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GBTIDL Release Notes Version 2.1

• Introduction
• Getting Started
• New Features
• Bug's Fixed
• Known Issues
• Register as a GBTIDL user
• Running GBTIDL in Green Bank, Socorro, or Charlottesville:
• Running your own copy of GBTIDL
  • IDL License
  • Download and Installation of GBTIDL

Introduction

We are pleased to announce the release of GBTIDL, version 2.1. GBTIDL is an interactive package for reduction and analysis of spectral line data taken with the Robert C. Byrd Green Bank Telescope. The package consists of a set of straightforward yet flexible calibration, averaging, and analysis procedures (the "GUIDE layer") modeled after the UniPOPS and CLASS data reduction philosophies, a customized plotter with many built-in visualization features, and Data I/O and toolbox functionality that can be used for more advanced tasks. The entire package is written in IDL.

GBTIDL version 2.1 contains numerous new features and bug fixes, as described in these release notes.

Users may wish to also read the release notes of the latest version of sdfits which includes changes of interest to GBTIDL users (some of which are also described here).

A patch to this version has been released. Users should read the patch release notes for details of the patch and instructions on downloading and installing that patch.

Getting Started

• The starting point for GBTIDL documentation, bug reporting and tracking, and discussion is here: http://gbtidl.nrao.edu/
• A comprehensive User's Guide is also available as of this release.

New Features

• Documentation
  • A new User's Guide. This combines documentation previously scattered across several wiki pages. It also updates and clarifies many items. A pdf version is available.
  • A new calibration document. This describes the philosophy, algorithms, and limitations of the current suite of calibration procedures available in GBTIDL.
• New data container fields: radesys, target_longitude, target_latitude, caltype. These fields are now filled by the latest release of sdfits (released at the same time as version 2.0 of GBTIDL) and they are available in the data containers. GBTIDL will still be able to read older SDFITS files although these new fields will have any useful information in them for this older data.
  • RADESYS: This is a standard FITS keyword required to tell what coordinate system is used for equatorial coordinates. It has 3 possible values: FK4, FK5, and GAPPT.
  • TARGET_LONGITUDE and TARGET_LATITUDE: These are the coordinates, in decimal degrees, found in the GO FITS file. These will typically be a source position for single pointings or a map center for mapping procedures. They are the same coordinate system as the pointing positions also found in the data container.
  • CALTYPE: This is a string recording whether the "high" or "low" cal was used.
• New data selection parameters: TRGTLONG, TRGTLAT, and OBSID. TRGTLONG and TRGTLAT correspond to the new TARGET_LONGITUDE and TARGET_LATITUDE data container fields. OBSID corresponds to the OBSID data container field. OBSID is something that can be optionally set by the observer.
• New data file index. The index version number has changed because of the new data selection fields. When you open a data file with an index having an older version number GBTIDL will automatically recreate the index from the data file without any loss of information. The new index file will have OBSID values since those have always been in the SDFITS files produced by sdfits but they will not have useful values for the target positions since those are only found in the latest sdfits output.
• Renamed data container and selection field. The data container and selection field SUBSCAN has been renamed to PROCSEQN to avoid confusion with similar terms at the telescope. This field is used in multi-scan procedures to record which scan in that multi-scan procedure a particular scan corresponds to. This is a simple copy of the PROCSEQN value already found in the SDFITS file which itself is a copy of the PROCSEQN value recorded in the GO FITS file. PROCSEQN counts from 1 to the total number of scans in the procedure. The old value of SUBSCAN counted from 0 to one less than the total number and that has caused confusion during observing. Most users will not use this value or notice this change
• Improved default aperture efficiency (ap_eff) values.
• New arguments to existing procedures.
  • fileout now has an optional /new keyword. When supplied the output file will be created from scratch even if it already exists (deleting the existing file in the process).
  • list and summary now have an optional file keyword. This allows you to send the output of these two procedures to a named file instead of to the terminal.
• Renamed keyword: the fdnum keyword in getnod and getbs has been renamed to trackfdnum to highlight the different meaning of this keyword in these calibration routines as compared to the fdnum keyword in the other calibration routines.
• The mean_tcal in the data container(s) that result from all calibration routines is now set to the actual value used in that calibration routine. With this change, if you use the optional tcal keyword (overriding the mean_tcal found in the data containers) then the resulting data container(s) will have their mean_tcal value set to this user-supplied value.
• As discussed in the sdfits release notes sdfits has improved the handling of all types of correlations from the spectrometer. The cross-correlations were wrong in previous versions. The raw values for auto-correlation data are now 2 times larger than they were in previous versions of sdfits. This has been done to preserve the correct total power in the raw values. When properly calibrated this factor of 2 does not influence the final result and users looking only at the calibrated values will not notice any difference.

Bug's Fixed

• eta_l was being incorrectly applied in all calibration routines. eta_l is an estimate of the rear spillover, ohmic loss and blockage efficiency. Prior to this fix a value of 1/0.99 was being used instead of the correct 0.99. The resulting error of 2% in data calibrated to Ta* or Jy is less than the advertised precision of GBTIDL calibration routines.
• nrecords did not work with the /keep keyword
• replace failed in some circumstances when there were more than 32K channels.
• gbtoplot was changing the supplied "y" values when no "x" values were given
• in some circumstances users were finding that they had accidentally generated a printout from the plotter when the plotter was first started.
• show works better with continuum data and the small header option
• Large file support. A bug was found and fixed in the Goddard IDL file_open procedure that affected large file support.

Known Issues

• The numbering of the different IFs within a scan can be different from the numbering seen in GFM at the telescope.

Register as a GBTIDL user

• You can do this on the GBTIDL web site. Our on-line registration form was apparently not working properly for an unknown amount of time, so even if you think you are already registered, please re-register when you download version 2.1.

Running GBTIDL in Green Bank, Socorro, or Charlottesville:

• At the unix prompt, simply type 'gbtidl'

Running your own copy of GBTIDL

IDL License

• You must have an IDL license to run GBTIDL. IDL version 6.0 and later is supported. If you don't have a license you can run GBTIDL remotely, using the computers in CV or GB. See the GBTIDL homepage for details. IDL 6.3 is needed for large file support on a Mac.

Download and Installation of GBTIDL

• To obtain GBTIDL, download the files here
• Create a directory for the installation and unzip the tar ball:

    mkdir mygbtidl
    mv gbtidl-2.1.tar.gz mygbtidl/.
    cd mygbtidl
    gzip -d gbtidl-2.1.tar.gz
    tar -xvf gbtidl-2.1.tar

• go to the top level directory, 'gbtidl':

    cd gbtidl

• copy 'run_gbtidl' to 'gbtidl':

    cp run_gbtidl gbtidl

• edit the 'gbtidl' script to replace "PLACE_INSTALLATION_DIR_HERE" with the full path to the gbtidl executable script. It should then look something like this:

    export GBT_IDL_DIR=/home/mygbtidl/gbtidl

• start the package by calling the script 'gbtidl':

    ./gbtidl

• You may wish to add the installation directory to your unix path.

- -- BobGarwood - 14 Feb 2007