Hall of dangers

Table of contents

1. LINC output
   1. LINC Calibrator
      1. Bad polalign
   2. LINC Target
      1. 3C295
      2. GalField3
      3. L801462

This page summarises examples of calibration solutions etc. gone wrong for various pipelines. In general the key plots to look at are those of the calibration solutions. Noisy solutions are problematic and can be indiciative of a variety of issues, such as model incompleteness, certain baselines being starved of signal or the ionosphere being wild.

LINC output

LINC Calibrator

LINC Calibrator corrects for systematic effects: an offset between the XX and YY correlations, a bandpass correction and an average clock drift.

Bad polalign

Problems:

• strange wood grain pattern on many core stations
• large spread in values between core stations
• horizontal ripples on CS103 and CS302
• weird banding in CS002
• DE604 and SE607 show no phase structure

LINC Target

LINC Target mainly solves for direction-independent ionospheric effects. The resulting phase solutions should reflect ionospheric behaviour and must therefore appear physical. This means that you expect smooth variations, especially as a function of frequency, that is trackable by eye. If solutions get noisy, discrete or you can no longer see a smooth pattern by eye that are indications of problems and depending on their severity demand further inspection of your data before proceeding to further more complicated pipelines. In general it is useful to think of it as any problem you introduce at a given step being uncorrectable in later steps.

3C295

Extremely bright 3C source that is just resolved on the longest Dutch baselines.

Problems:

• extreme phase wrapping-like behaviour on remote stationsnoisy
• noisy corners on core stations
• certain bad times (vertical noise stripes)
• Poldif plot showing XX-YY displays noise

Causes: TGSS model does not have enough resolution to represent structure seen by the furthest remotes.

GalField3

Galactic plane field with complex, large-scale diffuse emission.

Problems:

• exremely noisy, descretised solutions on many remote stations, basically wiping out any signal
• complex structure core station solutions
• XX-YY polarisation difference extremely noisy

Causes: model incompleteness TGSS model does not contain this scale of diffuse emission.

L801462

Problems:

• wild time fluctuations on core stations, indicative of a wild ionosphere
• extreme phase wrapping-like behaviour on remote stations.

Causes: very bad ionosphere and possible model incompleteness.