./guide
getps.pro

Last modification date:

Wed Sep 28 13:27:09 2016

getps

procedure getps, scan, [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], [/keepints], [useflag=boolean or string], [skipflag=boolean or string], [instance=integer], [file=string], [timestamp=string], [status=variable]

Procedure getps retrieves and calibrates a total power, position switched scan pair.

Position switched data are usually taken with the observing procedures "OnOff" or "OffOn". This routine 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 using scan, ifnum, intnum, plnum and fdnum or, alternatively, sampler and intnum if you know the specific sampler name (e.g. "A10"). The other scan in the scan pair is found using scan (see comments below). The same sampler name is used for both scans.
• Individual integrations are processed separately. The same integration number in both the "On" and "Off" scans are processed together. Each integration is processed using dofullsigref.
• The integrations are calibrated in Ta (K). 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 first Tsys displayed is that of the result. This all comes from the "Off" scan integrations. The second Tsys is the weighted average of the Tsys values from the "On" scan integrations.
• 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.
• VEGAS will sometimes record scans of different numbers of integrations even though the setups are the same. If this occurs in an On/Off scan pair then this routine procedes by ignoring the final integration in the longer scan (after first checking that the difference in the number of integrations is one, otherwise an error is reported). This is safe to do, with no loss of data, in all known cases because the extra integration in the longer scan will be a partial integration (missing data from one of the switching states, likely also much shorter than the other integrations). So, that extra integration is unusable.

Parameters

The scan number is a required parameter. Either scan in the sequence of two total power scans can be given, and the paired scan is determined from the header. Arguments to identify the IF number, polarization number and feed number are optional.

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 "Off" 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. If the data are calibrated to Ta* or Jy, additional parameters are used. A zenith opacity (tau) 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. 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.

Summary Information

The scan number printed in the status line is that of the "On" scan followed by the ifnum, fdnum, and plnum used. The first Tsys printed is the tsys of the result (and they come only from the "Off" scan). The second Tsys printed is a weighted average of the Tsys values associated with the "On" 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.

Once a unique match is found to the desired scan (using instance, file, or timestamp) then the scan paired with that scan necessary to finish this procedure is found. The match must be found within the same file as the desired scan. It must have the appropriate matching scan number (scan-1 if scan is the second scan in the procedure or scan+1 if scan is the first scan in the procedure). If those two rules are not sufficient to find a unique match, the matching scan with the closest timestamp in the appropriate direction (before or after depending on which procseqn is associate with scan) is used. Finally, the matched pair must have the appropriate procseqn given the procseqn that scan is.

Examples

    ; average both polarizations from ifnum=1
    sclear
    getps, 76, ifnum=1, plnum=0
    accum
    getps, 76, ifnum=1, plnum=1
    accum
    ave
 

Uses

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

Version

$Id$

Parameters
scan in, required integer	M&C scan number

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 (default=all}, 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, defaults to 1 (no smoothing).
units in, optional string	takes the value 'Jy', 'Ta', or 'Ta*', defaults is Ta.
eqweight in, optional boolean	When set, all integrations are averaged with equal weight (1.0), defaults 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 have any effect on error messages. Default is unset.
keepints in, optional boolean	When set, the individual integrations are saved to the current output file (fileout). This option 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.
instance in, optional integer	Which occurence of this scan should be used. Default is 0.
file in, optional string	When specified, limit the search for this scan (and instance) to this specific file. Default is all files.
timestamp in, optional string	The M&C timestamp associated with the desired scan. When supplied, scan and instance are ignored.
status out, optional variable	An utput 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 getps is called within another procedure or function.