Articles
2014, 43(1): 1-5.
In infrared detection systems, when the target signal is relatively weak, the noise caused by a spot of stray light will greatly reduce the SNR of system, thus reduce the system's detection capability. For highly sensitive infrared imaging system and low temperature environment simulation system, the thermal radiation emitted from the optical surfaces is the largest source of stray light. In this paper, the certainty and near-field property of self-emitted thermal radiation stray light were analyzed, and a new computational model based on ray optics was proposed. Some key problems in the calculation model were discussed, the solutions were proposed. Moreover, the near-field thermal radiation of objects was accurately numerical simulated. Distribution of irradiance on the detector was gained, the effects of temperature, distance, radiation coefficient and other parameters on the stray light level were analyzed, which has a guiding significance on reducing the system' s thermal radiation noise reasonably and efficiently.
2014, 43(1): 48-52.
In order to solve the problem of automatic selection of tracking point in target tracking after automatic target recognition of IR warship targets in the infrared imaging and tracking systems, a new automatic detection algorithm of ship aimpoint was proposed. Based on the waterline' s geometrical relationship below the warship and the high brightness characteristics of engine compartment, the cross part of the waterline and engine compartment was detected. This cross part was taken as the primary aimpoint of IR warship target. Otherwise, the central part of the waterline would be taken as the aim point of IR warship target. First of all, the de-noising pretreatment of target area was used, through the Canny egde-detection, edge closed and two connected domain de-noising operations, the background texture clutter was removed to determine the edge of target. Then, piecewise linear fitting on the target bottom edge was used and the curve fitting results would be taken as the waterline. Finally, the gray In order to solve the problem of automatic selection of tracking point in target tracking after automatic target recognition of IR warship targets in the infrared imaging and tracking systems, a new automatic detection algorithm of ship aimpoint was proposed. Based on the waterline' s geometrical relationship below the warship and the high brightness characteristics of engine compartment, the cross part of the waterline and engine compartment was detected. This cross part was taken as the primary aimpoint of IR warship target. Otherwise, the central part of the waterline would be taken as the aim point of IR warship target. First of all, the de-noising pretreatment of target area was used, through the Canny egde-detection, edge closed and two connected domain de-noising operations, the background texture clutter was removed to determine the edge of target. Then, piecewise linear fitting on the target bottom edge was used and the curve fitting results would be taken as the waterline. Finally, the gray value statistics was calculated to get the brightest area as the position of engine compartment. The experimental results show that this method has stability testing results and good robustness. It can be applied to detect the aim point of IR warship target in different viewing directions. The algorithm provides an effective solution for the problem of automatic selection of tracking point in target tracking.
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 ℃.
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