Subaperture RMA Imaging for Stripmap SAR via Global-Reference Coherent Synthesis

Abstract

Subaperture processing forms an early low-resolution synthetic aperture radar (SAR) image from a partial aperture and improves its azimuth resolution as additional data segments become available. However, conventional subaperture methods may rely on overlapping data or additional image-domain resampling. To overcome these limitations, this letter proposes a global-reference coherent synthesis method for subaperture range migration algorithm (RMA) imaging in stripmap SAR. Each nonoverlapping subaperture is first processed by a local RMA procedure and then mapped to a common full-aperture reference through chirp-based azimuth mapping and global-reference phase compensation. The proposed method preserves coordinate, sampling, and phase consistency, enabling coherent accumulation without overlapping, image-domain resampling, or empirical phase alignment. Simulated point-target experiments show that the proposed method has no observable paired echoes and comparable focusing quality to the full-aperture RMA. Real airborne SAR data further verify its practical applicability.