Entrada Departamento Notícias Palestra - Phase retrieval and phase diversity in astronomy

Palestra - Phase retrieval and phase diversity in astronomy

Robert A. Gonsalves, Ph. D.

Emeritus Professor, Tufts University, USA

 

2 de maio de 2017, 15:00
Edifício FC3, Anfiteatro -120


ABSTRACT

Phase retrieval (PR) uses the image of a star to estimate T, the phase aberration introduced by the atmosphere and the telescope. Phase diversity (PD), first suggested by the presentor in 1982, is an extension of PR, in which 2 or more images of an extended object are measured, with optical changes (diversities) inserted. This allows simultaneous estimation of both T and the object. The major advantage of PR and PD is that they use only the measured output of the telescope. No auxiliary hardware, like a guide star or a Shack-Hartmann sensor is needed.

In 1990, when the Hubble Space Telescope was found to have an optical flaw, both PD and PR were used to help scientists determine a prescription to fix the flaw. Proposed uses include in-orbit phasing of the 18 mirror segments of the James Webb Space Telescope, imaging of exoplanets, reducing the deleterious effect of non-common optical paths in a telescope with adaptive optics, and sequential diversity imaging in which changes in the AO are diversities.

 

Robert A. Gonsalves is an Emeritus Professor of Engineering at Tufts. His research is in image processing with applications in the graphic arts, medicine, astronomy, and historical images. In 1990 he helped NASA fix the Hubble Space Telescope by calculating a prescription to correct a flaw in the HST's optics. He was an advisor on image processing for Frontline's 1993 program on the Kennedy assassination and for NASA on the optics for the Next Generation Space Telescope.

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