2. Checking Observations & Pipelines

Data quality assessments for completed observations are performed to ensure the observations are acceptable within the LOFAR data policy. Before assessing the observations, ensure the observation cannot be considered failed (the criteria for a failed observation is outlined in the LOFAR data policy). If this is the case, the following assessment can be skipped and the procedure for failed observations described below should be followed. 

The data quality assessment is done using a variety of tools that help assess the data at various stages along the data flow from the station. Most of the diagnostic tools are found on the inspection plot page of the observation here. To check the observations select the SAS ID of the observation for which you wish to inspect. A page will open, containing the following diagnostic information:

• COBALT error log: reports any errors during the processing and recording in the correlator of the data stream.
• Input loss report: reports the data loss from each station (if any).
• Station dynamic spectra: shows the signal power at each station as a function of time and frequency. The core, remote and international station dynamic spectra are shown and can be used to check and report any unusual features in the station behaviour (such as RFI, presence of bright off-axis sources in the station beam and its sidelobes, oscillating tiles, etc.). For a detailed description of different features on individual inspection plots, see the What do I see here? page.
• Visibility amplitudes plots: these are listed under the station dynamic spectra with format eg. SAP000 SB000. Each link shows the visibility amplitudes as a function of time for each individual subbands (frequency). From the displayed plots the behaviour as a function of frequency in the bandwidth of the observation can be checked. The different colour lines you see in the plots are relative to 4 signal combinations xx=dark blue, yy=red, xy=light blue, yx=pink. For an unpolarised source, xy and yx should be zero (within the noise), while xx and yy will contain the signals. Note that these plots are available for interferometric observations only. For a detailed description of the individual inspection plots, select the What do I see here? link.

In case of a failed observation (the criteria for a failed observation is outlined in the LOFAR data policy), the expert-user must mark the failure on the google schedule, notify the SDCO team and report the failure:

• Mark the observation as failed on the google schedule.
• Since the data is automatically ingested by TMSS, notify the SDCO team through the project Jira ticket with the SASID so that they can remove it from the LTA.
• Navigate to the LOFAR Observing Failures form and log the failure.