The GaoFen7(GF7)optical satellite is the first Chinese civilian sub-meter high-resolution stereo mapping satellite and is equipped with a double linear array camera and laser altimeter to achieve large-scale topograph...The GaoFen7(GF7)optical satellite is the first Chinese civilian sub-meter high-resolution stereo mapping satellite and is equipped with a double linear array camera and laser altimeter to achieve large-scale topographic mapping.To improve the accuracy of attitude determination,an attitude determination system comprised of four star sensors is loaded.According to the measurement accuracy and steady performance,the star sensors 1a and 1b is usually used together for satellite attitude calculation,which is called the conventional mode of attitude determination.Then,the combination of star sensors 2a and 2b is called the unconventional mode of attitude determination.Affected by variations in the incident angle of sunlight and solar radiation,thermal deformation occurs in the body and installation structure of the star sensor,which causes Attitude Low-Frequency Error(ALFE)and seriously influences the consistency of attitude determination results of different combination modes for multiple star sensors system.This study proposes an ALFE analysis and calibration approach for the multiple star sensors system of GF7 satellite to ensure the consistency of attitude determination results of different combination modes.Based on the statistical characteristics of the angles of the three axes,the installation parameters of the four star sensors are first calibrated.After analyzing the characteristics of the optical axis angles within 1420 orbit periods over 135 days,the segmented ALFE compensation model between the unconventional and conventional modes is proposed based on the Fourier series model and input parameter of latitude.Based on the on-orbit installation parameters and the ALFE model,the precise attitude determination results of the unconventional mode are calculated.Experimental results show that the attitude determination consistency after compensation is better than 2″.Moreover,the reliable application time range of the compensation model is 30 days to satisfy the requirements for high-precision attitude determination of GF7 satellite.展开更多
In the machining of high-end optical components,the aerostatic spindle error of an ultra-precision machine tool has a significant impact on the surface quality of the machined surfaces.The surfaces of many high-end op...In the machining of high-end optical components,the aerostatic spindle error of an ultra-precision machine tool has a significant impact on the surface quality of the machined surfaces.The surfaces of many high-end optical components need to meet the extremely stringent requirements of the full-frequency band error,which poses significant challenge to the control of the aerostatic spindle error.In this research,we put forward an active control method for the frequency domain error of the aerostatic spindle based on acoustic levitation,in which the acousticmagnetism-fluid-solid multi-field coupling rotor dynamics modeling method of the aerostatic spindle was proposed and the corresponding multi-field coupling model was established.Through the numerical simulation and preliminary experiments,the influence law of acoustic levitation on the frequency domain error of the aerostatic spindle is obtained.The results showed that acoustic levitation can be used to control the frequency domain error of the aerostatic spindle to some extent,which verified the effectiveness of the proposed method.展开更多
The large-aperture pulse compression grating(PCG) is a critical component in generating an ultra-high-intensity, ultra-short-pulse laser;however, the size of the PCG manufactured by transmission holographic exposure i...The large-aperture pulse compression grating(PCG) is a critical component in generating an ultra-high-intensity, ultra-short-pulse laser;however, the size of the PCG manufactured by transmission holographic exposure is limited to large-scale high-quality materials. The reflective method is a potential way for solving the size limitation, but there is still no successful precedent due to the lack of scientific specifications and advanced processing technology of exposure mirrors. In this paper, an analytical model is developed to clarify the specifications of components, and advanced processing technology is adopted to control the spatial frequency errors. Hereafter, we have successfully fabricated a multilayer dielectric grating of 200 mm × 150 mm by using an off-axis reflective exposure system with Φ300 mm. This demonstration proves that PCGs can be manufactured by using the reflection holographic exposure method and shows the potential for manufacturing the meter-level gratings used in 100 petawatt class high-power lasers.展开更多
A frequency error estimation is presented for the isogeometric free vibration analysis of Kirchhoff–Love cylindrical shells using both quadratic and cubic basis functions.By analyzing the discrete isogeometric equati...A frequency error estimation is presented for the isogeometric free vibration analysis of Kirchhoff–Love cylindrical shells using both quadratic and cubic basis functions.By analyzing the discrete isogeometric equations with the aid of harmonic wave assumption,the frequency error measures are rationally derived for the quadratic and cubic formulations for Kirchhoff–Love cylindrical shells.In particular,the governing relationship of the continuum frequency for Kirchhoff–Love cylindrical shells is naturally embedded into the frequency error measures without the need of explicit frequency expressions,which usually are not trivial for the shell problems.In accordance with these theoretical findings,the 2nd and 4th orders of frequency accuracy are attained for the isogeometric schemes using quadratic and cubic basis functions,respectively.Numerical results not only thoroughly verify the theoretical convergence rates of frequency solutions,but also manifest an excellent magnitude match between numerical and theoretical frequency errors for the isogeometric free vibration analysis of Kirchhoff–Love cylindrical shells.展开更多
<div style="text-align:justify;"> According to the problem that the low measurement accuracy of TH-1 satellite star sensor, the low frequency and “slow drift” error which cannot be ignored in the att...<div style="text-align:justify;"> According to the problem that the low measurement accuracy of TH-1 satellite star sensor, the low frequency and “slow drift” error which cannot be ignored in the attitude determination system, resulting in obvious random error in the horizontal position and elevation direction, and the change of the error with time and latitude, cannot be calibrated by the ground field of the real problem. In this paper, a low frequency detection model is established by using the principle of relative orientation, and the low frequency error is obtained by parallax elimination. Finally, the satellite attitude is compensated and the more accurate exterior orientation elements are obtained, thus improving the positioning accuracy and stability. The experimental results show that: the proposed methods are feasible, and by using the model to dynamically calibrate the exterior orientation angle elements on orbit, the plane and elevation errors of the ground points can be basically eliminated. The global uncontrollable positioning accuracy and stability of the photogrammetry satellite are improved. </div>展开更多
The method of using a narrowband filter to realize matched filtering is derived.A novel method of using spectrum sampling to realize matched filtering is presented,and the method can conquer the disadvantages that the...The method of using a narrowband filter to realize matched filtering is derived.A novel method of using spectrum sampling to realize matched filtering is presented,and the method can conquer the disadvantages that the narrowband filter cannot adopt the adaptive scheduling of phased array radars and realize matched filtering for several waveforms.A novel error extraction method is proposed,which uses a time division multipath method to realize the intermediate frequency extraction.This method can save lots of space for vehicle-born radar systems,reduce the influence of amplitude and phase distortion caused by devices,and enhance the system reliability.Simulation results show that the spectrum sampling method is applicable,and the implementation of frequency spectrum sampling is elaborated.展开更多
Due to frequency-selective and time-variant property of wireless channel together with additive noise and mismatch of oscillators between transmitter and receiver, there are always time and frequency synchronization e...Due to frequency-selective and time-variant property of wireless channel together with additive noise and mismatch of oscillators between transmitter and receiver, there are always time and frequency synchronization errors in a practical OFDM system. To investigate the effect of the two kinds of errors on system performance, the average normalized interference power (NIP) is defined. A simple supper bound for NIP caused by time synchronization error (TSE) and the tighter upper bound for NIP resulting from frequency synchronization error (FSE) are derived independently. Simulations in typical short wave (SW) and medium wave (MW) channels further verify the correctness and tightness of these upper bounds. They actually provide good approximations to NIPs. Moreover, the upper bound for NIP resulting from FSE is tighter than traditional upper bound. Additionally, a new solution is proposed to relax the precision requirement for time synchronization algorithm, which can achieve a better tradeoff between time synchronization precision and bandwidth efficiency. These upper bounds will be useful in developing and choosing time and frequency synchronization algorithms in OFDM system to achieve a specific NIP value for a given channel condition.展开更多
Higher transmission rate is one of the technological features of promi-nently used wireless communication namely Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing(MIMO–OFDM).One among an effec...Higher transmission rate is one of the technological features of promi-nently used wireless communication namely Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing(MIMO–OFDM).One among an effective solution for channel estimation in wireless communication system,spe-cifically in different environments is Deep Learning(DL)method.This research greatly utilizes channel estimator on the basis of Convolutional Neural Network Auto Encoder(CNNAE)classifier for MIMO-OFDM systems.A CNNAE classi-fier is one among Deep Learning(DL)algorithm,in which video signal is fed as input by allotting significant learnable weights and biases in various aspects/objects for video signal and capable of differentiating from one another.Improved performances are achieved by using CNNAE based channel estimation,in which extension is done for channel selection as well as achieve enhanced performances numerically,when compared with conventional estimators in quite a lot of scenar-ios.Considering reduction in number of parameters involved and re-usability of weights,CNNAE based channel estimation is quite suitable and properlyfits to the video signal.CNNAE classifier weights updation are done with minimized Sig-nal to Noise Ratio(SNR),Bit Error Rate(BER)and Mean Square Error(MSE).展开更多
基金supported by the National Science Fund for Distinguished Young Scholars[grant number 61825103]the Shanghai Aerospace Science and Technology Innovation Fund.
文摘The GaoFen7(GF7)optical satellite is the first Chinese civilian sub-meter high-resolution stereo mapping satellite and is equipped with a double linear array camera and laser altimeter to achieve large-scale topographic mapping.To improve the accuracy of attitude determination,an attitude determination system comprised of four star sensors is loaded.According to the measurement accuracy and steady performance,the star sensors 1a and 1b is usually used together for satellite attitude calculation,which is called the conventional mode of attitude determination.Then,the combination of star sensors 2a and 2b is called the unconventional mode of attitude determination.Affected by variations in the incident angle of sunlight and solar radiation,thermal deformation occurs in the body and installation structure of the star sensor,which causes Attitude Low-Frequency Error(ALFE)and seriously influences the consistency of attitude determination results of different combination modes for multiple star sensors system.This study proposes an ALFE analysis and calibration approach for the multiple star sensors system of GF7 satellite to ensure the consistency of attitude determination results of different combination modes.Based on the statistical characteristics of the angles of the three axes,the installation parameters of the four star sensors are first calibrated.After analyzing the characteristics of the optical axis angles within 1420 orbit periods over 135 days,the segmented ALFE compensation model between the unconventional and conventional modes is proposed based on the Fourier series model and input parameter of latitude.Based on the on-orbit installation parameters and the ALFE model,the precise attitude determination results of the unconventional mode are calculated.Experimental results show that the attitude determination consistency after compensation is better than 2″.Moreover,the reliable application time range of the compensation model is 30 days to satisfy the requirements for high-precision attitude determination of GF7 satellite.
基金Supported by National Natural Science Foundation of China(Grant No.52475494)Zhejiang Provincial Natural Science Foundation of China(Grant No.LY22E050003)Fundamental Research Funds for the Provincial Universities of Zhejiang(Grant No.RF-A2020005).
文摘In the machining of high-end optical components,the aerostatic spindle error of an ultra-precision machine tool has a significant impact on the surface quality of the machined surfaces.The surfaces of many high-end optical components need to meet the extremely stringent requirements of the full-frequency band error,which poses significant challenge to the control of the aerostatic spindle error.In this research,we put forward an active control method for the frequency domain error of the aerostatic spindle based on acoustic levitation,in which the acousticmagnetism-fluid-solid multi-field coupling rotor dynamics modeling method of the aerostatic spindle was proposed and the corresponding multi-field coupling model was established.Through the numerical simulation and preliminary experiments,the influence law of acoustic levitation on the frequency domain error of the aerostatic spindle is obtained.The results showed that acoustic levitation can be used to control the frequency domain error of the aerostatic spindle to some extent,which verified the effectiveness of the proposed method.
基金supported by the National Key R&D Program of China(2020YFA0714500)the National Natural Science Youth Foundation of China(62205352)+5 种基金the Member of Youth Innovation Promotion Association of the Chinese Academy of Sciencesthe International Partnership Program of the Chinese Academy of Sciences(181231KYSB20200040)the Chinese Academy of Sciences President’s International Fellowship Initiative(2023VMB0008)the Shanghai Sailing Program(20YF1454800)the Natural Science Foundation of Shanghai(21ZR1472000)the Shanghai Strategic Emerging Industry Development Special Fund(31011442501217020191D3101001)。
文摘The large-aperture pulse compression grating(PCG) is a critical component in generating an ultra-high-intensity, ultra-short-pulse laser;however, the size of the PCG manufactured by transmission holographic exposure is limited to large-scale high-quality materials. The reflective method is a potential way for solving the size limitation, but there is still no successful precedent due to the lack of scientific specifications and advanced processing technology of exposure mirrors. In this paper, an analytical model is developed to clarify the specifications of components, and advanced processing technology is adopted to control the spatial frequency errors. Hereafter, we have successfully fabricated a multilayer dielectric grating of 200 mm × 150 mm by using an off-axis reflective exposure system with Φ300 mm. This demonstration proves that PCGs can be manufactured by using the reflection holographic exposure method and shows the potential for manufacturing the meter-level gratings used in 100 petawatt class high-power lasers.
基金support of this work by the National Natural Science Foundation of China(Grant Nos.12072302,11772280)the Natural Science Foundation of Fujian Province of China(No.2021J02003)is gratefully acknowledged.
文摘A frequency error estimation is presented for the isogeometric free vibration analysis of Kirchhoff–Love cylindrical shells using both quadratic and cubic basis functions.By analyzing the discrete isogeometric equations with the aid of harmonic wave assumption,the frequency error measures are rationally derived for the quadratic and cubic formulations for Kirchhoff–Love cylindrical shells.In particular,the governing relationship of the continuum frequency for Kirchhoff–Love cylindrical shells is naturally embedded into the frequency error measures without the need of explicit frequency expressions,which usually are not trivial for the shell problems.In accordance with these theoretical findings,the 2nd and 4th orders of frequency accuracy are attained for the isogeometric schemes using quadratic and cubic basis functions,respectively.Numerical results not only thoroughly verify the theoretical convergence rates of frequency solutions,but also manifest an excellent magnitude match between numerical and theoretical frequency errors for the isogeometric free vibration analysis of Kirchhoff–Love cylindrical shells.
文摘<div style="text-align:justify;"> According to the problem that the low measurement accuracy of TH-1 satellite star sensor, the low frequency and “slow drift” error which cannot be ignored in the attitude determination system, resulting in obvious random error in the horizontal position and elevation direction, and the change of the error with time and latitude, cannot be calibrated by the ground field of the real problem. In this paper, a low frequency detection model is established by using the principle of relative orientation, and the low frequency error is obtained by parallax elimination. Finally, the satellite attitude is compensated and the more accurate exterior orientation elements are obtained, thus improving the positioning accuracy and stability. The experimental results show that: the proposed methods are feasible, and by using the model to dynamically calibrate the exterior orientation angle elements on orbit, the plane and elevation errors of the ground points can be basically eliminated. The global uncontrollable positioning accuracy and stability of the photogrammetry satellite are improved. </div>
文摘The method of using a narrowband filter to realize matched filtering is derived.A novel method of using spectrum sampling to realize matched filtering is presented,and the method can conquer the disadvantages that the narrowband filter cannot adopt the adaptive scheduling of phased array radars and realize matched filtering for several waveforms.A novel error extraction method is proposed,which uses a time division multipath method to realize the intermediate frequency extraction.This method can save lots of space for vehicle-born radar systems,reduce the influence of amplitude and phase distortion caused by devices,and enhance the system reliability.Simulation results show that the spectrum sampling method is applicable,and the implementation of frequency spectrum sampling is elaborated.
基金supported by the National Natural Science Foundation of China(Grant No.60496311).
文摘Due to frequency-selective and time-variant property of wireless channel together with additive noise and mismatch of oscillators between transmitter and receiver, there are always time and frequency synchronization errors in a practical OFDM system. To investigate the effect of the two kinds of errors on system performance, the average normalized interference power (NIP) is defined. A simple supper bound for NIP caused by time synchronization error (TSE) and the tighter upper bound for NIP resulting from frequency synchronization error (FSE) are derived independently. Simulations in typical short wave (SW) and medium wave (MW) channels further verify the correctness and tightness of these upper bounds. They actually provide good approximations to NIPs. Moreover, the upper bound for NIP resulting from FSE is tighter than traditional upper bound. Additionally, a new solution is proposed to relax the precision requirement for time synchronization algorithm, which can achieve a better tradeoff between time synchronization precision and bandwidth efficiency. These upper bounds will be useful in developing and choosing time and frequency synchronization algorithms in OFDM system to achieve a specific NIP value for a given channel condition.
文摘Higher transmission rate is one of the technological features of promi-nently used wireless communication namely Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing(MIMO–OFDM).One among an effective solution for channel estimation in wireless communication system,spe-cifically in different environments is Deep Learning(DL)method.This research greatly utilizes channel estimator on the basis of Convolutional Neural Network Auto Encoder(CNNAE)classifier for MIMO-OFDM systems.A CNNAE classi-fier is one among Deep Learning(DL)algorithm,in which video signal is fed as input by allotting significant learnable weights and biases in various aspects/objects for video signal and capable of differentiating from one another.Improved performances are achieved by using CNNAE based channel estimation,in which extension is done for channel selection as well as achieve enhanced performances numerically,when compared with conventional estimators in quite a lot of scenar-ios.Considering reduction in number of parameters involved and re-usability of weights,CNNAE based channel estimation is quite suitable and properlyfits to the video signal.CNNAE classifier weights updation are done with minimized Sig-nal to Noise Ratio(SNR),Bit Error Rate(BER)and Mean Square Error(MSE).
