Abstract: The spaceborne synthetic aperture radar (SAR) at low frequencies can be affected by the ionosphere, the relevant compensation therefore needs to be considered in low-frequency SAR system design. Aiming at this issue, a model of Legendre orthogonal polynomials to evaluate the ionospheric effects was first proposed in this paper, which was suitable for the SAR systems with low frequency and wide band. This new model can avoid coupling of traditional model. Then, based on the signal echo, the compensation techniques for ionospheric dispersion and Faraday rotation were analyzed, which avoided traditional ionosphere data with low accuracy, different paths and ground receiving stations. Based on the autofocus algorithm, the compensation precision of dispersion can reach 04TECU, which can significantly improve the SAR image quality. Compared with the results of official website, a further 27% reduction of Faraday rotation error is achieved according to the information of scattering matrix. At last, the joint observation with PALSAR and ionosonde was applied. The accuracy of the result was improved by 30% compared with the result based on only the ionosonde. This study can provide technical support for the future system design of spaceborne SAR at low frequencies.

Key words: synthetic aperture radar, ionosphere, dispersion, scintillation, Faraday rotation, error compensation