Mitigation of ionospheric phase delay error for SAR interferometry: an application of FR-based and azimuth offset methods

Synthetic aperture radar (SAR) signals interact with the ionosphere layer when they propagate through the atmosphere, leading to the phase delay error for SAR interferometry (InSAR). Although several methods have been proposed to mitigate the ionospheric phase delay, the application of these methods has not been fully investigated. In this study, an application of two ionospheric mitigating methods, azimuth offset and Faraday Rotation (FR), is investigated and analysed through processing two Phased Array type L-band Synthetic Aperture Radar onboard the Advanced Land Observing Satellite-1 full-polarimetric SAR images over Alaska. The result indicates that both methods can effectively mitigate the ionospheric phase delay error for SAR interferometry, where the standard deviations of the ionosphere-corrected result have decreased to 3.2 cm for FR-based method and 2.0 cm for azimuth offset method compared to those before correction (7.3 cm). However, it is also found that the FR-based method is easily contaminated by the noise, which may be a limitation in practical applications. Moreover, analysis of the residual ionospheric phase from azimuth offset method suggests that the residual phase contribution in the azimuth offset and interferometric phase images is a limitation when using the azimuth offset to mitigate the ionospheric effect on SAR interferometry. This study may provide useful information when using these two methods to mitigate the ionospheric phase delay error on InSAR.