for the determination of mode effective refractive index in the free propagation region of AWG.
2013, 42(8): 2150-2155.
The anti-jamming performance of the Beidou navigation satellite receiver attracted the users' extensive attention due to the increasingly complex electromagnetic environment. A indoor wireless anti-jamming performance test system for the Beidou dynamic receiver was proposed. Semi-physical simulation system is constructed in anechoic chamber by the combination of scene mapping based on grey relational analysis(GRA), instrumentation script-based drive technology and corresponding simulators, microwave switches. By adjusting the output power of the interference, and the receiver effective carrier-to-noise ratio(C/N0), where is used to represent the anti-jamming performance, then the jam-to-signal ratio(J/S) can be obtained when the receiver is loss of lock. The simulation results show that the anti-jamming performance test of the receiver can be reflected by J/S versus C/N0 curve, and this method provides a test platform for the Beidou receiver anti-jamming performance test.
2013, 42(8): 2190-2196.
To improve the efficiency of star sensor during the transition from star tracking mode to full-sky star identification mode, a novel method of synchronously predicting and tracking guidance star sub-catalog while in star tracking mode was proposed. The work mode transition was always prepared, therefore the real-time property of star sensor was improved. The overall catalog architecture which was hierarchical storage and sequentially mapping' was designed. Based on this architecture, guidance stars were homogenized, the overlapped sub-catalogs were generated, and fast searching and management of data were realized. The attitude of star sensor at next time was predicted by using the attitude data of air vehicle. The address of sub-catalog was predicted and tracked by the built index relationship between bore sight of star sensor and addresses of sub-catalogs. Once star tracking failed, full-sky star identification implemented in four redundant sub-catalogs, therefore the process of star identification was simplified, and the efficiency was improved. Experimental results show that the designed star catalog is more scientific and reasonable. The proposed method has strong robustness. The real-time property in work mode transition of star sensor at highly dynamic condition can be effectively improved.
The azimuth was often a large angle because navigation accuracy of fiber-optic inertial navigation system was not high, and the filtering equations of initial alignment were non-linear. In order to improve the initial alignment accuracy of nonlinear models, a improved Sage_Husa adaptive kalman filtering method was put forward, and applied to initial alignment of fiber-optic inertial navigation system. Established initial alignment nonlinear model of large azimuth misalignment angle, contributed the system noise statistics estimators, and used improved Sage_Husa adaptive kalman filtering to simulate for nonlinear error equations. The simulation results show that the improved Sage_Husa adaptive kalman filtering could deal with nonlinear problems, improve the accuracy of initial alignment. Azimuth misalignment angle error estimation precision improved 27% than EKF.
2013, 42(8): 2202-2208.
Near-infrared star detection system used three detectors to detect stars at the same time, analysed the relation between contrast and the detection parameters of near-infrared band during daytime, what's more, compared the contrast of different detectors, the result showed that: with the observer zenith angle increased, the star-background contrast increased linearly; when the solar zenith angle was greater than the observer zenith angle, the contrast similar to the exponential growth; out of a certain height, the contrast exponentially increased with the height increased; with the increased of the detection azimuth, contrast approximation Gaussian distribution; at the same time, background radiation contrast of different fields got minimum when the main field is 0; star-background contrast nearly symmetrical distribution with the alter of main field's detection azimuth, provide a better basis for the magnitude amendment.
2013, 42(8): 2209-2215.
Tracking performance of gyro-stabilized seeker (following called seeker for short) is a main factor of the guidance precision. To analyze the tracking performance of seeker, seeker's tracking performance index Q was defined. Coupled dynamics model of seeker was established, and transfer functions of the image stabilization and tracking performance and the stability of dynamics model were analyzed. The fundamental reason to the limits of seeker's tracking performance was derived from the point of view of dynamics stability. Seeker's dynamic model was proved correct when compared the Hardware-In-Loops simulation with the mathematical simulation results. In order to reduce boresight and improve tracking performance of seeker, PI compensation was proposed. The simulation results show that boresight can be reduced as well as other performance is not deteriorated by adjusting the proportion and integration parameters. It is discussed further that how to extract line of sight rate when boresight is 0. It can provide guidance to design the dynamics and control system of seeker.
2013, 42(8): 2216-2220.
Axial ratio(AR) test requires continuous rotation of polarization axis of linear polarization(LP) antenna, however high-speed rotation of rotary joint brings cable jitter, which causes inconsistencies between amplitude and phase. Since it is difficult to eliminate the jitter at high frequency, a fast and accurate measurement method of the AR of CP antennas was presented. The method, which is based on the orthogonal decomposition theory of elliptically polarized wave, employs LP antenna to measure two groups of orthogonal LP amplitude of the CP antennas under test. Therefor axial ratio of circularly polarized antennas and other parameters of elliptic polarization can be obtained by calculating. And on this basis, an innovative method of measuring the AR of CP antennas using only three linear polarization components was proposed. By measuring CP antennas in an anechoic chamber repeatedly, the method was proved to be effective. This method can increase the efficiency of measuring CP antennas, ease the difficulty level of test, and is of great importance to engineering application.
2013, 42(8): 2221-2225.
In order to meet the demand of precision measurement of radius of curvature, precision ROC measurement system was designed based on laser interferometry. High precision, non-contact ROC measurement of optic elements was achieved, whose diameter was 100-300 mm and ROC 500-200 mm. The factors of ROC measurement results was analyzed and combination of standard uncertainty was caculated. Installation and adjustment of the system and verification experiments was finished. The relative uncertainty of ROC experiment results is above 710-6, it can meet the design demand of 1010-10.
2013, 42(8): 2226-2230.
Laser ceilometer is one of the most powerful instruments to monitor the spatial and temporal distribution of cloud automatically and uninterruptedly. For the reason of algorithm, low signal-to-noise ratio and existence of aerosol layer may lead to inaccuracy during cloud observation. Based on the analyses to raw signal, differential signal and second-order differential signal, the differential enhancing method for detection of cloud was presented as well as the construction of two new signal series. The new method could realize the enhancement and separation of the signal feature of cloud peak and boundary and results in reduction of influence of low signal-to-noise ratio and existence of aerosol layer. Comparison experiments using both the differential zero-crossing method and the differential enhancing method were conducted. The results show the differential enhancing method can reduce the rates of missing judgement and misjudgement while has no influence to the judgement of cloud heights.
2013, 42(8): 2231-2237.
In recent years,the hypersonic aircraft technology is paid more and more attention for its great significance for military application. The guidance, navigation and control technology is one of the key technologies of hypersonic aircraft. And as one of widely used automatic navigation method,which is of such advantages as high navigation accuracy, good anti-interference ability, and auto-navigation ability, the restoration algorithm of star map for hypersonic aircraft was studied in this paper. Considered the aero-optical effects caused by hypersonic flight, the simulation of turbulence-degrade star map was studied, and the increment Wiener filter and the restoration algorithm of iterative blind deconvolution in limitation support region were used for restoration of the turbulence-degraded star map, respectively. The simulation result shows that, the latter method is of higher precision and the restored star map can be identified by the celestial navigation system correctly.
2013, 42(8): 2238-2243.
A series of interferometric images were acquired by pushbroom in the image plane interferometric hyperspectral technology, where the fringe pattern of every point was extracted and the spectrum was reconstructed by Fourier transform. Compared with the traditional interference imaging spectrometer, it had the advantages of high flux, high spectral resolution, high target resolution and so on. The basic principle of imaging plane interference spectrometer was introduced and a new push-broom method was presented. The petreatment such as apodization and DC removal are researched. Then the phase error correction methods were discussed, so as their advantages and disadvantages. A Sagnac image plane interference spectrometer was set up, and the spectral curve of the measured light was got.
2013, 42(8): 2244-2251.
Active polarization imaging technology is a hot research field in recent years both at home and abroad, which has great value in terms of military and civilian aspects. Compared with passive imaging technology, active polarization imaging technology can remedy the deficiencies of imaging completely relying on the radiation or reflection from the target. As a result, the imaging distance and signal to noise ratio of the image can be greatly improved. Besides, by adding a light source with its parameters known, the Muller matrix of the target can be calculated according to the incident light and the output. Furthermore, the characteristics of intensity, coherence and depolarization of the light emitted or reflected from the target can be analyzed. The development of active polarization imaging technology, as well as system structure and principle were introduced. In addition, several typical polarization imaging systems, as well as their advantages and disadvantages, were presented. At the end, the future of active polarization imaging was predicted.
2013, 42(8): 2252-2261.
Master-slave camera system had been widely used in visual surveillance domain because both large-view information and high-resolution local-view information of the tracked object could be obtained at the same time. For the widely demanding of intelligent visual surveillance, a master-salve tracking algorithm using dual PTZ(pan-tilt-zoom) cameras based on ground plane constraint was presented. The proposed method could be divided into two stages: offline calibration and online tracking. In offline stage, the view-to-view homography induced by the ground plane was computed using object matching from two cameras. A novel method that automatically estimated homography from synchronized video streams of the two cameras was presented. Compared with traditional methods, the proposed method didn't need calibration tools, and without the need of manual intervention. Then principal point and equivalent focal length were estimated using matched features. In online stage, the calculated homography transformation was used to establish coordinate correspondence of the master and slave cameras. With the estimated principal point and equivalent focal length, the control parameters of the salve camera could be computed. Therefore, master-salve tracking could be realized. Compared with other methods, the proposed algorithm can be used in the case of wide baseline. The proposed method can also adapt to the depth change of tracked target. Meanwhile, the requirements for real time master-salve tracking can be meeted. Quantitative results in the indoor and outdoor scene show good performance of the proposed approach.
2013, 42(8): 2262-2268.
Topic of the paper was to correct the vignetting of mosaic images based on reflector. The generation mechanism of the vignetting phenomenon was analyzed through geometrical optics, and the vignetting energy distribution model in the middle of the optical field was proposed. According to the analysis result, a degenerate model which was calculated by the steepest descent method was proposed. The parameters of Hesse matrix were deduced to solve the problem of irregular quadrics fitting, then to correct the vignetting. The experiment result illuminates that the parameters of the degenerate model can be estimated effectively, the image's SNR after correction can be increased by 15 dB, and the vignetting can be removed effectively. The method can work in real-time working mode, and has extensive application value.
2013, 42(8): 2269-2274.
The Fourier basis compressed sensing(CS) algorithm was applied in inversed synthetic aperture radar(ISAR) imaging of smoothly moving target successfully. But it ignored the higher order terms of ISAR echo in azimuth when constructing the ISAR echo model, the sparse representation based on Fourier basis for azimuth information of ISAR echo whose target is maneuvering was invalid, which leaded to the lack of information of Doppler frequency in the local range of time domain. As a result, the imaging results of maneuvering target were blurred in azimuth. The time-frequency analysis technology, because of its good time-frequency characteristics in local, was introduced into the analysis of ISAR echo in azimuth: A Gauss window was used to improve the sparse basis which represented the Doppler frequency of ISAR echo data in a selected short time slice while the size of sparse basis matrix remained constant. Then CS technology which includes time-frequency analysis based sparse basis to represent the echo data, Gauss random observation matrix to reduce the sampling rate and Orthogonal Matching Pursuit (OMP) algorithm to solve the coefficients of the sparse representation was used to analyze the azimuth information in that time slice. As a result of CS's advantage in improving resolution, the resolution of image supported by limited data was high at the same time. The target models of uniformly accelerated motion and varying accelerated motion were both designed to simulate the ISAR echo data of maneuvering target. Compared with the existing imaging methods such as Fourier basis CS algorithm, Range Doppler(RD) algorithm and the Range instantaneous Doppler(RID) algorithm based on Gabor transform, the new one achieves significant improvement in terms of imaging results in azimuth. The corresponding imaging results show the effectiveness of the algorithm from both subjective observation results and objective evaluation indicators including Peak Side Lobe Ratio(PSLR) and azimuth resolution.
2013, 42(8): 2275-2280.
It is challenging to detect moving objects from a moving camera as a motion field in the entire image can be induced by the camera motion. A fast and memory-saving detection method is proposed to resolve this problem. First, a fast and memory-saving registration scheme is used to estimate the homography transform between two neighboring frames. Then, neighboring frames is registered with the estimated transform, and frame-to-frame difference is performed to capture the motion cue. Finally, the motion cues are aggregated to construct a constantly updated motion image. After thresholding the motion image, separation of moving objects from the background is achieved. The effectiveness of the proposed method in detecting moving objects from cluttered scenes is validated via experiments on several different video sequences. In addition, this method performs better than previous techniques, while using a fraction of the computation time and a fraction of the memory as well. Specifically, with a memory usage of 825 kByte only, this method runs at 16 frames per second for a sequence with an image resolution of 480360.
2013, 42(8): 2281-2287.
It is a problem to detect small moving target in infrared images, especially under the circumstances of complex background and noise. Now aiming at this problem, a novel method based on cycle spinning Contourlet transform and the multi-orientation gradient character of Facet model was proposed. Firstly, through cycle spinning Contourlet transform, the infrared image was decomposed so that the noise was removed and the signal-to-noise ratio and smoothness were increased. Then, a median filter based on the multi-orientation gradient character of facet model was designed to filter the reconstructed image, so the complex background and noise were restrained effectively. After that, the algorithm of 2-level maximum between-cluster variance was used to segment the filtered image. Finally, further detection of the small target was made according to the relationship of position and velocity in images. The results prove that the method concerned in this paper can restrain the complex background with strong clutter to good effect and can test small target efficiently.
2013, 42(8): 2288-2293.
Aiming at the problem of combination detection of targets with various shapes in space based infrared surveillance system, an adaptive target detection method based on extended Markov random field (E-MRF) was proposed. First, the target characteristics in space based infrared surveillance system were analyzed and the extended MRF neighborhood system was established by using the typical target shapes as templates. Then the new MRF potential function was constructed. By using the potential differences between the infrared background and target, the detection problem of targets with various shapes under complex background was formulated as a discrimination problem of MRF potential function and finally the problem of mixed shape targets detection under MRF theory framework was efficiently solved. Simulation and experimental results show that the proposed method can adaptively adjust the operator according to the target shapes and perfectly detect targets with different shapes under various image SCRs. So the proposed method has a stabile performance.
2013, 42(8): 2294-2298.
To solve the problem of not good enough target detection results while applying present hyperspectral remote sensing band selection methods, a novel band selection method based on target detection-Two Step Band Selection(TSBS) was proposed. Primarily, hyperspectral bands were initially selected and sorted via typical band selection method. Then according to the target detection results of different band subsets after successively accumulating each band, the initially selected bands were reselected again. Finally, the band subset with better target detection result was obtained. The proposed method could not only inherit the advantages of typical methods, but also had higher application pertinence and simple implementation due to its direct target detection-based band selection. Experimental results show that TSBS method has better general applicability. Both hyperspectral data dimensionality reduction and improvement of target detection result can be realized effectively.
2013, 42(8): 1997-2002.
Based on the theory of the optical phased array (OPA) and behavior of the mode propagation in Ti-diffused Lithium Niobate (Ti_LiNbO3) waveguide, a novel array of integrated optical waveguides applied in OPA system was proposed. According to the beam propagation method (BPM) and the existing semiconductor technology and parameters, optical characteristics of the waveguide array, loss characteristics, and coupling characteristics were simulated. The structure of phased array parameters was presented. Simulation result shows that the OPA based on the array of integrated optical waveguides performs well. This array of integrated optical waveguides can steer consequently and precisely with the steering angle of more than 4.5. The half-wave voltage is less than 6 V, and the control unit has low loss and quick response.
2013, 42(8): 2003-2007.
In order to correct laser beam pointing error for the high accuracy tracking and lasing system, a laser beam tip measurement method of laser backward scattering was developed. Firstly, the opto-mechanical structure and the backward scattering theory were introduced, and the relationship between detect distance of laser beam tip and binocular parallax was analysed. Secondly, based on the long time observation, the detect distances of laser beam tip in good weather condition, medium weather condition and bad weather condition were obtained respectively. Finally, the validating experiment of laser beam tip measurement method by targeting method in predetermined orbit was carried out in good weather condition. The difference of two methods was 2.5, which indicates that laser beam pointing accuracy could be improved greatly by the laser beam tip measurement method.
2013, 42(8): 2008-2011.
LD clad-pumped high efficient Tm-doped fiber lasers with quantum efficiencies beyond the Stokes Limit were reported. Different laser cavities, including dichroic mirror with fiber end reflection, high reflective fiber Bragg grating(FBG) with fiber end reflection and dichroic mirror with low reflective FBG, were studied. A maximum slope efficiency of 56.9% was obtained with the dichroic mirror and the fiber end flection forming the laser cavity, corresponding to a quantum efficiency of 142%. Spectral linewidth of the laser output was closely related to the reflective mirrors used in different cavities. Selected by the broadband dichroic mirror, the laser resonated randomly with the high reflective band of the dichroic mirror. With an FBG as the high reflective mirror of the laser cavity, narrow linewidth of 38 pm was attained at an output of 1 W. In another laser configuration, one low reflective FBG was exploited as the output coupler, and narrow linewidth of 69 pm was achieved at an output of 0.9 W. And the laser linewidth was limited by the reflection bandwidth of the FBG used.
2013, 42(8): 2012-2016.
One-dimensional non-homogeneous media irradiated with short pulse laser was treated in this paper. The influences of size, location, absorption coefficient and scattering coefficient on boundary signals were analyzed. According to the changes of parameter sensitivity, the sampling time range of time-resolved signals can be determined. Under such conditions, multi-parameters in one dimension non-homogeneous participating media were reconstructed simultaneously with conjugate gradient(CG) method. The simulation results have shown that different sensitivities were obtained for different irradiated locations, when the other conditions remain unchanged. The peak value of sensitivity appeared in different moment for different parameters. However, most variable information was contained in the twice transmission time. Therefore, the twice transmission time was proposed as the best sampling time range in inverse problems. Accurate results were obtained in multi-parameters inversion. The differences between the inversed results and true values increases with the increase of measure errors. Lager errors were obtained in the inversed results for the parameters with small sensitivities.
2013, 42(8): 2017-2021.
The concentric rings were reported for the first time when 532 nm YAG pulsed laser interfered CCD imaging system at the distance of 31.5 m under infield. According to analysis of experimental process, relative intensity distribution of concentric rings and imaging properties of CCD system, the generation conditions of concentric rings were found to be stable and inherent to the optical system.Meanwhile, the imaging properties of the concentric rings and laser spot were different. Aiming at various diffractions and interferences of the CCD optical system, the theory analysis and contrast of experimental results were done by combining with central spot size, positional distribution, relative intensity distribution, imaging properties and occurring probability of concentric rings in this paper. The results indicate that the concentric rings are formed from equal thickness interference of reflected laser between the top and bottom surface of the optical system cemented lens.
2013, 42(8): 2022-2026.
Range-gated underwater laser imaging system is a kind of underwater photoelectric imaging system which is based on the principle of time label. It can effectively restrain the backscatter of water and improve the range of target detection, and has superior value for military and civil use. In the range-gated underwater laser imaging system, the lights received by ICCD include the backscatter of water, the direct component and forward scatter of reflected light of the target. Computing model of light energy received by ICCD was built. Giving the moment and the width of ICCD opening gate, the direct component and forward scatter of reflected light were analyzed and the calculation methods based on PSF theory were studied. The backscatter of water was calculated through water layering. According to those studies, the signal to noise ratio of range-gated underwater laser imaging system was given. Finally, the impact of target range on the SNR was analyzed and simulation result was given.
2013, 42(8): 2027-2031.
Based on the LFM(linear frequency modulation) signal and the principle of the heterodyne, the expression of the output of the heterodyne detection in synthetic aperture ladar was induced in detail. The data image of the array target was simulated in a strip-map mode sequentially. The object image was reconstructed by the method that Fourier transform and some emendation were used in the range direction while the correlation operation was used in the azimuth direction. The analytical expression of the object image was induced in both the range direction and the azimuth direction, so that the intensity distribution of the object image were analyzed in the azimuth direction and the range direction separately. Therefore, many improving methods were advanced by analyzing the factors on the image quality, which may provide many references for further optimization.
2013, 42(8): 2032-2035.
Aiming at the detection threat on photoelectric equipment caused by active laser detection technology, the stealth technology by weakening the cat's eye effect was studied in this paper. Take the night vision objective lens as an example, the stealth technology was studied quantitatively by means of matrix optics tracing, and was proved by experiments. The results show that the echo intensity of the cat's eye effect was affected easily by reconnaissance environment and system assembly errors, such as the tilt and the defocus of photosensitive surface. Thus, under the premise of the limited change optical structure of photoelectric devices and the reduction of their image quality, some assembly errors created artificially can weaken the cat's eye echo of the system, so as to achieve stealth. This technology can effectively reduce the probability of being detected and attacked by the enemy in military confrontation, so it has certain reference value in the military. Key words: stealth technology; echo; cat's eye effect; matrix optics
2013, 42(8): 2036-2040.
The observation of the capillary discharge-pumped Ne-like Ar 46.9 nm soft X-ray laser output was reported under the condition of pure Ar and gaseous mixture of Ar-He, Ar-Ne, Ar-N2 and Ar-Kr. Mixing Ar with an appropriate quantity of He, the laser output was enhanced evidently, and there was an optimum ratio of He in the gaseous mixture of Ar-He, which could be the best for laser output. The experimental results of Ar-Ne, Ar-N2 and Ar-Kr mixture show that Ne, N2 and Kr decrease the laser output. The source research of discharged produced plasma in extreme ultraviolet lithography also mixes an appropriate quantity of He, in order to enhance 13.5 nm.
2013, 42(8): 2041-2044.
In order to improve laser range ability of the pulse laser ranging finder system with the photoelectric detecting device in navigation system, a laser echo wave receiver circuit was designed based on cooling-APD (avalanche photodiode detector). According to the characteristics of cooling-APD, the most appropriate TEC (thermo electric cooler) cooling power was output to reduce temperature on APD, thus the APD ran in best condition with not only lower noise voltage but also higher detecting sensibility. Experiments show that when incident light power is 80 W with attenuation of 45.6 dB, false alarm rate declines from 8.57% to 0.49% after cooling of APD. So applying the circuit into new airborne photoelectric detecting device, it will promote sensitivity of the receiver system, and at the same time, it will help make a great improvement on the long-distance laser range ability, which can meet the new airborne photoelectric detection system of remote distance military requirements.
2013, 42(8): 2045-2049.
In order to satisfy complicated electromagnetic environment, electromagnetic shielding for electro-optic reconnaissance platform was designed specially. Shielding is one of the most effective methods for inhibiting radicalization interference and improving electromagnetic compatibility(EMC) of the system. Shielding difficult points of electro-optics reconnaissance platform was analyzed in detail, and the resultful measures were taken to solve the problem of radicalization interference for electro-optics reconnaissance platform. Radiated emission(RE102) tests were made to prove the effects of the improved reconnaissance electro-optics platform. Test results show that the degree of RE102 can be reduced about 10 dBV/m, and the EMC of electro-optics reconnaissance platform is improved. Through the combination of analyses and calculations by shielding, grounding and filtering, the EMC of electro-optics reconnaissance platform can satisfy the requirements of standard GJB 151A-1997.
2013, 42(8): 2050-2054.
A monolithic front-end amplifier for portable laser rangefinder was realized in 0.5 m CMOS technology, owing to attaining adequate performance and lower cost simultaneity. It consists of transimpedance pre-amplifier(TIPA), differential voltage post-amplifier(DVPA), band gap reference and other interface circuits. Attention has been paid to design the TIPA and DVPA, which are most appropriate for the laser rangefinder signal processing. The measurement results show that the chip achieves 87.27 dB transimpedance, 952.8 MHz bandwidth, 17.64 pA/Hz1/2 input referred noise current. The die area occupies 2.816 mm2 including pads and dissipates 106.9 mW power consumption with 75% from the output buffer.
2013, 42(8): 2055-2059.
Covering width is an important index of the panoramic aerial camera, so the effect of imaging starting angle error on the sawtooth result of panoramic aerial camera imaging was analyzed in detail. Based on introducing the operating mode and scheduling of panoramic aerial camera, the relationship between the ratio, which was defined as , of image margin difference to covering width, target slope angle, transverse scanning angle and imaging starting angle error was given. When panoramic aerial camera was on operating, one special constant angle was reserved for the imaging starting angle. The imaging starting angle error would be appreciably high when this method was used. So improved iterative arithmetic was imported. In the improved method, the imaging starting angle error of every frame was recorded and was used to correct that of next frame. At last, experimental result was given. Result shows that the root-mean-square of imaging starting angle errors are respectively 0.045 and 0.005 when general and improved methods are used. And the corresponding ranges of are[0.009 1,0.014 8] and [0.001 0,0.001 7]. Compared with general method, the imaging starting angle error is reduced to be 1/9 when induced iterative arithmetic is used, and the corresponding maximum of is 0.001 7, which could comply with engineering requirement.
2013, 42(8): 2060-2067.
Focal plane in aerial plane, which has strict temperature requirement, is an important component in airborne electronic devices. The quality imaging of focal plane will fall off due to thermal noise and dark current generated during its working process. The characteristic of thermal design for focal plane in aerial camera was discussed and analyzed. Phase change system encapsulating phase change material was adopted to eliminate heat. According to the design feature and heat transfer path in focal plane, thermal design scheme of component was given. Thermal equilibrium equation and numerical analysis model of the heat transfer in focal plane were established by finite element analysis method. Based on the given temperature boundary condition, transient-state thermal analysis of component was carried out through IDEAS-TMG, which was a finite element thermal analysis software. The thermal response performance of focal plane was given. Thermal analysis results show that the operating temperature range of focal plane and radiator are 18-31.1 ℃ and 18-28.2 ℃ respectively. Simulation results obtained can meet the requirements of heat control. Thermal design scheme based on phase change is verified through thermal test, and there is a well consistency between the results derived from confirmatory test and numerical analysis. The maximum deviation between thermal analysis and thermal test are all not exceeding 5%. The correctness of numerical simulation and the validity of temperature prediction are verified. In thermal test, the operating temperature range of focal plane and radiator are 18-32.3 ℃ and 18-29.6 ℃ respectively.
2013, 42(8): 2068-2075.
In order to solve the problem of imaging system instability caused by high work frequency of image composing circuit on the satellite, the camera's structure was improved, a composing and compression method of TDICCD based on FPGA platform for satellite remote sensing images was proposed. First, the principle of real-time composing and compression for multi-channel satellite remote sensing image was introduced. Then, based on TDICCD linear array push-broom imaging mode characteristics, line-based 2D-DWT integer lifting scheme was used. EBCOT of bit-plane and coding parallel structure was proposed. Composing and compression of image data was simultaneously achieved. At last, experiment platform for the validation was established. Experimental results indicate that the system clock reduce to 80 MHz and 64 MHz respectively from the original 100 MHz in the lossless and 2 times compression. Reconstruct image's PSNR is 84 dB that is bigger than 80 dB. The average processing time of one line image is 61.2 s that is smaller than camera's smallest line period. The proposed algorithm is stable and reliable. It achieves the composing and compression within camera, it satisfy engineering requirements.
2013, 42(8): 2076-2079.
Pointing Polaris error directly affects measure accuracy for equatorial telescope, and searching for an effective method of finding true north is very important. The equatorial telescope was fixed to point to the south equator, if the trace of star which traversed in the field of view was not a horizontal line, and then the polar axis of telescope was rotated about vertical axis until the trace of star being a horizontal line. The equatorial telescope was fixed to point to the east or west equator, if the trace of star which traversed in the field of view was not a horizontal line, and then the polar axis of telescope was rotated about horizontal axis until the trace of star was a horizontal line. The principle for the method of finding true north was deduced and analyzed on the base of spherical triangle. Horizontal pointing error of polar axis was adjusted when telescope pointed to the south equator, and vertical pointing error of polar axis was adjusted when telescope pointed to the east or west equator. The equatorial telescope which is adjusted by using the method rotated about polar axis with constant speed in 50 minutes, and target error projected to Y axis of star which was measured transfered 4. Observation result confirms that the method was simple and effective, and pointing error of polar axis of equatorial telescope adjusted by using the method is limited.
2013, 42(8): 2080-2084.
Autofocusing is one of the key techniques for space cameras to ensure a high quality image. The optical system of the camera defocuses in all probability due to many influential factors, such as the impulsion or jitter during launching, changes of temperature and air pressure. So, in order to retrieve the defocus, focus measure algorithm based on power spectrum was studied, where the algorithm was used in TDI CCD space cameras which imaging scenes changed anytime. Firstly, an improvement over Fourier transform power spectrum was proposed, namely wavelet power spectrum(WPS) estimation, which took advantage of the multi-resolution and band-passing characters of wavelet transform. Then, directional WPS was proposed in order to reduce the influence of image-moving-mismatching. Lastly, according to the theory that power spectrum is independent of scenes and defocus made the power spectrum's high frequency losing, the evaluation function for image definition was designed, using the weighted sum of directional WPS. The experimental results of the real pushblooming images show that the new definition evaluation method can reflect the real remote images' defocusing state validly. Moreover, the directional WPS is less sensitive to the scenes' variety compared to FFT PSS, which reduces the error ratio from 0.36 to 0, and the curve gets more saturated. In addition, the error ratio of all the 100 emulational samples is only 0.06. So the proposed algorithm meets the principles of monotony, excellent sensitivity and precision, and suits for the autofocus in TDI CCD remote sensing cameras better.
2013, 42(8): 2156-2161.
To design high-quality optical filters and optical switches,the effect of double negative medium on the transmission spectrum of one-dimensional photonic crystal quantum well (AB)m(CBAABC)n(BA)m was studied with transfer matrix method. The results show that when layer C is double positive medium, there are 2n+1 narrow transmission peaks in the spectrum. While layer C is negative medium, there are only 2n-1 narrow transmission peaks in the spectrum, presenting degeneration. When the negative value of refractive index of double negative medium in layer C increases, the spectrum moves towards two sides of the forbidden band center and the quality factor of the transmission peaks improves quickly. When the negative value of optical thickness of double negative medium in layer C decreases, the spectrum draws close to the center of the forbidden band and the quality factor of the transmission peaks also speedily improves. The effect of the transmission quality factor of optical crystal quantum well on the optical thickness of double negative medium is more sensitive than the one on the negative value of refractive index. The law, the effect of the double negative medium on the characteristics of transmission spectrum in the optical crystal quantum well, can provide reference for optical crystal theoretical research and designing new quantum optical devices.
2013, 42(8): 2162-2166.
The ultra-compact microwave photonic filter based on silicon-on-insulator microring resonator was designed to increase the integration density of microwave photonic devices and enlarge the free spectral range. According to the coupled mode theory of waveguide optics, the optical intensity transfer function of the microring resonator with parallel-coupled structure was deduced and the transmission spectrums were simulated numerically. The results show that when the radius of resonator of resonator is 0.79 m, the straight waveguide width is 0.3 m and the ring waveguide width is 0.25 m, the filter with full wave at half maximum(FWHM) of 7 nm can be achieved, which also has an exceeding free spectral rang 140 nmof and an insertion loss less of 0.5 dB. The performance of this filter can meet the requirements of coarse wavelength division multiplexing system.
2013, 42(8): 2167-2172.
The topology and operational principle of fiber optic current transducer(FOCT) were introduced, and the /4 wave plate affecting the performance of FOCT were analyzed. The fabrication of /4 wave plate was studied and several factors that affect the fabrication were introduced, according to the analysis, the improved /4 wave plate that meet the claims is manufactured by using suitable material and method. The experimental results show that the FOCT's measurement precision is improved by using the improved /4 wave plate, and the FOCT can satisfy the accuracy requirements of the 0.2S class can be satisfied by the FOCT, meeting the requirements of digital substation.
2013, 42(8): 2173-2180.
This research aims to design a maximum power point tracking algorithm which tracks the global maximum among multiple local maximums. Multiple local maxima can be exhibited on the power-current characteristic curve under non-uniform insolation conditions. The research was based on a significant number of data simulations of photovoltaic cell and the discovery that PV panels' P-I curves obeied the following rule. The values of local maxima monotonically decreased with respect to the distance from the global maximum. Moreover, statistical studies had been conducted on the slopes of the curves, distances between two local maxima, etc. Based on these observations and discoveries, the algorithm was thus designed. The algorithm obtained the location of the global maximum of a P-I curve by partially scanning the curve, during which Regional Scanning Mechanism was adopted to enhance the precision and efficiency of the algorithm. In addition, another two simple and fast PO algorithms were compared, their appropriate uses were discovered and be applies smoothly in real practices. The design of this algorithm also ensures reasonable time complexity, efficiency and guarantees that no maxima will be ignored. It is also equipped with an interesting property such that the more the maxima a P-I curve possesses, the faster the algorithm is correspondingly.
2013, 42(8): 2181-2185.
The photocathode surface barrier formation process of the GaAs photocathode was simulated according to the variation of the photocurrent while the photocathode was activating and in situ tests of spectra response, the two-dipole model was amended to establish a three dipole model. It was considered from the new model that the photocathode surface barrier formed by three kind of dipole layers, the first dipole layer was composed of GaAs(Zn)-Cs+ dipole, the second dipole layer was composed of Cs2O dipole and the third dipole layer was composed of GaAs-O-Cs dipole, the second and third dipole layer embedded in the first dipole layer. The barrier potential distribution which was piecewise uniform was established according to tunnel effect and results of quantum efficiency tests, it was calculated that the width of the barrier is 1.65 nm, and the effective electron affinity energy is -0.44 eV. The establishment of the new model is of great significance to further understand the photocathode surface emission mechanism.
2013, 42(8): 2186-2189.
In order to obtain a method for low damage and steaty mesa structures, the damage mechanism of InGaAs by Cl2/N2 ICP etching was studied in this paper. The surfaces of InGaAs before and after etching was investigated using Raman spectroscopy and X-ray diffraction(XRD) technology. The results indicate that lattice defects are the main damages. The surface damage of different treatment process was characterised and analysed by the method of microwave photoconductivity decay measurement. The results show that the surface defects and broken bonds of etching damage are decreased to a certain extent by wet etching and surface sulfur treatment, but deep defects still cannot be avoided.
