Changes/atlod

atlod
Item	Complexity	Research	Milestone	Time
Sampler Statistics	easy	none	6	1d
Storage Of SYSCAL Data	moderate	some	6	2*5d
ApplyingXYPhaseCorrections	easy	little	6	5d
Data Size Limits	easy	little	6	2d
FlaggingWithinATLOD - basics	easy	little	6	5d
MoreSelectionOptions?	easy	little	6	5d
IdentifyParentWindow?	moderate	some	8	2*5d
Flagging Within ATLOD - autoflagging	moderate	some	9	4*5d

SYSCAL Record Changes

The SYSCAL records will change from their current form.

SamplerStatistics?

Not present in CABB data; do not execute flagging or "samcorr" code.

StorageOfSYSCALData

AT correlator data format holds 24 scalar values of Tsys (6 antennae * 2 polarizations * 2 IFs) written into every integration, and 12 (6 ant. * 2 IFs) of XYPhase.

CABB data will include autocorrelation for both ON and OFF phases of the switched noise diode.
ATLOD will calculate

Tsys(f) = OFF(f) * Tcal(f) / ( ON(f) - OFF(f) )
for each of the XX and YY polarization products. In the equation above 'f' is the frequency.
Tcal(f) will be included in the RPFITS file once per scan.
ATLOD will also calculate

XYPhase(f) = arg( XYPhase_ON(f) - XYPhase_OFF(f) )
ATLOD will record in the Miriad data TsysXX(f), TsysYY(f) and XYPhase(f). Input option 'noauto' will determine whether autocorrelation spectra are kept.
Deciding what to do here in terms of data representation requires discussions with WarwickWilson?. Making changes here has flow on effects to other tasks that use Tsys or XYPhase.

ApplyingXYPhaseCorrections

ATLOD applies the XYPhase correction, but retains the XYPhase(f) spectrum in the output. A few tasks (eg atxy and varplt ) use these data.

Research needed: The phase values computed on a per channel basis will be noisy, and applying them will just introduce noise. We need to understand how much smoothing across frequency will be needed. Need to do some experiments to understand the sequence of events in reading in a file.
Research needed: Does ATLOD work in a streaming mode?

Data Size Limits

Research needed: check for size limits on the data dimensions - number of windows, channels, etc

Identify Parent Window

Each spectral window output by the correlator can have some ZoomBands? defined. Miriad will keep track of each window's parent window. There will be 0 or 1 parents.

Research needed: Determine whether it is necessary to keep track of the children of a particular band.

Flagging Within ATLOD

atlod does not copy bad data to its output. This makes flagging in ATLOD qualitatively different to other parts of Miriad. Other editing tasks in Miriad set flags in a flag table to mask out bad data.

For CABB data, ATLOD's birdie flagging will change:

• a different set of birdie frequencies (to be determined)
• removal of every second frequency channel will not be needed.

Research needed

• What are the birdie frequencies in the new system?
• Can data be flagged automatically by ATLOD using autocorrelations?? (Could we use algorithms from 'pieflag'?)

More Selection Options

Miriad will need the capability to inspect an RPFITS file in order to determine the identity of the various spectral windows in the file.

MarkCalabretta? wrote the 'rpfhdr' utility which does most of this.

Research needed: How are zoom bands to be represented in the RPFITS data format?

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