The ensemble optimal interpolation （EnOI） is applied to the regional ocean modeling system （ROMS） with the ability to assimilate the along-track sea level anomaly （TSLA）. This system is tested with an eddy-resol...The ensemble optimal interpolation （EnOI） is applied to the regional ocean modeling system （ROMS） with the ability to assimilate the along-track sea level anomaly （TSLA）. This system is tested with an eddy-resolving system of the South China Sea （SCS）. Background errors are derived from a running seasonal ensemble to account for the seasonal variability within the SCS. A fifth-order localization function with a 250 km localization radius is chosen to reduce the negative effects of sampling errors. The data assimilation system is tested from January 2004 to December 2006. The results show that the root mean square deviation （RMSD） of the sea level anomaly decreased from 10.57 to 6.70 cm, which represents a 36.6% reduction of error. The data assimilation reduces error for temperature within the upper 800 m and for salinity within the upper 200 m, although error degrades slightly at deeper depths. Surface currents are in better agreement with trajectories of surface drifters after data assimilation. The variance of sea level improves significantly in terms of both the amplitude and position of the strong and weak variance regions after assimilating TSLA. Results with AGE error （AGE） perform better than no AGE error （NoAGE） when considering the improvements of the temperature and the salinity. Furthermore, reasons for the extremely strong variability in the northern SCS in high resolution models are investigated. The results demonstrate that the strong variability of sea level in the high resolution model is caused by an extremely strong Kuroshio intrusion. Therefore, it is demonstrated that it is necessary to assimilate the TSLA in order to better simulate the SCS with high resolution models.展开更多
As part of the Chinese Tianwen-1 mission,the Zhurong Rover began its scientific investigation in the southern Utopia Planitia after its successful landing in 15 May,2021.The Zhurong Rover magnetometer(RoMAG),one of th...As part of the Chinese Tianwen-1 mission,the Zhurong Rover began its scientific investigation in the southern Utopia Planitia after its successful landing in 15 May,2021.The Zhurong Rover magnetometer(RoMAG),one of the six payloads onboard the rover,includes two identical high-sensitivity triaxial fluxgate magnetometers and can implement mobile magnetic measurements on the surface of Mars.Although a rover magnetic compensation procedure was conducted to remove the magnetic interferences pre-launch,due to the different state of the payloads and electric power system such as the solar panel,an along-track calibration of the magnetometer is necessary to obtain a more accurate Martian magnetic field.Two methods,mast yaw rotations and Rover yaw rotations were utilized separately to determine the Martian horizontal magnetic components.Results show that the Martian horizontal magnetic components determined by the two methods are in good agreement,with the root mean square deviation less than 2.0 nT.The vertical component was also constrained through the pitch movements of the mast by assuming the interferences field distributes like a dipole field.A linear correlation between magnetic field measurements and the solar array currents was derived to calibrate the body field during the regular exploration.We conclude that more accurate measurements could be made when applying the calibration results in the magnetic survey on the surface of Mars.展开更多
Remote sensing products are significant in the data assimilation of an ocean model. Considering the resolution and space coverage of different remote sensing data, two types of sea surface height（SSH） product are em...Remote sensing products are significant in the data assimilation of an ocean model. Considering the resolution and space coverage of different remote sensing data, two types of sea surface height（SSH） product are employed in the assimilation, including the gridded products from AVISO and the original along-track observations used in the generation. To explore their impact on the assimilation results, an experiment focus on the South China Sea（SCS） is conducted based on the Regional Ocean Modeling System（ROMS） and the four-dimensional variational data assimilation（4 DVAR） technology. The comparison with EN4 data set and Argo profile indicates that, the along-track SSH assimilation result presents to be more accurate than the gridded SSH assimilation, because some noises may have been introduced in the merging process. Moreover, the mesoscale eddy detection capability of the assimilation results is analyzed by a vector geometry–based algorithm. It is verified that, the assimilation of the gridded SSH shows superiority in describing the eddy＇s characteristics, since the complete structure of the ocean surface has been reconstructed by the original data merging.展开更多
On the basis of gravity field model （EIGEN_CG01C）, together with multi-altimeter data, the improved deflection of the vertical gridded in 2＇×2＇ in China marginal sea and gridded in 5＇×5＇ in the global ...On the basis of gravity field model （EIGEN_CG01C）, together with multi-altimeter data, the improved deflection of the vertical gridded in 2＇×2＇ in China marginal sea and gridded in 5＇×5＇ in the global sea was determined by using the weighted method of along-track least squares, and the accuracy is better than 1.2^# in China marginal sea. As for the quality of the deflection of the vertical, it meets the challenge for the gravity field of high resolution and accuracy, it shows that, compared with the shipboard gravimetry in the sea, the accuracy of the gravity anomalies computed with the marine deflection of the vertical by inverse Vening-Meinesz formula is 7.75 m.s ^-2.展开更多
Two approximations, center-beam approximation and reference digital elevation model （DEM） approximation, are used in synthetic aperture radar （SAR） motion compensation procedures. They usually introduce residual m...Two approximations, center-beam approximation and reference digital elevation model （DEM） approximation, are used in synthetic aperture radar （SAR） motion compensation procedures. They usually introduce residual motion compensation errors for airborne single-antenna SAR imaging and SAR interferometry. In this paper, we investigate the effects of residual uncompensated motion errors, which are caused by the above two approximations, on the performance of airborne along-track interferometric SAR （ATI-SAR）. The residual uncompensated errors caused by center-beam approximation in the absence and in the presence of elevation errors are derived, respectively. Airborne simulation parameters are used to verify the correctness of the analysis and to show the impacts of residual uncompensated errors on the interferometric phase errors for ATI-SAR. It is shown that the interferometric phase errors caused by the center-beam approximation with an accurate DEM could be neglected, while the interferometric phase errors caused by the center-beam approximation with an inaccurate DEM cannot be neglected when the elevation errors exceed a threshold. This research provides theoretical bases for the error source analysis and signal processing of airborne ATI-SAR.展开更多
Airborne Along-Track Interferometric Synthetic Aperture Radar (ATI-SAR) baseline error is a main error resource affecting the precision of velocity measurement of moving objects and therefore should be calibrated exte...Airborne Along-Track Interferometric Synthetic Aperture Radar (ATI-SAR) baseline error is a main error resource affecting the precision of velocity measurement of moving objects and therefore should be calibrated externally. The Jet Propulsion Laboratory (JPL) has proposed a calibration scheme for tasks of PacRim98 and PacRim2000 based on several static objects on the ground. In this paper, the influence of phase center uncertainty on baseline determination by using PacRim method proposed by JPL is analyzed. According to the analysis, the phase center uncertainty can cause a constant part of error to the result of baseline calibration. In order to deal with this problem, an improved calibration method on the basis of sensitivity equations and some ground moving targets, whose velocities are already known, is proposed in this paper. The simulation results show that our proposed calibration method has improved the accuracy of baseline calibration and has obviously prohibited the effect of antennas' phase center uncertainty.展开更多
Synthetic aperture radar （SAR） systems have become an important tool for fine-resolution mapping and other remote sensing operations. The multi-channel SAR ground moving-target indication （GMTI） must process its d...Synthetic aperture radar （SAR） systems have become an important tool for fine-resolution mapping and other remote sensing operations. The multi-channel SAR ground moving-target indication （GMTI） must process its data to produce not only the image of surveillance area but also the information of the ground moving-targets. The topic of moving-target detection in clutter has been extensively studied, and there are many methods that are used to detect moving targets, such as displaced phase center antenna （DPCA） method, along-track interfero-metric （ATI） phase, space-time adaptive processing （STAP）, or some other metrics. A canonical framework is proposed that encompasses all the multi-channel SAR-GMT methods, namely, DPCA and ATI. The statistical test metric for multi-channel SAR-GMTI is established in a simple form, via the definition of the complex central Wishart distribution, to deduce the statistics of the test metric, and the probability distribution of the test metric for multichannel SAR-GMTI has the complex central Wishart distribution of 1×1 case, namely the X^2 distribution. The theory foundation offers the possibility to construct the united multi-channel SAR-GMTI detector, and derives the constant false alarm rate （CFAR） detector tests for separating moving targets from clutter.展开更多
基金The Major State Basic Research Development Program of China under contract Nos 201-1CB403606 and 2011CB403500the National Natural Science Foundation of China under contract Nos 41222038,41076011and 41206023the National Marine Environmental Forecasting Center Operational Development Foundation of the State Oceanic Administration of China under contract No.2013002
文摘The ensemble optimal interpolation （EnOI） is applied to the regional ocean modeling system （ROMS） with the ability to assimilate the along-track sea level anomaly （TSLA）. This system is tested with an eddy-resolving system of the South China Sea （SCS）. Background errors are derived from a running seasonal ensemble to account for the seasonal variability within the SCS. A fifth-order localization function with a 250 km localization radius is chosen to reduce the negative effects of sampling errors. The data assimilation system is tested from January 2004 to December 2006. The results show that the root mean square deviation （RMSD） of the sea level anomaly decreased from 10.57 to 6.70 cm, which represents a 36.6% reduction of error. The data assimilation reduces error for temperature within the upper 800 m and for salinity within the upper 200 m, although error degrades slightly at deeper depths. Surface currents are in better agreement with trajectories of surface drifters after data assimilation. The variance of sea level improves significantly in terms of both the amplitude and position of the strong and weak variance regions after assimilating TSLA. Results with AGE error （AGE） perform better than no AGE error （NoAGE） when considering the improvements of the temperature and the salinity. Furthermore, reasons for the extremely strong variability in the northern SCS in high resolution models are investigated. The results demonstrate that the strong variability of sea level in the high resolution model is caused by an extremely strong Kuroshio intrusion. Therefore, it is demonstrated that it is necessary to assimilate the TSLA in order to better simulate the SCS with high resolution models.
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB41010304)the National Natural Science Foundation of China(Grant Nos.42374217,42274224)+2 种基金the National Key R&D Program of China(Grant No.2022YFF0503200)the Key Research Program of the Chinese Academy of Sciences(Grant No.ZDBS-SSW-TLC001)the Key Research Programs of the Institute of Geology and Geophysics,Chinese Academy of Sciences(Grant No.IGGCAS-202102)。
文摘As part of the Chinese Tianwen-1 mission,the Zhurong Rover began its scientific investigation in the southern Utopia Planitia after its successful landing in 15 May,2021.The Zhurong Rover magnetometer(RoMAG),one of the six payloads onboard the rover,includes two identical high-sensitivity triaxial fluxgate magnetometers and can implement mobile magnetic measurements on the surface of Mars.Although a rover magnetic compensation procedure was conducted to remove the magnetic interferences pre-launch,due to the different state of the payloads and electric power system such as the solar panel,an along-track calibration of the magnetometer is necessary to obtain a more accurate Martian magnetic field.Two methods,mast yaw rotations and Rover yaw rotations were utilized separately to determine the Martian horizontal magnetic components.Results show that the Martian horizontal magnetic components determined by the two methods are in good agreement,with the root mean square deviation less than 2.0 nT.The vertical component was also constrained through the pitch movements of the mast by assuming the interferences field distributes like a dipole field.A linear correlation between magnetic field measurements and the solar array currents was derived to calibrate the body field during the regular exploration.We conclude that more accurate measurements could be made when applying the calibration results in the magnetic survey on the surface of Mars.
基金The National Key Research and Development Program of China under contract No.2016YFC1401800the National Natural Science Foundation of China under contract Nos 41576176 and 11401140the Key Project of Science and Technology of Harbin Institute of Technology at Weihai of China under contract No.2014 DXGJ14
文摘Remote sensing products are significant in the data assimilation of an ocean model. Considering the resolution and space coverage of different remote sensing data, two types of sea surface height（SSH） product are employed in the assimilation, including the gridded products from AVISO and the original along-track observations used in the generation. To explore their impact on the assimilation results, an experiment focus on the South China Sea（SCS） is conducted based on the Regional Ocean Modeling System（ROMS） and the four-dimensional variational data assimilation（4 DVAR） technology. The comparison with EN4 data set and Argo profile indicates that, the along-track SSH assimilation result presents to be more accurate than the gridded SSH assimilation, because some noises may have been introduced in the merging process. Moreover, the mesoscale eddy detection capability of the assimilation results is analyzed by a vector geometry–based algorithm. It is verified that, the assimilation of the gridded SSH shows superiority in describing the eddy＇s characteristics, since the complete structure of the ocean surface has been reconstructed by the original data merging.
基金Supported by the National Nature Science Foundation of China（No. 40474030, 40674013）.Acknowledgements Thanks to professor Hwang at the Department of Civil Engineering, National Chiao Tung University for altimeter data.
文摘On the basis of gravity field model （EIGEN_CG01C）, together with multi-altimeter data, the improved deflection of the vertical gridded in 2＇×2＇ in China marginal sea and gridded in 5＇×5＇ in the global sea was determined by using the weighted method of along-track least squares, and the accuracy is better than 1.2^# in China marginal sea. As for the quality of the deflection of the vertical, it meets the challenge for the gravity field of high resolution and accuracy, it shows that, compared with the shipboard gravimetry in the sea, the accuracy of the gravity anomalies computed with the marine deflection of the vertical by inverse Vening-Meinesz formula is 7.75 m.s ^-2.
基金Project supported by the National Natural Science Foundation of China （Nos. 61331017 and 61401428）
文摘Two approximations, center-beam approximation and reference digital elevation model （DEM） approximation, are used in synthetic aperture radar （SAR） motion compensation procedures. They usually introduce residual motion compensation errors for airborne single-antenna SAR imaging and SAR interferometry. In this paper, we investigate the effects of residual uncompensated motion errors, which are caused by the above two approximations, on the performance of airborne along-track interferometric SAR （ATI-SAR）. The residual uncompensated errors caused by center-beam approximation in the absence and in the presence of elevation errors are derived, respectively. Airborne simulation parameters are used to verify the correctness of the analysis and to show the impacts of residual uncompensated errors on the interferometric phase errors for ATI-SAR. It is shown that the interferometric phase errors caused by the center-beam approximation with an accurate DEM could be neglected, while the interferometric phase errors caused by the center-beam approximation with an inaccurate DEM cannot be neglected when the elevation errors exceed a threshold. This research provides theoretical bases for the error source analysis and signal processing of airborne ATI-SAR.
基金Supported by the Key Project of National Natural Science Foundation of China (No. 60890070)
文摘Airborne Along-Track Interferometric Synthetic Aperture Radar (ATI-SAR) baseline error is a main error resource affecting the precision of velocity measurement of moving objects and therefore should be calibrated externally. The Jet Propulsion Laboratory (JPL) has proposed a calibration scheme for tasks of PacRim98 and PacRim2000 based on several static objects on the ground. In this paper, the influence of phase center uncertainty on baseline determination by using PacRim method proposed by JPL is analyzed. According to the analysis, the phase center uncertainty can cause a constant part of error to the result of baseline calibration. In order to deal with this problem, an improved calibration method on the basis of sensitivity equations and some ground moving targets, whose velocities are already known, is proposed in this paper. The simulation results show that our proposed calibration method has improved the accuracy of baseline calibration and has obviously prohibited the effect of antennas' phase center uncertainty.
基金the National Natural Science Foundation of China (60472097 and 60502054)
文摘Synthetic aperture radar （SAR） systems have become an important tool for fine-resolution mapping and other remote sensing operations. The multi-channel SAR ground moving-target indication （GMTI） must process its data to produce not only the image of surveillance area but also the information of the ground moving-targets. The topic of moving-target detection in clutter has been extensively studied, and there are many methods that are used to detect moving targets, such as displaced phase center antenna （DPCA） method, along-track interfero-metric （ATI） phase, space-time adaptive processing （STAP）, or some other metrics. A canonical framework is proposed that encompasses all the multi-channel SAR-GMT methods, namely, DPCA and ATI. The statistical test metric for multi-channel SAR-GMTI is established in a simple form, via the definition of the complex central Wishart distribution, to deduce the statistics of the test metric, and the probability distribution of the test metric for multichannel SAR-GMTI has the complex central Wishart distribution of 1×1 case, namely the X^2 distribution. The theory foundation offers the possibility to construct the united multi-channel SAR-GMTI detector, and derives the constant false alarm rate （CFAR） detector tests for separating moving targets from clutter.
