./guide
flagspurs.pro

Last modification date:

Wed Sep 28 13:27:08 2016

flagspurs

procedure flagspurs, [/flagcenteradc]

Set the flags for the VEGAS spurs in the currently opened input data source (either a single sdfits file or a directory).

VEGAS produces spurs (spikes) at channels corresponding to integer multiples of the ADC sampler frequency divided by 64. The normal behavior of sdfits is to flag these channels when the data are filled (use listflags to see the list of flags for the currently opened input data set). This routine can be used to recreate those flags if the original flag file has been lost or corrupted.

A spur is also produced at the center channel (NCHAN/2 when counting from 0). That spur does not arise in the ADC in VEGAS and so does not move as the spectral window is tuned across the ADC bandpass. This routine does not flag that spur. Normal sdfits use will replace that spur with the average of the two adjacent channels and so it generally is not necessary to flag that spur. Since that spur does not move as the spectral window is tuned it can be flagged using the standard flag command if necessary.

The routine first unflags all flags with the idstring "VEGAS_SPUR"

This routine expects to encounter uncalibrated VEGAS data filled by sdfits. It checks that there is both an SDFITVER keyword and an INSTRUME keyword on the primary header of all SDFITS files. The value of the INSTRUME keyword must be "VEGAS".

This spur locations are determined using the VSPDELT, VSPRPIX, and VSPRVAL columns. For data filled using older versions of sdfits, these values are not present in the SDFITS tables. Such older data should be refilled using the most recent version of sdfits to make use of this procedure.

Version

$Id$

Keywords
flagcenteradc in, optional boolean	When set, the center ADC spur is also flagged. Normally that spur is left unflagged because sdfits usually replaces the value at that location with an average of the two adjacent channels and so that spur does not need to be flagged since it's been interpolated.