The geosynchronous circular synthetic aperture radar (GEOCSAR) is an innovative SAR system,which can produce high resolution three-dimensional (3D) images and has the potential to provide 3D deformation measurement.Wi...The geosynchronous circular synthetic aperture radar (GEOCSAR) is an innovative SAR system,which can produce high resolution three-dimensional (3D) images and has the potential to provide 3D deformation measurement.With an orbit altitude of approximately 36 000 km,the orbit motion and orbit disturbance effects of GEOCSAR behave differently from those of the conventional spaceborne SAR.In this paper,we analyze the effects of orbit errors on GEOCSAR imaging and interferometric processing.First,we present the GEOCSAR imaging geometry and the orbit errors model based on perturbation analysis.Then,we give the GEOCSAR signal formulation based on imaging geometry,and analyze the effect of the orbit error on the output focused signal.By interferometric processing on the 3D reconstructed images,the relationship between satellite orbit errors and the interferometric phase is deduced.Simulations demonstrate the effects of orbit errors on the GEOCSAR images,interferograms,and the deformations.The conclusions are that the required relative accuracy of orbit estimation should be at centimeter level for GEOCSAR imaging at L-band,and that millimeter-scale accuracy is needed for GEOCSAR interferometric processing.展开更多
Interplanetary shock can greatly disturb the Earth's magnetosphere and ionosphere, causing the temporal and spatial changes of the magnetic field and plasmas at the geosynchronous orbit. In this paper, we use the ...Interplanetary shock can greatly disturb the Earth's magnetosphere and ionosphere, causing the temporal and spatial changes of the magnetic field and plasmas at the geosynchronous orbit. In this paper, we use the magnetic field data of GOES satellites from 1997 to 2007 and the plasma data of MPA on the LANL satellites from 1997 to 2004 to study the properties of magnetic field and plasma (0.03―45 keV) at the geosynchronous orbit (6.6 RE) within 3 hours before and after the arrival of shock front at the geosynchronous orbit through both case study and superposed epoch analysis. It is found that following the arrival of shock front at the geosynchronous orbit, the magnetic field magnitude, as well as GSM BZ component increases significantly on the dayside (8―16 LT), while the BY component has almost no change before and after shock impacts. In response to the interplanetary shock, the proton becomes much denser with a peak number density of 1.2 cm-3, compared to the typical number density of 0.7 cm-3. The proton temperature increases sharply, predominantly on the dusk and night side. The electron, density increases dramatically on the night side with a peak number density of 2.0 cm-3. The inferred ionospheric O+ density after the interplanetary shock impact reaches the maximum value of 1.2 cm-3 on the dusk side and exhibits the clear dawn-dusk asymmetry. The peak of the anisotropy of proton's temperature is located at the noon sector, and the anisotropy decreases towards the dawn and dusk side. The minimum of temperature anisotropy is on the night side. It is suggested that the electromagnetic ion cyclotron (EMIC) wave and whistler wave can be stimulated by the proton and electron temperature anisotropy respectively. The computed electromagnetic ion cyclotron wave (EMIC) intense on the day side (8―16 LT) with a frequency value of 0.8 Hz, and the wave intensity decreases towards the dawn and dusk side, the minimum value can be found on the night side. The computed electron whistler wave locates on the day side (8―16 LT) with a value of 2 kHz.展开更多
The rapid change in the Earth’s magnetosphere caused by solar wind disturbances has been an important part of the solar wind-magnetosphere interaction.However most of the previous studies focused on the perturbation ...The rapid change in the Earth’s magnetosphere caused by solar wind disturbances has been an important part of the solar wind-magnetosphere interaction.However most of the previous studies focused on the perturbation of the Earth’s magnetic field caused by solar wind dynamic pressure changes.In this paper,we studied the response of geosynchronous magnetic field and the magnetic field to the rapid southward turning of interplanetary magnetic field during the interval 1350 1420 UT on 7May 2007.During this event,BZ component of the interplanetary magnetic field decreased from 15 nT to 10 nT within 3 min(1403 1406 UT).The geosynchronous magnetic field measured by three geosynchronous satellites(GOES 10 12)first increased and then decreased.The variations of magnetic field strength in the morning sector(9 10 LT)were much larger than those in the dawn sector(5 LT).Meanwhile,the H components of geomagnetic field on the ground have similar response features but exhibit latitude and LT dependent variations.Compared with H components,the D components do not have regular variations.Although the solar wind dynamical pressure encounters small variations,the magnetic field both in space and on the ground does not display similar variations.Therefore,the increase of geomagnetic field in the dawn sector is caused by the southward turning of IMF(interplanetary magnetic field)BZ.These results will help to better understand the coupling process of geomagnetic filed and interplanetary magnetic field.展开更多
On July 22, 2004, the WIND spacecraft detected a typical interplanetary shock. There was sustaining weak southward magnetic field in the preshock region and the southward field was suddenly enhanced across the shock f...On July 22, 2004, the WIND spacecraft detected a typical interplanetary shock. There was sustaining weak southward magnetic field in the preshock region and the southward field was suddenly enhanced across the shock front (i.e., southward turning). When the shock impinged on the magnetosphere, the magnetospheric plasma convection was abruptly enhanced in the central plasma sheet, which was directly observed by both the TC-1 and Cluster spacecraft located in different regions. Simultaneously, the Cluster spacecraft observed that the dawn-to-dusk electric field was abruptly enhanced. The variations of the magnetic field observed by TC-1, Cluster, GOES-10 and GOES-12 that were distributed in different regions in the plasma sheet and at the geosynchronous orbit are obviously distinct. TC-1 observations showed that the magnetic intensity kept almost unchanged and the elevation angle decreased, but the Cluster spacecraft, which was also in the plasma sheet and was further from the equator, observed that the magnetic field was obviously enhanced. Simultaneously, GOES-12 located near the midnight observed that the magnetic intensity sharply increased and the elevation angle decreased, but GOES-10 located in the dawn side observed that the magnetic field was merely compressed with its three components all sharply increasing. Furthermore, the energetic proton and electron fluxes at nearly all channels observed by five LANL satellites located at different magnetic local times (MLTs) all showed impulsive enhancements due to the compression of the shock. The responses of the energetic particles were much evident on the dayside than those on the nightside. Especially the responses near the midnight were rather weak. In this paper, the possible reasonable physical explanation to above observations is also discussed. All the shock-induced responses are the joint effects of the solar wind dynamic pressure pulse and the magnetic field southward turning.展开更多
Based on its ability to obtain two-dimensional(2D)high-resolution images in all-time and all-weather conditions,spaceborne synthetic aperture radar(SAR)has become an important remote sensing technique and the study of...Based on its ability to obtain two-dimensional(2D)high-resolution images in all-time and all-weather conditions,spaceborne synthetic aperture radar(SAR)has become an important remote sensing technique and the study of such systems has entered a period of vigorous development.Advanced imaging modes such as radar interferometry,tomography,and multi-static imaging,have been demonstrated.However,current in-orbit spaceborne SARs,which all operate in low Earth orbits,have relatively long revisit times ranging from several days to dozens of days,restricting their temporal sampling rate.Geosynchronous SAR(GEO SAR)is an active research area because it provides significant new capability,especially its much-improved temporal sampling.This paper reviews the research progress of GEO SAR technologies in detail.Two typical orbit schemes are presented,followed by the corresponding key issues,including system design,echo focusing,main disturbance factors,repeat-track interferometry,etc,inherent to these schemes.Both analysis and solution research of the above key issues are described.GEO SAR concepts involving multiple platforms are described,including the GEO SAR constellation,GEO-LEO/airborne/unmanned aerial vehicle bistatic SAR,and formation flying GEO SAR(FF-GEO SAR).Due to the high potential of FF-GEO SAR for three-dimensional(3D)deformation retrieval and coherence-based SAR tomography(TomoSAR),we have recently carried out some research related to FF-GEO SAR.This research,which is also discussed in this paper,includes developing a formation design method and an improved TomoSAR processing algorithm.It is found that GEO SAR will continue to be an active topic in the aspect of data processing and multi-platform concept in the near future.展开更多
A Chinese geosynchronous satellite was launched on June 23,2020.It carried a plasma detection package to monitor the space environment around the orbit.Here we report the inflight performance of a low energy ion spect...A Chinese geosynchronous satellite was launched on June 23,2020.It carried a plasma detection package to monitor the space environment around the orbit.Here we report the inflight performance of a low energy ion spectrometer(LEIS),one of the primary instruments in the plasma detection package,and its initial observations in flight.Benefiting from the state-of-the-art design of a top-hat electrostatic analyzer cooperated with angular scanning deflectors,three-dimensional measurement of ions in space with a large field of view of 360°×90°and a wide energy range from 50 eV to 25 keV per charge has been achieved.The differential energy flux spectra of ions around the orbit have shown clear signatures of surface charging and storm/substorm ion injections.The occurrence of surface charging could be caused by the lack of photoemission at the Earth's eclipse(near the midnight)or the storm energetic electron injection at the dawn sector.The present results demonstrated a good performance of the LEIS payload in flight for monitoring the space ion environment around the orbit.In situ measurements of the LEIS payload provide us an opportunity to understand the magnetospheric ion dynamics and forecast the associate space weather impacts.展开更多
基金Project(No.2009CB724003) supported by the National Basic Re-search Program (973) of China
文摘The geosynchronous circular synthetic aperture radar (GEOCSAR) is an innovative SAR system,which can produce high resolution three-dimensional (3D) images and has the potential to provide 3D deformation measurement.With an orbit altitude of approximately 36 000 km,the orbit motion and orbit disturbance effects of GEOCSAR behave differently from those of the conventional spaceborne SAR.In this paper,we analyze the effects of orbit errors on GEOCSAR imaging and interferometric processing.First,we present the GEOCSAR imaging geometry and the orbit errors model based on perturbation analysis.Then,we give the GEOCSAR signal formulation based on imaging geometry,and analyze the effect of the orbit error on the output focused signal.By interferometric processing on the 3D reconstructed images,the relationship between satellite orbit errors and the interferometric phase is deduced.Simulations demonstrate the effects of orbit errors on the GEOCSAR images,interferograms,and the deformations.The conclusions are that the required relative accuracy of orbit estimation should be at centimeter level for GEOCSAR imaging at L-band,and that millimeter-scale accuracy is needed for GEOCSAR interferometric processing.
基金Supported by the National Natural Science Foundation of China (Grant No. 40831061)
文摘Interplanetary shock can greatly disturb the Earth's magnetosphere and ionosphere, causing the temporal and spatial changes of the magnetic field and plasmas at the geosynchronous orbit. In this paper, we use the magnetic field data of GOES satellites from 1997 to 2007 and the plasma data of MPA on the LANL satellites from 1997 to 2004 to study the properties of magnetic field and plasma (0.03―45 keV) at the geosynchronous orbit (6.6 RE) within 3 hours before and after the arrival of shock front at the geosynchronous orbit through both case study and superposed epoch analysis. It is found that following the arrival of shock front at the geosynchronous orbit, the magnetic field magnitude, as well as GSM BZ component increases significantly on the dayside (8―16 LT), while the BY component has almost no change before and after shock impacts. In response to the interplanetary shock, the proton becomes much denser with a peak number density of 1.2 cm-3, compared to the typical number density of 0.7 cm-3. The proton temperature increases sharply, predominantly on the dusk and night side. The electron, density increases dramatically on the night side with a peak number density of 2.0 cm-3. The inferred ionospheric O+ density after the interplanetary shock impact reaches the maximum value of 1.2 cm-3 on the dusk side and exhibits the clear dawn-dusk asymmetry. The peak of the anisotropy of proton's temperature is located at the noon sector, and the anisotropy decreases towards the dawn and dusk side. The minimum of temperature anisotropy is on the night side. It is suggested that the electromagnetic ion cyclotron (EMIC) wave and whistler wave can be stimulated by the proton and electron temperature anisotropy respectively. The computed electromagnetic ion cyclotron wave (EMIC) intense on the day side (8―16 LT) with a frequency value of 0.8 Hz, and the wave intensity decreases towards the dawn and dusk side, the minimum value can be found on the night side. The computed electron whistler wave locates on the day side (8―16 LT) with a value of 2 kHz.
基金supported by the National Natural Science Foundation of China(Grant Nos.40931054 and 41174141)the National Basic Research Program of China("973" Program)(Grant No.2011CB811404)
文摘The rapid change in the Earth’s magnetosphere caused by solar wind disturbances has been an important part of the solar wind-magnetosphere interaction.However most of the previous studies focused on the perturbation of the Earth’s magnetic field caused by solar wind dynamic pressure changes.In this paper,we studied the response of geosynchronous magnetic field and the magnetic field to the rapid southward turning of interplanetary magnetic field during the interval 1350 1420 UT on 7May 2007.During this event,BZ component of the interplanetary magnetic field decreased from 15 nT to 10 nT within 3 min(1403 1406 UT).The geosynchronous magnetic field measured by three geosynchronous satellites(GOES 10 12)first increased and then decreased.The variations of magnetic field strength in the morning sector(9 10 LT)were much larger than those in the dawn sector(5 LT).Meanwhile,the H components of geomagnetic field on the ground have similar response features but exhibit latitude and LT dependent variations.Compared with H components,the D components do not have regular variations.Although the solar wind dynamical pressure encounters small variations,the magnetic field both in space and on the ground does not display similar variations.Therefore,the increase of geomagnetic field in the dawn sector is caused by the southward turning of IMF(interplanetary magnetic field)BZ.These results will help to better understand the coupling process of geomagnetic filed and interplanetary magnetic field.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 40731054, 40804046, 40704031 and 40704027)Specialized Research Fund for State Key Laboratories
文摘On July 22, 2004, the WIND spacecraft detected a typical interplanetary shock. There was sustaining weak southward magnetic field in the preshock region and the southward field was suddenly enhanced across the shock front (i.e., southward turning). When the shock impinged on the magnetosphere, the magnetospheric plasma convection was abruptly enhanced in the central plasma sheet, which was directly observed by both the TC-1 and Cluster spacecraft located in different regions. Simultaneously, the Cluster spacecraft observed that the dawn-to-dusk electric field was abruptly enhanced. The variations of the magnetic field observed by TC-1, Cluster, GOES-10 and GOES-12 that were distributed in different regions in the plasma sheet and at the geosynchronous orbit are obviously distinct. TC-1 observations showed that the magnetic intensity kept almost unchanged and the elevation angle decreased, but the Cluster spacecraft, which was also in the plasma sheet and was further from the equator, observed that the magnetic field was obviously enhanced. Simultaneously, GOES-12 located near the midnight observed that the magnetic intensity sharply increased and the elevation angle decreased, but GOES-10 located in the dawn side observed that the magnetic field was merely compressed with its three components all sharply increasing. Furthermore, the energetic proton and electron fluxes at nearly all channels observed by five LANL satellites located at different magnetic local times (MLTs) all showed impulsive enhancements due to the compression of the shock. The responses of the energetic particles were much evident on the dayside than those on the nightside. Especially the responses near the midnight were rather weak. In this paper, the possible reasonable physical explanation to above observations is also discussed. All the shock-induced responses are the joint effects of the solar wind dynamic pressure pulse and the magnetic field southward turning.
基金This work was funded in part by the National Natural Science Foundation of China under Grant Nos.61960206009,61971039,and 61971037the Distinguished Young Scholars of Chongqing(Grant No.cstc2020jcyj-jqX0008)+2 种基金the National Ten Thousand Talents Program‘Young Top Talent’(Grant No.W03070007)the Special Fund for Research on National Major Research Instruments(NSFC Grant Nos.61827901,31727901)the Young Elite Scientists Sponsorship Program by CAST(2017QNRC001).
文摘Based on its ability to obtain two-dimensional(2D)high-resolution images in all-time and all-weather conditions,spaceborne synthetic aperture radar(SAR)has become an important remote sensing technique and the study of such systems has entered a period of vigorous development.Advanced imaging modes such as radar interferometry,tomography,and multi-static imaging,have been demonstrated.However,current in-orbit spaceborne SARs,which all operate in low Earth orbits,have relatively long revisit times ranging from several days to dozens of days,restricting their temporal sampling rate.Geosynchronous SAR(GEO SAR)is an active research area because it provides significant new capability,especially its much-improved temporal sampling.This paper reviews the research progress of GEO SAR technologies in detail.Two typical orbit schemes are presented,followed by the corresponding key issues,including system design,echo focusing,main disturbance factors,repeat-track interferometry,etc,inherent to these schemes.Both analysis and solution research of the above key issues are described.GEO SAR concepts involving multiple platforms are described,including the GEO SAR constellation,GEO-LEO/airborne/unmanned aerial vehicle bistatic SAR,and formation flying GEO SAR(FF-GEO SAR).Due to the high potential of FF-GEO SAR for three-dimensional(3D)deformation retrieval and coherence-based SAR tomography(TomoSAR),we have recently carried out some research related to FF-GEO SAR.This research,which is also discussed in this paper,includes developing a formation design method and an improved TomoSAR processing algorithm.It is found that GEO SAR will continue to be an active topic in the aspect of data processing and multi-platform concept in the near future.
基金supported by the grants from Chinese Academy of Sciences(Grant Nos.XDB41000000,QYZDB-SSW-DQC015)the National Natural Science Foundation of China(Grant No.42188101)。
文摘A Chinese geosynchronous satellite was launched on June 23,2020.It carried a plasma detection package to monitor the space environment around the orbit.Here we report the inflight performance of a low energy ion spectrometer(LEIS),one of the primary instruments in the plasma detection package,and its initial observations in flight.Benefiting from the state-of-the-art design of a top-hat electrostatic analyzer cooperated with angular scanning deflectors,three-dimensional measurement of ions in space with a large field of view of 360°×90°and a wide energy range from 50 eV to 25 keV per charge has been achieved.The differential energy flux spectra of ions around the orbit have shown clear signatures of surface charging and storm/substorm ion injections.The occurrence of surface charging could be caused by the lack of photoemission at the Earth's eclipse(near the midnight)or the storm energetic electron injection at the dawn sector.The present results demonstrated a good performance of the LEIS payload in flight for monitoring the space ion environment around the orbit.In situ measurements of the LEIS payload provide us an opportunity to understand the magnetospheric ion dynamics and forecast the associate space weather impacts.
