Haystack Observatory Postprocessing System (HOPS)

The Haystack Observatory Postprocessing System (HOPS) is a software package designed to analyze the data generated by DiFX VLBI correlators. It is written in C for Linux computers, and emphasizes quality-control aspects of data processing. It sits between the correlator and an image-processing and/or geodetic-processing package, and performs basic fringe-fitting, data editing, problem diagnosis, and correlator support functions. 


  • HOPS tarball The most recent tarball and an associated README file. The installation script uses autotools to properly configure for your architecture. You will need to have the pgplot package installed prior to building HOPS, otherwise it is self-contained.

Data processing manual

General information


  • Amplitude scaling: A comparison of the visibility amplitudes produced by the Mk4 hardware correlator with those of the DiFX software correlator.

Aedit, the main edit/display program of HOPS

  • General information
  • Psplot command example: This is an array of time versus baseline, and represents an entire experiment. Each colored rectangle is a baseline/scan. The entire view surface is active, and the user can select, delete, filter and display data at will using the mouse.
  • Plot command example: The color coding indicates the quality of the points. All aedit plots are active, in the sense that data can be interactively selected and deleted using the cursor, and an arbitrary level of detailed information can be retrieved about any selected point using the cursor. This plot shows multiband delay versus time, six plots per page. There are many possible axes and modes of plotting.

fourfit, the fringe-fitting program

vhelp output

  • Sample vhelp output: The output of a HOPS utility called vhelp, an online help system for the package. This sample provides a snapshot of the capabilities of the package as of February 1995. These capabilities are undergoing fairly rapid enhancement.

Historical notes