This paper investigates a simplified model for describing the gravitational fields of non- axisymmetric elongated asteroids. The connection between the simplified model and the target aster-oid is built by considering...This paper investigates a simplified model for describing the gravitational fields of non- axisymmetric elongated asteroids. The connection between the simplified model and the target aster-oid is built by considering the positions of equilibrium points. To improve the performance of po-sition matching for the equilibrium points associated with these non-axisymmetric asteroids, a non-axisymmetric triple-particle-linkage model is proposed based on two existing axisymmetric particle- linkage models. The unknown parameters of the simplified model are determined by minimizing the matching error using the nonlinear optimization method. The proposed simplified model is applied for three realistic elongated asteroids, 243 Ida, 433 Eros and （8567） 1996 HW1. The simulation re-sults verify that the current particle-linkage model has better matching accuracy than the two existing particle-linkage models. The comparison, between the simplified model and the polyhedral model, on the topological cases of the equilibrium points and the distribution of gravitational potential further validate the rationality and accuracy of the simplified model.展开更多
In the framework of the circular restricted three-body problem, the center manifolds associated with collinear libration points contain all the bounded orbits moving around these points. Semianalytical computation of ...In the framework of the circular restricted three-body problem, the center manifolds associated with collinear libration points contain all the bounded orbits moving around these points. Semianalytical computation of the center manifolds and the associated canonical transformation are valuable tools for exploring the design space of libration point missions. This paper deals with the refinement of reduction to the center manifold procedure. In order to reduce the amount of calculation needed and avoid repetitive computation of the Poisson bracket, a modified method is presented. By using a polynomial optimization technique, the coordinate transformation is conducted more efficiently. In addition, an alternative way to do the canonical coordinate transformation is discussed, which complements the classical approach. Numerical simulation confirms that more accurate and efficient numerical exploration of the center manifold is made possible by using the refined method.展开更多
The importance of Remote Sensing and Geographic Information System in map making cannot be overemphasized because of its ability to integrate spatial data with non-spatial data and also communicate the resulting infor...The importance of Remote Sensing and Geographic Information System in map making cannot be overemphasized because of its ability to integrate spatial data with non-spatial data and also communicate the resulting information in a way that everyone would understand. Several works have taken advantage of the abilities of these technologies to produce street maps using High Resolution Images. The increase in development in Ile Ife, Osun State, Nigeria, has brought about navigation challenge and associated difficulties. This work intends to produce a street map that will ease navigation within the study area and help in road network analysis, site suitability analysis etc. Aerial Photographs, captured in the year 2009 and GeoEye1 Satellite Image of 2011 were used to extract the road network of Ife Metropolis. The image was imported into ArcGIS environment, where the database was created having feature datasets such as roads and special features. To have all the elements in vector format, the image was digitized. The street names collected from the field work was inputted into the database and then subjected to cartographical processes. 512 Roads were captured within four classes of Road Network namely Express road (5), Secondary Road (25), Primary Roads (22) and Street Road (460). This field work revealed that a larger percentage of the roads were not paved, while most of the paved ones have deteriorated and the newly constructed ones were not documented. It also showed that some of the roads were not named according to the standard and some were not named at all. From this study, we recommend that the naming system should be standardized across the study area. It is also recommended that provision should be made for street map revision on a yearly basis so as to account for changes.展开更多
The urban environment has continued to experience changes from increasing impervious surfaces, which alters the proper functioning of the ecological zones and impairs water quality in the watershed. Impervious cover i...The urban environment has continued to experience changes from increasing impervious surfaces, which alters the proper functioning of the ecological zones and impairs water quality in the watershed. Impervious cover is predominantly used as an indicator to assist in understanding and forecasting the impact of human actions and other related activities on aquatic resources. In this study, the rate of change in land uses using the impervious surface as an indicator, and the percentage of imperviousness on the effect on water quality in the urban watershed were assessed. Ile-Ife was delineated as an urban watershed, and the percentage of imperviousness from 2008 to 2016 and the effect of imperviousness on water bodies were assessed. The study utilized ASTERDEM, Worldview (0.46 m), IKONOS (1.4 m), Landsat (30 m) for 2008 and 2016, GPS and Drone (10 cm). Water sampling was carried out in selected locations as generated by the impervious surface analyst tool, (ISAT). The percentage (%) of impervious surfaces accounted for 59.4% (4567.1/7691.5ha) in 2008 and 70.3% (5408.2/7691.5ha) in 2016, from the total number of lands investigated. The turbidity values from low to high regions were 32.3, 55.9 and 82.4 NUT. Changes in LULC of the watershed led to increased surface temperature, impermeable surfaces, and decreased vegetation, which exposes the area to flooding and reduced water quality. This study emphasized the importance of GIS and its integration into urban changes and water quality assessment.展开更多
Effective planning relies on accurate and up-to-date information on existing land use and land cover. The timely detection of trends in land use and land cover change and a quantification of such trends are of specifi...Effective planning relies on accurate and up-to-date information on existing land use and land cover. The timely detection of trends in land use and land cover change and a quantification of such trends are of specific interest to planners and decision makers. The aim of this research is to use remote sensing and GIS to monitor landuse and land cover change in Egbeda Local Government Area, Oyo State with a view to determining how useful such information can be to planners and decision makers for effective urban management. The research was conducted using remote sensing and Geographical information System at determining the trend and extent of land use and land cover change and its driving force in Egbeda Local Government Area, Oyo State. The methods used include: digitization, digital image processing and spatial analysis using an inverse distance weighted (IDW) technique, Maximum likelihood supervised classification and post classification change detection techniques were applied to Landsat imageries acquired in 1984, 2006 and 2018. Imageries were classified into built-up area, vegetation, bare surface, cultivation and water body. The results of the analysis obtained showed drastic change in built-up area which rose to 32.8% from 25.4% between 1984 and 2018 periods. To reduce the effect of land use expansion in the study areas, policy measures were recommended which include proper inventory of land use and land cover, regular monitoring of urban areas spread of development and regional development programs. These will enable the government, stakeholders, policy makers and planners to make informed decisions provided by these technologies to attain and sustain future urban development.展开更多
Relative navigation is a key enabling technology for space missions such as on-orbit servicing and space situational awareness.Given that there are several special advantages of space relative navigation using angles-...Relative navigation is a key enabling technology for space missions such as on-orbit servicing and space situational awareness.Given that there are several special advantages of space relative navigation using angles-only measurements from passive optical sensors,angles-only relative navigation is considered as one of the best potential approaches in the field of space relative navigation.However,angles-only relative navigation is well-known for its range observability problem.To overcome this observability problem,many studies have been conducted over the past decades.In this study,we present a comprehensive review of state-of-the-art space relative navigation based on angles-only measurements.The emphasis is on the observability problem and solutions to angles-only relative navigation,where the review of the solutions is categorized into four classes based on the intrinsic principle:complicated dynamics approach,multi-line of sight(multi-LOS)approach,sensor offset center-of-mass approach,and orbit maneuver approach.Then,the fight demonstration results of angles-only relative navigation in the two projects are briefly reviewed.Finally,conclusions of this study and recommendations for further research are presented.展开更多
The space environment has become highly congested due to the increasing space debris,seriously threatening the safety of orbiting spacecraft.Space-based situational awareness,as a comprehensive capability of threat kn...The space environment has become highly congested due to the increasing space debris,seriously threatening the safety of orbiting spacecraft.Space-based situational awareness,as a comprehensive capability of threat knowledge,analysis,and decision-making,is of significant importance to ensure space security and maintain normal order.Various space situational awareness systems have been designed and launched.Data acquisition,target recognition,and monitoring constituting key technologies make major contributions,and various advanced algorithms are explored as technical supports.However,comprehensive reviews of these technologies and specific algorithms rarely emerge.It disadvantages the future development of space situational awareness.Therefore,this paper further reviews and analyzes research advancements in key technologies for space situational awareness,emphasizing target recognition and monitoring.Many mature and emerging methods are presented for these technologies while discussing application advantages and limitations.Specially,the research prospects of multiagent and synergetic constellation technologies are expected for future situational awareness.This paper indicates the future directions of the key technologies,aiming to provide references for space-based situational awareness to realize space sustainability.展开更多
The pose determination between nanosatellites and the cooperative spacecraft is essential for swarm in-orbit services.Timeof–flight(ToF)sensors are one of the most promising sensors to achieve the tasks.This paper pr...The pose determination between nanosatellites and the cooperative spacecraft is essential for swarm in-orbit services.Timeof–flight(ToF)sensors are one of the most promising sensors to achieve the tasks.This paper presented an end-to-end assessment of how these sensors were used for pose estimation.First,an embedded system was designed based on the ToF camera with lasers as a driven light source.Gray and depth images were collected to detect and match the cooperative spacecraft in real time,obtaining the pose information.A threshold-based segmentation was proposed to find a small set of the pixels belonging to reflector markers.Only operating on the defined active pixel set reduced computational resources.Then,morphological detection combined with an edge following-based ellipse detection extracted the centroid coordinate of the circular marker,while the center-of-heart rate was calculated as the recognition condition.Next,the marker matching was completed using a deterministic annealing algorithm,obtaining two sets of 3D coordinates.A singular value decomposition(SVD)algorithm estimated the relative pose between the nanosatellite and the spacecraft.In the experiments,the pose calculated by the TOF camera reached an accuracy of 0.13 degrees and 2 mm.It accurately identified the markers and determined the pose,verifying the feasibility of the ToF camera for rendezvous and docking.展开更多
基金supported by the National Natural Science Foundation of China (Grant No.11672126)the Innovation Funded Project of Shanghai Aerospace Science and Technology (Grant Nos.SAST2017032 and SAST2015036)the Scientific Research Foundation for New Staffs of Nanjing University of Aeronautics and Astronautics (Grant No.1011-YAH17071)
文摘This paper investigates a simplified model for describing the gravitational fields of non- axisymmetric elongated asteroids. The connection between the simplified model and the target aster-oid is built by considering the positions of equilibrium points. To improve the performance of po-sition matching for the equilibrium points associated with these non-axisymmetric asteroids, a non-axisymmetric triple-particle-linkage model is proposed based on two existing axisymmetric particle- linkage models. The unknown parameters of the simplified model are determined by minimizing the matching error using the nonlinear optimization method. The proposed simplified model is applied for three realistic elongated asteroids, 243 Ida, 433 Eros and （8567） 1996 HW1. The simulation re-sults verify that the current particle-linkage model has better matching accuracy than the two existing particle-linkage models. The comparison, between the simplified model and the polyhedral model, on the topological cases of the equilibrium points and the distribution of gravitational potential further validate the rationality and accuracy of the simplified model.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11403013 and 11672126)the Fundamental Research Funds for the Central Universities (Nos. 56XAA14093 and 56YAH12036)the Postdoctoral Foundation of Jiangsu Province (No. 1301029B)
文摘In the framework of the circular restricted three-body problem, the center manifolds associated with collinear libration points contain all the bounded orbits moving around these points. Semianalytical computation of the center manifolds and the associated canonical transformation are valuable tools for exploring the design space of libration point missions. This paper deals with the refinement of reduction to the center manifold procedure. In order to reduce the amount of calculation needed and avoid repetitive computation of the Poisson bracket, a modified method is presented. By using a polynomial optimization technique, the coordinate transformation is conducted more efficiently. In addition, an alternative way to do the canonical coordinate transformation is discussed, which complements the classical approach. Numerical simulation confirms that more accurate and efficient numerical exploration of the center manifold is made possible by using the refined method.
文摘The importance of Remote Sensing and Geographic Information System in map making cannot be overemphasized because of its ability to integrate spatial data with non-spatial data and also communicate the resulting information in a way that everyone would understand. Several works have taken advantage of the abilities of these technologies to produce street maps using High Resolution Images. The increase in development in Ile Ife, Osun State, Nigeria, has brought about navigation challenge and associated difficulties. This work intends to produce a street map that will ease navigation within the study area and help in road network analysis, site suitability analysis etc. Aerial Photographs, captured in the year 2009 and GeoEye1 Satellite Image of 2011 were used to extract the road network of Ife Metropolis. The image was imported into ArcGIS environment, where the database was created having feature datasets such as roads and special features. To have all the elements in vector format, the image was digitized. The street names collected from the field work was inputted into the database and then subjected to cartographical processes. 512 Roads were captured within four classes of Road Network namely Express road (5), Secondary Road (25), Primary Roads (22) and Street Road (460). This field work revealed that a larger percentage of the roads were not paved, while most of the paved ones have deteriorated and the newly constructed ones were not documented. It also showed that some of the roads were not named according to the standard and some were not named at all. From this study, we recommend that the naming system should be standardized across the study area. It is also recommended that provision should be made for street map revision on a yearly basis so as to account for changes.
文摘The urban environment has continued to experience changes from increasing impervious surfaces, which alters the proper functioning of the ecological zones and impairs water quality in the watershed. Impervious cover is predominantly used as an indicator to assist in understanding and forecasting the impact of human actions and other related activities on aquatic resources. In this study, the rate of change in land uses using the impervious surface as an indicator, and the percentage of imperviousness on the effect on water quality in the urban watershed were assessed. Ile-Ife was delineated as an urban watershed, and the percentage of imperviousness from 2008 to 2016 and the effect of imperviousness on water bodies were assessed. The study utilized ASTERDEM, Worldview (0.46 m), IKONOS (1.4 m), Landsat (30 m) for 2008 and 2016, GPS and Drone (10 cm). Water sampling was carried out in selected locations as generated by the impervious surface analyst tool, (ISAT). The percentage (%) of impervious surfaces accounted for 59.4% (4567.1/7691.5ha) in 2008 and 70.3% (5408.2/7691.5ha) in 2016, from the total number of lands investigated. The turbidity values from low to high regions were 32.3, 55.9 and 82.4 NUT. Changes in LULC of the watershed led to increased surface temperature, impermeable surfaces, and decreased vegetation, which exposes the area to flooding and reduced water quality. This study emphasized the importance of GIS and its integration into urban changes and water quality assessment.
文摘Effective planning relies on accurate and up-to-date information on existing land use and land cover. The timely detection of trends in land use and land cover change and a quantification of such trends are of specific interest to planners and decision makers. The aim of this research is to use remote sensing and GIS to monitor landuse and land cover change in Egbeda Local Government Area, Oyo State with a view to determining how useful such information can be to planners and decision makers for effective urban management. The research was conducted using remote sensing and Geographical information System at determining the trend and extent of land use and land cover change and its driving force in Egbeda Local Government Area, Oyo State. The methods used include: digitization, digital image processing and spatial analysis using an inverse distance weighted (IDW) technique, Maximum likelihood supervised classification and post classification change detection techniques were applied to Landsat imageries acquired in 1984, 2006 and 2018. Imageries were classified into built-up area, vegetation, bare surface, cultivation and water body. The results of the analysis obtained showed drastic change in built-up area which rose to 32.8% from 25.4% between 1984 and 2018 periods. To reduce the effect of land use expansion in the study areas, policy measures were recommended which include proper inventory of land use and land cover, regular monitoring of urban areas spread of development and regional development programs. These will enable the government, stakeholders, policy makers and planners to make informed decisions provided by these technologies to attain and sustain future urban development.
基金supported by the National Natural Science Foundation of China(12272168,11802119)Foundation of Science and Technology on Space Intelligent Control Laboratory(6142208200303,2021-JCJQ-LB-010-04).
文摘Relative navigation is a key enabling technology for space missions such as on-orbit servicing and space situational awareness.Given that there are several special advantages of space relative navigation using angles-only measurements from passive optical sensors,angles-only relative navigation is considered as one of the best potential approaches in the field of space relative navigation.However,angles-only relative navigation is well-known for its range observability problem.To overcome this observability problem,many studies have been conducted over the past decades.In this study,we present a comprehensive review of state-of-the-art space relative navigation based on angles-only measurements.The emphasis is on the observability problem and solutions to angles-only relative navigation,where the review of the solutions is categorized into four classes based on the intrinsic principle:complicated dynamics approach,multi-line of sight(multi-LOS)approach,sensor offset center-of-mass approach,and orbit maneuver approach.Then,the fight demonstration results of angles-only relative navigation in the two projects are briefly reviewed.Finally,conclusions of this study and recommendations for further research are presented.
基金supported by the National Natural Science Foundation of China(Grant No.11972182)funded by the Science and Technology on Space Intelligent Control Laboratory(Grant Nos.HTKJ2020KL502019,6142208200203,and 2021-JCJQ-LB-010-04).
文摘The space environment has become highly congested due to the increasing space debris,seriously threatening the safety of orbiting spacecraft.Space-based situational awareness,as a comprehensive capability of threat knowledge,analysis,and decision-making,is of significant importance to ensure space security and maintain normal order.Various space situational awareness systems have been designed and launched.Data acquisition,target recognition,and monitoring constituting key technologies make major contributions,and various advanced algorithms are explored as technical supports.However,comprehensive reviews of these technologies and specific algorithms rarely emerge.It disadvantages the future development of space situational awareness.Therefore,this paper further reviews and analyzes research advancements in key technologies for space situational awareness,emphasizing target recognition and monitoring.Many mature and emerging methods are presented for these technologies while discussing application advantages and limitations.Specially,the research prospects of multiagent and synergetic constellation technologies are expected for future situational awareness.This paper indicates the future directions of the key technologies,aiming to provide references for space-based situational awareness to realize space sustainability.
基金supported by the National Natural Science Foundation of China(Grant No.11972182 and No.U20B2056)sponsored by the Science and Technology Innovation Action Plan of Shanghai(Grant No.19511120900)+1 种基金funded by the Science and Technology on Space Intelligent Control Laboratory(Grant Nos.HTKJ2020KL502019 and 2021-JCJQ-LB-010-04)sponsored by the National Basic Research Program of China(Grant No.JCKY2018203B036 and No.JCKY2021606B002).
文摘The pose determination between nanosatellites and the cooperative spacecraft is essential for swarm in-orbit services.Timeof–flight(ToF)sensors are one of the most promising sensors to achieve the tasks.This paper presented an end-to-end assessment of how these sensors were used for pose estimation.First,an embedded system was designed based on the ToF camera with lasers as a driven light source.Gray and depth images were collected to detect and match the cooperative spacecraft in real time,obtaining the pose information.A threshold-based segmentation was proposed to find a small set of the pixels belonging to reflector markers.Only operating on the defined active pixel set reduced computational resources.Then,morphological detection combined with an edge following-based ellipse detection extracted the centroid coordinate of the circular marker,while the center-of-heart rate was calculated as the recognition condition.Next,the marker matching was completed using a deterministic annealing algorithm,obtaining two sets of 3D coordinates.A singular value decomposition(SVD)algorithm estimated the relative pose between the nanosatellite and the spacecraft.In the experiments,the pose calculated by the TOF camera reached an accuracy of 0.13 degrees and 2 mm.It accurately identified the markers and determined the pose,verifying the feasibility of the ToF camera for rendezvous and docking.
