Data processing for fabrication of GMT primary segments: Raw data to final surface maps

Michael T. Tuell, William Hubler, Hubert M. Martin, Steven C. West, Ping Zhou

Research output: Chapter in Book/Report/Conference proceedingConference contribution

4 Scopus citations

Abstract

The Giant Magellan Telescope (GMT) primary mirror is a 25 meter f/0.7 surface composed of seven 8.4 meter circular segments, six of which are identical off-axis segments. The fabrication and testing challenges with these severely aspheric segments (about 14 mm of aspheric departure, mostly astigmatism) are well documented. Converting the raw phase data to useful surface maps involves many steps and compensations. They include large corrections for: image distortion from the off-axis null test; misalignment of the null test; departure from the ideal support forces; and temperature gradients in the mirror. The final correction simulates the active-optics correction that will be made at the telescope. Data are collected and phase maps are computed in 4D Technology's 4SightTM software. The data are saved to a.h5 (HDF5) file and imported into MATLAB® for further analysis. A semi-automated data pipeline has been developed to reduce the analysis time as well as reducing the potential for error. As each operation is performed, results and analysis parameters are appended to a data file, so in the end, the history of data processing is embedded in the file. A report and a spreadsheet are automatically generated to display the final statistics as well as how each compensation term varied during the data acquisition. This gives us valuable statistics and provides a quick starting point for investigating atypical results.

Original languageEnglish (US)
Title of host publicationAdvances in Optical and Mechanical Technologies for Telescopes and Instrumentation
EditorsColin R. Cunningham, Ramon Navarro, Allison A. Barto
PublisherSPIE
ISBN (Electronic)9780819496195
DOIs
StatePublished - Jan 1 2014
EventAdvances in Optical and Mechanical Technologies for Telescopes and Instrumentation - Montreal, Canada
Duration: Jun 23 2014Jun 27 2014

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
Volume9151
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X

Other

OtherAdvances in Optical and Mechanical Technologies for Telescopes and Instrumentation
CountryCanada
CityMontreal
Period6/23/146/27/14

Keywords

  • Alignment aberrations
  • Automation
  • Data processing
  • Force and temperature compensations
  • MATLAB®
  • Morphing distortion correction
  • Surface maps

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering

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