2012 Vol. 32, No. 1

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Gyrosynchrotron Radiation of Interplanetary CMEs
SUN Weiying, WU Ji, WANG Chuanbing, WANG Shui
2012, 32(1): 1-7. doi: 10.11728/cjss2012.01.001
Abstract(2386) PDF 202KB(1241)
Abstract:
CMEs (Coronal Mass Ejections) are an important means of energy release in the solar corona. Solar Polar Orbit Radio Telescope (SPORT) is a mission being proposed for observing the propagation of interplanetary CMEs from solar polar orbit. The main payload onboard SPORT is a synthetic aperture interferometric radiometer, which receives radio emission of interplanetary CMEs. It is identified that there are mainly three radio emission mechanisms of CMEs, i.e., bremsstrahlung, gyrosynchrotron emission and plasma emission. Among these emission types, bremsstrahlung emission is the main emission mechanism of the high-density plasma clouds of interplanetary CMEs. Gyrosynchrotron emission is the continuous emission generated by high-energy electrons from CMEs, while plasma emission is the main mechanism of transient radio bursts from CMEs. In this paper, the gyrosynchrotron emission of interplanetary CMEs is focused on. Firstly, the mechanism of gyrosynchrotron emission is reviewed. Secondly, a review of the physical parameter models of background solar wind and interplanetary CMEs is presented. After these, the brightness temperature and polarization of gyrosynchrotron emission of interplanetary CMEs are calculated and analyzed. Finally, the detectability of gyrosynchrotron emission of interplanetary CMEs by radio meters is discussed briefly.
Mission Planning and Modeling Analysis for Unmanned Aerial Exploration Vehicle on Mars
YAO Keming, WANG Xiaolan, LIU Yanbin, LU Yuping, XIAO Dibo
2012, 32(1): 8-13. doi: 10.11728/cjss2012.01.008
Abstract(2879) PDF 644KB(1385)
Abstract:
With the development of socio-economy and technology, more and more people from various countries pay more attention to deep-space exploration. Mars is the closest planet where life is possible. So, Mars exploration is a hot issue on international deep space exploration in recent years. There are many advantages for the use of unmanned aerial exploration vehicles on Mars, including the wide range of exploration, the visualization of terrain changes, etc. In this paper, the overall mission planning is described for unmanned aerial exploration vehicle on Mars, and the difference between flight on earth and on Mars is discussed. Then the longitudinal nonlinear model is established for unmanned aerial exploration vehicle on Mars, and Taylor expansion is applied to the nonlinear model at the trim point, hence to obtain the linear model. By further analysis of the linear model, the stable performance and flight characteristics have been grasped for unmanned aerial exploration vehicle on Mars. These work will provide the platform for the follow-up research for Mars Unmanned Aerial Vehicle (UAV) navigation and control method.
Influence of Solar Wind Disturbance on Ring Current and Auroral Electrojet Indexes
ZOU Ziming, CAO Jinbin, LI Yi
2012, 32(1): 14-19. doi: 10.11728/cjss2012.01.014
Abstract(2895) PDF 484KB(1238)
Abstract:
Using the data of solar wind recorded by WIND and geomagnetic activity index, we studied the influence of the variation of solar wind dynamical pressure on ring current index SYM-H and auroral electrojet indexes (AU and AL). The increase and decrease of solar wind dynamical pressure can produce simultaneous or delayed disturbances in geomagnetic activity indexes, which include the transient increase of ring current index SYM-H, increase of eastward electrojet index AU and decrease of westward electrojet index AL. The sudden large increase of solar wind dynamical pressure can trigger super substorm and large geomagnetic storm. The response of geomagnetic activity indexes to solar wind dynamical pressure impulse is complicated and various, indicating the geomagnetic effect of solar wind dynamical pressure impulse not only depends on the strength and duration of solar wind dynamical pressure impulse, but also on the state of magnetosphere. Large geomagnetic storm, which last long and consume more energy, can only be triggered by strong and long impulse of solar wind dynamical pressure.
Electrodynamics in the Polar Ionosphere During the IMF-north Substorm on 13 December 2004
LIU Junming, ZHANG Beichen, Kamide Y, WU Zhensen, YANG Huigen
2012, 32(1): 20-24. doi: 10.11728/cjss2012.01.020
Abstract(2590) PDF 570KB(1107)
Abstract:
Previous studies have shown that substorm can occur even during northward Interplanetary Magnetic Field (IMF). However, the electrodynamics in the polar ionosphere has not been studied for this kind of events. In this paper, the KRM magnetogram-inversion algorithm, combined with the magnetic record at the north hemisphere, was utilized to deduce the distribution of the current vector, the current function, and the electric potential in the polar ionosphere during the substorm event on 13 Dec. 2004. The results show a sudden enhancement of the westward electrojet at the midnight sector after the expansion onset. The equivalent current system was characterized as a two-vortex structure at the nightside, in association with a southward electric field. All these indicate an absolutely dominant role of the unloading process at the expansion phase. The two-cell convection structure could not be found, which suggests a weak directly driven process in association with the northward IMF. The contribution of the conductivity and electric field to the enhancement of the current were also examined. The results showed that the enhancement of the conductivity is responsible for the increase of the westward electrojet.
Statistical Analysis of Geomagnetic Disturbances and Ionospheric Scintillations Over Guangzhou Region During Solar Minimum
HUANG Linfeng, DENG Baichang, HUANG Jiang, XU Jie, LIU Weifeng, LIU Zuolian, QUAN Hongjun
2012, 32(1): 25-32. doi: 10.11728/cjss2012.01.025
Abstract(3162) PDF 714KB(1192)
Abstract:
The correlations between geomagnetic disturbance and GPS ionospheric scintillations are studied here using geomagnetic monitoring data of Zhaoqing geomagnetic station and the ionospheric scintillations observed by GPS monitoring network of South China, which is established by Guangzhou meteorological satellite ground stations. With the use of geomagnetic K values converted from the variation of geomagnetic horizontal component H at Zhaoqing to represent geomagnetic disturbance over Guangzhou region, the relationships between the geomagnetic disturbance and amplitude scintillation index (S4) over Guangzhou region during solar minimum are statistically analyzed.
Analysis indicates that most storms/strong magnetic disturbances of the year did not trigger the scintillation occurrence, that the ionosphere scintillation occurrence is mainly confined to the periods of lower K values, and that the ionosphere scintillation occurrence declined for periods of higher K values (K ≥ 4). Occurrence rate of ionosphere scintillations is changed with seasons and the geomagnetic activities. The scintillations occurrence rate is obviously correlated with the variation of geomagnetic activity K index, i.e., as the index K is raised, scintillation occurrence rate of above medium at night and weak in spring, as well as scintillations above medium in summer decreases. But there is no obvious relationship between occurrence rate of ionosphere scintillation and K values in autumn and winter. In addition, comprehensive analyses for the effects of geomagnetic and solar activity on ionosphere activity show that there are more ionosphere scintillations over Guangzhou region during geomagnetic quiet and low solar activity periods.
Comparison of Ionospheric Modification by Different Chemicals Release
HUANG Yong, SHI Jiaming, YUAN Zhongcai
2012, 32(1): 33-39. doi: 10.11728/cjss2012.01.033
Abstract(2214) PDF 579KB(1081)
Abstract:
Six chemicals, H2, H2O, CO2, SF6, CF3Br and Ni(CO)4, are considered as ionospheric modification materials. Each of these chemicals reacts in the F region to produce localized plasma depletions and form large scale electron holes. In the active ionospheric modification experiments, the criteria for selecting the released chemicals include the cost and effectiveness. The effectiveness of released chemicals depends on the amount which goes into the vapor state. In this paper, the thermodynamics governing the vapor fraction of the released chemicals were investigated. Additionally, the size and magnitude of the electron depletions were calculated with finite element simulation method. The results show that H2O has the lowest vapor yield of about 19% from a heated, pressurized tank, and over 60% of the other five chemicals should be vented in gaseous form. To reduce the cost, the chemicals with small density, such as H2 or CO2 may be chosen. Based on estimating the electron density reduction, the chemicals which have slow diffusion speed and large chemical reaction rates, such as SF6 or Ni(CO)4, may be selected. These chemicals can produce a larger, deeper and more durable electron hole.
Correlation Analysis of the TEC at Wuhan Station With Solar Activities and Geomagnetic Activities During 23rd Solar Cycle
WANG Weimin, XU Zhenzhong, ZHANG Ren, WANG Bo, YANG Shenggao
2012, 32(1): 40-47. doi: 10.11728/cjss2012.01.040
Abstract(2286) PDF 959KB(1085)
Abstract:
By using Total Electron Content (TEC) at Wuhan station from 1997 to 2007, based on continuous wavelet, cross wavelet and wavelet coherence transform methods, the periodic variation of TEC at this station, the characteristic of TEC association with solar activities and geomagnetic activities are analyzed. Analysis results show that long-term variations of TEC at Wuhan station are mainly controlled by the variations of solar activities. In local time field, several remarkable components including 128～256 days, 256～512 days and 512～1024 days time-scale periodicities exist in TEC daily variation and correspond to the periodic characteristics of sunspot number and the geomagnetic Dst index closely during the same period of time. The average time delay between variations of the TEC and sunspot number is about 1/6 period in 512～1024 days time-scale. TEC at Wuhan station and geomagnetic Dst index are anti-phasic in semiannual time-scale, but this response only exists during high solar activity, further specific mechanism needed to be analyzed in the future.
Calculation Analysis of Ionospheric Irregularity Zonal Drift Velocity in Guangzhou Based on GPS Measurements
LIU Weifeng, HUANG Jiang, DENG Baichang, XU Jie, QUAN Hongjun, HUANG Linfeng, LIU Miao
2012, 32(1): 48-54. doi: 10.11728/cjss2012.01.048
Abstract(2560) PDF 649KB(1174)
Abstract:
Using data observed by two GPS ionospheric scintillation monitors located near each other at Guangzhou station, the amplitude scintillation was measured, and the zonal drift velocity of the ionospheric irregularities was studied by choosing three scintillation events, with methods of signal intensity power spectrum and cross-correlation technology. The results show that each of the scintillation registered in two receiver monitors occurs at the same time and induced by the same ionospheric irregularity. The zonal drift velocity is about 50m/s to 160m/s, on average about 120m/s from the two calculating methods, varies significantly at the beginning of the scintillation, decreased with time and eastward. The characteristics of the zonal drift velocity in Guangzhou are consistent with the observation at other stations in the low latitude region, which indicate that the two calculating methods are feasible and effective.
Measurement Error and Correction of the Ionospheric Effect
HAN Yong, LI Qingbo
2012, 32(1): 55-59. doi: 10.11728/cjss2012.01.055
Abstract(2250) PDF 449KB(1076)
Abstract:
Electromagnetic waves, when propagate through the ionosphere, would get delays due to the ionosphere refraction. According to certain experimental data, the difference of the group delay is up to 105 ns. It is close to the time of the earth surface echoes when the signal generator is about 15 kilometers above ground in the air, and they are difficult to be distinguished (30 km/(3×108 m·s-1) = 105 ns). So the time when the transient electromagnetic waves reach satellite receiver cannot be utilized directly in doing Time Difference of Arrival (TDOA). In this paper, the ionospheric Total Electron Content (TEC) is derived by Dual-Frequency Method, and on this basis, the time received by satellite receiver is modified. The result shows that it is inaccurate with the error being about 100 ns. The potential origins of the error are provided.
Match Function Method for Space Debris Detection Using Incoherent Scatter Radar
LIU Yongjun, GE Debiao, JIN Wang
2012, 32(1): 60-67. doi: 10.11728/cjss2012.01.060
Abstract(2336) PDF 619KB(1088)
Abstract:
Beam-park experiments done by powerful and highly sensitive radar allow us to gain insight into the debris population. But any cost-effective approach demands a multi-use concept where the system can be reconfigured easily to perform a variety of different tasks. In this paper we present a flexible digital signal process method for space debris measurements using the conventional ionospheric data. Based on the conventional ionospheric data obtained by European incoherent scatter radar on 25 March 2010, the “mutation” phenomenon of the sounding data power was studied. Generally, the “mutation” power in more than 500 km is not produced by geophysical effects, but due to satellites or space debris. Matched filtering method was used to achieve the space debris detection and the debris's character extraction, and the signal to noise ratio is improved by using coherent accumulation method. A total of 363 pieces were captured, and the distribution of debris with height and time has been obtained. The result shows that the debris was concentrated in the height of 800 km, and the distribution of debris with height was consistent with the results of European Incoherent Scatter organizations.
Using Lidar to Simultaneously Observe the Sodium Layer and Potassium Layer Over Wuhan
LI Yongjie, CHENG Xuewu, LI Faquan, YANG Yong, LIN Xin, GONG Shunsheng
2012, 32(1): 68-74. doi: 10.11728/cjss2012.01.068
Abstract(2391) PDF 670KB(1012)
Abstract:
A dual-wavelength lidar with 532nm and 589nm was setup inWuhan Institute of Physics and Mathematics (30.5°N, 114.3°E) to detect atmosphere from 1～110km simultaneously. Recently, a pulse dye laser (ND6000) pumped by the 532 nm beam was employed to transmit a 770 nm laser beam, which allow the new dual-wavelength lidar to measure the potassium layer and sodium layer simultaneously. In this paper, the dual-wavelength lidar systems and resonant fluorescence data processing method are introduced. The number density and column density of the sodium layer and potassium layer over Wuhan were calculated also. The results show that the density and column density of sodium layer and potassium layer both are almost the same with previous results observed by other sodium and potassium lidar in Mid-latitude region. Moreover, another interesting thing found is that potassium and sodium layer are not always the same.
Research on Observing and Analyzing Phase Differences of All-sky Meteor Radar
SHEN Jincheng, NING Baiqi, WAN Weixing, HU Lianhuan
2012, 32(1): 75-84. doi: 10.11728/cjss2012.01.075
Abstract(2414) PDF 1049KB(1229)
Abstract:
A new method is developed on analyzing and estimating phase differences between each antenna of All-sky meteor radar by the mathematical model derived from the distribution of meteors and the antenna configuration. Using the observational data collected from the meteor radar, the temporal-spatial distribution properties of meteors and their effect upon the spatial distribution of meteors, especially the effect upon the variance properties of height distribution result from the phase difference variations of the antennas, are achieved. On this basis a simulation is created to estimate the phase difference variations by the variance of meteors' height distribution. Then this method is applied to analyze data collected from Sanya All-sky meteor radar. The results show that phase difference variations from one antenna or more are able to be estimated by analyzing the observational data without any additional hardware. And the accuracy is less than 2 degree. The calibration to the phase different variations can efficiently improve the measurement precision of the meteors' angles of arrival and the relevant data quality.
Solving Shapes of Hydrostatic Surface in Rectangular and Revolving Symmetrical Tanks Under Microgravity Using Shooting Method
YANG D, an, YUE Baozeng, ZHU Lemei, SONG Xiaojuan
2012, 32(1): 85-91. doi: 10.11728/cjss2012.01.085
Abstract(2588) PDF 681KB(1080)
Abstract:
The application of Shooting Method in solving nonlinear second order differential equations with unknown parameters is briefly introduced. Moreover, shapes of hydrostatic surface in rectangular and revolving symmetrical tanks under microgravity are controlled by nonlinear second order differential equations with unknown parameters, hence can be solved by Shooting Method. This paper solves the shapes of hydrostatic surface in rectangular and revolving symmetrical tanks under microgravity using Shooting Method. There is one unknown parameter in the Shooting Method solving the shapes in rectangular tanks under microgravity. There are two unknown parameters in the Shooting Method solving the shapes in columnar tanks under microgravity. And there are both three unknown parameters in the Shooting Method solving the shapes in spheroidal tanks and Cassini tanks under microgravity. When the initial values of these unknown parameters are set aptly, Shooting Method is indicated to be fast and effective through large amount of calculations. Last but not the least, Shooting Method is compared with Runge-Kutta method in other literatures for solving shapes of rectangular and revolving symmetrical tanks under microgravity, and the advantage and disadvantage of these two methods are analyzed respectively. The conclusion is that Shooting Method is always a better choice.
Lunar Soft-landing Trajectory Design Based on Evolutionary Strategy
LUO Zongfu, MENG Yunhe, TANG Guojian
2012, 32(1): 92-98. doi: 10.11728/cjss2012.01.092
Abstract(3051) PDF 735KB(1192)
Abstract:
Lunar soft-landing trajectory design methods using evolutionary strategies and differential correction are investigated. According to the launch site and vehicle of the Chinese Lunar Exploration Program, the general constraints and objectives of lunar soft-landing missions are given. The primary trajectory is calculated by evolutionary strategies based on patched conic model. Then the differential correction method is adopted to modify the error introduced by the inaccurate model. The trajectories of cislunar and lunar orbiter phase before the soft-landing are also simulated by the commercial software STK, and the feasibility of the methods delivered in this paper is confirmed by the comparison of results. The difference of parameters between the preliminary and accurate model indicates that the design based on evolutionary strategies gives a proper value for the differential correction. This approach will be significant for the lunar soft-landing trajectory design of Chinese Chang'E Mission.
Genetic Algorithm for Orbital Optimization to Approach Multiple Constellation Satellites
ZHANG Jing, WU Meiping, FU Xiaofeng
2012, 32(1): 99-105. doi: 10.11728/cjss2012.01.099
Abstract(2458) PDF 541KB(1114)
Abstract:
Taking three Walker constellation satellites which locate in different orbit as objects, the probability of a spacecraft approaching them without orbital maneuver is studied. The genetic algorithm is used to optimize the initial orbit which is obtained by Lambert method. The position and velocity's variation of the initial orbit on the reference time is encoded to form population. The minimum distance between the spacecraft and three constellation satellites is adopted as fitness function. The optimization result can be attained through the population's propagation. Finally, followed by the simulation, the performances of the least square method and the genetic algorithm are analyzed. At the same time, the orbital perturbation in the approaching process is taken into account. The genetic algorithm is suited for this problem of orbital optimization. The study results can be taken as the theoretical proof for a single spacecraft close approaching multiple constellation satellites without orbital maneuver.
Study of Spacecraft Attitude Tracking Using Variable Speed Control Moment Gyros
JIA Feilei, XU Wei, LI Hengnian, HOU Liqiang, ZHANG Zhibin
2012, 32(1): 106-112. doi: 10.11728/cjss2012.01.106
Abstract(2461) PDF 502KB(1162)
Abstract:
The attitude tracking problem of spacecraft using VSCMG (Variable Speed Control Moment Gyros) as actuators is studied. The attitude dynamic model of spacecraft with VSCMG attached is built, and an angular velocity filter state governed through the stable liner differential equation is introduced. Based on the Lyapunov stability theory, the adaptive control law is designed. In order to determine the attitude control vector of the VSCMG, a weighted minimum norm solution is applied. A new singularity measurement is constructed which describes the configuration singularity. The null motion of the VSCMG, is designed using the gradient method based on the singularity measurement, and is employed to avoid the singularity, as well as to make the rotary speed of rotors to tend to their expected values. In the end, the VSCMG with four-pyramid configuration is applied in the simulation, and the simulation results validate the feasibility and efficiency of the VSCMG systems on the spacecraft attitude tracking.
Steering Law Design for SGCMG Based on Optimal Output Torque Capability
SUN Zhiyuan, JIN Guang, XU Kai, ZHANG Liu, YANG Xiubin
2012, 32(1): 113-122. doi: 10.11728/cjss2012.01.113
Abstract(2260) PDF 730KB(1132)
Abstract:
A new steering law for Single Gimbal Control Moment Gyros (SGCMG), which aims at precisely exporting commanded torque and meanwhile avoiding singularity, is designed based on the optimal output torque capability principle. Firstly, a new system singularity index is introduced and the optimal gimbal angle rates are given. Then, a mixed two-norm and least-squares minimization problem is introduced to guaranty that the gimbal rates are in good accordance with the optimal gimbal rates, and that the minimum of the output torque error is obtained. Singularity value decomposition theory is also adopted to analyze the output torque error and to prove that there exists no phenomenon of gimbal lock at singularity surfaces for united steering law. Finally, simulations on constant commanded torque and large angle maneuver of a small satellite are presented respectively, which suggest that the designed steering law could escape singularity surfaces, having no gimbal lock phenomenon and much smaller output torque error than off-diagonal singularity robust steering law, and that a large-angle maneuver mission could be performed wonderfully using the designed steering law.
Analysis and Study of Ranging Code Performance Based on Deep Space Pseudo-Noise (PN) Ranging System
GAO Yang, YAN Yi, CUI Yongshun, YAO Xiujuan
2012, 32(1): 123-129. doi: 10.11728/cjss2012.01.123
Abstract(2144) PDF 552KB(1520)
Abstract:
The selection of ranging codes influences many parameters of the deep space ranging system, such as the ambiguity distance, ranging resolution, acquisition time and hardware implementation, etc. In this paper, several ranging codes commonly used in the deep space ranging system are simulated, analyzed, compared and studied, especially for their spectrum, cycle, DC, ranging clock attenuation, acquisition time and ranging jitter error. The signal space figure method with in-phase/out-phase correlative coefficient is used to analyze the acquisition time. And in-phase/midphase integration loop, as a chip tracking loop, is applied to analyze the ranging jitter error. Also, the influences of acquisition time and ranging jitter error due to sinusoidal pulse shaping and squarewave pulse shaping are analyzed. Through the research and analysis, some results are proposed as that T4B is chosen as ranging code in deep space ranging system, DDS method is selected to create arbitrary chip phase shift, sinusoidal pulse shaping modulation and sinusoidal pulse shaping matched filter scheme are adopted, and in-phase/mid-phase integration loop is applied to track the ranging code.
Analysis and Calculation for Current Leakage Effect of High Voltage Solar Array in LEO
SHI Liqin, LIU Siqing, ZHENG Huinan
2012, 32(1): 130-135. doi: 10.11728/cjss2012.01.130
Abstract(2132) PDF 500KB(1004)
Abstract:
A method for calculating current leakage effect of high voltage solar array in LEO was developed in this paper. This method is based on current balance, a simplified structure of solar array and an empirical model of current collection for solar array. Using this method, the relationships between power loss and plasma environment, solar array voltage, the area of solar array exposed conductor were analyzed in current leakage. The main results are concluded as follows. Firstly, the power loss of solar array in current leakage declines quickly with the increasing of orbital altitude. The most serious range for current leakage is region among 300～400 km of orbital altitude where the plasma density is high. Secondly, the power loss increases exponentially with the voltage of solar array. Meanwhile, is also noticed that the power loss is far less than 1% of total power when the voltage of solar array is below 200 V. Thirdly, the power loss increases linearly with the area of solar array exposed conductor. Accordingly, the current leakage effect can be reduced by decreasing the area of solar array exposed conductor.
Research of Blue/Red Reflecting for Space Silicon Solar Cell
LEI Gang, SHEN Zhenjue, CAO Jiaye
2012, 32(1): 136-140. doi: 10.11728/cjss2012.01.136
Abstract(2112) PDF 483KB(1180)
Abstract:
The non-reflective silicon cells could increase cell efficiency in comparison to cells with smooth surface, while they would also increase the operational temperature as IR and UV energy is efficiently absorbed. This temperature increase completely offsets the initial efficiency gain when the non-reflective silicon cells were used in space. A Blue/Red Reflecting (BRR) for space silicon solar cell has been developed to improve the performance of silicon solar cell. The BRR consists of UVR on the front surface of the coverglass and the IRR on the rear surface produced in method of electron-beam gun evaporation with ion-assisted deposition. The operating temperature reduction between 6℃ and 12℃ and the in-orbit efficiency gains between 1.8% and 4.1% for silicon solar cell with BRR have been predicted. The potential benefits of the BRR are greatest for the non-reflective silicon cells.
A High-speed Simulation Method of Star Map Based on Three Orthogonal Axis Planes
QUAN Wei, XU Liang, NING Xiaolin
2012, 32(1): 141-146. doi: 10.11728/cjss2012.01.141
Abstract(2184) PDF 512KB(1035)
Abstract:
In order to test the algorithms of star map identification and the performance of star sensor by simulating star map on the ground, a new and high-speed method for simulating star map is presented. This method makes use of the property of sectional circle and fixed field to divide the unit celestial according to three orthogonal axis planes and derive the angles between the vectors of stars and the axis planes based on latitude and longitude value as the condition for selecting stars. And then, star map can be simulated according to the principle of coordinate transformation. In order to verify the advantages of the proposed method compared with current methods, a lot of simulation is conducted. The simulation results show that compared with current common star map simulation methods, the proposed method guarantees the accuracy of choosing guide stars and its speed of choosing guide stars is three times faster than other methods.
Coordinated Motion Control and Vibration Suppression of Rigid-Flexible Space Robot Based on Neural Network
CHEN Zhiyong, CHEN Li
2012, 32(1): 147-153. doi: 10.11728/cjss2012.01.147
Abstract(2176) PDF 572KB(2247)
Abstract:
The joint motion control and vibration suppression problems of rigid-flexible space robot with an attitude controlled base were discussed. With Lagrangian method and singular perturbation theory, the singular perturbation model of the system was derived. To guarantee the accurate coordinated motion control of the base attitude and the arm's joints under the effects of unknown system parameters, the compensation control strategy based on Radial Basis Function (RBF) neural network was proposed for the slow subsystem. Simultaneously, the linear quadratic optimal controller was given for the fast subsystem to suppress the elastic vibration of the system. Simulation results demonstrate that the presented control scheme can effectively compensate for the influence of unknown system parameters, and control the system to track the desired trajectory and suppress the elastic vibration preferably.
Automatic Mosaic Method of Large Field View and Multi-Channel Remote Sensing Images of TDICCD Cameras
LU Jinbo, HE Bin
2012, 32(1): 154-160. doi: 10.11728/cjss2012.01.154
Abstract(2329) PDF 692KB(1015)
Abstract:
In terms of mosaic of TDICCD large field view and multi-channel remote sensing images, noise immunity and robustness of the previous classical method is not high, which is difficult to achieve high accuracy and fast image mosaic because of imaging resonance, flutter and other factors in the imaging platforms. For that reason, this paper proposes a more appropriate method, namely the spatial cross-correlation self-tuning sub-pixel registration method. Firstly, because of the characteristics of overlapping pixels between TDICCD multi-channel images, the method uses the cross correlation of variable search window as the evaluation function. Secondly, the local detection method is employed to monitor change of parameter to figure out the best parameters of each part of images. Thirdly, the matching error points are controlled by interference elimination method, so that parameters are more credible. Finally, sub-pixel locating algorithm is proposed to reduce error of image registration. The results of practical remote sensing image mosaic indicate that accuracy of the algorithm excesses 0.1pixel, while rapidity, stability, noise immunity and robustness are higher than other methods and image mosaic obtains expected results.

Journal Introduction

ISSN 0254-6124       CN 11-1783/V

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