Frequency-modulated continuous wave (FMCW), ice-sounding radar (ISR), nonlinear phase correction, range migration algorithm (RMA), Ocean engineering, TC1501-1800, Geophysics. Cosmic physics, QC801-809

The accumulation rate is a key parameter for calculating the surface mass balance of ice sheets and estimating sea level rise. Frequency-modulated continuous wave ice-sounding radar (FMCW-ISR) can be used to detect internal layers of ice sheets, and data of these layers are crucial for calculating the accumulation rate. However, during FMCW-ISR scanning, the same ice layer target may appear multiple times in the data matrix, leading to defocusing in the azimuth direction. In addition, FMCW-ISR systems are typically ultra-wideband, making it difficult to maintain absolute signal linearity throughout the entire sweep period. This nonlinear modulation results in high sidelobe levels, complicating the interpretation of ice layer structures. To address these problems, this article proposes a high-resolution FMCW shallow ice radar imaging method that combines the range migration algorithm (RMA) with nonlinear phase estimation and correction techniques. The proposed method effectively improves azimuth focusing accuracy and reduces sidelobe levels in the range direction, thereby better preserving the clear structure of the internal layers of the ice sheets. Validation using both simulated and measured data demonstrates that the proposed method significantly improves imaging quality, thereby making the layered structure of the shallow ice sheet more distinct.