Zexia Zhang

1 Introduction Predicting the interaction between turbulent river flow and bed topography in the field-scale meandering rivers is essential for various river engineering and geoscience problems. For example, such predictions allow engineers to gain insight into the evolution of the riverbeds and, thus, to design effective flood management and mitigation strategies.

Abstract Cophasing is crucial for segmented or sparse aperture telescopes to achieve high resolution. In this Letter, we propose a novel, to the best of our knowledge, model-based piston correction method that can remove large-scale piston errors within a few iterations using extended objects. The relation between the piston error and a metric function is derived theoretically under broadband illumination.

Abstract On-orbit cophasing is essential for high-resolution imaging of space telescopes with a segmented primary mirror. A model-based fine phasing method for a segmented mirror is proposed and demonstrated in this Letter. The tip-tilt error is related to the second moment of spot intensity, and the piston error is related to the Strehl ratio. Chebyshev segmented piston-tip-tilt (CSPTT) modes are used to express cophasing errors to suppress the effect of imaging noises.