An increasing interest in the use of low frequency Synthetic Aperture Radar(SAR)systems,e.g.,L-and P-bands,makes the research of the ionospheric effects on SAR interferograms become urgent and significant.As the most ...An increasing interest in the use of low frequency Synthetic Aperture Radar(SAR)systems,e.g.,L-and P-bands,makes the research of the ionospheric effects on SAR interferograms become urgent and significant.As the most pronounced signature in interferograms,the ionosphere-induced azimuth streak was thoroughly investigated in this study through processing of the 19 L-band Advanced Land-Observing Satellite(ALOS)Phased Array type L-band Synthetic Aperture Radar(PALSAR)images over the Chongqing City,China.The investigations show that the visible ionosphere-induced stripe-shape azimuth shifts with the invariable direction of 26°E,113°N are observed in some interferometric pairs.Relating these anomalous azimuth shifts to the International GNSS Service(IGS)final ionospheric products shows that the detected ionosphere-contaminated SAR images display the relatively large ionospheric variation with time during SAR satellite travelled through the study area,indicating a somewhat correlation between them.After detecting the ionosphere-contaminated interferograms,we estimated the Ionospheric Phase Streak(IPS)based on an approximate linear relationship between IPS and azimuth shift,and then removed them from the original interferograms.The corrected results show that ionospheric phase patterns are largely removed from the ionosphere-contaminated interferograms.The investigation indicates that the direction of the IPS keeps approximately constant in space and time,which provides the potential chance to develop methods to correct the ionospheric effect.Furthermore,this study once more proves that the ionospheric effect on SAR interferogram can be detected,estimated and corrected from azimuth shifts.展开更多
Direct quadrature modulation technology is suitable for wide-band radar signal generation. However, this method has rigorous requirements on amplitude and phase balance of the orthogonal input signals. If the requirem...Direct quadrature modulation technology is suitable for wide-band radar signal generation. However, this method has rigorous requirements on amplitude and phase balance of the orthogonal input signals. If the requirements are not satisfied, there would be modulation errors such as image frequency and oscillator leakage that cannot be filtered. The modulation errors will therefore raise the noise floor of the range profile and reduce the dynamic range of the Synthetic Aperture Radar (SAR) image as a whole. In this paper, the wide-band In-phase/Quadrature-phase (I/Q) modulation errors are modeling analyzed, and the influence of wide-band I/Q modulation errors on SAR imaging is discussed. Furthermore, a compensation method of modulation errors is proposed, and the circuit implementation of the radar signal generation and pre-distortion is presented. The experimental results illustrate that the curves of the I/Q amplitude and phase imbalance errors are successfully extracted and the rejection of image frequency improved significantly, thus meets the requirements of the SAR imaging.展开更多
An efficient implementation of the topography adaptive filter based on local frequency estimation is proposed, where chirp z transform is applied to enhance the accuracy of the frequency estimation. As a by product of...An efficient implementation of the topography adaptive filter based on local frequency estimation is proposed, where chirp z transform is applied to enhance the accuracy of the frequency estimation. As a by product of this adaptive filter, the linear approximated phase model of the interferogram is employed to improve the coherence estimation. The impacts of the adaptive filter on global and local phase unwrapping algorithms are discussed. Finally, aiming at the negative effect that the adaptive filter can bring to local phase unwrapping algorithms, a fusion scheme that takes advantage of least square and several local phase unwrapping algorithms is presented.展开更多
基金Natural Science Foundation of China projects(Nos.42074040,41941019,41731066,41790445)National Key R&D Program of China(Nos.2020YFC1512001,2019YFC1509800)China Geological Survey Project(No.DD20190647)。
文摘An increasing interest in the use of low frequency Synthetic Aperture Radar(SAR)systems,e.g.,L-and P-bands,makes the research of the ionospheric effects on SAR interferograms become urgent and significant.As the most pronounced signature in interferograms,the ionosphere-induced azimuth streak was thoroughly investigated in this study through processing of the 19 L-band Advanced Land-Observing Satellite(ALOS)Phased Array type L-band Synthetic Aperture Radar(PALSAR)images over the Chongqing City,China.The investigations show that the visible ionosphere-induced stripe-shape azimuth shifts with the invariable direction of 26°E,113°N are observed in some interferometric pairs.Relating these anomalous azimuth shifts to the International GNSS Service(IGS)final ionospheric products shows that the detected ionosphere-contaminated SAR images display the relatively large ionospheric variation with time during SAR satellite travelled through the study area,indicating a somewhat correlation between them.After detecting the ionosphere-contaminated interferograms,we estimated the Ionospheric Phase Streak(IPS)based on an approximate linear relationship between IPS and azimuth shift,and then removed them from the original interferograms.The corrected results show that ionospheric phase patterns are largely removed from the ionosphere-contaminated interferograms.The investigation indicates that the direction of the IPS keeps approximately constant in space and time,which provides the potential chance to develop methods to correct the ionospheric effect.Furthermore,this study once more proves that the ionospheric effect on SAR interferogram can be detected,estimated and corrected from azimuth shifts.
基金Supported by 863 Program (2009AA12Z103)973 Program (2009CB72400)
文摘Direct quadrature modulation technology is suitable for wide-band radar signal generation. However, this method has rigorous requirements on amplitude and phase balance of the orthogonal input signals. If the requirements are not satisfied, there would be modulation errors such as image frequency and oscillator leakage that cannot be filtered. The modulation errors will therefore raise the noise floor of the range profile and reduce the dynamic range of the Synthetic Aperture Radar (SAR) image as a whole. In this paper, the wide-band In-phase/Quadrature-phase (I/Q) modulation errors are modeling analyzed, and the influence of wide-band I/Q modulation errors on SAR imaging is discussed. Furthermore, a compensation method of modulation errors is proposed, and the circuit implementation of the radar signal generation and pre-distortion is presented. The experimental results illustrate that the curves of the I/Q amplitude and phase imbalance errors are successfully extracted and the rejection of image frequency improved significantly, thus meets the requirements of the SAR imaging.
文摘An efficient implementation of the topography adaptive filter based on local frequency estimation is proposed, where chirp z transform is applied to enhance the accuracy of the frequency estimation. As a by product of this adaptive filter, the linear approximated phase model of the interferogram is employed to improve the coherence estimation. The impacts of the adaptive filter on global and local phase unwrapping algorithms are discussed. Finally, aiming at the negative effect that the adaptive filter can bring to local phase unwrapping algorithms, a fusion scheme that takes advantage of least square and several local phase unwrapping algorithms is presented.
