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This PDF file contains the front matter associated with SPIE Proceedings Volume 10463 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
Satellite navigation system plays an important role in people's daily life and war. The strategic position of satellite navigation system is prominent, so it is very important to ensure that the satellite navigation system is not disturbed or destroyed. It is a critical means to detect the jamming signal to avoid the accident in a navigation system. At present, the detection technology of jamming signal in satellite navigation system is not intelligent , mainly relying on artificial decision and experience. For this issue, the paper proposes a method based on deep learning to monitor the interference source in a satellite navigation. By training the interference signal data, and extracting the features of the interference signal, the detection sys tem model is constructed. The simulation results show that, the detection accuracy of our detection system can reach nearly 70%. The method in our paper provides a new idea for the research on intelligent detection of interference and deception signal in a satellite navigation system.
The rotation center of the optical tomography is not strict in the actual device, resulting in the deviation of the rotation center, so that the final projection image reconstruction effect is not ideal. The method proposed in this paper introduces the sampling and fitting circle method on the basis of the original projection sinusoidal center calibration method, makes a preliminary calibration of the rotation center and makes it more accurate with the gradient operator after the center of the projection sinusoid is positioned. A further central calibration of the object imaging in the optical path transmission is made at the center of the detector target surface according to the gradient. Experiments show that the center position of this method is more accurate than the original sinusoidal calibration and has a reliable basis. Using the gradient operator to judge the effective image clarity, the final reconstructed image also has high resolution and anti-jamming. The feature recognition rate of the image has greatly improved. The experimental results have made a great contribution to obtaining clear and effective information.
In recent years, the increasing numbers of scientific payloads and growing constraints on the probe have made constraint processing technology a hotspot in the deep space planning field. In the procedure of planning, the ordering of variables and values plays a vital role. This paper we present two heuristic ordering methods for variables and values. On this basis a graphplan-like constraint-programmed planner is proposed. In the planner we convert the traditional constraint satisfaction problem to a time-tagged form with different levels. Inspired by the most constrained first principle in constraint satisfaction problem (CSP), the variable heuristic is designed by the number of unassigned variables in the constraint and the value heuristic is designed by the completion degree of the support set. The simulation experiments show that the planner proposed is effective and its performance is competitive with other kind of planners.
Due to the suddenness and complexity of modern warfare, land-based weapon systems need to have precision strike capability on roads and railways. The vehicle navigation system is one of the most important equipments for the land-based weapon systems that have precision strick capability. There are inherent shortcomings for single source navigation systems to provide continuous and stable navigation information. To overcome the shortcomings, the multi-source positioning technology is developed. The All Source Positioning and Navigaiton (ASPN) program was proposed in 2010, which seeks to enable low cost, robust, and seamless navigation solutions for military to use on any operational platform and in any environment with or without GPS. The development trend of vehicle positioning technology was reviewed in this paper. The trend indicates that the positioning technology is developed from single source and multi-source to ASPN. The data fusion techniques based on multi-source and ASPN was analyzed in detail.
A new visual navigation method is proposed in the paper, which take advantage of natural landmarks and image local features. Images of natural landmarks are first collected and organized as database. SURF features of natural landmarks are also extracted and saved. In practice, real-time images are captured by camera, and their SURF features are also extracted. For each real-time image, its SURF features are used to match with corresponding ones of images of natural landmarks. According to match rules, it can be decided that which landmark the real-time image belongs to. Experimental results demonstrate that this method has high accuracy and strong robustness in complex environment.
Aiming at vehicle detection on the ground through low resolution SAR images, a method is proposed for determining the region of the vehicles first and then detecting the target in the specific region. The experimental results show that this method not only reduces the target detection area, but also reduces the influence of terrain clutter on the detection, which greatly improves the reliability of the target detection.
Enriching mission planning approach with state transition graph heuristics for deep space exploration
As to support the mission of Mars exploration in China, automated mission planning is required to enhance security and robustness of deep space probe. Deep space mission planning requires modeling of complex operations constraints and focus on the temporal state transitions of involved subsystems. Also, state transitions are ubiquitous in physical systems, but have been elusive for knowledge description. We introduce a modeling approach to cope with these difficulties that takes state transitions into consideration. The key technique we build on is the notion of extended states and state transition graphs. Furthermore, a heuristics that based on state transition graphs is proposed to avoid redundant work. Finally, we run comprehensive experiments on selected domains and our techniques present an excellent performance.
A decision-making method of navigation for the small spacecraft is proposed. Attitude information is obtained by microelectromechanical gyroscope and geomagnetism sensor. Kalman filter and other information fusion techniques are used to improve the navigation accuracy. The long-term on-orbit navigation control of small aircraft is realized, reducing the cost of on-orbit navigation.
When space homing aerocraft long term flighting on orbit, the accuracy and rapidity of its attitude and orientation are the key factors for its combat effectiveness and survivability. Fiber optic gyro is suitable for the navigation requirements of space vehicles, but in the long run, it is necessary to calibrate the fog. Aiming at the problem, A self calibration method based on fusion filter is presented. According to the observation of the star sensor, the gyro drift and the four part number vector of the attitude are used as the state estimation by UKF. The gyro axis misalignment error and scale factor error are used as the model error to be estimated by the prediction filter. This method can guarantee the precision, decrease the computation and improve the algorithm speed.
Images and videos taken outside the foggy day are serious degraded. In order to restore degraded image taken in foggy day and overcome traditional Dark Channel prior algorithms problems of remnant fog in edge, we propose a new dehazing method.We first find the fog area in the dark primary color map to obtain the estimated value of the transmittance using quadratic tree. Then we regard the gray-scale image after guided filtering as atmospheric light map and remove haze based on it. Box processing and image down sampling technology are also used to improve the processing speed. Finally, the atmospheric light scattering model is used to restore the image. A plenty of experiments show that algorithm is effective, efficient and has a wide range of application.
Predicting the random drift of MEMS gyroscope based on K-means clustering and OLS RBF Neural Network
Measure error of the sensor can be effectively compensated with prediction. Aiming at large random drift error of MEMS(Micro Electro Mechanical System))gyroscope, an improved learning algorithm of Radial Basis Function(RBF) Neural Network(NN) based on K-means clustering and Orthogonal Least-Squares (OLS) is proposed in this paper. The algorithm selects the typical samples as the initial cluster centers of RBF NN firstly, candidates centers with K-means algorithm secondly, and optimizes the candidate centers with OLS algorithm thirdly, which makes the network structure simpler and makes the prediction performance better. Experimental results show that the proposed K-means clustering OLS learning algorithm can predict the random drift of MEMS gyroscope effectively, the prediction error of which is 9.8019e-007°/s and the prediction time of which is 2.4169e-006s
Optomechanical crystal (OMC) cavities are simultaneous have photonic and phononic bandgaps. The strong interaction between high co-localized optical mode and mechanical mode are excellent candidates for precision measurements due to their simplicity, sensitivity and all optical operation. Here, we investigate OMC nanobeam cavities in silicon operating at the near-infrared wavelengths to achieve high optomechanical coupling rate and ultra-small motion mass. Numerical simulation results show that the optical Q-factor reached to 1.2×105 , which possesses an optical mode resonating at the wavelength of 1181 nm and the extremely localized mechanical mode vibrating at 9.2GHz. Moreover, a novel type of doubly splited nanocavity tailored to sensitively measure torques and mass. In the nanomechanical resonator central hollow area suspended low-mass elements (<100fg) are sensitive to environmental stimulate. By changing the split width, an ultra-small effective motion mass of only 4fg with a mechanical frequency as high as 11.9GHz can be achieved, while the coupling rate up to 1.58MHz. Potential applications on these devices include sensing mass, acceleration, displacement, and magnetic probing the quantum properties of nanoscale systems.
An innovative Neural-Fuzzy adaptive Kalman filter for ultra-tightly coupled GPS/INS integrated system
Considering all integration methods of Global Positioning System (GPS) and Inertial Navigation System (INS) integrated system, ultra-tightly coupled method is with no doubt the best because the mutual assistance is further enhanced and navigation performance is obviously improved. However, UTC GPS/INS system is still affected by changing noise of GPS signals due to the pre-defined constant measurement noise model. To solve this problem a neural-fuzzy adaptive Kalman filter for UTC GPS/INS system is proposed. Fuzzy adaptive controller adjusts the measurement noise model online according to the innovation sequence provided by the Integration Kalman Filter (IKF). Since the design of the fuzzy logic controller is very empirical, a neural network (NN) is developed to achieve the parameter optimization for the fuzzy logic controller. To prove that the innovative neural-fuzzy adaptive IKF is efficient, a simulation package which includes all procedures of UTC GPS/INS system is employed and results are explained in detail. In conclusion, neural-fuzzy adaptive IKF further improves the performance of the UTC GPS/INS system in noise-changing environments.
Algorithm of GNSS positioning based on Doppler shift in incomplete condition of insufficient available satellites
To solve the problem that Global Navigation Satellite System(GNSS) receiver cannot realize positioning due to insufficient available satellites in incomplete condition, a positioning algorithm based on Doppler shift obtained from carrier loop is proposed in this paper. This algorithm can realize dual-satellite positioning in single system and three-satellite positioning in dual-system. Experiment shows that the proposed algorithm can achieve ideal positioning accuracy and significantly improve the continuity of GNSS navigation service in incomplete condition of insufficient available satellites.
Ultra-low expansion glass-ceramic is a kind of functional materials, which has been extensively researched and widely used in various aspects because of its high performance. This paper introduces the optical mechanism and research progress of glass-ceramic. Also the application in aerospace area as laser gyro, objects telescope is illustrated. In addition to this, the preparation methods and prospects of ultra-low expansion glass-ceramic is discussed.
A self-calibration method in single-axis rotational inertial navigation system with rotating mechanism
Rotary inertial navigation modulation mechanism can greatly improve the inertial navigation system (INS) accuracy through the rotation. Based on the single-axis rotational inertial navigation system (RINS), a self-calibration method is put forward. The whole system is applied with the rotation modulation technique so that whole inertial measurement unit (IMU) of system can rotate around the motor shaft without any external input. In the process of modulation, some important errors can be decoupled. Coupled with the initial position information and attitude information of the system as the reference, the velocity errors and attitude errors in the rotation are used as measurement to perform Kalman filtering to estimate part of important errors of the system after which the errors can be compensated into the system. The simulation results show that the method can complete the self-calibration of the single-axis RINS in 15 minutes and estimate gyro drifts of three-axis, the installation error angle of the IMU and the scale factor error of the gyro on z-axis. The calibration accuracy of optic gyro drifts could be about 0.003°/h (1σ) as well as the scale factor error could be about 1 parts per million (1σ). The errors estimate reaches the system requirements which can effectively improve the longtime navigation accuracy of the vehicle or the boat.
The attitude information acquisition of unresolved space objects, such as micro-nano satellites and GEO objects under the way of ground-based optical observations, is a challenge to space surveillance. In this paper, a useful method is proposed to estimate the SO attitude state according to the simulation analysis of photometric data in different attitude states. The object shape model was established and the parameters of the BRDF model were determined, then the space object photometric model was established. Furthermore, the photometric data of space objects in different states are analyzed by simulation and the regular characteristics of the photometric curves are summarized. The simulation results show that the photometric characteristics are useful for attitude inversion in a unique way. Thus, a new idea is provided for space object identification in this paper.
In this paper, we introduce a novel mixture model of the SAR amplitude image, which is proposed as an approximation to the heavy-tailed Rayleigh model. The limitation of the heavy-tailed Rayleigh model in SAR image application is discussed. We also present an expectation-maximization (EM) algorithm based parameter estimation method for the Cauchy-Rayleigh mixture. We test the new model on some simulated data in order to confirm that is appropriate to the heavy-tailed Rayleigh model. The performance is evaluated by some statistic values (cumulative square errors (CSE) < 0.013, correlation coefficient (CC) > 0.99 and Kolmogorov-Smirnov distance (K-S) < 0.03). Finally, the performance of the proposed mixture model is tested on some real SAR images and compared with other models, including the heavy-tailed Rayleigh and Nakagami mixture models. The result indicates that the proposed model can be an optional statistical model for amplitude SAR images.
Since a good knowledge of MEMS gyro stochastic errors is important and critical to MEMS INS/GPS integration system. Therefore, the stochastic errors of MEMS gyro should be accurately modeled and identified. The Allan variance method is IEEE standard method in the filed of analysis stochastic errors of gyro. This kind of method can fully characterize the random character of stochastic errors. However, it requires a large amount of data to be stored, resulting in large offline computational burden. Moreover, it has a painful procedure of drawing slope lines for estimation. To overcome the barriers, a simple linear state-space model was established for MEMS gyro. Then, a recursive EM algorithm was implemented to estimate the stochastic errors of MEMS gyro in real time. The experimental results of ADIS16405 IMU show that the real-time estimations of proposed approach are well within the error limits of Allan variance method. Moreover, the proposed method effectively avoids the storage of data.
In terms of the objective receiver being interfered by multiple Global Navigation Satellite System (GNSS) spoofing signals, the problem still exists that the performance of the other spoofing signals is quite poor since the power of a certain path signal among multiple spoofing signals increases. To this end, a novel power control scheme was proposed. First of all, the influence of multiple spoofing power on noise floor was analyzed based on cross-correlation interference of different Pseudo-Random Noise(PRN) codes, along with the performance of acquiring each spoofing branch with the prerequisite for this noise floor. Then an objective function was constructed and the genetic algorithm was utilized to obtain the optimized distribution of spoofing power. The simulation results indicate that the proposed approach can obviously improve the performance of acquiring each spoofing signal compared to the authentic signals on the condition of noise floor increasing less than 10dB. In addition, the proposed approach paves the way for many actual applications in theory.
Based on Programmable Multi-axes Controller (PMAC), a design of a multi axis motion control system for the simulator of spatial targets’ dynamic optical properties is proposed. According to analysis the properties of spatial targets’ simulator motion control system, using IPC as the main control layer, TurboPMAC2 as the control layer to meet coordinated motion control, data acquisition and analog output. A simulator using 5 servomotors which is connected with speed reducers to drive the output axis was implemented to simulate the motion of both the sun and the space target. Based on PMAC using PID and a notch filter algorithm, negative feedback, the speed and acceleration feed forward algorithm to satisfy the axis’ requirements of the good stability and high precision at low speeds. In the actual system, it shows that the velocity precision is higher than 0.04 s ° and the precision of repetitive positioning is better than 0.006° when each axis is at a low-speed. Besides, the system achieves the control function of multi axis coordinated motion. The design provides an important technical support for detecting spatial targets, also promoting the theoretical research.
The positioning navigation and timing (PNT) architecture was discussed in detail, whose history, evolvement, current status and future plan were presented, main technologies were listed, advantages and limitations of most technologies were compared, novel approaches were introduced, and future capacities were sketched. The concept of cyber-physical system (CPS) was described and their primary features were interpreted. Then the three-layer architecture of CPS was illustrated. Next CPS requirements on PNT services were analyzed, including requirements on position reference and time reference, requirements on temporal-spatial error monitor, requirements on dynamic services, real-time services, autonomous services, security services and standard services. Finally challenges faced by PNT applications in CPS were concluded. The conclusion was expected to facilitate PNT applications in CPS, and furthermore to provide references to the design and implementation of both architectures.
Currently, the design of embedded signal processing system is often based on a specific application, but this idea is not conducive to the rapid development of signal processing technology. In this paper, a parallel processing model architecture based on multi-core DSP platform is designed, and it is mainly suitable for the complex algorithms which are composed of different modules. This model combines the ideas of multi-level pipeline parallelism and message passing, and summarizes the advantages of the mainstream model of multi-core DSP (the Master-Slave model and the Data Flow model), so that it has better performance. This paper uses three-dimensional image generation algorithm to validate the efficiency of the proposed model by comparing with the effectiveness of the Master-Slave and the Data Flow model.
The modeling and forecasting of the receiver clock bias is of practical significance, including the improvement of positioning accuracy, etc. When the clock frequency of the receiver is stable, the model can be established according to the historical clock bias data and the clock bias of the following time can be predicted. For this, we adopted the Kalman model to predict the receiver clock bias based on the calculated clock bias data obtained from the laboratory via sliding mode. Meanwhile, the relevant clock-aided positioning algorithm was presented. The results show that: the Kalman model can be used in practical work; and that under the condition that only 3 satellite signal can be received, this clock-aided positioning results can meet the needs of civilian users, which improves the continuity of positioning in harsh conditions.
Multiple AUVs cooperative localization as a new kind of underwater positioning technology, not only can improve the positioning accuracy, but also has many advantages the single AUV does not have. It is necessary to detect and isolate the fault to increase the reliability and availability of the AUVs cooperative localization system. In this paper, the Extended Multiple Model Adaptive Cubature Kalmam Filter (EMMACKF) method is presented to detect the fault. The sensor failures are simulated based on the off-line experimental data. Experimental results have shown that the faulty apparatus can be diagnosed effectively using the proposed method. Compared with Multiple Model Adaptive Extended Kalman Filter and Multi-Model Adaptive Unscented Kalman Filter, both accuracy and timelines have been improved to some extent.
Attitude errors in a strapdown inertial navigation system due to gravity disturbances and system noises can be relatively large, although they are bound within the Schuler and the Earth rotation period. The principal objective of the investigation is to determine to what extent accurate gravity data can improve the attitude accuracy. The way the gravity disturbances affect the attitude were analyzed and compared with system noises by the analytic solution and simulation. The gravity disturbances affect the attitude accuracy by introducing the initial attitude error and the equivalent accelerometer bias. With the development of the high precision inertial devices and the application of the rotation modulation technology, the gravity disturbance cannot be neglected anymore. The gravity compensation was performed using the EGM2008 and simulations with and without accurate gravity compensation under varying navigation conditions were carried out. The results show that the gravity compensation improves the horizontal components of attitude accuracy evidently while the yaw angle is badly affected by the uncompensated gyro bias in vertical channel.
One mission devoted to detect the mechanism between Earth magnetosphere and solar wind is briefly introduced. Its orbit is an elliptic one with a perigee altitude of 6378km and an apogee altitude of 7*6378km. The space environment of such an orbit in space has seldom been probed. In order to carry out a successful mission, it is necessary to simulate some vital radiation characteristics in the space environment. some electronic devices and optical devices onboard the spacecraft are liable to be affected by the space environment, where solar wind might greatly influence the operation of spacecraft. The simulation results will give great supports to the devising the of the spacecraft and successful operation of the mission.
The star sensor is one of the sensors which are used to determine the spatial attitude of the space vehicle. An optical system of star sensor with large aperture and wide field of view was designed in this paper. The effective focal length of the optics was 16mm, and the F-number is 1.2, the field of view of the optical system is 20°.The working spectrum is 500 to 800 nanometer. The lens system selects a similar complicated Petzval structure and special glass-couple, and get a high imaging quality in the whole spectrum range. For each field-of-view point, the values of the modulation transfer function at 50 cycles/mm is higher than 0.3. On the detecting plane, the encircled energy in a circle of 14μm diameter could be up to 80% of the total energy. In the whole range of the field of view, the dispersion spot diameter in the imaging plane is no larger than 13μm. The full field distortion was less than 0.1%, which was helpful to obtain the accurate location of the reference star through the picture gotten by the star sensor. The lateral chromatic aberration is less than 2μm in the whole spectrum range.
Passive source localization utilizing time difference of arrival (TDOA) has widely application in radar, navigation, surveillance, wireless communication, distributed sensor network, etc. This paper presents two robust algorithms named Modified Taylor-seriesmethod (MTS) and Modified Newton (MNT) method. The proposed algorithms are the improvement of the Taylor-series (TS) and Newton (NT) methods for solving the convergent problem which is critical in the iterative methods. The key component of the proposed algorithms is to produce a new modified Hessian matrix intelligently using the Regularization theory which can turn the ill-posed Hessian matrix into a well-conditioned matrix. The regularization parameter which controls the properties of the regularized solution can be automatically determined by the L-curve method. With this procedure, the proposed methods are robust to make the iteration convergence with a bad initial. Simulation results show that the proposed methods improve the convergent probability and have better capability to distinguish the local minimums from the global solutions compared with the TS and NT methods. The proposed methods give superiorperformances of the location accuracy comparing with the closed-form algorithms at large measurement noises.
Optical synthetic aperture (OSA) can greatly improve the spatial resolution of the optical system. However, due to its long manufacturing cycle, it is difficult and expensive to manufacture. In this paper, we propose a method for numerical simulation of OSA imaging system, which can simulate the image process of the system before the system is manufactured and thus can greatly reduce the manufacturing costs. Firstly, the relationship of energy on the pixel of image plane between OSA systems of different filling factor are analyzed. Then based on the characteristics of the OSA imaging system, imaging model of optical synthetic aperture is analyzed. Moreover, after those methods of simulating space variant image system and space invariant image system are given. At last, a method assessing of the quality of optical synthetic aperture system was given. Simulation results are presented to demonstrate the feasibility of the proposed technique, in terms of spatially variant and spatially invariant optical synthetic aperture system was achieved.
Data link is the key information system for the cooperation of weapons, single physical layer anti-jamming technology has been unable to meet its requirements. High dynamic precision-guided weapon nodes like missiles, anti-jamming design of data link system need to have stronger pertinence and effectiveness: the best anti-jamming communication mode can be selected intelligently in combat environment, in real time, guarantee the continuity of communication. We discuss an anti-jamming intelligent networking technology of data link based on interference awareness, put forward a model of intelligent anti-jamming system, and introduces the cognitive node protocol stack model and intelligent anti-jamming method, in order to improve the data chain of intelligent anti-jamming ability.
In order to solve the problem of poor effect in modeling the large density BRDF measured data with five-parameter semi-empirical model, a refined statistical model of BRDF which is suitable for multi-class space target material modeling were proposed. The refined model improved the Torrance-Sparrow model while having the modeling advantages of five-parameter model. Compared with the existing empirical model, the model contains six simple parameters, which can approximate the roughness distribution of the material surface, can approximate the intensity of the Fresnel reflectance phenomenon and the attenuation of the reflected light’s brightness with the azimuth angle changes. The model is able to achieve parameter inversion quickly with no extra loss of accuracy. The genetic algorithm was used to invert the parameters of 11 different samples in the space target commonly used materials, and the fitting errors of all materials were below 6%, which were much lower than those of five-parameter model. The effect of the refined model is verified by comparing the fitting results of the three samples at different incident zenith angles in 0° azimuth angle. Finally, the three-dimensional modeling visualizations of these samples in the upper hemisphere space was given, in which the strength of the optical scattering of different materials could be clearly shown. It proved the good describing ability of the refined model at the material characterization as well.
In order to solve the problem that the movement state analysis method of the space target based on OCS is not related to the real motion state. This paper proposes a method based on OCS for analyzing the state of space target motion. This paper first establish a three-dimensional model of real STSS satellite, then change the satellite’s surface into element, and assign material to each panel according to the actual conditions of the satellite. This paper set up a motion scene according to the orbit parameters of STSS satellite in STK, and the motion states are set to three axis steady state and slowly rotating unstable state respectively. In these two states, the occlusion condition of the surface element is firstly determined, and the effective face element is selected. Then, the coordinates of the observation station and the solar coordinates in the satellite body coordinate system are input into the OCS calculation program, and the OCS variation curves of the three axis steady state and the slow rotating unstable state STSS satellite are obtained. Combining the satellite surface structure and the load situation, the OCS change curve of the three axis stabilized satellite is analyzed, and the conclude that the OCS curve fluctuates up and down when the sunlight is irradiated to the load area; By using Spectral analysis method, autocorrelation analysis and the cross residual method, the rotation speed of OCS satellite in slow rotating unstable state is analyzed, and the rotation speed of satellite is successfully reversed. By comparing the three methods, it is found that the cross residual method is more accurate.
Design of optical-mechanical structure for off-axis reflective star sensor ground calibration equipment
Before the star sensor completes the attitude measurement task with the launch of the spacecraft, it must be calibrated on the ground. In order to meet the requirements of high precision star sensor calibration, according to some specific problems of optical structure of conventional ground calibration equipment in response to large aperture, long focal length and wide spectrum requirements, an off-axis collimator was designed as a collimating optical system, and the image quality was evaluated, and mechanical structure of the off-axis collimator was also designed in detail. Control technology of star brightness was researched and analyzed, and a set of lighting control system is designed. Analysis and test results show that a variety of seven consecutive magnitudes can be simulated by the lighting control system, and the simulated error between neighboring magnitudes is less than 8‰, to meet the current high precision star sensor calibration technical requirements.
Rearranging the lenslet array of the compact passive interference imaging system with high resolution
With the development of aeronautics and astronautics, higher resolution requirement of the telescope was necessary. However, the increase in resolution of conventional telescope required larger apertures, whose size, weight and power consumption could be prohibitively expensive. This limited the further development of the telescope. This paper introduced a new imaging technology using interference—Compact Passive Interference Imaging Technology with High Resolution, and proposed a rearranging method for the arrangement of the lenslet array to obtain continuously object spatial frequency.
There is a clear need for miniaturized, lightweight, accurate and inexpensive star tracker for spacecraft with large anglar rate. To face these new constraints, the Beijing Institute of Space Long March Vehicle has designed, built and flown a low cost miniaturized star tracker that provides autonomous (“Lost in Space”) inertial attitude determination, 2 Hz 3-axis star tracking, and digital imaging with embedded compression. Detector with high sensitivity is adopted to meet the dynamic and miniature requirement. A Sun and Moon avoiding method based on the calculation of Sun and Moon’s vector by astronomical theory is proposed. The produced prototype weight 0.84kg, and can be used for a spacecraft with 6°/s anglar rate. The average angle measure error is less than 43 arc second. The ground verification and application of the star tracker during the pick-up flight test showed that the capability of the product meet the requirement.
The conventional compressive sensing works based on the non-adaptive linear projections, and the parameter of its measurement times is usually set empirically. As a result, the quality of image reconstruction is always affected. Firstly, the block-based compressed sensing (BCS) with conventional selection for compressive measurements was given. Then an estimation method for the sparsity of image was proposed based on the two dimensional discrete cosine transform (2D DCT). With an energy threshold given beforehand, the DCT coefficients were processed with both energy normalization and sorting in descending order, and the sparsity of the image can be achieved by the proportion of dominant coefficients. And finally, the simulation result shows that, the method can estimate the sparsity of image effectively, and provides an active basis for the selection of compressive observation times. The result also shows that, since the selection of observation times is based on the sparse degree estimated with the energy threshold provided, the proposed method can ensure the quality of image reconstruction.
In order to solve the problem of push-broom optical camera’s imagery quality difficult to content request which windows size is too large, the author proposed a kind of project for camera’s following windows. The author analysed the characteristic of the push-broom optical camera’s windows, and proposed the ideal model of the push-broom optical camera’s windows. Simultaneously, analyzed the transformational rule of the windows’ location and size in the ideal condition. The author proposed the design project of the push-broom optical camera’s following windows according to the result of the ideal windows’ analysis, and performed an analysis of kinematics simultaneously. Finally, the author designed and analyzed kinematics for the following windows in allusion to a certain push-broom optical camera. According the analysis result, this project could decrease a half size of the light opening area compare with the current technique. It could decrease the stray light’s influence of the camera’s imagery quality, the following windows move smoothly, and this project could be satisfied to the requirements of engineering use.
To accomplish the interference testing to an off-axis parabolic mirror, we provided a kind of hybrid compensation modal combining compensator with stitching testing. To verify the validity of the above modal, we measured a Φ1450mm off-axis parabolic mirror with the above method. It can be seen from the stitching map that the stitching map is smooth and continuous in the full aperture. At the same time, to evaluate the stitching testing accuracy, we compared the stitching testing map and the subaperture testing map. It shows that the RMS of the residual map between them is 0.003λ, verifying the validity and accuracy of the model.
Design of control system for piezoelectric deformable mirror based on fuzzy self-adaptive PID control
With the rapid development of adaptive optics technology, it is widely used in the fields of astronomical telescope imaging, laser beam shaping, optical communication and so on. As the key component of adaptive optics systems, the deformable mirror plays a role in wavefront correction. In order to achieve the high speed and high precision of deformable mirror system tracking control, it is necessary to find out the influence of each link on the system performance to model the system and design the controller. This paper presents a method about the piezoelectric deformable mirror driving control system.
Adaptive optics correction based on stochastic parallel gradient descent technique using Zernike polynomials
Adaptive optics systems based on stochastic parallel gradient descent optimization (SPGD) have yet shown great potential on compensation of phase distortions induced by wave propagation through atmosphere turbulence. One of the key technique is increasing the converge rate of SPGD correction system. In the present study, it is shown that the convergence rate of the algorithm will be greatly reduced with the increase of the number of corrector units. In this paper, an improved SPGD optimization process which is based on Zernike-mode is developed. The optimized object is changed from the voltage to Zernike coefficient. Adaptive optics correction system simulation model base on SPGD for a laser beam projecting system, and the numerical simulation of compensation process of random atmosphere turbulence is proposed. To improve the converge speed, we explore to ameliorate the correction system by controlling the perturbation considering atmosphere aberration proportion. The results show that the system converges smoothly and increasingly after considering the aberration proportion by Zernike correction.
In order to avoid the resonance between the two dimensional turntable and the satellite, the modal simulation of the two dimensional turntable is carried out in this paper. And the simulation results are compared with the experimental results, combined with modal experiment, the simulation results before and after optimization are further verified. Firstly, two dimensional turntable as the research object in this paper, and it is modeled with the finite element method, then we use Patran/Nastran to conduct the modal simulation. In the modal simulation process, the bearing can be equivalent to the spring element, and the MPC element is used to instead of the spring element. And we introduce the modeling method of the MPC unit, the fundamental frequency of two dimensional turntable is obtained through modal simulation. At last, the model experiment is verified by hammering method, the frequency response functions in each direction of x, y and z are measured. Simulations and experimental results show: after optimization, the fundamental frequency of the two dimensional turntable is 42 Hz, which is higher than that of the base frequency 25 Hz, illustrating that the optimized structural design of the two dimensional turntable meets the requirements; The natural frequency and the experimental errors of three - dimensional turntable in x, y, z are 5%, which shows that MPC can simulate the bearing accurately, and is suitable for the simulation of two dimensional turntable.
Research on the method of improving the accuracy of CMM (coordinate measuring machine) testing aspheric surface
Large aspheric surface，which have the deviation with spherical surface，are being used widely in various of optical systems. Compared with spherical surface, Large aspheric surfaces have lots of advantages, such as improving image quality, correcting aberration, expanding field of view, increasing the effective distance and make the optical system compact, lightweight. Especially, with the rapid development of space optics, space sensor resolution is required higher and viewing angle is requred larger. Aspheric surface will become one of the essential components in the optical system. After finishing Aspheric coarse Grinding，surface profile error is about Tens of microns.In order to achieve the final requirement of surface accuracy,the aspheric surface must be quickly modified, high precision testing is the basement of rapid convergence of the surface error . There many methods on aspheric surface detection, Geometric ray detection, hartmann detection, ronchi text, knifeedge method, direct profile test, interferometry, while all of them have their disadvantage. In recent years，the measure of the aspheric surface become one of the import factors which are restricting the aspheric surface processing development. A two meter caliber industrial CMM（coordinate measuring machine） is avaiable, but it has many drawbacks such as large detection error and low repeatability precision in the measurement of aspheric surface coarse grinding , which seriously affects the convergence efficiency during the aspherical mirror processing. To solve those problems, this paper presents an effective error control, calibration and removal method by calibration mirror position of the real-time monitoring and other effective means of error control, calibration and removal by probe correction and the measurement mode selection method to measure the point distribution program development. This method verified by real engineer examples, this method increases the original industrial-grade coordinate system nominal measurement accuracy PV value of 7 microns to 4microns, Which effectively improves the grinding efficiency of aspheric mirrors and verifies the correctness of the method. This paper also investigates the error detection and operation control method, the error calibration of the CMM and the random error calibration of the CMM .
With the increase of the diameter of the silicon carbide (SiC) mirror, the amount of material removed increases dramatically. The SiC material has the characteristics of high hardness and chemical stability, so the higher requirement of the convergence efficiency is put forward. The current SiC mirror processing is carried out through a series of different processes or parameters. The combined processing converge the surface residual error. But this method relies on the experience of personnel experience to determine the transfer conditions of process sequencing. This paper research on improve the convergence efficiency at the same time ensuring the accuracy of processing. The quantified evaluation function is put forward to help estimating the transfer conditions of process sequencing. On this basis, the multi-process combination calculation is carried out. The dwell time of multiple remove functions is solved at the same time in the optimization process. The combination of large and small removal function is optimized. Combined with the simulation calculation, the optimized process of large diameter silicon carbide mirror is given.
Signal noise ratio analysis and on-orbit performance estimation of a solar occultation Fourier transform spectrometer
Taking the advantages of high spectral resolution, high sensitivity and wide spectral coverage, space borne Fourier transform infrared spectrometer (FTS) plays more and more important role in atmospheric composition sounding. The combination of solar occultation and FTS technique improves the sensitivity of instrument. To achieve both high spectral resolution and high signal to noise ratio (SNR), reasonable allocation and optimization for instrument parameters are the foundation and difficulty. The solar occultation FTS (SOFTS) is a high spectral resolution (0.03 cm-1) FTS operating from 2.4 to 13.3 μm (750-4100cm-1), which will determine the altitude profile information of typical 10-100km for temperature, pressure, and the volume mixing ratios for several dozens of atmospheric compositions. As key performance of SOFTS, SNR is crucially important to high accuracy retrieval of atmospheric composition, which is required to be no less than 100:1 at the radiance of 5800K blackbody. Based on the study of various parameters and its interacting principle, according to interference theory and operation principle of time modulated FTS, a simulation model of FTS SNR has been built, which considers satellite orbit, spectral radiometric features of sun and atmospheric composition, optical system, interferometer and its control system, measurement duration, detector sensitivity, noise of detector and electronic system and so on. According to the testing results of SNR at the illuminating of 1000 blackbody, the on-orbit SNR performance of SOFTS is estimated, which can meet the mission requirement.
The number of space debris has been increasing dramatically in the last few years, and is expected to increase as much in the future. As the orbital debris population grows, the risk of collision between debris and other orbital objects also grows. Therefore, space debris detection is a particularly important task for space environment security, and then supports for space debris modeling, protection and mitigation. This paper aims to review space debris detection systematically and completely. Firstly, the research status of space debris detection at home and abroad is presented. Then, three kinds of optical observation methods of space debris are summarized. Finally, we propose a space-based detection scheme for space debris by photometric and polarimetric characteristics.
The optical system of lunar rover navigation camera has a direct influence on imaging quality, and an indirect influence on the programming of march forward of lunar rover. One type of lunar rover navigation camera optical system with the symmetrical structure was introduced. It also set up the suitable position of stop to achieve the relative distortion lower than 0.053 percent under the 60 degrees wide field-of-view. It applied the hyperfocal distance principle to achieve the clear imaging from 0.5 meter to infinity. The modulation transfer function is close to diffraction limit at the Nyquist frequency (at standard object distance). Considering the complicate environment of lunar surface and the demand of exploration, it selected the appropriate work spectral coverage and was cooperated by the irradiation reinforce. As a result, it can bear 1×104 Rad (Si) space irradiation and is capable of keeping working normally in the severe environment with its temperature varying from -60°C to + 90°C.
Variable curvature mirror (VCM) can change its curvature radius dynamically and is usually used to correct the defocus and spherical aberration caused by thermal lens effect to improve the output beam quality of high power solid-state laser. Recently, the probable application of VCM in realizing non-moving element optical zoom imaging in visible band has been paid much attention. The basic requirement for VCM lies in that it should provide a large enough saggitus variation and still maintains a high enough surface figure at the same time. Therefore in this manuscript, by combing the pressurization based actuation with a variable thickness mirror design, the purpose of obtaining large saggitus variation and maintaining quite good surface figure accuracy at the same time could be achieved. A prototype zoom mirror with diameter of 120mm and central thickness of 8mm is designed, fabricated and tested. Experimental results demonstrate that the zoom mirror having an initial surface figure accuracy superior to 1/80λ could provide bigger than 36um saggitus variation and after finishing the curvature variation its surface figure accuracy could still be superior to 1/40λ with the spherical aberration removed, which proves that the effectiveness of the theoretical design.
To achieve the efficient, controllable, digital processing and high-precision detection of the high-caliber off-axis aspheric mirror, meeting the high-level development needs of the modern high-resolution, large field of space optical remote sensing camera, we carried out the research on high precision machining and testing technology of off-axis aspheric mirror. First, we forming the off-axis aspheric sample with diameter of 574mm × 302mm by milling it with milling machine, and then the intelligent robot equipment was used for off-axis aspheric high precision polishing. Surface detection of the sample will be proceed with the off-axis aspheric contact contour detection technology and offaxis non-spherical surface interference detection technology after its fine polishing using ion beam equipment. The final surface accuracy RMS is 12nm.
The laser communication terminal is a precision optical, mechanical, electrical integration device which operations extremely high accuracy. It is hard to improve the space environment adaptability in the hash vibration, thermal cycling, high vacuum and radiation conditions space environment. Accordingly, the optical antenna will be influenced by space thermal environment. Laser energy will be absorbed when optical antenna under the irradiation of laser. It can contribute to thermal distortion and make the beam quality degradation which affects the performance of laser communications links. This influence will aggravate when the laser power rising.Wavefront aberration is the distance between the ideal reference sphere and the actual distorted wavefront. The smaller the wavefront aberration, the better the optical performance of the optical antenna. On the contrary, the greater the wavefront aberration, the worse the performance of the optical antenna or even affect the normal operation of the optical antenna. The performance index of the optical antenna generally requires the wavefront aberration to be better than λ/20. Due to the different thermal and thermal expansion coefficients of the material, the effect of thermal deformation on the optical antenna can be reduced by matching the appropriate material. While the appropriate support structure and proper heat dissipation design can also reduce the impact. In this paper, the wavefront aberration of the optical antenna is better than λ/50 by the material matching and the appropriate support structure and the secondary design of the diameter of 5mm hole thermal design.
This paper describes an approach to reconstructing wavefronts on finer grid using the frozen flow hypothesis (FFH), which exploits spatial and temporal correlations between consecutive wavefront sensor (WFS) frames. Under the assumption of FFH, slope data from WFS can be connected to a finer, composite slope grid using translation and down sampling, and elements in transformation matrices are determined by wind information. Frames of slopes are then combined and slopes on finer grid are reconstructed by solving a sparse, large-scale, ill-posed least squares problem. By using reconstructed finer slope data and adopting Fried geometry of WFS, high-resolution wavefronts are then reconstructed. The results show that this method is robust even with detector noise and wind information inaccuracy, and under bad seeing conditions, high-frequency information in wavefronts can be recovered more accurately compared with when correlations in WFS frames are ignored.
Current efficiency calibration of detectors need to establish primary and transfer standard, the precision will be reduced by transfer chain. We propose a scheme for efficiency calibration of infrared single photon detectors by means of twin photons.Comparing with traditional methods, the advantages of this method are mentioned. Using ultraviolet laser to pump BBO crystal, the calibration system of infrared single photon detectors based on twin photons is performed. Quantum efficiency of ID220 detector is measured as (8.71±0.02) % at wavelength of 1550nm.
The lens of Mars detector is exposed to solar radiation and space temperature for long periods of time during orbit, so that the ambient temperature of the optical system is in a dynamic state. The optical and mechanical change caused by heat will lead to camera's visual axis drift and the wavefront distortion. The surface distortion of the optical lens includes the displacement of the rigid body and the distortion of the surface shape. This paper used the calculation method based on the integrated optomechanical analysis, to explore the impact of thermodynamic load on image quality. Through the analysis software, established a simulation model of the lens structure. The shape distribution and the surface characterization parameters of the lens in some temperature ranges were analyzed and compared. the PV / RMS value, deformation cloud of the lens surface and quality evaluation of imaging was achieved. This simulation has been successfully measured the lens surface shape and shape distribution under the load which is difficult to measure on the experimental conditions. The integrated simulation method of the optical machine can obtain the change of the optical parameters brought by the temperature load. It shows that the application of Integrated analysis has play an important role in guiding the designing the lens.
Temperature and nonlinearity correction methods for commercial CCD array spectrometers used in field
CCD array based spectrometers are widely used in radiometric measurements. Ambient temperature and nonlinearity effects are significant factors for high accuracy measurement in the field. Here, a temperature correction method for the CCD array spectrometers was developed, which calculated the spectrometer response at each pixel. The deviation between measured and calculated spectrometer responses at a randomly selected temperature is less than 1%. In addition, the radiant power nonlinearity effects were investigated by supplementary-light methods. The gain settings nonlinearity effect was evaluated using FEL-type transfer standard lamps. The nonlinearity correction coefficients were calculated and analyzed based on the experiment, respectively.
CCD based array spectrometers are widely applied in remote sensing, earth observation, and other industries. However, the signals of ultraviolet region are very weak. Thus, the stray light is one of the most important factors on accurate measurements. In this work, the in-range stray light of commercial UV/VIS CCD array spectrometer and VIS/NIR CCD spectrometer were corrected by mathematical correction method. The measured stray light value at any pixel is of the order of 10−3 ~10−5 of the true in-range. A reduction of the stray light effect by 1-2 orders of magnitude can be achieved using a correction matrix based on line-spread functions (LSFs), which can be determined with the help of spectrally tunable lasers. On the other hand, the bandwidth of the commercial CCD array spectrometer was corrected due to the increasing needs for high accurate calibration and measurement of spectral radiometry. The correction outcome is in good agreement with the measured results by monochromator spectroradiometer.
When the noise in the surface error data given by the interferometer has no effect on the iterative convergence of the RL algorithm, the RL algorithm for deconvolution in image restoration can be applied to the CCOS model to solve the dwell time. By extending the initial error function on the edge and denoising the noise in the surface error data given by the interferometer , it makes the result more available . The simulation results show the final residual error 10.7912nm nm in PV and 0.4305 nm in RMS, when the initial surface error is 107.2414 nm in PV and 15.1331 nm in RMS. The convergence rates of the PV and RMS values can reach up to 89.9% and 96.0%, respectively . The algorithms can satisfy the requirement of fabrication very well.
A design of an on-orbit radiometric calibration device for high dynamic range infrared remote sensors
With the demand of quantitative remote sensing technology growing, high reliability as well as high accuracy radiometric calibration technology, especially the on-orbit radiometric calibration device has become an essential orientation in term of quantitative remote sensing technology. In recent years, global launches of remote sensing satellites are equipped with innovative on-orbit radiometric calibration devices. In order to meet the requirements of covering a very wide dynamic range and no-shielding radiometric calibration system, we designed a projection-type radiometric calibration device for high dynamic range sensors based on the Schmidt telescope system. In this internal radiometric calibration device, we select the EF-8530 light source as the calibration blackbody. EF-8530 is a high emittance Nichrome (Ni-Cr) reference source. It can operate in steady or pulsed state mode at a peak temperature of 973K. The irradiance from the source was projected to the IRFPA. The irradiance needs to ensure that the IRFPA can obtain different amplitude of the uniform irradiance through the narrow IR passbands and cover the very wide dynamic range. Combining the internal on-orbit radiometric calibration device with the specially designed adaptive radiometric calibration algorithms, an on-orbit dynamic non-uniformity correction can be accomplished without blocking the optical beam from outside the telescope. The design optimizes optics, source design, and power supply electronics for irradiance accuracy and uniformity. The internal on-orbit radiometric calibration device not only satisfies a series of indexes such as stability, accuracy, large dynamic range and uniformity of irradiance, but also has the advantages of short heating and cooling time, small volume, lightweight, low power consumption and many other features. It can realize the fast and efficient relative radiometric calibration without shielding the field of view. The device can applied to the design and manufacture of the scanning infrared imaging system, the infrared remote sensing system, the infrared early-warning satellite, and so on.
A topological optimization design for the lightweight technology of supporting plate of the primary mirror is presented in this paper. The supporting plate of the primary mirror is topologically optimized under the condition of determined shape, loads and environment. And the optimal structure is obtained. The diameter of the primary mirror in this paper is 450mm, and the material is SiC1 . It is better to select SiC/Al as the supporting material. Six points of axial relative displacement can be used as constraints in optimization2 . Establishing the supporting plate model and setting up the model parameters. After analyzing the force of the main mirror on the supporting plate, the model is applied with force and constraints. Modal analysis and static analysis of supporting plates are calculated. The continuum structure topological optimization mathematical model is created with the variable-density method. The maximum deformation of the surface of supporting plate under the gravity of the mirror and the first model frequency are assigned to response variable, and the entire volume of supporting structure is converted to object function. The structures before and after optimization are analyzed using the finite element method. Results show that the optimized fundamental frequency increases 29.85Hz and has a less displacement compared with the traditional structure.
For aim to find an effective method to structure to enhance these adaptive system with some complex function and look forward to establish an universally applicable solution in prototype and optimization. As the most attractive component in adaptive system, wave front corrector is constrained by some conventional technique and components, such as polarization dependence and narrow working waveband. Advanced configuration based on a polarized beam split can optimized energy splitting method used to overcome these problems effective. With the global algorithm, the bandwidth has been amplified by more than five times as compared with that of traditional ones. Simulation results show that the system can meet the application requirements in MTF and other related criteria. Compared with the conventional design, the system has reduced in volume and weight significantly. Therefore, the determining factors are the prototype selection and the system configuration, Results show their effectiveness.
In photometry and radiometry, photodetectors such as silicon detector and PMT detector are widely used. In precision metrology, the uncertainty of the nonlinearity should be considered. Superposition method is used to analyse the linearity. The silicon trap detector is measured using both nonmochromator light and monochromator light. First, integrating sphere with broadband light is used to test the linearity. The result shows that the nonlinearity is (1-3)×10-4 from 1uA to 1mA. The monchromator light result shows that the nonlinearity is below 3×10-4 from 1uA to 1mA, which is consistent with the integrating sphere method. For the PMT detector, the linearity is measured only using monochromator light. Experiment shows that the nonlinearity is less than 1×10-3 through three orders of magnitude.
The modeling and analysis of the image-rotation of the stabilizing mirror based on the spatial coordinate transformation
The image stabilization system plays an important role in stabilizing the optical axis in the optical system. The two-dimensional compensation of the stabilizing mirror causes the image-rotation. The mathematical model of stabilizing mirror working mode based on spatial coordinate transformation is established. The mathematical formula of image-rotation angle and distortion based on spatial vector representation is deduced. The influence of the initial posture and the compensation angle of the stabilizing mirror on the rotation angle and the distortion are analyzed. The model is used to simulate the actual working mode of the stabilizing mirror in a space optical system, and the image-rotation angle and image distortion caused by the stabilization system are calculated to provide data support for the space optical system design.
Design of high precision optical image stabilization system for high resolution Earth observation remote sensing
The high-resolution remote sensing camera has higher requirements on the optical axis stability. However, during the in-orbit operation, the main structure of the remote sensing camera and the attitude drift of the satellite will cause the optical axis to be unstable and cause the image quality declines. In this paper, an optical image stabilization system based on fast steering mirror is designed on the basis of a large-aperture high-resolution gaze-type remote sensing camera. The system divides the sub-field of view at the edge of the field of the remote sensing camera, installs the high frame rate and high sensitivity to the camera in the field of view, and then uses the related characteristic of the acquired image to measure the image and obtain the jitter information of the optical axis. Finally, the system will feedback the information to the control system to drive the fast steering mirror, in order to achieve the optical axis of the jitter compensation to ensure the optical axis stability.For the typical ground scene image, the system can improve the control precision and bandwidth by optimizing the image shift measurement algorithm and improving the calculation speed. In summary, the image stabilization system with high precision, high bandwidth and high success rate.
Segmented primary mirror will be adopted widely in giant telescopes in future, such as TMT, E-ELT and GMT. High-performance control technology of the segmented primary mirror is one of the difficult technologies for telescopes using segmented primary mirror. The control of each segment is the basis of control system in segmented mirror. Correcting the tilt and tip of single segment is the main work of this paper which is divided into two parts. Firstly, harmonic response done in finite element model of single segment matches the Bode diagram of a two-order system whose natural frequency is 45 hertz and damping ratio is 0.005. Secondly, a control system model is established, and speed feedback is introduced in control loop to suppress resonance point gain and increase the open-loop bandwidth, up to 30Hz or even higher. Corresponding controller is designed based on the control system model described above.
Modulation transfer function (MTF) is an important parameter for image quality evaluation of on-orbit optical image systems. Various methods have been proposed to determine the MTF of an imaging system which are based on images containing point, pulse and edge features. In this paper, the edge of the moon can be used as a high contrast target to measure on-orbit MTF of image systems based on knife-edge methods. The proposed method is an extension of the ISO 12233 Slanted-edge Spatial Frequency Response test, except that the shape of the edge is a circular arc instead of a straight line. In order to get more accurate edge locations and then obtain a more authentic edge spread function (ESF), we choose circular fitting method based on least square to fit lunar edge in sub-pixel edge detection process. At last, simulation results show that the MTF value at Nyquist frequency calculated using our lunar edge method is reliable and accurate with error less than 2% comparing with theoretical MTF value.
A new effective combined design method of optics and baffles for low obscuration ratio three-mirror system
：A new effective combined design method for low obscuration ratio (OR) three-mirror imaging system is proposed, which involves the correction of varied aberrations, such as spherical aberration, coma, astigmatism, etc., as well as the control of the OR introduced by the secondary mirror’s (SM) baffle effect at the optical design stage. The initial theoretical works include the derivation of the all-spherical system’s 3th-order aberration equations and the calculation of the baffles’ edge coordinates using paraxial ray-tracing. Next,the aberration equations are solved with the boundary conditions of suppressing stray lights to determine the focal powers and first-order parameters of each mirror. And then the system’s initial configuration is obtained as the starting point. During the optimization, conic aspheric surfaces are employed to correct aberrations with the consideration of decreasing the manufacture cost and fabrication difficulties. Meanwhile, the relationship between the SM’s baffle size and the baffles’ edge coordinates based on real ray-tracing is built to minimize the obscuration. Finally, a three- aspheric-mirror system with low OR and high imaging performance is achieved. An infrared-middle-wave system design of % OR is shown and the design result shows that the system’s limited spatial frequency is 33lp/mm and the MTFs of each field-of-view approach the diffraction limits. The stray-light analysis results utilizing FRED software verify the stray light suppression effectiveness of the baffles design of the proposed method.
The jitter of the transmitting system can cause the light intensity fluctuation at the target position of the laser transmission, which affects the performance of the laser communication, imaging and the adaptive optical system. In this paper, the platform jitter is modeled by Gaussian random fluctuation phase and the analytic expression of the system jitter effect on the fluctuation of light intensity is obtained under the vacuum condition based on extended Huygens-Fresnel principle. The numerical simulation is compared with the theoretical expression and the consistency is obtained. At the same time, the influence of the jitter of the launch system on the intensity fluctuation of the target system under different turbulence conditions is analyzed by numerical simulation. The result show that normalized intensity fluctuation variance induced by platform jitter seems to be unrestricted. The jitter of the transmitting system has a more important influence on the fluctuation of the target position caused by the atmospheric turbulence, as the jitter increase. This result provides a reference for the application of the actual laser transmission system.
Grayscale camera can only obtain gray scale image of object, while the multicolor imaging technology can obtain the color information to distinguish the sample structures which have the same shapes but in different colors. In fluorescence microscopy, the current method of multicolor imaging are flawed. Problem of these method is affecting the efficiency of fluorescence imaging, reducing the sampling rate of CCD etc. In this paper, we propose a novel multiple color fluorescence microscopy imaging method which based on the Frequency division multiplexing (FDM) technology, by modulating the excitation lights and demodulating the fluorescence signal in frequency domain. This method uses periodic functions with different frequency to modulate amplitude of each excitation lights, and then combine these beams for illumination in a fluorescence microscopy imaging system. The imaging system will detect a multicolor fluorescence image by a grayscale camera. During the data processing, the signal obtained by each pixel of the camera will be processed with discrete Fourier transform, decomposed by color in the frequency domain and then used inverse discrete Fourier transform. After using this process for signals from all of the pixels, monochrome images of each color on the image plane can be obtained and multicolor image is also acquired. Based on this method, this paper has constructed and set up a two-color fluorescence microscope system with two excitation wavelengths of 488 nm and 639 nm. By using this system to observe the linearly movement of two kinds of fluorescent microspheres, after the data processing, we obtain a two-color fluorescence dynamic video which is consistent with the original image. This experiment shows that the dynamic phenomenon of multicolor fluorescent biological samples can be generally observed by this method. Compared with the current methods, this method can obtain the image signals of each color at the same time, and the color video’s frame rate is consistent with the frame rate of the camera. The optical system is simpler and does not need extra color separation element. In addition, this method has a good filtering effect on the ambient light or other light signals which are not affected by the modulation process.