Abstract

Some applications of optimal filter theory and other signal processing for the Mark III interferometer are presented. The Mark III interferometer is a phase-coherent Michelson stellar interferometer for astrometry and imaging, employing active optics with real-time control for automated operation. For the angle tracker, an optimal-correlation angle sensor is implemented with a PAPA photon camera and digital correlation hardware. This sensor provides an error signal with a photon-noise standard deviation up to 3.6 times smaller than achievable with a quad-cell sensor for a 2:3 aspect annular tracker aperture. This error signal feeds an optimal filter adapted to the photon rate. For the siderostat pointer, an iterated extended Kalman filter is used to update an 8-geometric-parameter siderostat model. This filter improves on the performance of the previous off-line least-squares algorithm and yields pointing residuals of ~10 sec of arc for this unencoded system. For the fringe tracker, a real-time visibility gradient algorithm is used to detect phase-unwrapping errors; in the offline processing, a Kalman filter matched to the statistics of the fringe phase provides greatly improved phase unwrapping in comparison to a conventional first-difference algorithm.

© 1986 Optical Society of America