Detection, Estimation and Compensation of Ionospheric Effect on SAR Interferogram Using Azimuth Shift

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.