Array-coherent synthetic aperture ladar imaging with centimeter-level resolution at a distance of 101.8 km

Synthetic aperture ladar (SAL) can rapidly form optical images of remote targets with resolutions surpassing the diffraction limit of the physical receive aperture, and it is therefore promising for sensing ultra-distant space objects in LEO, MEO, GEO, and cis-lunar orbits. SAL achieves single-photon-level sensitivity via coherent detection, but its imaging field of view (FOV) is fundamentally constrained by the optical diffraction limit, i.e., the FOV is inversely proportional to the receive aperture. To increase the received echo power without sacrificing wide-field imaging capability, we propose an array-coherent SAL imaging method in which the image signal-to-noise ratio (SNR) improves with the array size. To validate this concept, we build a 4×4 array-coherent SAL system and conduct open-air field experiments over 101.8 km. Well-focused images of cooperative targets are obtained with an imaging swath width of at least 11.0 m. Resolution repeatability is quantified over multiple frames, yielding 18.3±3.1 mm in range and 1.5±0.3 mm in azimuth ( mean ±standard deviation). Over five days (100 frames per day), array-coherent synthesis provides a mean SNR improvement of 10.14 dB, while >90 % of frames exhibit an improvement exceeding 8.20 dB, demonstrating stable gain under varying atmospheric conditions. These results indicate that the proposed method effectively increases the equivalent receiving aperture and improves SNR, offering a practical technical route toward long-range SAL imaging for space domain awareness.