PTI Data Overview and Access

Contents

• Data flow
• Data access
• Interferometer modes
• Formats for Level 1 and Level 2 files and plots
• Quality assessment
• Data rights

Data flow

• The raw data are processed into fringe amplitudes and other necessary information by a program called vis. The algorithms and applied calibrations are described in detail in this paper. This processing is done automatically at the end of each observing night.
• The output of this reduction is called Level 1 data, i.e. fringe data that have been corrected for detector biases and averaged, but not yet corrected for the system visibility.
• The Level 1 data are contained in a group of files, described in detail in the links below. The primary data files are called .sum and .spec files and contain the wideband (or white light) and narrow band data respectively. The prefix for Level 1 files is the UT observation date in the form yyyyddd.
• The sum and spec files also contain all other information (delay line positions, time, etc.) needed to calibrate the data for the system visibility (by the programs wbCalib and nbCalib as described below).
• Other Level 1 files contain other instrument information such as the baseline (.baseline).
• Once the PTI user has obtained his/her Level 1 data for science targets and corresponding calibrators, the programs wbCalib and nbCalib take these files as input in order to produce fully calibrated data (Level 2 files). At this time, PTI users must calibrate their own data, a task that is greatly simplified if making use of our calibration packages, which may be obtained from our software download page or using the web interface. A guide to calibrating PTI data using these programs is available here.

  Data access

  The Level 1 data are available through a web interface which accesses all the desired Level 1 data from a database. The database allows selection of data across many nights, and using a variety of selection criteria. For instance, all data with a given project ID, or a for a given target, or for a range of dates, can be retrieved in one query. The interface allows exporting your L1 data in ASCII or FITS formats.
  

  Public users have access to PTI data once the proprietary period has expired by self-registering for an account to our web access tool.
  

  Interferometer modes
  

  Although PTI operates in several modes, only visibility amplitude (also called V² or NIRV²) data are publicly available.

  Formats for L1 and L2 files
  

  The PTI Level 1 and Level 2 data are available in both FITS and ASCII formats. The following links detail the file format in each case:
  • Detailed description of L1 and L2 ASCII files
  • Detailed description of L1 and real-time plots
  • Level 1 FITS description
  • Level 2 FITS description  (IAU OI-FITS standard)
    

  Quality Assessment

  As part of the Level 1 file set, we include information which characterizes the data quality at different levels. For details, please consult the QA description page.
  

  Data rights
  

  The default data proprietary period is 18 months.
  

  Return to PTI Support page

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  last updated Jan 5, 2006