Experimental demonstration of scene-based cophasing in optical synthetic aperture imaging using the SPGD algorithm

• Makoto Hirose and Norihide Miyamura
• received 03/06/2024; accepted 04/29/2024; posted 04/29/2024; Doc. ID 522829
• Abstract: Large-aperture telescopes based on optical synthetic aperture imaging are investigated for recent highresolution spaceborne observations. An enabling technique of aperture synthesis is a cophasing methodto suppress a piston-tip-tilt error between sub-apertures. This paper proposes a scene-based cophasingtechnique using the stochastic parallel gradient descent (SPGD) algorithm, assuming application to highresolution Earth observation. A significant advantage of the SPGD algorithm is a model-less cophasingcapability based on extended scenes, but the simultaneous scene-based piston-tip-tilt correction betweenmultiple apertures has not been demonstrated. In this paper, we developed a tabletop synthetic apertureimaging system with 37 sub-apertures and demonstrated extended-scene-based piston-tip-tilt control byoptimizing applied voltages to 111 actuators simultaneously. The demonstration experiments used notonly static scenes but also a time-varying dynamic scene for observation targets. In every measurement, theproposed scene-based approach reduced the initially defined piston-tip-tilt errors, and the image sharpnesssignificantly improved, although the correction rate in the dynamic scene observation was slower. Finally,this paper discusses the influence of scene dynamics on image-based cophasing.