./guide
getnod.pro

Last modification date:

Thu Jun 2 23:56:08 2005

getnod

procedure getnod, scan, [ifnum=integer], [intnum=integer], [plnum=integer], [fdnum=integer], [tau=float], [tsys=float], [ap_eff=float], [smthoff=integer], [units=string], [noweight=flag]

This procedure retrieves and calibrates a total power nod scan pair. It should be used as a template for the user who may wish to develop more sophisticated calibration schemes. The routine produces a spectrum calibrated in degrees K of antenna temperature (other recognized units are 'Ta*' and 'Jy').

The only required parameter is the scan number. This can be either scan in the sequence of two nod scans. Arguments to identify the IF number, polarization number, and feed number are optional. The default feed number (0) is the lowest numbered FEED found in the data. This is assumed to have been the tracking (source) feed for the first scan. This can be overridden by specifying fdnum=1 which will use the second FEED in the data as the tracking feed. Data with more than two feeds will be rejected by the procedure.

The procedure calculates Tsys based on the Tcal values, and cal_on/cal_off phases. The user can override this calculation by entering a zenith system temperature. The procedure will then correct the Tsys for the observed elevation. If the data are calibrated to Ta* or Jy, then additional parameters are used. A zenith tau value may be specified, and an aperture efficiency may be specified. The user is *strongly* encouraged to enter values for these calibration parameters, but they will be estimated if none is provided.

A parameter called smthoff can be used to smooth the reference spectrum prior to calibration. In certain cases this can improve the signal to noise ratio, but it may degrade baseline shapes and artificially emphasize spectrometer glitches. Use with care. A value of smthoff=16 is often a good choice.

All averaging is done using dcaccum and accumave. This means that integrations are weighted using the default weight given in dcaccum. To turn off this weighting so that all integrations have equal weight in the average, use the /noweight flag.

Version

$Id: getnod.pro,v 1.16 2005/05/30 04:03:43 bgarwood Exp $

Parameters
scan in, required integer	M&C scan number

Keywords
ifnum in, optional integer	IF number (starting with 0)
intnum in, optional integer	Integration number (default=all)
plnum in, optional integer	polarization number (default 0)
fdnum in, optional integer	feed number (default 0)
tau in, optional float	tau at zenith
tsys in, optional float	tsys at zenith
ap_eff in, optional float	aperture efficiency
smthoff in, optional integer	smooth factor for reference spectrum
units in, optional string	takes the value 'Jy', 'Ta', or 'Ta*' (default Ta)
noweight in, optional flag	if set, the default weighting is turned off and all integrations are averaged with the same weight (1.0).