Computer Science – Performance
Scientific paper
Jul 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010pasp..122..795c&link_type=abstract
Publications of the Astronomical Society of the Pacific, Volume 122, issue 893, pp.795-807
Computer Science
Performance
3
Astronomical Instrumentation
Scientific paper
The paper describes the measurement and control algorithms of the near-infrared fringe trackers of the Keck Interferometer (KI). The fringe trackers provide fringe amplitude measurements for visibility science, and feedback and feedforward signals for fringe tracking and cophasing, respectively. Fringe measurement uses temporal path length modulation with synchronous array readout, and implements bias corrections of both the quadratures and the fringe power to provide high accuracy. The KI implementation uses sliding-window estimation to reduce control latency, and implements signal-to-noise (S/N) estimators that minimize biases from intensity scintillation. An inner-loop/outer-loop controller is used for ordinary fringe tracking, and a discrete-unwrapping controller is used for cophasing. A robust algorithm is used to estimate the slowly-varying dispersion to provide a target for the discrete-unwrapping controller and to estimate water-vapor seeing. The cophasing system is optimized for low control latency, and includes active control of narrowband disturbances. Measurements of the feedback and feedforward transfer functions as implemented are consistent with the predictions of a controls model; on-sky performance data are also presented.
Booth Andrew J.
Colavita Mark M.
Garcia-Gathright J. I.
Johnson Leah R.
Summers Kellee R.
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