Gaofen-3-02(GF3-02)is the first C-band synthetic aperture radar(SAR)satellite with terrain observation with progressive scans of SAR(TOPSAR)imaging mode in China,which plays an essential role in marine environment mon...Gaofen-3-02(GF3-02)is the first C-band synthetic aperture radar(SAR)satellite with terrain observation with progressive scans of SAR(TOPSAR)imaging mode in China,which plays an essential role in marine environment monitoring.Given the weak scattering characteristics of the ocean,the system thermal noise superimposed on SAR images has significant interference,especially in cross-polarization channels.Noise-Equivalent Sigma-Zero(NESZ)is a measure of the sensitivity of the radar to areas of low backscatter.The NESZ is defined to be the scattering cross-section coefficient of an area which contributes a mean level in the image equal to the signal-independent additive noise level.For TOPSAR,NESZ exhibits the shape of the SAR scanning gain curve in the azimuth and the shape of the antenna pattern in the range.Therefore,the accurate measurement of NESZ plays a vital role in the application of spaceborne SAR sea surface cross-polarization data.This paper proposes a theoretical calculation method for the NESZ curve in GF3-02 TOPSAR mode based on SAR noise inner calibration data and the imaging algorithm.A method for correcting the error existing in the theoretical curve of NESZ is also proposed according to the relationship between sea surface backscattering and wind speed and the same characteristics of target scattering in the overlapping area of adjacent sub-swaths.According to assessment with wide-swath TOPSAR cross-polarization data,the GF3-02 TOPSAR mode has a very low thermal noise level,which is better than−33 dB at the edge of each beam,and controlled below−38 dB at the center of the beam.The two-dimensional reference curves of the NESZ of each beam are provided to the GF3-02 TOPSAR users.After discussing the relationship between normalized radar cross section(NRCS)and wind speed,we provide a formula for NRCS related to wind speed and radar incidence angle.Compared with the NRCS derived from this formula and the NESZ-subtracted NRCS of SAR images,the bias is−0.0048 dB,the Root Mean Square Error is 1.671 dB and the correlation coefficient is 0.939.展开更多
Multi-frequency C and L bands in the TOPSAR data have been utilized to reconstruct three-dimensional(3-D)bathymetry pattern.The main objective of this study is to utilize fuzzy arithmetic to reduce the errors arising ...Multi-frequency C and L bands in the TOPSAR data have been utilized to reconstruct three-dimensional(3-D)bathymetry pattern.The main objective of this study is to utilize fuzzy arithmetic to reduce the errors arising from speckle in synthetic aperture radar(SAR)data when constructing ocean bathymetry from polarized SAR data.In doing so,two 3-D surface models,the Volterra algorithm and a fuzzy B-spline(FBS)algorithm,which construct a global topological structure between the data points,were used to support an approximation to the real surface.Volterra algorithm was used to express the non-linearity of TOPSAR data intensity gradient based on the action balance equation(ABC).In this context,a first-order kernel of Volterra algorithm was used to express ABC equation.The inverse of Volterra algorithm then performed to simulate 2-D current velocities from CVV and LHH band.Furthermore,the 2-D continuity equation then used to estimate the water depth.In order to reconstruct 3-D bathymetry pattern,the FBS has been performed to water depth information which was estimated from 2-D continuity equation.The best reconstruction of coastal bathymetry of the test site in Kuala Terengganu,Malaysia,was obtained with polarized L and C bands SAR acquired with HH and VV polarizations,respectively.With 10 m spatial resolution of TOPSAR data,bias of0.004 m,the standard error mean of 0.023 m,r2 value of 0.95,and 90%confidence intervals in depth determination was obtained with LHH band.展开更多
基金The National Natural Science Foundation of China under contract No.41976169.
文摘Gaofen-3-02(GF3-02)is the first C-band synthetic aperture radar(SAR)satellite with terrain observation with progressive scans of SAR(TOPSAR)imaging mode in China,which plays an essential role in marine environment monitoring.Given the weak scattering characteristics of the ocean,the system thermal noise superimposed on SAR images has significant interference,especially in cross-polarization channels.Noise-Equivalent Sigma-Zero(NESZ)is a measure of the sensitivity of the radar to areas of low backscatter.The NESZ is defined to be the scattering cross-section coefficient of an area which contributes a mean level in the image equal to the signal-independent additive noise level.For TOPSAR,NESZ exhibits the shape of the SAR scanning gain curve in the azimuth and the shape of the antenna pattern in the range.Therefore,the accurate measurement of NESZ plays a vital role in the application of spaceborne SAR sea surface cross-polarization data.This paper proposes a theoretical calculation method for the NESZ curve in GF3-02 TOPSAR mode based on SAR noise inner calibration data and the imaging algorithm.A method for correcting the error existing in the theoretical curve of NESZ is also proposed according to the relationship between sea surface backscattering and wind speed and the same characteristics of target scattering in the overlapping area of adjacent sub-swaths.According to assessment with wide-swath TOPSAR cross-polarization data,the GF3-02 TOPSAR mode has a very low thermal noise level,which is better than−33 dB at the edge of each beam,and controlled below−38 dB at the center of the beam.The two-dimensional reference curves of the NESZ of each beam are provided to the GF3-02 TOPSAR users.After discussing the relationship between normalized radar cross section(NRCS)and wind speed,we provide a formula for NRCS related to wind speed and radar incidence angle.Compared with the NRCS derived from this formula and the NESZ-subtracted NRCS of SAR images,the bias is−0.0048 dB,the Root Mean Square Error is 1.671 dB and the correlation coefficient is 0.939.
文摘Multi-frequency C and L bands in the TOPSAR data have been utilized to reconstruct three-dimensional(3-D)bathymetry pattern.The main objective of this study is to utilize fuzzy arithmetic to reduce the errors arising from speckle in synthetic aperture radar(SAR)data when constructing ocean bathymetry from polarized SAR data.In doing so,two 3-D surface models,the Volterra algorithm and a fuzzy B-spline(FBS)algorithm,which construct a global topological structure between the data points,were used to support an approximation to the real surface.Volterra algorithm was used to express the non-linearity of TOPSAR data intensity gradient based on the action balance equation(ABC).In this context,a first-order kernel of Volterra algorithm was used to express ABC equation.The inverse of Volterra algorithm then performed to simulate 2-D current velocities from CVV and LHH band.Furthermore,the 2-D continuity equation then used to estimate the water depth.In order to reconstruct 3-D bathymetry pattern,the FBS has been performed to water depth information which was estimated from 2-D continuity equation.The best reconstruction of coastal bathymetry of the test site in Kuala Terengganu,Malaysia,was obtained with polarized L and C bands SAR acquired with HH and VV polarizations,respectively.With 10 m spatial resolution of TOPSAR data,bias of0.004 m,the standard error mean of 0.023 m,r2 value of 0.95,and 90%confidence intervals in depth determination was obtained with LHH band.
