2010 Vol. 3, No. 3
This paper introduces the developing trends of QuickBird, WorldView-1, WorldView-2 satellites from DigitaleGlobe Inc(USA) and the IKONOS, GeoEye-1, GeoEye-2 satellites from GeoEye Inc(USA), and then analyzes and reviews the specifications and characteristics of these high resolution earth imaging commercial satellites and their space cameras at different launch schedules. It points out that the development of earth imaging commercial satellites will trend towards small volumes and smart performance. Therefore, the next research should focus on the attitude control of satellites precisely, exploration of TDICCD with small pixel sizes and high integrated orders, design of optical systems in small related apertures and digital image processing technology for image enhancement.
The methods to generate the terahertz wave by optical rectification, photoconductive antennas, air plasmas and parametric generators are described in detail, then how to detect the terahertz wave by electro-optic sampling, photoconductive antennas and air plasmas are introduced as well. The terahertz time-domain spectroscopy and the asynchronous electro-optic sampling technique are also described. Furthermore, the applications of the terahertz technology to research fields, especially to the detection and identification of drugs are discussed. A terahertz spectrum database includes 38 kinds of drugs with a purity more than 99% is established. Moreover, the Artificial Neural Network(ANN) and a support vector machine are used to identify drugs automatically and the experimental methods and related theory are proposed to determine the purity and effective ingredients of drugs. By using a Gaussian software, individual species of drugs such as methyl-phenyl ammonia(MA), ketamine and heroin are conducted by spectral analysis, which provides a basis for implementing the drug inspection in laboratories. Finally, this paper reviews the developments of the terahertz technology briefly.
The thermal design of space optical systems is proved by an integrated method of optical-mechanical-thermal analysis. The general method for thermal-optical is explained, and the relationship between thermal-optical analysis and thermal design is expressed. Then, a thermal control system for space cameras is designed by active and pasitive thermal control methods according to its space environment and structure characteristics. The temperature field and thermal elastics at some special boundary conditions are analyzed based on the finite element method, and the displacements and deformations of all the optics surfaces are fitted with Zernike polynomials. Finally, the Modulation Transfor Function(MTF) of space optical system is calculated by CodeⅤ. The results show that the MTF of space optical system is better than 0.5 when its resolution is 50 lp, which meets the requirements of optical design, and proves that the thermal design is reasonable and feasible.
A convergence algorithm of field stitching and intersection measurement is proposed based on the development of two prototypes of high-speed video-measuring systems with external field stitching. Five coordinates are established for the earth centroid and optoelectronical systems. The definations of the coordinates are introduced and coordinate transforms are discussed. The experiment of intersection measurement and field stitching for an identical moving target is carried out with the data from eight cameras in two high-speed TV measuring instruments. The result shows that the stitching algorithm is correct and effective, and has obtained an unique solution. Meanwhile, the influences of earth curvature and meridional convergent errors are fully correated, which indicates that the intersection measurement algorithm can also be used in the intersection measurement of other optoelectronical measurement and control instruments.
In order to satisfy the strict requirements of the surface-shapes and lightweight ratios for space mirrors, the topological method was introduced to design the reflect mirror with a Ф 700 mm. According to the density method, the Solid Isotropic Microstructure with Penalization(SIMP) model was established. In the condition of axial-oriented gravity, by taking the general flexibility as a design constraint, and the minimum volume as a design objective, a better structure with a RMS of 8.89 nm and a lightweight ratio of 82% was obtained after iterations. In the same weight, the conventional triangular lightweight structure shows its RMS in 11.75 nm and lightweight ratio in 65%. In the condition of radial-oriented gravity, the surface-shape of the topological structure also meets the requirements of the design. In the considerations of the surface-shape and lightweight ratio, the computational result shows that the topological optimization method is better than the conventional method.
The basic principle of Fourier Transform Profilometry(FTP) is introduced, then a new Adaptive Main Frequency Bandpass Filter(A-MFBF) algorithm is proposed based on the simulation result of phase modulation frequency spectrum. The proposed algorithm is used to design the A-MFBF to filter out the main frequency and reconstruct the phase of a measured object. Results show that the precision of 3-D measurement system can be improved by 5% relative to that of the average ones, and its metrical precision can be repeated steadily. The real-time 3-D shape reconstruction is implemented by proposed A-MFBF without effect by subjective factors. Furthermore, a experiment of reconstructing phase for the steel with ribs is carried out, and the precision of reconstructed measurement is calculated and analyzed. The results show that the precision from the theoretical simulation is in good agreement with the experimental results, which demonstrates the validity of the algorithm.
To detect precisely small and dim targets in a complicated background with ocean waves and cloud clutters, a new algorithm is presented which picks up the sea-sky line at first, then efficiently detects the targets on the special region under sky, ocean, and nearby the sea-sky line. On the basis of the line gray characteristics of sea and sky, this algorithm combines the gradient method and morphologic operation to segment the sub-band image in a potential area of sea-sky line, further to fit the sea-sky line by Hough transform to implement the precise location of the sea-sky line. The experiment result shows that this method can extract the sea-sky line from the complicated sea-sky background and can detect the small targets fast and efficiently. For a 256 pixel256 pixel file, the sea-sky line can be located in 4.1 ms and a small target can be detected in 5.3 ms, which demonstrates that the algorithm can meet the requirements of high frame image processing in real time.
The stray light reflected from the anterior surface of a cornea is about 10~100 times of the effective reflectivity of a retina, which can greatly reduce the precision of eye aberration detection and retinal imaging quality. Therefore, it is necessary to avoid the stray light. In this paper, some methods to eliminate the stray light reflected from the anterior surface of cornea are introduced and compared, such as the Polarization Beam Splitting(PBS), confocal hole, annular illumination, and the illumination with decentered thin beam. Analyzed results show that although the methods can remove the stray light reflected from the anterior surface of cornea in some degrees, they are not ideal. After analyzing, it is pointed out that the combination of annular illumination and confocal hole is the best, and the method not only has the high light-efficiency, but also is much more effective and handy than other methods.
A micro flat-field near-infrared spectrometer with simple structures and lower stray light was designed and developed. By comparing with the conventional method in which a additional installment was taken as a dispersion system to suppress the stray light, this method installed a plane mirror with a diameter of 8.5 mm in front of the collimation mirror to control the incident light. By adjusting the mirror, the angle of the incident light was changed and the light could be received by the collimation mirror totally without bypass light. Using this method, the stray light of the system has been reduced approximately by 1.13%. Furthermore, a linear array CCD detector was chosen as a receiving component to avoid the cooling system and scanning rotary mechanism of plane grating. By using the CCD detector and new stray light suppressing method, the flat-field near-infrared spectrometer has been microminiaturized.
Focusing systems play an important role in a variety of optical measurements and detection instruments. In this paper, several kinds of auto-focusing methods were described and the relevant focusing evaluation functions were introduced based on image processing methods. An auto-focusing system based on image processing was designed by using the TMS320DM642 digital signal processing chip as a platform, and its programming was implemented by a real-time multi-tasking operating system DSP/BIOS developed by TI company. The real-time multi-tasking operating system provides a guarantee for the realization of task scheduling and real-time focusing. Moreover, some problems and solutions which are needed to pay attention in the realization of auto-focusing system were demonstrated. The system designed in this paper can find the image plane in 4-5 steps(about 2 s), which meets the requirements of practical applications.
In order to meet the special requirements of semiconductor lasers and YAG lasers for films synchronously, the principles of a high reflectance film were researched. Then, by choosing the TiO2 and SiO2 films as the higher and lower reflectance materials, a high laser-induced damage threshold reflectance film was deposited. The optical and mechanical properties of the materials were investigated and the depolarization and anti-laser-induced damage of the film were overcome. In experiments, the electron beam vacuum coating and the Kaufman ion source assisted technique were used to deposit the film and the TFC software was used to design the thin-film structure. By adjusting the parameters of coating process and monitor method, the high reflectance film was successfully deposited on a 10 mm1.8 mm K9 substrate. Obtained results show that the both reflectances of p-component and s-component have exceeded 99.95% at the wavelength of 900 nm~1 100 nm when the incidence of laser is 45. The experiments demonstrate that the high reflectance film has a stable property and a high laser-induced damage threshold, and it is suitable for both semiconductor lasers and YAG lasers.
A new optical structure in a dual-frequency laser interferometer for measuring lead screws in diffraction grating ruling engines is proposed, and a formula which can quickly correct the Abbe error is deduced in this paper. In the process of testing lead screws, because the Abbe error in the measured data can be compensated in real time, the measurement system which doesn't meet Abbe principle can achieve high measurment accuracy. In addition, by adjusting the reference angle of the conical prisms, this method can also eliminate the measurement error induced by the axial movement of a lead screw in measuring process. The experimental result shows that the maximum residual error is only 0.48 m within a 300 mm stroke after the maximum Abbe error of 1.39 m is corrected. In conclusion, this method effectively improves the measurement accuracy of lead screws.
In order to meet the practical needs of laser-beam riding guided sighting instruments which can be tested overall indoor, a parameter solution in the testing system is demonstrated to test the performance parameters. Each part in the parameter testing solution is discussed separately. The system can test the parallel error of the fixed focal length between laser axial and sighting axial, the typical position output characteristic of a controlling field, the biggest parallel error in the whole process of zoom, and the irradiance uniformity of a laser spot by applying the technique of CCD image processing. The system has advantages in simple structure, convenient operation, high accuracy and so on. In the analog test, the solution of the system meets the challenge of practical needs in engineering.
A video system with a transmission speed of 622 Mbps is designed and realized by taking the high speed characteristic of wireless laser communication. Functions of the system such as video converting, data processing and buffering, laser transmitting/receiving are implemented on a single circuit board to achieve a better flexibility. The ping-pong operation which is made up of internal asynchronous FIFO(First in First out) is utilized to effectively switch the continuous video data flow. Manchester code is employed to obtain better recoveries of data and clocks from the received signals. Moreover, it is also easier to detect the byte boundary from serialized data flow and to synchronize the communication. Experimental results show that the system can transmit video signals stably and meet the application need in the under ground distance, and the system provides a platform for further research on laser communication technologies.
A ring-unit FSS is designed and put into absorbing materials to form the composite FSS absorbing structure, then the structure is numerically simulated through the spectral domain approach. The reflection coefficient of the structure at a microwave band in 2-16 GHz is calculated and the influence of ring-unit's sizes and aligning cycles on absorbing characteristics is studied. The results show that when the ring-unit FSS's unit spacing is 10 mm and unit size is 3.3 mm, the resonance frequency reflectivity decreases from -8.15 dB to -14.5 dB, and the absorbing band with whose reflectivity is larger than -5 dB broadens from 1.2 GHz to 3.05 GHz. Meanwhile, the resonance frequency reflectivity increases with the increasing of ring-unit size, and the absorbing material's bandwidth expands with the expansion of unit aligning cycles. Experimental results indicate that the FSS can be used in absorbing materials to improve its absorbing properties. Moreover, the required composite FSS absorbing structure can be obtained by adjusting the corresponding parameters, which expands the application scope of FSS in absorbing materials.