./guide
getsigref.pro

Last modification date:

Wed Sep 28 13:27:09 2016

getsigref

procedure getsigref, sigscan, refscan, [ifnum=integer], [intnum=integer], [plnum=integer], [fdnum=integer], [sampler=string], [tau=float], [tsys=float], [ap_eff=float], [smthoff=integer], [units=string], [/eqweight], [tcal=float], [/quiet], [/avgref], [/keepints], [useflag=boolean or string], [skipflag=boolean or string], [siginstance=integer], [sigfile=string], [sigtimestamp=string], [refinstance=integer], [reffile=string], [reftimestamp=string], [status=variable]

This procedure retrieves a pair of total power scans and calibrates the spectrum.

The signal and reference scans are identified separately and do not need to be associated in a single observing procedure. This procedure can be used as a template for the user who may wish to develop more tailored calibration schemes. The spectrum is calibrated in Ta (K) by default. Other recognized units are Ta* and Jy.

Summary

• Data are selected for the two scans using sigscan, refscan, ifnum, intnum, plnum and fdnum or, alternatively, sampler and intnum if you know the specific sampler name (e.g. "A10"). The same sampler name is used for both sigscan and refscan.
• If the avgref option is not set (the default) and both scans have the same number of integrations, then individual integrations are processed separately. The same integration number in sigscan and refscan are processed together. If the avgref option is set or both scans do not have the same number of integrations then the total power value from each integration in refscan is found using dototalpower and the individual integrations are averaged together to produce one reference spectrum that is used for each integration of sigscan. Each integration is processed using dofullsigref If there is no cal switching (TPnoCal) then there is no attempt to determine TCal and the sig and ref values are used as is.
• The integrations are calibrated in Ta (K) by default. If units of Ta* or Jy are requested via the units keyword, then dcsetunits is used to convert to the desired units.
• Averaging of individual integrations is then done using dcaccum. By default, integrations are weighted as described in dcaccum. If the eqweight keyword is set, then integrations are averaged with an equal weight.
• The final average is left in the primary data container (buffer 0), and a summary line is printed. The printing of the summary line can be suppressed by setting the quiet keyword.
• The individual integration results can be saved to the currently opened output file by setting the keepints keyword. The final average is still produced in that case.

Parameters

Arguments for sig and ref scan numbers are required. 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.

If ifnum, fdnum, or plnum are not supplied then the lowest values for each of those where data exists (all combinations may not have data) will be used, using any user-supplied values. The value of ifnum is determined first, followed by fdnum and finally plnum. If a combination with data can not be found then showiftab is used to show the user what the set of valid combinations are. The summary line includes the ifnum, fdnum, and plnum used.

Tsys and Available Units

The procedure calculates Tsys based on the Tcal values and the data in the reference scan. The user can override this calculation by entering a zenith system temperature. The procedure will then correct the user-supplied Tsys for the observed elevation of the reference scan. If the data are calibrated to Ta* or Jy, 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 are provided. The user can also supply a mean tcal using the tcal keyword. That will override the tcal found in the data.

Smoothing the Reference Spectra

A parameter called smthoff can be used to smooth the reference spectrum prior to calibration of each integration. 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.

Weighting of Integrations in Scan Average

By default, the averaging of integrations is weighted using tsys, exposure, and frequency_resolution as described in the dcaccum documentation. To give all integrations equal weight instead of the default weighting based on Tsys, use the /eqweight keyword. This same weighting is used when averaging the reference scans if the avgref option is on or there are different numbers of integrations in each scan.

Using or Ignoring Flags

Flags (set via flag) can be selectively applied or ignored using the useflag and skipflag keywords. Only one of those two keywords can be used at a time (it is an error to use both at the same time). Both can be either a boolean (/useflag or /skipflag) or an array of strings. The default is /useflag, meaning that all flag rules that have been previously set are applied when the data is fetched from disk, blanking data as described by each rule. If /skipflag is set, then all of the flag rules associated with this data are ignored and no data will be blanked when fetched from disk (it may still contain blanked values if the actual values in the disk file have already been blanked by some other process). If useflag is a string or array of strings, then only those flag rules having the same idstring value are used to blank the data. If skipflag is a string or array of strings, then all flag rules except those with the same idstring value are used to blank the data.

Dealing With Duplicate Scan Numbers

There are 3 ways to attempt to resolve ambiguities when the same scan number appears in the data source. The instance keyword refers to the element of the returned array of scan_info structures that scan_info returns. So, if scan 23 appears 3 times then instance=1 refers to the second time that scan 23 appears as returned by scan_info. The file keyword is useful if a scan is unique to a specific file and multiple files have been accessed using dirin. If file is specified and instance is also specified, then instance refers to the instance of that scan just within that file (which may be different from its instance within all opened files when dirin is used). The timestamp keyword is another way to resolve ambiguous scan numbers. The timestamp here is a string used essentially as a label by the monitor and control system and is unique to each scan. The format of the timestamp string is "YYYY_MM_DD_HH:MM:SS". When timstamp is given, scan and instance are ignored. If more than one match is found, an error is printed and this procedure will not continue. These are specified independently for each of the two scans (sigscan and refscan).;

Examples

Suppose scans 13 and 14 are a position switched pair and scans 21 and 22 are also a position switched pair. There was a problem with the off or reference scan in 13 and 14 (scan 13 in this example) so you want to use the other reference scan (scan 21) in it's place. Note that as this is currently written, for this to work scan 21 must have the same number of integrations and switching phases as scan 13. If that isn't the case, you may want to look at using the underlying dosigref procedure to work with each integration or an average of all integrations in each scan directly.

   getsigref, 14, 21
   ;
   ; you could do this, uses dosigref directly
   ;
   gettp, 14        ; averages total power of all ints in scan 14
   copy, 0, 10      ; remember for later use
   gettp, 21        ; total power avg in scan 21
   copy, 0, 11
   dosigref, result, !g.s[10], !g.s[11]
   set_data_container, result ; put result into buffer 0
   data_free, result ; delete the pointer in result
 

Uses

accumave accumclear calsummary check_calib_args data_free dcaccum dcscale dcsetunits dofullsigref find_scan_info get_calib_data set_data_container showiftab

Version

$Id$

Parameters
sigscan in, required integer	M&C scan number for the signal scan
refscan in, required integer	M&C scan number for the reference scan

Keywords
ifnum in, optional integer	IF number (starting with 0). Defaults to the lowest value associated with data taking into account any user-supplied values for fdnum, and plnum.
intnum in, optional integer	integration number, defaults to all integrations.
plnum in, optional integer	Polarization number (starting with 0). Defaults to the lowest value with data after determining the values of ifnum and fdnum if not supplied by the user.
fdnum in, optional integer	Feed number. Defaults to the lowest value with data after determining the value of ifnum if not supplied by the user and using any value of plnum supplied by the user.
sampler in, optional string	sampler name, this is an alternative way to specify ifnum,plnum, and fdnum. When sampler name is given, ifnum, plnum, and fdnum must not be given.
tau in, optional float	tau at zenith, if not supplied, it is estimated using get_tau tau is only used when the requested units are other than the default of Ta and when a user-supplied tsys value at zenith is to be used.
tsys in, optional float	tsys at zenith, this is converted to a tsys at the observed elevation. If not suppled, the tsys for each integration is calculated as described elsewhere.
ap_eff in, optional float	aperture efficiency, if not suppled, it is estimated using get_ap_eff ap_eff is only used when the requested units are Jy.
smthoff in, optional integer	smooth factor for reference spectrum, default is no smoothing (1).
units in, optional string	takes the value 'Jy', 'Ta', or 'Ta*', default is Ta.
eqweight in, optional boolean	When set, all integrations are averaged with equal weight (1.0), default is unset.
tcal in, optional float	Cal temperature (K) to use in the Tsys calculation. If not supplied, the mean_tcal value from the header of the cal_off switching phase data in each integration is used. This must be a scalar, vector tcal is not yet supported. The resulting data container will have it's mean_tcal header value set to this keyword when it is set by the user.
quiet in, optional boolean	When set, the normal status message on successful completion is not printed. This will not affect error messages. default is unset.
avgref in, optional boolean (def. unset)	When set, the total power values for the individual integrations in refscan are averaged together using the current weighting option (using Tsys or equal weighting) to produce a single reference spectrum that is then used to calibrate each integration of sigscan. This option will automatically be selected whenever the number of integrations in refscan is not the same as in sigscan.
keepints in, optional boolean	When set, the individual integrations are saved to the current output file (fileout). This is ignored if a specific integration is requested using the intnum keyword. Default is unset.
useflag in, optional boolean or string	Apply all or just some of the flag rules? Default is set.
skipflag in, optional boolean or string	Do not apply any or do not apply a few of the flag rules? Default is unset.
siginstance in, optional integer	Which occurrence of sigscan should be used, default is 0.
sigfile in, optional string	When specified, limit the search for sigscan (and instance) to this specific file, default is all files.
sigtimestamp in, optional string	The M&C timestamp associated with the desired signal scan. When supplied, sigscan and siginstance are ignored.
refinstance in, optional integer	Which occurrence of refscan should be used, default is 0.
reffile in, optional string	When specified, limit the search for refscan (and instance) to this specific file, default is all files.
reftimestamp in, optional string	The M&C timestamp associated with the desired reference scan. When supplied, refscan and refinstance are ignored.
status out, optional variable	An output parameter to indicate whether the procedure finished as expected. A value of 1 means there were no problems, a value of -1 means there were problems with the arguments before any data was processed, and a value of 0 means that some of the individual integrations were processed (and possibly saved to the output file if keepints was set) but there was a problem with the final average and buffer 0 likely contains just the result from the last integration processed. This keyword is primarily of use when using getsigref with another procedure or function.