Optical transfer function identification from satellite images

The on-orbit identification of the transfer function (TF) of a spaceborne optical telescope is useful for the acceptance test of the instrument, for the on-orbit refocusing and for the restoration of the recorded images. An original method is presented to perform such an identification from a single image. It is based on a physical modeling of the TF via the optical aberrations of the instrument, and on the automatic extraction of sub-images containing patterns that can be described with few parameters, e.g. step functions. The estimation of the TF is performed by minimizing a least-square criterion incorporating all extracted sub-images, as a function of the unknowns, which are the aberrations and the step parameters. Aliasing is explicitly incorporated in the image modeling, so that the TF can be estimated up to the optical cutoff frequency. The method is validated first on simulated images of step functions, then on a realistic, undersampled and noisy simulated image.