usage:
    sdfits [OPTIONS] PROJECT_DIR [OUTPUT_PREFIX]

sdfits will reduce a GBT observation indicated by PROJECT_DIR into a set of
single dish (SD) FITS files whose names are prefixed with OUTPUT_PREFIX.
If OUTPUT_PREFIX is not given, the project name is used for this purpose.

PROJECT_DIR must be a complete path to a GBT observation directory.

OUTPUT FILES
    A separate SDFITS file is generated for each backend requested.

    Each file generated will have a name beginning with OUTPUT_PREFIX and
    ending with a suffix that reflects the data mode chosen by the user
    as well as the backend.

    The suffix has the form ".MODE.BACKEND.fits", where MODE is "avg",
    "cal", or "raw", and BACKEND is "acs", "sp", or "dcr".
    Examples are "MyData.avg.sp.fits" and "MyData.raw.dcr.fits".

OPTIONS
    -backends=DEVICES
          The DEVICES can be one or more (comma-separated) of the following:
              acs - autocorrelating spectrometer
              sp  - spectral processor
              dcr - digital continuum receiver
          Backends are processed in user-listed order.

          If -backends is not given, data from all three backends will be
          processed.

    -mode=MODE
          The MODE can be only one of the following:

              avg - Each row is from one sampler, and is the spectrum of the
                    entire scan, averaged over all calibrated integrations
                    from that scan.

              cal - Each row is from one sampler, and is the spectrum of a
                    calibrated integration.
              raw - Each row is from one sampler, and is the spectrum of the
                    raw data of a single phase.

          If -mode is not given, raw mode is assumed.

    -quiet
          All non-error related messages are suppressed.

    -scans=SCAN_NUMBER_LIST
          This option can be used to specify which scans to target.  If not
          given, all scans are targeted.  This list is a comma-separated
          sequence of items, with no spaces.  An item can be a single
          integer, or a range specification.  If more then one of the
          specified scan numbers exists in the project for the requested
          backends, each instance of the scan will be targeted.  To target
          only one of these duplicate scan numbers, use the -timestamp option.

          A range specification can have one of three forms:
            a:b     Scan numbers a through b, inclusive.
            a:      Scan numbers no less than a.
            :b      Scan numbers no greater than b.

          Scans are processed in user-listed order (per backend).  Example scan
          lists are:
            -scans=1,4,5:18
            -scans=2,18:40,5
            -scans=:24
            -scans=1,2,18:

    -timestamp=STARTTIME,ENDTIME
          This option can be used to target scans by the UTC timestamp of the
          start of the scan (used to name the raw M&C FITS) files.
          If STARTTIME is omitted then all data from STARTTIME to the
          end of available data is filled (-scans is also used to possibly
          limit the data to be filled). If STARTTIME is omitted so that the
          option is ",ENDTIME" with the leading comma then data will be filled
          up to and including ENDTIME (again, using -scans). If both times are
          included then all data from STARTTIME to ENDTIME is filled
          consistent with -scans. The times are specified exactly as they
          appear in the raw M&C FITS file names: YYYY_MM_DD_HH:MM:SS. This is
          identical to how TIMESTAMP is specified within GBTIDL to resolve
          duplicate scan numbers. The timestamps will be compared only against
          this date in the M&C files for that scan. If a timestamp occurs in
          the middle of a scan then either that scan is excluded (if the
          comparison is with STARTTIME) or included (if the comparison is with
          ENDTIME). No attempt will be made to select individual integrations
          based on the -timestamp arguments.

          Example timestamps are:
            -timestamps=2006_08_13_02:51:42,2006_08_13_08:22:06
            -timestamps=,2006_08_13_08:22:06
            -timestamps=2006_08_13_02:51:42

    -noindex
          Do not create an Index File in parallel with sdfits file.

    -append
          Files are appended instead of being overwritten.

    -fixbadlags
          Attempt to find and fix bad lags in ACS data.  The locations
          of the lags that were fixed are written to a log file.  The
          name of the log file is OUTPUT_PREFIX.MODE.acs.fixed_lags.
          This fix should only be used if you know that your data suffer
          from lag dropouts.  Full documentation on how the lags fixed is
          applied is available at 
          http://wiki.gb.nrao.edu/bin/view/Software/ModificationRequest15C306


    -sigmafactor=SIGMA_FACTOR
          This is part of the fixbadlags option.
          Lags are bad when they deviate from a comparison mean value
          by more than SIGMA_FACTOR times the standard deviation of the
          comparison data around that mean.  This defaults to 6.

    -spikestart=SPIKE_START
          This is part of the fixbadlags option.
          Single bad lags (spikes or drop outs) are searched for starting
          with the SPIKE_START lag.  This defaults to 200.

    -version
          Show the program version information.