For Lars Henrik and Harald‘s GEOF105 class we are deploying home-made surface drifters on the student cruise. Today I had the opportunity to join the cruise again, and since the weather today made for beautiful pictures, I just have to share them here.
First, at the end of every rainbow, as we all know, you’ll find … home-made surface drifters!
Inga and Algot getting the drifters ready for deployment
The research ship we are on is the Hans Brattstrøm — cosy ship with a super nice and helpful crew!
We are sailing on RV Hans Brattstrøm
The drifters themselves are equipped with a sea anchor made from a plastic bucket and four paint roller trays underneath a buoy, and then on top all kinds of equipment to make sure nobody runs over it: A safety flag, a lamp, a radar reflector. And, of course, the GPS sender!
Isn’t it cool how those wave rings radiate from our drifter?
What we are using those surface drifters for? To determine the circulation in the fjord right outside Bergen. There are several things that might have an influence: Tides, wind, freshwater runoff from the land… And a tilted sea surface (although it is probably not as tilted as in the picture below…)
Drifter in front of RV Hans Brattstrøm in front of mountains covered in clouds
Another amazing day “at sea”, thanks for having me along, Lars Henrik!
A bicycle safety flag, a plastic bucket, four paint roller trays — what are those people doing there?! Until now this might almost count as kitchen oceanography!
Home-made surface drifters
But it’s only almost kitchen oceanography; at least my kitchen isn’t usually stocked with GPS trackers, which is what is mounted on this contraption. Let alone the research ship we used to deploy it. So this must surely count as real oceanography then!
Lars Henrik and students deploying a surface drifter to measure the surface current in a fjord
Above, you see Lars Henrik and his students deploying a surface drifter. The red buoy keeps it floating at the surface, the chain hanging below is heavy enough to make sure it stays upright. The bucket and four paint roller trays act as sea anchor so the whole thing moves with the water rather than being blown about by the wind. A safety flag, radar reflector and light make sure nobody accidentally sails over it, and the GPS sender lets the position be tracked.
For example like this:
Screen shot of the map and the drifter positions from my mobile phone
Above, you see what it looked like when we had already deployed three of our four surface drifters (the red ones that are moving so slowly that the software tells us they aren’t moving at all), while the fourth one is still onboard the ship, moving to the position where it will be deployed (the green one moving at 3km/h).
Follow their positions on your mobile device!
Following surface drifters’ paths in real time is pretty awesome in itself, but what makes it even better is that the GPS positions can be accessed online from any device. Below, for example, you see the positions on my phone with the drifters behind it in the water (if you look really closely, that is. But they were there!).
My mobile phone with the drifters’ positions and the drifters in the background
What you also see is that three of the drifters have huddled together after a couple of hours out in the fjord. Nobody really knows why yet, but that’s what we are here to find out!
Just from observing the wind and the movement of the drifters throughout the day, it seemed that the surface circulation in this fjord is dominated by the wind over the tides. But there will be a Master’s thesis written on the data we collected today (plus a lot more data and a regional ocean model!) so we’ll soon know how good my assumptions are and what really drives the surface currents here.
Three of the drifters huddling together due to currents that have yet to be understood
Come time to recover the drifters, the weather wasn’t quite as nice as earlier throughout the day. Just to give you an impression of the conditions under which the drifters were recovered:
Algot and Inga recovering a drifter
Yep, if you look at the sea state, there is nothing to complain about, really, just a little water coming from the sky! But it was cold water… ;-)
And everything got recovered safely and made it back to port — ready to be deployed again tomorrow to gather more data and understand the fjord a little better. Exciting times! Thanks for letting me be part of this GEOF105 adventure, Lars Henrik!
I’m sure I’ve talked about stream lines and streak lines and all the other kinds of lines that you learn about in hydrodynamics at some point. The other day I saw a very nice (and slightly disgusting) example of trajectories.
Trajectories of ducks
The ducks paddling in muddy waters left distinct trajectories of where they had been. Additionally there was some flow, so the ducks as well as their trajectories were advected with the flow. Very interesting to watch!