2013 Vol. 6, No. 6
As polarization imaging detection can offer its unique advantage in the target detection, this paper discusses its technological development. Firstly, the concept of polarization imaging detection technology is introduced, and the research process of polarization imaging detection technology in abroad is summarized. On this basis, the key technologies of polarization detection, including the polarization properties of target, the polarization transmission in channel environments and polarization imaging acquisition technology, are discussed. Finally, this paper summarizes several problems to be solved and suggests the future developing direction of the polarization imaging detection.
The concepts, composition, applications and key techniques of space-based laser weapons are introduced in detail in this article. The destruction degree of laser on the target has been analyzed and the corresponding reference threshold is given. Some solutions to the key problems of the systems are put forward, including the development and variety of high-energy laser, the development technology of large aperture mirror and its structure, as well as affecting factors on system precision and methods of improving the accuracy about space-based target acquisition tracking and pointing(ATP). The research direction and basic theory are provided for the further development and improvement of the precision of the systems through the research of the development of space-based laser weapon systems.
The principle of infrared stealth is introduced based on the Stefan-Boltzmann law firstly in this paper. Several methods for infrared stealth are given. The working mechanism of the infrared stealth materials are introduced, and some unsolved problems are put forward. Then, military applications and research progress are briefly described. Finally, the development trend of infrared stealth is summarized. It suggests that the future research will mainly include two aspects:one is to solve the combination of various waveband stealth technologies; the other is to improve existing methods and to explore new methods of infrared stealth.
On the basis of the applications of surface modified silicon carbine mirrors in space optical systems, this paper summarizes the research status and developing trends of this kinds of mirrors at home and abroad. It introduces the widely used silicon carbide materials and their different properties, then gives several kinds of preparation technics of the silicon carbide mirror blanks, such as moulding, modification and different polishing methods. Based on the analysis of manufacture and modification process, a way to improve the manufacture technology of silicon carbide mirrors in China is summed up.
In consideration of the requirements of monitoring and researching the harmful trace gases in the air, the widely used spectral remote sensing technologies are reviewed. The principle of the atmosphere optical remote sensing and monitoring is introduced and several practical measurement methods such as Fourier transform infrared spectroscopy, differential optical absorption spectroscopy, laser long path absorption, tunable diode laser absorption spectroscopy and differential absorption lidar are described. Furthermore, the characteristics of these methods are given, then their advantageous and disadvantageous are analyzed via comparing the aspects among these methods.
Electronic Image Stabilization(EIS) technology usually is employed to remove the random jitter generated by the imaging equipment and to stabilize its video output. Firstly, the development status of EIS is introduced. Then the motion estimation module is studied in details, which is one of the most important modules of EIS. Both the direction motion estimation algorithms and the feature-points-based matching algorithms are discussed. Furthermore, the motion correction and compensation algorithm are presented. Finally, according to the difficulties and the future trends of the EIS, the developing direction for feature matching algorithms of EIS is proposed.
To modify the image motion blurring induced by the relative position motion between a camera and a subject, a robust blind deconvolution method based on single image motion blurring was proposed. Firstly, the strong edges of a latent image was predicted. By constraining image gradient, the point spread function in frequency domain was estimated fast and robustly by this method. After that, the non-blind deconvolution algorithm based on the gradient constrain was used to restore the latent image. Meanwhile, a new edge preserving filter-guided filter was used to suppress the ringing and noise. Experiments show that the proposed method can restore a high quality image with clear edges and tissues from single motion blurring image, and the operation time is less than 20 s.
To improve the image resolution of a hyper spectral image, an image motion compensation algorithm was proposed. The mechanisms of image degradation caused by forward image motion were analyzed and a digital Image Motion Compensation(IMC) was adopted to restore the blurred image. Then, the Point Spread Function(PSF) and noise power were estimated, and the improved algorithm of Wiener filtering was selected to restore the blurred image. By taking the average absolute error and the peak signal to noise ratio as the evaluation criteria, the proved experiments were performed. Experimental results under the known quality of PSF and noise power show that the absolute average error of the image for improved Wiener filtering algorithm decreases by 9.31% and the peak signal to noise ratio increases by 13.98% as compared to the traditional Wiener filter. It is concluded that the quality of the hyper spectral image can be improved effectively by the proposed algorithm.
By focusing on hyper-spectral remote sensing images, the spectral correlation and spatial correlation of images from an interferential imaging spectrometer was analyzed. A 3D Differential Pulse Code Modulation(DPCM) lossless compression scheme was submitted. This scheme includes three aspects:spectral DPCM, intra-DPCM to prediction error image and adaptive bit-level arithmetic coding to differential coefficients. The experimental data show that the algorithm has achieved lossless compression and the average of compression ratio is up to 1.662, 15.6% increasement in comparison with that of the 2D integer wavelet transform. This algorithm uses addition-subtration and shifts to complete data compression, which is easier for hardware implementation.
To improve the precision of long-ranged laser spot position measurement in an outdoor experiment, blind deconvolution technology was proposed to restore the spot image afterwards to lower the impact of atmospheric turbulence on spot imaging. First, classical blind deconvolution algorithms were introduced, of which the shortage is analyzed. Second, an improved blind deconvolution algorithm was designed. The penalty terms were added to TV(Total Variation)objective function and the alternative iterative method was also redesigned. Then, the convergence of the improved method was testified mathematically. Finally, the improved method was compared with other classical methods by experimental simulation. The capability of improved method was testified with several objective figures, and the results show that the Signal to Noise Ratio(SNR) is improved by 15% at least. The restoration result of outdoor experiment proves that the improved method is effective.
The reasons of ineffectiveness of median filtering and its improved algorithm for eliminating the high-density salt-and-pepper noise are analyzed. A variational inpainting method is adopted to remove the high-density salt-and-pepper noise, and a inpainting model of Non-local Total Variation(NL-TV) based on the existing model of Total Variation(TV) is proposed in this article. In the NL-TV model based on the characteristics of salt-and-pepper noise(uniform distribution and the gray value of 0 or 255), we view the noise points as the lost or damaged points of an image to find the districts similar to the neighborhoods of noise points in an image, and then interpolate the noise points by taking the central pixel in a similar district as a new neighborhood of noise points. By this method, we transform the problem of image denoising into a problem of image restoration to remove the high-density noise. The experimental results show that the Peak Signal to Noise Ratios(PSNRs) are 22.85 and 28.77 after removing the noise for a color and gray-scale image with 90% of noise density, which is better than the results obtained by median filter and its improved algorithm in terms of the objective evaluation criteria. Using this model, we can effectively remove the high-density salt-and-pepper noise and restore the image details better, which provides a new approach to remove the high-density noise.
By using the commutative Clifford algebra method to model for a color image, the parallel processing of R, G and B components in the color image can be realized in a holistic manner and the integrating processing for the color image can be implemented. This paper reviews the progress of color image modeling, researches a type of commutative Clifford algebra, namely Cl2com and gives the definitions of the arithmetic operations, unit element, inverse element, conjugation, and the norm for the commutative Clifford algebra. Then, it describes the expression of the color image based on the commutative Clifford algebra and introduces an application example of this method:the edge detection of color image. In comparison with the quaternion-based color image modeling, the proposed method can remove the data redundancy and reduce the computational complexity to the utmost extent. The proposed color image modeling method can be applied in color image processing tasks as a useful tool.
Under haze, fog, and rain weather conditions, the image received by a photoelectric imaging system will lose the contrast and color fidelity owing to the absorption and scattering in atmosphere. To overcome the image degradation mentioned above, this paper proposes a new dark channel image estimation method using morphology filter based on the analysis of the atmospheric optical model and the dark channel priority. It further utilizes a dynamic parameter strategy to solve the color distortion in a large area of sky or white wall. Results on a variety of outdoor haze images show that the proposed method can effectively restore a haze-degraded image and improve the image quality. As for the image with 600 pixel400 pixel, the restoration simulation time by Matlab is only 0.4 s. The dynamic parameter strategy is simple but effective to reduce the color distortion phenomenon.
A material with specific refractive index is prepared according to the requirement for the preparation of the laser protective coating for solar arrays. In this method, we apply the electron beam co-evaporation technique based on doped material preparation methods. Tests show that the refractive index of the doped material is 1.75, according with the result of optimized scheme. The material is then used in the preparation of optical thin films to achieve a further optimization of the laser protective coating properties. Obtained laser protective coating has excellent properties and its solar radiation transmittance is increased by more than 6%. The film thickness mask technology is applied to improve the film thickness uniformity of large area thin films prepared by co-evaporation method. The thickness nonuniformity of doped material film prepared by this method within 400 mm area is less than 2.1%. It is showed that the technical process of electron beam co-evaporation technique is simple, reliable and suitable for practical applications. Test results of the film performance are consistent with the theoretical optimized results.
Single AlF3 layers were deposited upon fused-silica substrates placed on a simulated fixture which has the same radius of curvature with the spherical element to characterize the optical and microstructural properties of the AlF3 films. First, transmittance and reflectance spectra of AlF3 layers at different positions on the fixture were measured by an UV-visible spectrophotometer from 185 nm to 800 nm, and their refractive indexes and extinction coefficients were obtained. Then the surface morphologies and surface roughnesses of AlF3 layers were assessed with an Atomic Force Microscopy(AFM). Finally, the X-ray Diffraction(XRD) was used to characterize the microstructure of AlF3 layers. Experimental results indicate that for AlF3 layers deposited at different diameters on the spherical element, their optical losses increase along with the diameters. The extinction coefficients of AlF3 layers at the edge position are 1.8 times of that at the center, and surface roughness are 17.7 times of that at the center. The results suggest that for the coating on the surface of spherical element, the difference in optical loss along the diameter caused by steam incident angles should be considered.
On the basis of the characteristics of an airborne electro-optical platform, six coordinate systems were established and eight linear coordinate transformations were performed. A coordinate transformation model from a camera sensor plane to geodetic coordinate systems was established by using linear coordinate transformation, and the computation formula of geodetic coordinate of the target was derived based on the transformation of different coordinates. The influence of target localization due to various error factors was discussed, and the localization error was analyzed with Mont Carlo method. The experimental results show that the target location is affected by aircraft position errors, aircraft attitude errors and EO platform pose errors, among which the aircraft position errors are transferred directly into the target location, and the aircraft attitude errors and EO platform pose errors are tranferred scaling with the range of 10-4~10-2 to the target location. This method is efficient and useful to the localization of targets for airborne EO platforms.
A high power electronic control cabinet for space optical remote sensors was designed according to the design demands of space electronic equipment. Firstly, the thermal design principle was summarized for space electronic equipment. Then, the thermal design process of the electronic cabinet was generalized, the temperature difference of typical high power electronic components was calculated and the thermal design schemes of printed circuit boards and high power electronic components were introduced. Finally, the design schemes were validated by the means of thermal analysis and thermal test. The test results indicate that the thermal balance temperature of the electronic control cabinet is less than 30 ℃ in a stable working state and the shell temperatures of electronic components are under 54.2 ℃, which proves that the design schemes fully meet the design requirements of thermal control.
To ensure the temperature requirements of the solar observer working at L1 Lagrangian point, the thermal design for Lyman Coronagraphy Imager(LACI) and Lyman Disk Image(LADI) was carried out, and the heat flux of the orbit was calculated. The thermal designs of light trap, filter components, detector components, electric box, and entirety of the observer were discussed in details. By using collector panels settled in the side facing to the Sun, the active heating power could be reduced by 73%. In order to reduce the temperature gradient caused by long-term observation facing to the sun, a heat pipe was embedded in the frame. Simulation results show that all conditions meet the temperature indicator in 4 typical cases. The thermal design system with a low active power solves many problems, such as the cooling of the observer in orbit, insulation during orbital transfer phase, and meets the working temperature requirement of below -50 ℃ for a CCD plane.
To complete high speed and high Signal-to-Noise Ratio(SNR) imaging of a multispectral TDI CCD, a high-performance imaging circuit system is designed on a multispectral TDI CCD sensor which can be applied to space. The system is composed of a Field Programming Gate Array(FPGA) to be a kernel logic part, a RS422 communication interface, and an output interface of CAMERALINK, which is capable of outputting the photos under a dynamic scan in two output modes of monochrome and colored image data. A target with grey stripes is used to calibrate the white balance on three multispectral regions(R,G,B) and the imaging test for this system is carried out using colored stripe target. The output image data rate reaches 1.2 Gbps under a driving frequency of 15 MHz. The SNRs of monochrome and colored images are up to 53.56 dB. The system meets the specification of space observation with high resolution on multispectral sensors and provides a support for the design of high-speed multispectral cameras in space.
The effect of synchronous motion error for the focusing mechanism of a space camera on the image quality is explored. For a large size focusing mechanism, the paper analyzes the reasons causing the synchorman motion error. According to the optical system parameters of a certain space camera, it draws a conclusion that when the Modulation Transfer Function(MTF) of the optical system declines no more than 5%, the allowable maximum error of synchronous motion is 0.02 mm. Then, based on the focusing mechanism, we deduce the formula of synchronous motion error and calculate that the maximum error of synchronous motion is 0.015 mm. Finally, the actual errors of synchronous motion before and after a vibration test are measured to be 0.012 mm and 0.013 mm respectively, which indicates that the focusing mechanism has great stability. Both the theoretical analysis and the experiments demonstrate that this focusing mechanism meets the requirements of practical application quite well.
When the pinhole filter is applied in the converging illuminating optics of a 193 nm excimer laser with high repetition rate and high power, the laser-induced damage threshold of the pinhole filter should also be considered besides the fabrication feasibility, thickness and the pinhole size. In this paper, one dimensional conduction mathematic model based on laser-induced damage theory is used to analyse the laser-induced damage threshold for different thickness metals illuminated by the high power 193 nm excimer laser. The results indicate that Al has a higher laser-induced damage threshold of 1.161010 W/cm2 at 1.2 m thickness. Furthermore, the Al also has the advantage of easy fabrication. Ion beam machining method is used to fabricate the pinhole filters with diameters of 1.2 m and 1.5 m and the obtained sample are observed by a scanning microscope. It shows that the pinhole filters have good roundnesses and inner roughnesses, which almost satisfies the need of a shearing interferometer.