The exact radar cross-section （RCS） measurement is difficult when the scattering of targets is low. Ful polarimetric cali-bration is one technique that offers the potential for improving the accuracy of RCS measurem...The exact radar cross-section （RCS） measurement is difficult when the scattering of targets is low. Ful polarimetric cali-bration is one technique that offers the potential for improving the accuracy of RCS measurements. There are numerous polarimetric calibration algorithms. Some complex expressions in these algo-rithms cannot be easily used in an engineering practice. A radar polarimetric coefficients matrix （RPCM） with a simpler expression is presented for the monostatic radar polarization scattering matrix （PSM） measurement. Using a rhombic dihedral corner reflector and a metal ic sphere, the RPCM can be obtained by solving a set of equations, which can be used to find the true PSM for any target. An example for the PSM of a metal ic dish shows that the proposed method obviously improves the accuracy of cross-polarized RCS measurements.展开更多
Radiation cross-calibration is an effective method to check and verify theaccuracy and stability of sensor measurements. Satellites with high radiation accuracy areused to calibrate satellites with low radiation accur...Radiation cross-calibration is an effective method to check and verify theaccuracy and stability of sensor measurements. Satellites with high radiation accuracy areused to calibrate satellites with low radiation accuracy. In order to ensure the reliability ofthe radiation cross-calibration method, we propose to obtain the gain and offset of theGaoFen-1 satellite by linear regression after the radiation cross-calibration of the satellitewith low precision and compare with the official coefficient. Finally, we get therelationship between the error in radiation cross-calibration results and side swing angle.The linear correction coefficients of each band are: 0.618, 0.625, 0.512 and 0.474. Theresults show that after the method is corrected by the linear correction coefficient, theerror caused by the side swing angle during the cross-calibration of the orbital radiation isreduced. The accuracy of radiation cross-calibration is improved, the frequency ofcalibration is improved and the requirements of remote sensing applications in the newera are adapted.展开更多
In this paper, a flexible high-precision calibration method suitable for industrial field was proposed. The complexity of the coordinate transformation was simplified by choosing the camera coordinate system as the un...In this paper, a flexible high-precision calibration method suitable for industrial field was proposed. The complexity of the coordinate transformation was simplified by choosing the camera coordinate system as the unified reference coordinate system. A flexible planar calibration pattern was introduced to the calibration process, which can be arbitrarily placed and from which the known feature points can be extracted to construct other unknown feature points. With the known intrinsic parameters, the laser projector plane equation was fitted by the multi-noncollinear points, which were acquired through the principle of triangulation and the projective invariance of cross ratio. With this method, the strict alignment and multiple times of coordinate transformation can be avoided. Experimental results showed that the arithmetic mean of the root mean square(RMS) error of distance was 0.000 7 mm.展开更多
As a key part of the diagnosis system in the International Thermonuclear Experimental Reactor(ITER),the neutron flux monitor(NFM),which measures the neutron intensity of the fusion reaction,is a Counting-Campbelling s...As a key part of the diagnosis system in the International Thermonuclear Experimental Reactor(ITER),the neutron flux monitor(NFM),which measures the neutron intensity of the fusion reaction,is a Counting-Campbelling system with a large dynamic counting range.A dynamic linear calibration method is proposed in this paper to solve the problem of cross-over between the different counting and Campbelling channels,and improve the accuracy of the cross-calibration for long-term operation.The experimental results show that the NFM system with the dynamic linear calibration system can obtain the neutron flux of the fusion reactor in real time and realize the seamless measurement area connection between the two channels.展开更多
To address the eccentric error of circular marks in camera calibration,a circle location method based on the invariance of collinear points and pole–polar constraint is proposed in this paper.Firstly,the centers of t...To address the eccentric error of circular marks in camera calibration,a circle location method based on the invariance of collinear points and pole–polar constraint is proposed in this paper.Firstly,the centers of the ellipses are extracted,and the real concentric circle center projection equation is established by exploiting the cross ratio invariance of the collinear points.Subsequently,since the infinite lines passing through the centers of the marks are parallel,the other center projection coordinates are expressed as the solution problem of linear equations.The problem of projection deviation caused by using the center of the ellipse as the real circle center projection is addressed,and the results are utilized as the true image points to achieve the high precision camera calibration.As demonstrated by the simulations and practical experiments,the proposed method performs a better location and calibration performance by achieving the actual center projection of circular marks.The relevant results confirm the precision and robustness of the proposed approach.展开更多
本文对海洋气象漂流观测仪实测、CMA最佳路径数据集、第5代全球气象再分析产品(ERA5)、交叉检验多平台融合矢量风场(CCMP)四种资料的海面风在超强台风“利奇马”期间的变化特征进行分析。ERA5、CCMP两种分析/再分析风资料与实测风的对...本文对海洋气象漂流观测仪实测、CMA最佳路径数据集、第5代全球气象再分析产品(ERA5)、交叉检验多平台融合矢量风场(CCMP)四种资料的海面风在超强台风“利奇马”期间的变化特征进行分析。ERA5、CCMP两种分析/再分析风资料与实测风的对比分析表明:(1)风速:当风力<10级时,漂流观测仪轨迹上的ERA5、CCMP风速较漂流观测仪实测风速偏小;将漂流观测仪实测风速订正到10 m高度,风力≤5级时偏差(Bias)绝对值最小,ERA5(CCMP)为4.3 m s^(-1)(4.6 m s^(-1)),风力为7~9级时Bias绝对值最大,约9.2~10.2 m s^(-1);“利奇马”近中心海域ERA5、CCMP最大风速较CMA最佳路径数据集偏小,ERA5(CCMP)偏小约10.7 m s^(-1)(4.6 m s^(-1));ERA5(CCMP)最大风速极值较CMA最佳路径数据集偏低54.5%(12.7%)。(2)风向:ERA5、CCMP与漂流观测仪实测风向相关系数接近于0;风力≤5级时风向较实测偏右,风力>5级时偏左。(3)ERA5、CCMP风向、风速在“利奇马”近中心海域偏差明显,远离中心海域二者吻合度较高。通过对ERA5、CCMP资料进一步分析发现:CCMP能清楚描述热带气旋风场结构及演变过程,“利奇马”为超强台风时结构参数η=Vr/Vmax分布上有闭合环状结构,表明该区域有环状大风速带;“利奇马”强迫时间T_f分布于移动路径两侧,ERA5(CCMP)最大强迫时间为45 h(54 h)。展开更多
The Chinese Ocean Color and Temperature Scanner (COCTS) is the main sensor launched in May of 2002 on the Chinese first ocean color satellite named HY-1A. In this paper, first, the properties of HY-1A and COCTS are in...The Chinese Ocean Color and Temperature Scanner (COCTS) is the main sensor launched in May of 2002 on the Chinese first ocean color satellite named HY-1A. In this paper, first, the properties of HY-1A and COCTS are introduced briefly. Second, the theory and methodology of cross-calibration for COCTS ocean color bands by using the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data are discussed in detail. Third, with the quasi-synchronized SeaWiFS data, we simulate the COCTS radiances at the top of atmosphere (TOA), and then obtain the calibration coeffi- cients for COCTS ocean color bands. The results show that the cross-calibration TOA radiances are consistent with the in situ vicarious calibration TOA radiances at the COCTS ocean color bands. Finally, we compare the COCTS-re- trieved water leaving radiances with SeaWiFS-retrieved ones and the results show that the cross-calibration method could provide reasonable accuracy for ocean color measurement.展开更多
For the application of the CCD camera, the most important payload on CBERS-02, the key is to provide long-term stable radiometric calibration coefficients. Although the vicarious calibration had been proved successful...For the application of the CCD camera, the most important payload on CBERS-02, the key is to provide long-term stable radiometric calibration coefficients. Although the vicarious calibration had been proved successful, it had its limitations such as test site requirement and unsuitable for historical data. Cross-calibration is one of the alternative methods, but it needs synchro surface spectrum to achieve spectral band matching factors. Our effort is to probe the influences on these factors. Simulations with a lot of surface spectrum showed that the factors changed with the viewing geometry, atmospheric condition and surface targets. However, simulating with the same viewing geometry and atmospheric condition, the spectral band matching factors of the same or similar surface targets’ spectrum acquired from different dates and different places would like to be consistent to each other within 1%―5%. Thus, the synchro measurement data can be substituted by the same or similar target from other source. Based on this method, using the MODIS as the reference, the cross-calibration was performed for CCD camera. The research demonstrated that the traditional method with single calibration site was inappropriate for CCD camera, since the offsets for its four spectral bands were not zeros. With four calibration sites, these offsets were obtained. And the camera was detected to degrade with dates based on four times of cross-calibrations.展开更多
Radiometric calibration of sensor is the basis of quantitative remote sensing,and uncertainty analysis is critical to ensure the accuracy of cross-calibration.Therefore,firstly,cross-calibration formulas were improved...Radiometric calibration of sensor is the basis of quantitative remote sensing,and uncertainty analysis is critical to ensure the accuracy of cross-calibration.Therefore,firstly,cross-calibration formulas were improved by redefining calibration coefficient and spectral band matching factor.In these formulas,cci was redefined as the calibration coefficient of normalized apparent reflectance,and spectral band matching factor as the ratio of normalized apparent reflectance.Secondly,based on the contrast of ideal and actual conditions in cross-calibration,8 sources of cross-calibration uncertainty were proposed:calibration uncertainty of standard sensor;pixel matching uncertainty;spectral band matching factor uncertainty caused by site altitude setting error,atmospheric parameters setting error,surface spectrum source,surface bidirectional reflectance characteristic,and error of atmospheric radiative transfer model;and uncertainty caused by other factors which were not considered.Finally,the contribution of each uncertainty was further analyzed and discussed for the HJ-1 CCD camera.The results provide many valuable references for evaluating the feasibility of alternative cross-calibration measurements.展开更多
In order to make quantitative watercolor sensing with China-Brazil Earth Resources Satellite (CBERS-02) CCD camera, the MODIS data with higher accuracy is used to cross-calibrate the CCD camera over water targets. In ...In order to make quantitative watercolor sensing with China-Brazil Earth Resources Satellite (CBERS-02) CCD camera, the MODIS data with higher accuracy is used to cross-calibrate the CCD camera over water targets. In homogeneous clear water area, two pairs of images obtained over the same area on the same day by the two sensors are selected. The top-of-atmosphere (TOA) radiances of the multispectral bands of CCD are calculated with the water and aerosol parameters from MODIS based on a water-atmosphere radiative transfer algorithm. The stripes in CCD image that caused by unequal response of the CCD array detectors are firstly removed before making the cross-calibration. The same part of CCD detectors is selected for the calibrations in the two images to eliminate the residual error of destriping and uniformity correction for the focus plane irradiance. It is shown that the calibration results from two different images are consistent. The error of this method is about 5%.展开更多
The instrument cross-calibration is an effective way to assess the quality of satellite data. In this study, a new method is proposed to cross-calibrate the sensors among satellite instruments by using a RObotic Lunar...The instrument cross-calibration is an effective way to assess the quality of satellite data. In this study, a new method is proposed to cross-calibrate the sensors among satellite instruments by using a RObotic Lunar Observatory(ROLO) model and Apollo sample reflectance in reflective solar bands(RSBs). The ROLO model acts as a transfer radiometer to bridge between the instruments. The reflective spectrum of the Apollo sample is used to compensate for the difference in the instrument's relative spectral responses(RSRs). In addition, the double ratio between the observed lunar irradiance and the simulated lunar irradiance is used to reduce the difference in instrument lunar viewing and illumining geometry. This approach is applied to the Moderate Resolution Imaging Spectroradiometer(MODIS), the Sea-Viewing Wide Field-of-View Sensor(Sea Wi FS), and the Advanced Land Imager(ALI) on board three satellites, respectively. The mean difference between MODIS and Sea Wi FS is less than 3.14%, and the difference between MODIS and ALI is less than 4.75%. These results indicate that the proposed cross-calibration method not only compensates for the RSR mismatches but also reduces the differences in lunar observation geometry. Thus,radiance calibration of any satellite instrument can be validated with a reference instrument bridged by the moon.展开更多
基金supported by the National Basic Research Program of China(973 Program)(2010CB731905)
文摘The exact radar cross-section （RCS） measurement is difficult when the scattering of targets is low. Ful polarimetric cali-bration is one technique that offers the potential for improving the accuracy of RCS measurements. There are numerous polarimetric calibration algorithms. Some complex expressions in these algo-rithms cannot be easily used in an engineering practice. A radar polarimetric coefficients matrix （RPCM） with a simpler expression is presented for the monostatic radar polarization scattering matrix （PSM） measurement. Using a rhombic dihedral corner reflector and a metal ic sphere, the RPCM can be obtained by solving a set of equations, which can be used to find the true PSM for any target. An example for the PSM of a metal ic dish shows that the proposed method obviously improves the accuracy of cross-polarized RCS measurements.
基金funded by the National Key Research Program ofChina (No. 2016YFB0502500)Guangxi innovative Development Grand Grant (GuiKeAA18118038)+2 种基金Land Observation Satellite Supporting Platform of National civilspace infrastructureNational Natural Science Foundation of China (No. 41671345)theNanjing University of Information Science and Technology Talent Start-up Fund.
文摘Radiation cross-calibration is an effective method to check and verify theaccuracy and stability of sensor measurements. Satellites with high radiation accuracy areused to calibrate satellites with low radiation accuracy. In order to ensure the reliability ofthe radiation cross-calibration method, we propose to obtain the gain and offset of theGaoFen-1 satellite by linear regression after the radiation cross-calibration of the satellitewith low precision and compare with the official coefficient. Finally, we get therelationship between the error in radiation cross-calibration results and side swing angle.The linear correction coefficients of each band are: 0.618, 0.625, 0.512 and 0.474. Theresults show that after the method is corrected by the linear correction coefficient, theerror caused by the side swing angle during the cross-calibration of the orbital radiation isreduced. The accuracy of radiation cross-calibration is improved, the frequency ofcalibration is improved and the requirements of remote sensing applications in the newera are adapted.
基金Supported by the National Natural Science Foundation of China(No.51105273)
文摘In this paper, a flexible high-precision calibration method suitable for industrial field was proposed. The complexity of the coordinate transformation was simplified by choosing the camera coordinate system as the unified reference coordinate system. A flexible planar calibration pattern was introduced to the calibration process, which can be arbitrarily placed and from which the known feature points can be extracted to construct other unknown feature points. With the known intrinsic parameters, the laser projector plane equation was fitted by the multi-noncollinear points, which were acquired through the principle of triangulation and the projective invariance of cross ratio. With this method, the strict alignment and multiple times of coordinate transformation can be avoided. Experimental results showed that the arithmetic mean of the root mean square(RMS) error of distance was 0.000 7 mm.
基金Supported by ITER Plan National Major Project(No.2008GB109000)
文摘As a key part of the diagnosis system in the International Thermonuclear Experimental Reactor(ITER),the neutron flux monitor(NFM),which measures the neutron intensity of the fusion reaction,is a Counting-Campbelling system with a large dynamic counting range.A dynamic linear calibration method is proposed in this paper to solve the problem of cross-over between the different counting and Campbelling channels,and improve the accuracy of the cross-calibration for long-term operation.The experimental results show that the NFM system with the dynamic linear calibration system can obtain the neutron flux of the fusion reactor in real time and realize the seamless measurement area connection between the two channels.
基金supported by the Aerospace Science and Technology Joint Fund(6141B061505)the National Natural Science Foundation of China(61473100).
文摘To address the eccentric error of circular marks in camera calibration,a circle location method based on the invariance of collinear points and pole–polar constraint is proposed in this paper.Firstly,the centers of the ellipses are extracted,and the real concentric circle center projection equation is established by exploiting the cross ratio invariance of the collinear points.Subsequently,since the infinite lines passing through the centers of the marks are parallel,the other center projection coordinates are expressed as the solution problem of linear equations.The problem of projection deviation caused by using the center of the ellipse as the real circle center projection is addressed,and the results are utilized as the true image points to achieve the high precision camera calibration.As demonstrated by the simulations and practical experiments,the proposed method performs a better location and calibration performance by achieving the actual center projection of circular marks.The relevant results confirm the precision and robustness of the proposed approach.
文摘本文对海洋气象漂流观测仪实测、CMA最佳路径数据集、第5代全球气象再分析产品(ERA5)、交叉检验多平台融合矢量风场(CCMP)四种资料的海面风在超强台风“利奇马”期间的变化特征进行分析。ERA5、CCMP两种分析/再分析风资料与实测风的对比分析表明:(1)风速:当风力<10级时,漂流观测仪轨迹上的ERA5、CCMP风速较漂流观测仪实测风速偏小;将漂流观测仪实测风速订正到10 m高度,风力≤5级时偏差(Bias)绝对值最小,ERA5(CCMP)为4.3 m s^(-1)(4.6 m s^(-1)),风力为7~9级时Bias绝对值最大,约9.2~10.2 m s^(-1);“利奇马”近中心海域ERA5、CCMP最大风速较CMA最佳路径数据集偏小,ERA5(CCMP)偏小约10.7 m s^(-1)(4.6 m s^(-1));ERA5(CCMP)最大风速极值较CMA最佳路径数据集偏低54.5%(12.7%)。(2)风向:ERA5、CCMP与漂流观测仪实测风向相关系数接近于0;风力≤5级时风向较实测偏右,风力>5级时偏左。(3)ERA5、CCMP风向、风速在“利奇马”近中心海域偏差明显,远离中心海域二者吻合度较高。通过对ERA5、CCMP资料进一步分析发现:CCMP能清楚描述热带气旋风场结构及演变过程,“利奇马”为超强台风时结构参数η=Vr/Vmax分布上有闭合环状结构,表明该区域有环状大风速带;“利奇马”强迫时间T_f分布于移动路径两侧,ERA5(CCMP)最大强迫时间为45 h(54 h)。
文摘The Chinese Ocean Color and Temperature Scanner (COCTS) is the main sensor launched in May of 2002 on the Chinese first ocean color satellite named HY-1A. In this paper, first, the properties of HY-1A and COCTS are introduced briefly. Second, the theory and methodology of cross-calibration for COCTS ocean color bands by using the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data are discussed in detail. Third, with the quasi-synchronized SeaWiFS data, we simulate the COCTS radiances at the top of atmosphere (TOA), and then obtain the calibration coeffi- cients for COCTS ocean color bands. The results show that the cross-calibration TOA radiances are consistent with the in situ vicarious calibration TOA radiances at the COCTS ocean color bands. Finally, we compare the COCTS-re- trieved water leaving radiances with SeaWiFS-retrieved ones and the results show that the cross-calibration method could provide reasonable accuracy for ocean color measurement.
文摘For the application of the CCD camera, the most important payload on CBERS-02, the key is to provide long-term stable radiometric calibration coefficients. Although the vicarious calibration had been proved successful, it had its limitations such as test site requirement and unsuitable for historical data. Cross-calibration is one of the alternative methods, but it needs synchro surface spectrum to achieve spectral band matching factors. Our effort is to probe the influences on these factors. Simulations with a lot of surface spectrum showed that the factors changed with the viewing geometry, atmospheric condition and surface targets. However, simulating with the same viewing geometry and atmospheric condition, the spectral band matching factors of the same or similar surface targets’ spectrum acquired from different dates and different places would like to be consistent to each other within 1%―5%. Thus, the synchro measurement data can be substituted by the same or similar target from other source. Based on this method, using the MODIS as the reference, the cross-calibration was performed for CCD camera. The research demonstrated that the traditional method with single calibration site was inappropriate for CCD camera, since the offsets for its four spectral bands were not zeros. With four calibration sites, these offsets were obtained. And the camera was detected to degrade with dates based on four times of cross-calibrations.
基金supported by the Chinese Defence Advance Research Program of Science and Technology (Grant No. 07K00100KJ)the National High Technology Research and Development Program of China ("863"Project) (Grant No. 2006AA12Z113)+1 种基金the International Science and Technology Cooperation Program of China (Grant No. 2008DFA21540)A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)
文摘Radiometric calibration of sensor is the basis of quantitative remote sensing,and uncertainty analysis is critical to ensure the accuracy of cross-calibration.Therefore,firstly,cross-calibration formulas were improved by redefining calibration coefficient and spectral band matching factor.In these formulas,cci was redefined as the calibration coefficient of normalized apparent reflectance,and spectral band matching factor as the ratio of normalized apparent reflectance.Secondly,based on the contrast of ideal and actual conditions in cross-calibration,8 sources of cross-calibration uncertainty were proposed:calibration uncertainty of standard sensor;pixel matching uncertainty;spectral band matching factor uncertainty caused by site altitude setting error,atmospheric parameters setting error,surface spectrum source,surface bidirectional reflectance characteristic,and error of atmospheric radiative transfer model;and uncertainty caused by other factors which were not considered.Finally,the contribution of each uncertainty was further analyzed and discussed for the HJ-1 CCD camera.The results provide many valuable references for evaluating the feasibility of alternative cross-calibration measurements.
文摘In order to make quantitative watercolor sensing with China-Brazil Earth Resources Satellite (CBERS-02) CCD camera, the MODIS data with higher accuracy is used to cross-calibrate the CCD camera over water targets. In homogeneous clear water area, two pairs of images obtained over the same area on the same day by the two sensors are selected. The top-of-atmosphere (TOA) radiances of the multispectral bands of CCD are calculated with the water and aerosol parameters from MODIS based on a water-atmosphere radiative transfer algorithm. The stripes in CCD image that caused by unequal response of the CCD array detectors are firstly removed before making the cross-calibration. The same part of CCD detectors is selected for the calibrations in the two images to eliminate the residual error of destriping and uniformity correction for the focus plane irradiance. It is shown that the calibration results from two different images are consistent. The error of this method is about 5%.
基金Supported by the National Key Research and Development Program of China(2018YFB0504900)National Natural Science Foundation of China(41675036)
文摘The instrument cross-calibration is an effective way to assess the quality of satellite data. In this study, a new method is proposed to cross-calibrate the sensors among satellite instruments by using a RObotic Lunar Observatory(ROLO) model and Apollo sample reflectance in reflective solar bands(RSBs). The ROLO model acts as a transfer radiometer to bridge between the instruments. The reflective spectrum of the Apollo sample is used to compensate for the difference in the instrument's relative spectral responses(RSRs). In addition, the double ratio between the observed lunar irradiance and the simulated lunar irradiance is used to reduce the difference in instrument lunar viewing and illumining geometry. This approach is applied to the Moderate Resolution Imaging Spectroradiometer(MODIS), the Sea-Viewing Wide Field-of-View Sensor(Sea Wi FS), and the Advanced Land Imager(ALI) on board three satellites, respectively. The mean difference between MODIS and Sea Wi FS is less than 3.14%, and the difference between MODIS and ALI is less than 4.75%. These results indicate that the proposed cross-calibration method not only compensates for the RSR mismatches but also reduces the differences in lunar observation geometry. Thus,radiance calibration of any satellite instrument can be validated with a reference instrument bridged by the moon.
