Thursday 8 August 2013

The repair in the data

Over the last few days, we've been reporting on the damage and repair work to KAIRA LBA aerial L17. This story started with the data and so that's how we'll end it. The image for today is the data trace from the day of the repair. Yes, the data acquisition was running throughout this time, so it is possible to see (in the radio spectrum) the repair taking place.

If you look carefully, you can see distortions in the data in data after the point when the aerial was re-erected. This was due me being right next to the aerial during that time as I attached the nylon line and O-ring and then did up the knots and attach the cable ties. In total the whole process took about 5 minutes... excluding the time before re-righting the aerial, as I prepared the various items.

What this does show, though, is that people walking around the aerials do make a difference! Thus wandering on to the field during observations is not without consequence.

However, more significantly for us is that the discovery and repair were made on the 1st August... over a month since the aerial fell. Of course one aerial in 48 is not going to be a dramatic effect in the beamformed data, which is what we normally look at, but still it is a concern that we didn't notice this earlier.

While there are some procedures that exist for the main LOFAR network to test data integrity, they are not really suitable for the operations at KAIRA. However, we are now devising some new software to allow us to easily and automatically monitor the individual RCU data and thus hopefully detect such problems if they occur in the future.

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