An Improved Polar Format Algorithm With Out-of-Plane Motion Compensation for Earth-Based Radar Imaging of the Moon

The polar format algorithm (PFA) is widely regarded as an efficient imaging algorithm, typically performing well when either the out-of-plane motion of the radar is negligible, or the imaging scene is approximately planar. However, in Earth-based radar imaging of the Moon, these conditions are often violated. The unavoidable out-of-plane motion of the radar and the nonplanar terrain of the lunar surface introduce space-variant phase errors that cause geometric distortion and defocus. To address this issue, an improved PFA with out-of-plane motion compensation is proposed in this letter. First, an optimal focus plane is selected to eliminate the linear component of the out-of-plane motion and the resulting geometric distortion errors. Then, based on the mapping relationship of phase errors between the phase history domain and the wavenumber domain, space-variant filters are designed in the azimuth wavenumber domain to efficiently compensate for the space-variant defocus errors in PFA images. Finally, the effectiveness of the proposed algorithm is validated by the results obtained from experimental data.