As the number of array elements and bandwidth increase,the design challenges of the Phased Array Feed(PAF)front-end and its signal processing system increase.Aiming at the ng-PAF of the 110 m radio telescope,this arti...As the number of array elements and bandwidth increase,the design challenges of the Phased Array Feed(PAF)front-end and its signal processing system increase.Aiming at the ng-PAF of the 110 m radio telescope,this article introduces the concept of fully digital receivers and attempts to use Radio Frequency System-on-Chip(RFSo C)technology to digitize close to the feed array,reduce the complexity and analog components of the front-end,and improve the fidelity of the signals.The article discusses the digital beamforming topology and designs a PAF signal processing experimental system based on RFSo C+GPU hybrid architecture.The system adopts a ZCU111board to design RF-direct digitization and preprocessing front-end,which can sample eight signals up to 2.048GSPS,12 bit,channelize the signals into 1024 chunks,then reorder into four data streams and select one of the 256MHz frequency bands to output through four 10 Gb links.A GPU server is equipped with four RTX 3090 GPUs running four HRBF_HASHPIPE instances,each receiving a 64 MHz bandwidth signal for high-throughput realtime beamforming.The experimental system uses a signal generator to emulate Sa-like signals and propagates through rod antennas,which verifies the effectiveness of the beamforming algorithm.Performance tests show that after algorithm optimization,the average processing time for a given 4 ms data is less than 3 ms in the four-GPU parallel processing mode.The RFSo C integrated design shows significant advantages in power consumption and electromagnetic radiation compared with discrete circuits according to the measurement results.展开更多
Dome A in Antarctica has been demonstrated to be the best site on earth for optical,infrared,and terahertz astronomical observations by more and more evidence,such as excellent free-atmosphere seeing,extremely low per...Dome A in Antarctica has been demonstrated to be the best site on earth for optical,infrared,and terahertz astronomical observations by more and more evidence,such as excellent free-atmosphere seeing,extremely low perceptible water vapor,low sky background,and continuous dark time,etc.In this paper,we present a complete picture of the development of astronomy at Dome A from the very beginning,review recent progress in time-domain astronomy,demonstrate exciting results of the site testing,and address the challenges in instrumentation.Currently proposed projects are briefly discussed.展开更多
In the first part of this paper,four different Cassegrain optical systems with their correctors are designed and studied for multi-object fiber slit spectroscopic survey.The aperture in 6.5 m and field of view 3°...In the first part of this paper,four different Cassegrain optical systems with their correctors are designed and studied for multi-object fiber slit spectroscopic survey.The aperture in 6.5 m and field of view 3°are taken for these optical systems.Assuming observation wavelength range is 0.365-0.95μm,the maximum zenith distance for observing is 60°,the maximum diameter of these lenses is 1.66 m,the altitude of the telescope site is 2500 m,two correctors are composed of 4-piece lenses and the other two are 5-piece lenses.The results obtained are:f-ratio about 3.7,the image quality for all four systems with EE80D≤0.60″,the linear diameter of the focal surface is about 1.2 m and 11 000 fibers can be set on it.Considering the limit of size of fused silica and optical glass,the maximum diameter for lens is about 1.7 m.Such a 6.5 m telescope is about the largest one if using the above correctors.Considering the multiobject spectroscopic survey is greatly important,we also studied some telescope optical systems having their aperture near or larger than 10 m used for the multi-object fiber spectroscopic survey.Such ideas are introduced in the last section of this paper.展开更多
FAST,the largest single-dish radio telescope in the world,has a 500-meter diameter main reflector and a 300-meter diameter illuminated area.It has a main reflector that can vary its shape,which continuously changes th...FAST,the largest single-dish radio telescope in the world,has a 500-meter diameter main reflector and a 300-meter diameter illuminated area.It has a main reflector that can vary its shape,which continuously changes the shape of the illuminated area in reflector into a paraboloid.In this article,we propose a quasiCassegrain system for FAST.The detailed design results are provided.Such a quasi-Cassegrain system only needs to add a 14.6-meter diameter secondary reflector,which is close to the size of the feed cabin.The distance from the secondary reflector to the focus is only 5.08 m,and it has excellent image quality.In this quasi-Cassegrain system,the shape of the illuminated area in the main reflector continuously changes into an optimized hyperboloid.Using this quasi-Cassegrain system from frequency 0.5 GHz to 8 GHz,the multi-beam system can include 7 to 217 feeds.If this system is used in combination with Phased Array Feed(PAF)technology,more multi-beam feeds or a higher working frequency can be used.展开更多
To address the problem of real-time processing of ultra-wide bandwidth pulsar baseband data,we designed and implemented a pulsar baseband data processing algorithm(PSRDP)based on GPU parallel computing technology.PSRD...To address the problem of real-time processing of ultra-wide bandwidth pulsar baseband data,we designed and implemented a pulsar baseband data processing algorithm(PSRDP)based on GPU parallel computing technology.PSRDP can perform operations such as baseband data unpacking,channel separation,coherent dedispersion,Stokes detection,phase and folding period prediction,and folding integration in GPU clusters.We tested the algorithm using the J0437-4715 pulsar baseband data generated by the CASPSR and Medusa backends of the Parkes,and the J0332+5434 pulsar baseband data generated by the self-developed backend of the Nan Shan Radio Telescope.We obtained the pulse profiles of each baseband data.Through experimental analysis,we have found that the pulse profiles generated by the PSRDP algorithm in this paper are essentially consistent with the processing results of Digital Signal Processing Software for Pulsar Astronomy(DSPSR),which verified the effectiveness of the PSRDP algorithm.Furthermore,using the same baseband data,we compared the processing speed of PSRDP with DSPSR,and the results showed that PSRDP was not slower than DSPSR in terms of speed.The theoretical and technical experience gained from the PSRDP algorithm research in this article lays a technical foundation for the real-time processing of QTT(Qi Tai radio Telescope)ultra-wide bandwidth pulsar baseband data.展开更多
The origin of the highest-energy particles in nature, ultra-high-energy(UHE) cosmic rays, is still unknown. In order to resolve this mystery, very large detectors are required to probe the low flux of these particles ...The origin of the highest-energy particles in nature, ultra-high-energy(UHE) cosmic rays, is still unknown. In order to resolve this mystery, very large detectors are required to probe the low flux of these particles — or to detect the as-yet unobserved flux of UHE neutrinos predicted from their interactions. The‘lunar Askaryan technique' is a method to do both. When energetic particles interact in a dense medium,the Askaryan effect produces intense coherent pulses of radiation in the MHz–GHz range. By using radio telescopes to observe the Moon and look for nanosecond pulses, the entire visible lunar surface(20 million km^2) can be used as a UHE particle detector. A large effective area over a broad bandwidth is the primary telescope requirement for lunar observations, which makes large single-aperture instruments such as the Five-hundred-meter Aperture Spherical radio Telescope(FAST) well-suited to the technique. In this contribution, we describe the lunar Askaryan technique and its unique observational requirements. Estimates of the sensitivity of FAST to both the UHE cosmic ray and neutrino flux are given, and we describe the methods by which lunar observations with FAST, particularly if equipped with a broadband phased-array feed, could detect the flux of UHE cosmic rays.展开更多
Antarctic Survey Telescopes（AST3） are designed to be fully robotic telescopes at Dome A,Antarctica,which aim for highly efficient time-domain sky surveys as well as rapid response to special transient events（e.g.,g...Antarctic Survey Telescopes（AST3） are designed to be fully robotic telescopes at Dome A,Antarctica,which aim for highly efficient time-domain sky surveys as well as rapid response to special transient events（e.g.,gamma-ray bursts,near-Earth asteroids,supernovae,etc.）.Unlike traditional observations,a well-designed real-time survey scheduler is needed in order to implement an automatic survey in a very efficient,reliable and flexible way for the unattended telescopes.We present a study of the survey strategy for AST3 and implementation of its survey scheduler,which is also useful for other survey projects.展开更多
Based on the SDSS and SDSS-WISE quasar datasets, we put forward two schemes to estimate the photometric redshifts of quasars. Our schemes are based on the idea that the samples are firstly classified into subsamples b...Based on the SDSS and SDSS-WISE quasar datasets, we put forward two schemes to estimate the photometric redshifts of quasars. Our schemes are based on the idea that the samples are firstly classified into subsamples by a classifier and then a photometric redshift estimation of different subsamples is performed by a regressor. Random Forest is adopted as the core algorithm of the classifiers, while Random Forest and k NN are applied as the key algorithms of regressors. The samples are divided into two subsamples and four subsamples, depending on the redshift distribution. The performances based on different samples, different algorithms and different schemes are compared. The experimental results indicate that the accuracy of photometric redshift estimation for the two schemes generally improves to some extent compared to the original scheme in terms of the percents in |△z|1+zi< 0.1 and |△z|1+zi<0.2 and mean absolute error. Only given the running speed, k NN shows its superiority to Random Forest. The performance of Random Forest is a little better than or comparable to that of k NN with the two datasets. The accuracy based on the SDSS-WISE sample outperforms that based on the SDSS sample no matter by k NN or by Random Rorest. More information from more bands is considered and helpful to improve the accuracy of photometric redshift estimation. Evidently, it can be found that our strategy to estimate photometric redshift is applicable and may be applied to other datasets or other kinds of objects. Only talking about the percent in |△z|1+zi<0.3, there is still large room for further improvement in the photometric redshift estimation.展开更多
We combine K-nearest neighbors(KNN)with a genetic algorithm(GA)for photometric redshift estimation of quasars,short for GeneticKNN,which is a weighted KNN approach supported by a GA.This approach has two improvements ...We combine K-nearest neighbors(KNN)with a genetic algorithm(GA)for photometric redshift estimation of quasars,short for GeneticKNN,which is a weighted KNN approach supported by a GA.This approach has two improvements compared to KNN:one is the feature weighted by GA;the other is that the predicted redshift is not the redshift average of K neighbors but the weighted average of median and mean of redshifts for K neighbors,i.e.p×zmedian+(1-p)×zmean.Based on the SDSS and SDSS-WISE quasar samples,we explore the performance of GeneticKNN for photometric redshift estimation,comparing with the other six traditional machine learning methods,i.e.the least absolute shrinkage and selection operator(LASSO),support vector regression(SVR),multi-layer perceptrons(MLP),XGBoost,KNN and random forest.KNN and random forest show their superiority.Considering the easy implementation of KNN,we make improvement on KNN as GeneticKNN and apply GeneticKNN on photometric redshift estimation of quasars.Finally the performance of GeneticKNN is better than that of LASSO,SVR,MLP,XGBoost,KNN and random forest for all cases.Moreover the accuracy is better with the additional WISE magnitudes for the same method.展开更多
基于上海天马望远镜(Shanghai Tian Ma Telescope,简称TM),提出一种赋形卡塞格伦天线光程差的计算方法.首先,基于天线互易定理,建立天马望远镜光路的数学模型;其次,采用非均匀有理B样条拟合天马望远镜的主面和副面;最终,实现光程差的计...基于上海天马望远镜(Shanghai Tian Ma Telescope,简称TM),提出一种赋形卡塞格伦天线光程差的计算方法.首先,基于天线互易定理,建立天马望远镜光路的数学模型;其次,采用非均匀有理B样条拟合天马望远镜的主面和副面;最终,实现光程差的计算方法,并对鲁兹光程差公式在天马望远镜上的扩展应用进行研究.采用此方法可计算馈源、副面的轴向偏移和横向偏移以及副面旋转等非准直情况下的光程差,同时在非准直量较小时,可采用扩展鲁兹光程差公式快速计算光程差.为天马望远镜结构的实时测量和调整提供支持,同时相关研究也具有通用性,可为其他具有赋形面型的射电望远镜光程差的计算提供参考.展开更多
Stellar ranging is the basis for stellar dynamics research and in-depth research on astrophysics. The parallax method is the most widely used and important basic method for stellar ranging. However, it needs to perfor...Stellar ranging is the basis for stellar dynamics research and in-depth research on astrophysics. The parallax method is the most widely used and important basic method for stellar ranging. However, it needs to perform highprecision measurement of the parallax angle and the baseline length together. We aim to propose a new stellar ranging scheme based on second-order correlation that does not require a parallax angle measurement. We hope our solution can be as basic as the parallax method. We propose a new stellar ranging scheme by using the offset of second-order correlation curve signals. The optical path difference between the stars and different base stations is determined by the offset of the second-order correlation curve signals. Then the distance of the stars could be determined by the geometric relation. With the distance to stars out to 10 kpc away, our astrometric precision can be better compared to Gaia by simulation. We also design an experiment and successfully demonstrate the feasibility of this scheme. This stellar ranging scheme enables further and more accurate stellar ranging without requiring any prior information or angle measurement.展开更多
Location-based cross-matching is a preprocessing step in astronomy that aims to identify records belonging to the same celestial body based on the angular distance formula. The traditional approach involves comparing ...Location-based cross-matching is a preprocessing step in astronomy that aims to identify records belonging to the same celestial body based on the angular distance formula. The traditional approach involves comparing each record in one catalog with every record in the other catalog, resulting in a one-to-one comparison with high computational complexity. To reduce the computational time, index partitioning methods are used to divide the sky into regions and perform local cross-matching. In addition, cross-matching algorithms have been adopted on highperformance architectures to improve their efficiency. But the index partitioning methods and computation architectures only increase the degree of parallelism, and cannot decrease the complexity of pairwise-based crossmatching algorithm itself. A better algorithm is needed to further improve the performance of cross-matching algorithm. In this paper, we propose a 3d-tree-based cross-matching algorithm that converts the angular distance formula into an equivalent 3dEuclidean distance and uses 3d-tree method to reduce the overall computational complexity and to avoid boundary issues. Furthermore, we demonstrate the superiority of the 3d-tree approach over the 2d-tree method and implement it using a multi-threading technique during both the construction and querying phases. We have experimentally evaluated the proposed 3d-tree cross-matching algorithm using publicly available catalog data. The results show that our algorithm applied on two 32-core CPUs achieves equivalent performance than previous experiments conducted on a six-node CPU-GPU cluster.展开更多
Thousands of orbit tracks of space objects are collected by a radar each day,and many may be from uncatalogued objects.As such,it is an urgent demand to catalogue the uncatalogued objects,which requires to determine w...Thousands of orbit tracks of space objects are collected by a radar each day,and many may be from uncatalogued objects.As such,it is an urgent demand to catalogue the uncatalogued objects,which requires to determine whether two or more un-correlated tracks(UCTs)are from the same object.This paper proposes to apply the Lambert problem to associate two radar-measured orbit tracks of LEO and HEO objects.A novel method of position correction is proposed to correct the secular and short periodic effects caused by the J_2 perturbation,making the Lambert problem applicable to perturbed orbit tracks.After that,an orbit selection method based on the characteristics of residuals solves the multiple-revolution Lambert problem.Extensive experiments with simulated radar measurements of LEO and HEO objects are carried out to assess the performance of the proposed method.It is shown that the semi-major axis can be determined with an error less than 200 m from two tracks separated by 4 days.The true positive(TP)rates for associating two LEO tracks apart by less than 6 days are 94.2%.The TP rate is still at 73.1%even for two tracks apart by 8–9 days.The results demonstrate the strong applicability of the proposed method to associate radar measurements of uncatalogued objects.展开更多
基金funded by the National Natural Science Foundation of China(NSFC,Grant No.12073066)the National Key R&D Program of China under No.2021YFC2203502+3 种基金the Youth Innovation Promotion Association of CAS under No.2020063the NSFC(Grant Nos.61931002,12073067 and 11973077)the Natural Science Foundation of Xinjiang Uygur Autonomous Region under No.2021D01E07partly supported by the Operation,Maintenance and Upgrading Fund for Astronomical Telescopes and Facility Instruments,budgeted from the Ministry of Finance of China(MOF)and administrated by the Chinese Academy of Sciences(CAS)。
文摘As the number of array elements and bandwidth increase,the design challenges of the Phased Array Feed(PAF)front-end and its signal processing system increase.Aiming at the ng-PAF of the 110 m radio telescope,this article introduces the concept of fully digital receivers and attempts to use Radio Frequency System-on-Chip(RFSo C)technology to digitize close to the feed array,reduce the complexity and analog components of the front-end,and improve the fidelity of the signals.The article discusses the digital beamforming topology and designs a PAF signal processing experimental system based on RFSo C+GPU hybrid architecture.The system adopts a ZCU111board to design RF-direct digitization and preprocessing front-end,which can sample eight signals up to 2.048GSPS,12 bit,channelize the signals into 1024 chunks,then reorder into four data streams and select one of the 256MHz frequency bands to output through four 10 Gb links.A GPU server is equipped with four RTX 3090 GPUs running four HRBF_HASHPIPE instances,each receiving a 64 MHz bandwidth signal for high-throughput realtime beamforming.The experimental system uses a signal generator to emulate Sa-like signals and propagates through rod antennas,which verifies the effectiveness of the beamforming algorithm.Performance tests show that after algorithm optimization,the average processing time for a given 4 ms data is less than 3 ms in the four-GPU parallel processing mode.The RFSo C integrated design shows significant advantages in power consumption and electromagnetic radiation compared with discrete circuits according to the measurement results.
基金supported in part by the National Natural Science Foundation of China(Grant Nos.11733007,11673037 and 11273019)the National Basic Research Program(973 Program)of China(Grant No.2013CB834900)the Chinese Polar Environment Comprehensive Investigation&Assessment Program(Grant No.CHINARE2016-02-03)。
文摘Dome A in Antarctica has been demonstrated to be the best site on earth for optical,infrared,and terahertz astronomical observations by more and more evidence,such as excellent free-atmosphere seeing,extremely low perceptible water vapor,low sky background,and continuous dark time,etc.In this paper,we present a complete picture of the development of astronomy at Dome A from the very beginning,review recent progress in time-domain astronomy,demonstrate exciting results of the site testing,and address the challenges in instrumentation.Currently proposed projects are briefly discussed.
文摘In the first part of this paper,four different Cassegrain optical systems with their correctors are designed and studied for multi-object fiber slit spectroscopic survey.The aperture in 6.5 m and field of view 3°are taken for these optical systems.Assuming observation wavelength range is 0.365-0.95μm,the maximum zenith distance for observing is 60°,the maximum diameter of these lenses is 1.66 m,the altitude of the telescope site is 2500 m,two correctors are composed of 4-piece lenses and the other two are 5-piece lenses.The results obtained are:f-ratio about 3.7,the image quality for all four systems with EE80D≤0.60″,the linear diameter of the focal surface is about 1.2 m and 11 000 fibers can be set on it.Considering the limit of size of fused silica and optical glass,the maximum diameter for lens is about 1.7 m.Such a 6.5 m telescope is about the largest one if using the above correctors.Considering the multiobject spectroscopic survey is greatly important,we also studied some telescope optical systems having their aperture near or larger than 10 m used for the multi-object fiber spectroscopic survey.Such ideas are introduced in the last section of this paper.
文摘FAST,the largest single-dish radio telescope in the world,has a 500-meter diameter main reflector and a 300-meter diameter illuminated area.It has a main reflector that can vary its shape,which continuously changes the shape of the illuminated area in reflector into a paraboloid.In this article,we propose a quasiCassegrain system for FAST.The detailed design results are provided.Such a quasi-Cassegrain system only needs to add a 14.6-meter diameter secondary reflector,which is close to the size of the feed cabin.The distance from the secondary reflector to the focus is only 5.08 m,and it has excellent image quality.In this quasi-Cassegrain system,the shape of the illuminated area in the main reflector continuously changes into an optimized hyperboloid.Using this quasi-Cassegrain system from frequency 0.5 GHz to 8 GHz,the multi-beam system can include 7 to 217 feeds.If this system is used in combination with Phased Array Feed(PAF)technology,more multi-beam feeds or a higher working frequency can be used.
文摘星间链路测量是卫星导航系统实现自主运行的一项重要的关键技术.以GPS星座为例,基于非同时的星间双向测量模式,建立了星间时间同步的归算公式,给出了主要的系统误差的改正方法.利用IGS(International GNSS Service)精密星历,开展星间时间同步仿真试验,分析了非同时星间伪距数据历元归化、初始轨道以及主要系统误差对卫星钟时间同步的影响.并采用"集中式"星间自主时间同步法,计算了每颗导航卫星的广播钟差.试验结果表明,非同时星间伪距数据历元归化、初始轨道对卫星钟差影响较小,相对论效应和传播路径不对称引起的误差对卫星钟差影响大,需采用理论公式进行修正;与IGS精密钟差相比,广播钟差误差的RMS(Root Mean Square)约为0.4 ns.
基金supported by the National Key R&D Program of China Nos.2021YFC2203502 and 2022YFF0711502the National Natural Science Foundation of China(NSFC)(12173077 and 12003062)+5 种基金the Tianshan Innovation Team Plan of Xinjiang Uygur Autonomous Region(2022D14020)the Tianshan Talent Project of Xinjiang Uygur Autonomous Region(2022TSYCCX0095)the Scientific Instrument Developing Project of the Chinese Academy of Sciences,grant No.PTYQ2022YZZD01China National Astronomical Data Center(NADC)the Operation,Maintenance and Upgrading Fund for Astronomical Telescopes and Facility Instruments,budgeted from the Ministry of Finance of China(MOF)and administrated by the Chinese Academy of Sciences(CAS)Natural Science Foundation of Xinjiang Uygur Autonomous Region(2022D01A360)。
文摘To address the problem of real-time processing of ultra-wide bandwidth pulsar baseband data,we designed and implemented a pulsar baseband data processing algorithm(PSRDP)based on GPU parallel computing technology.PSRDP can perform operations such as baseband data unpacking,channel separation,coherent dedispersion,Stokes detection,phase and folding period prediction,and folding integration in GPU clusters.We tested the algorithm using the J0437-4715 pulsar baseband data generated by the CASPSR and Medusa backends of the Parkes,and the J0332+5434 pulsar baseband data generated by the self-developed backend of the Nan Shan Radio Telescope.We obtained the pulse profiles of each baseband data.Through experimental analysis,we have found that the pulse profiles generated by the PSRDP algorithm in this paper are essentially consistent with the processing results of Digital Signal Processing Software for Pulsar Astronomy(DSPSR),which verified the effectiveness of the PSRDP algorithm.Furthermore,using the same baseband data,we compared the processing speed of PSRDP with DSPSR,and the results showed that PSRDP was not slower than DSPSR in terms of speed.The theoretical and technical experience gained from the PSRDP algorithm research in this article lays a technical foundation for the real-time processing of QTT(Qi Tai radio Telescope)ultra-wide bandwidth pulsar baseband data.
文摘The origin of the highest-energy particles in nature, ultra-high-energy(UHE) cosmic rays, is still unknown. In order to resolve this mystery, very large detectors are required to probe the low flux of these particles — or to detect the as-yet unobserved flux of UHE neutrinos predicted from their interactions. The‘lunar Askaryan technique' is a method to do both. When energetic particles interact in a dense medium,the Askaryan effect produces intense coherent pulses of radiation in the MHz–GHz range. By using radio telescopes to observe the Moon and look for nanosecond pulses, the entire visible lunar surface(20 million km^2) can be used as a UHE particle detector. A large effective area over a broad bandwidth is the primary telescope requirement for lunar observations, which makes large single-aperture instruments such as the Five-hundred-meter Aperture Spherical radio Telescope(FAST) well-suited to the technique. In this contribution, we describe the lunar Askaryan technique and its unique observational requirements. Estimates of the sensitivity of FAST to both the UHE cosmic ray and neutrino flux are given, and we describe the methods by which lunar observations with FAST, particularly if equipped with a broadband phased-array feed, could detect the flux of UHE cosmic rays.
基金supported by the Chinese Polar Environment Comprehensive Investigation & Assessment Programmes(Grant No.CHINARE2017-02-04)the National Natural Science Foundation of China(Grant Nos.11003027,11403057,11403048,11203039 and 11273019)the National Basic Research Program of China(973 Program,Grant No.2013CB834900)
文摘Antarctic Survey Telescopes（AST3） are designed to be fully robotic telescopes at Dome A,Antarctica,which aim for highly efficient time-domain sky surveys as well as rapid response to special transient events（e.g.,gamma-ray bursts,near-Earth asteroids,supernovae,etc.）.Unlike traditional observations,a well-designed real-time survey scheduler is needed in order to implement an automatic survey in a very efficient,reliable and flexible way for the unattended telescopes.We present a study of the survey strategy for AST3 and implementation of its survey scheduler,which is also useful for other survey projects.
基金funded by the 973 Program (2014CB845700)the National Natural Science Foundation of China (Grant Nos. 11873066 and U1731109)
文摘Based on the SDSS and SDSS-WISE quasar datasets, we put forward two schemes to estimate the photometric redshifts of quasars. Our schemes are based on the idea that the samples are firstly classified into subsamples by a classifier and then a photometric redshift estimation of different subsamples is performed by a regressor. Random Forest is adopted as the core algorithm of the classifiers, while Random Forest and k NN are applied as the key algorithms of regressors. The samples are divided into two subsamples and four subsamples, depending on the redshift distribution. The performances based on different samples, different algorithms and different schemes are compared. The experimental results indicate that the accuracy of photometric redshift estimation for the two schemes generally improves to some extent compared to the original scheme in terms of the percents in |△z|1+zi< 0.1 and |△z|1+zi<0.2 and mean absolute error. Only given the running speed, k NN shows its superiority to Random Forest. The performance of Random Forest is a little better than or comparable to that of k NN with the two datasets. The accuracy based on the SDSS-WISE sample outperforms that based on the SDSS sample no matter by k NN or by Random Rorest. More information from more bands is considered and helpful to improve the accuracy of photometric redshift estimation. Evidently, it can be found that our strategy to estimate photometric redshift is applicable and may be applied to other datasets or other kinds of objects. Only talking about the percent in |△z|1+zi<0.3, there is still large room for further improvement in the photometric redshift estimation.
基金the National Key R&D Program of China(Grant No.2018YFB 1702703)funded by the National Natural Science Foundation of China(Grant Nos.11873066,U1531122 and U1731109)+3 种基金Funding for the Sloan Digital Sky Survey(SDSS)Ⅳhas been provided by the Alfred P.Sloan Foundationthe U.S.Department of Energy Office of Science,and the Participating Institutionssupport and resources from the Center for High-Performance Computing at the University of UtahThe Wide-field Infrared Survey Explorer(WISE)is a joint project of the University of California,Los Angeles,and the Jet Propulsion Laboratory/California Institute of Technology,funded by the National Aeronautics and Space Administration。
文摘We combine K-nearest neighbors(KNN)with a genetic algorithm(GA)for photometric redshift estimation of quasars,short for GeneticKNN,which is a weighted KNN approach supported by a GA.This approach has two improvements compared to KNN:one is the feature weighted by GA;the other is that the predicted redshift is not the redshift average of K neighbors but the weighted average of median and mean of redshifts for K neighbors,i.e.p×zmedian+(1-p)×zmean.Based on the SDSS and SDSS-WISE quasar samples,we explore the performance of GeneticKNN for photometric redshift estimation,comparing with the other six traditional machine learning methods,i.e.the least absolute shrinkage and selection operator(LASSO),support vector regression(SVR),multi-layer perceptrons(MLP),XGBoost,KNN and random forest.KNN and random forest show their superiority.Considering the easy implementation of KNN,we make improvement on KNN as GeneticKNN and apply GeneticKNN on photometric redshift estimation of quasars.Finally the performance of GeneticKNN is better than that of LASSO,SVR,MLP,XGBoost,KNN and random forest for all cases.Moreover the accuracy is better with the additional WISE magnitudes for the same method.
文摘基于上海天马望远镜(Shanghai Tian Ma Telescope,简称TM),提出一种赋形卡塞格伦天线光程差的计算方法.首先,基于天线互易定理,建立天马望远镜光路的数学模型;其次,采用非均匀有理B样条拟合天马望远镜的主面和副面;最终,实现光程差的计算方法,并对鲁兹光程差公式在天马望远镜上的扩展应用进行研究.采用此方法可计算馈源、副面的轴向偏移和横向偏移以及副面旋转等非准直情况下的光程差,同时在非准直量较小时,可采用扩展鲁兹光程差公式快速计算光程差.为天马望远镜结构的实时测量和调整提供支持,同时相关研究也具有通用性,可为其他具有赋形面型的射电望远镜光程差的计算提供参考.
基金supported by National Key Research and Development Program Earth Observation and Navigation Key Specialities (No. 2018YFB0504300)。
文摘Stellar ranging is the basis for stellar dynamics research and in-depth research on astrophysics. The parallax method is the most widely used and important basic method for stellar ranging. However, it needs to perform highprecision measurement of the parallax angle and the baseline length together. We aim to propose a new stellar ranging scheme based on second-order correlation that does not require a parallax angle measurement. We hope our solution can be as basic as the parallax method. We propose a new stellar ranging scheme by using the offset of second-order correlation curve signals. The optical path difference between the stars and different base stations is determined by the offset of the second-order correlation curve signals. Then the distance of the stars could be determined by the geometric relation. With the distance to stars out to 10 kpc away, our astrometric precision can be better compared to Gaia by simulation. We also design an experiment and successfully demonstrate the feasibility of this scheme. This stellar ranging scheme enables further and more accurate stellar ranging without requiring any prior information or angle measurement.
基金supported by the National Key Research and Development Program of China (2022YFF0711502)the National Natural Science Foundation of China (NSFC) (12273025 and 12133010)supported by China National Astronomical Data Center (NADC), CAS Astronomical Data Center and Chinese Virtual Observatory (China-VO)。
文摘Location-based cross-matching is a preprocessing step in astronomy that aims to identify records belonging to the same celestial body based on the angular distance formula. The traditional approach involves comparing each record in one catalog with every record in the other catalog, resulting in a one-to-one comparison with high computational complexity. To reduce the computational time, index partitioning methods are used to divide the sky into regions and perform local cross-matching. In addition, cross-matching algorithms have been adopted on highperformance architectures to improve their efficiency. But the index partitioning methods and computation architectures only increase the degree of parallelism, and cannot decrease the complexity of pairwise-based crossmatching algorithm itself. A better algorithm is needed to further improve the performance of cross-matching algorithm. In this paper, we propose a 3d-tree-based cross-matching algorithm that converts the angular distance formula into an equivalent 3dEuclidean distance and uses 3d-tree method to reduce the overall computational complexity and to avoid boundary issues. Furthermore, we demonstrate the superiority of the 3d-tree approach over the 2d-tree method and implement it using a multi-threading technique during both the construction and querying phases. We have experimentally evaluated the proposed 3d-tree cross-matching algorithm using publicly available catalog data. The results show that our algorithm applied on two 32-core CPUs achieves equivalent performance than previous experiments conducted on a six-node CPU-GPU cluster.
基金support from the National Natural Science Foundation of China(Grant No.41874035)the Natural Science Foundation of Hubei province,China(Grant No.2020CFB396)the Fundamental Research Funds for the Central Universities,China(Grant No.2042021kf0001)。
文摘Thousands of orbit tracks of space objects are collected by a radar each day,and many may be from uncatalogued objects.As such,it is an urgent demand to catalogue the uncatalogued objects,which requires to determine whether two or more un-correlated tracks(UCTs)are from the same object.This paper proposes to apply the Lambert problem to associate two radar-measured orbit tracks of LEO and HEO objects.A novel method of position correction is proposed to correct the secular and short periodic effects caused by the J_2 perturbation,making the Lambert problem applicable to perturbed orbit tracks.After that,an orbit selection method based on the characteristics of residuals solves the multiple-revolution Lambert problem.Extensive experiments with simulated radar measurements of LEO and HEO objects are carried out to assess the performance of the proposed method.It is shown that the semi-major axis can be determined with an error less than 200 m from two tracks separated by 4 days.The true positive(TP)rates for associating two LEO tracks apart by less than 6 days are 94.2%.The TP rate is still at 73.1%even for two tracks apart by 8–9 days.The results demonstrate the strong applicability of the proposed method to associate radar measurements of uncatalogued objects.
