Monday, 31 August 2009

Day 20 – 26th August

Well after a lot of hard work we successfully re-deployed the three moorings we recovered yesterday. It was not easy and both Humfrey and Joe were up to the early hours of the morning working to upload new software and construct the new anchors. Analysis of the data recovered from the last two years showed that the strong currents in the strait had shifted the orientation of the ADCPs at some point during their deployment. As I have mentioned before, this is not a problem in the low latitudes as a flux gate compass is installed with the ADCP to help correct the change. However up here, where the magnetic north pole is only a stones throw to the NE of us, the earths magnetic field is pretty much perpendicular rather than parallel to the earths surface, making flux gate compasses pretty much useless. This means any shift in the ADCPs orientation during the deployment makes the data analysis more complicated. Because of this the new anchors were particularly chunky, weighing in at 2700 lbs – that’s just over a metric ton!

Unfortunately we had no further luck with the lost mooring today. It appeared that what we thought was the lost mooring talking yesterday was in fact interference from one of the other acoustic releases. I spent quite a time in the morning, with Ron and Humfrey repeatedly pinging/ranging the releases as we drifted with the tide, but we heard nothing back. This is not surprising as during the four years the releases could easily have run out of battery, been damaged and leaked water or simply moved out of range of our transponder by the current.

I also unfortunately had a massive problem with the data I had analysed and loaded into ODV. Somehow as I tried to delete a single station that had some errors in it, I either clicked the wrong button or ODV decided that it would actually delete the whole collection without asking me if I was sure. Now this shouldn’t be a problem as of course any sensible person would have a backup copy. However, for some reason even unbeknown to me, I did not have a back up copy, so was left with the prospect of having to do it all again – I would guess at about a days solid work. Fortunately, the ships electronics officer managed to find a data recovery utility which was able to get back about 75% of the data. Phew!! I got away with it this time, but I have certainly learnt my lesson.

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