Multi-frequency radar signal measurements of ionospheric changes in the transmission path

With long synthetic aperture times, the ionosphere greatly affects the phase of the high-orbit Synthetic Aperture Radar (SAR) echo. Especially, the relative change of phase has a more significant effect on the imaging quality. To solve this problem and compensate for the radar echo phase error, a multi-frequency radar signal measurement method of ionospheric relative change is designed which can measure relative changes in electron concentration in the background ionosphere (using three frequencies) and relative changes in the ionosphere with irregularities (using four frequencies), and also effectively estimate the relative change of the slant distance error brought about by the precision orbiting error of the SAR platform, and at the same time, it can avoid most of the phase integer ambiguity problems in multi-frequency beacon phase measurement. Based on the scene of three-frequency radar signals emitted by the high-orbit SAR, a simulation is carried out to measure the relative changes of ionospheric concentration and slant distance error, and the simulation results show that the measurement results are consistent with the expectation, the theoretical error is controlled within 10%, and the relative changes of ionospheric electron concentration and slant distance can be distinguished from the relative phase error.