Mullard Space Science Laboratory

S. J. Welch
Real-time algorithms for optimal CCD data reduction in high energy astronomy

2001 (supervisor: G. Branduardi-Raymont)

This thesis presents novel and reusable algorithms and philosophies for the reduction of data produced by CCD detectors used for space astronomy. Some of the techniques described can be extended to other two-dimensional data sets, and all of them have relevance beyond the particular spacecraft on which they are currently being used.

The author began the work described in this thesis in January 1995, looking at ways in which the data produced from a spectroscopic instrument on the XMM-Newton spacecraft could be reduced sufficiently to fit into the comparatively meagre telemetry bandwidth available to it. The work was also constrained by the use of a processor system with many fewer resources available than ideal, but chosen for its reliability and tolerance to radiation, both important factors in a ten-year mission.

Chapter one introduces the need for spacecraft onboard data reduction, and the XMM-Newton spacecraft, and its instruments. Chapter two focuses on the principles of operation of CCDs, briefly considering the sources of noise that affect them in use. Chapter three examines the mechanics of the onboard software designed by the author, and arguments are made for trading data quality against data quantity. Chapter four describes the construction of a software, standalone instrument simulator to be able to quantify the quality of the existing onboard software, provide feedback to settings used, and analyse the impact of future modifications. Chapter five presents results from the testing of the onboard software and early data from the commissioning phase of XMM-Newton. The thesis concludes with some suggestions for further improvements to the onboard software, and hints at possible applications to other observational scenarios involving large data-sets.


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