Ms. Patricia A. Eliason Profile

Patricia A. Eliason

NSO/GONG Program Manager at NSFs National Optical-Infrared Astronomy Research Lab

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Proceedings Article | 12 July 2008 Paper

Operating the GONG worldwide network

Patricia Eliason

Proceedings Volume 7016, 70161S (2008) https://doi.org/10.1117/12.789966

KEYWORDS: Observatories, Sun, Data processing, Magnetism, Data archive systems, Failure analysis, Computing systems, Prototyping, Imaging systems, Data acquisition

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At the instigation of the international scientific community, the US National Solar Observatory (NSO) began to develop the six-site, semi-autonomously operating, helioseismology Global Oscillation Network Group (GONG) in 1984 and the network was officially established in 1995 when the sixth, and last, station was completed. Funded by the US National Science Foundation and enjoying in-kind support from numerous institutions, the project has become a notable international collaboration. The network provides essentially continuous, extremely sensitive observations of the velocity, intensity, and magnetic field of the Sun's surface every minute. Quick-look data are available in near-real-time for science and for diagnostics (http://gong.nso.edu), and the full data set is shipped to project headquarters weekly where the processed data and science-grade analyses are made available to the international community. As originally proposed, GONG was to have a three-year observing run. Over a number of years of operation however, both GONG and its space-borne sister the ESA/NASA SOHO MDI instrument clearly demonstrated the reality of internal solar-cycle structural changes, and in addition, local helioseismology programs were successfully developed. In 2003, NSO made a decision to add GONG to its Flagship facilities and extended the duration of the observing run indefinitely.

Proceedings Article | 9 July 2008 Paper

An intelligent modulator system

George Luis, Jack Harvey, Tim Purdy, Mike Soukup, Patricia Eliason

Proceedings Volume 7014, 701460 (2008) https://doi.org/10.1117/12.787996

KEYWORDS: Modulators, Polarization, Solar processes, Calibration, Liquid crystals, Microcontrollers, Polarizers, Switching, Magnetism, Photodiodes

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In 2001, the GONG+ instruments began acquiring solar magnetic field images (magnetograms) every minute. These observations offer a useful resource for the solar physics community. However, the quality of the magnetograms was reduced by a significant zero point error in the observations that varied across the solar image and with time. This precluded using the magnetograms for meaningful extrapolations of weak photospheric fields into the corona. The error was caused by the slow, asymmetric, locally varying switching of the LCD modulator (LCM) from one retardation state to the other. This generated a false magnetic field pattern as a result of different responses to weak instrumental linear polarization ahead of the LCM. The original modulator driver used a very simple design to excite the LCM. Liquid crystals like those in the LCM take different times to switch from one polarization state to the other than to return to the first polarization state. To eliminate the difference in switching times, a driver capable of varying its output during the change in LCM state was needed. A microcontroller-based design was chosen. The final driver design resulted in a factor of 100 improvement in the zero point error.

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