Wiping away the biofouling

I was offshore at the end of January on the Cefas Endeavour as part of our annual nutrient baseline survey and SmartBuoy maintenance trip. It was a pretty crazy trip due to extreme weather, but we managed to be fairly productive before we had to make port.

The Cefas SmartBuoys are a network of floating platforms fitted with sensors and data loggers. Primarily they are for eutrophication monitoring but they collect data which is used for much more.
We have two buoys and two sets of instruments for each SmartBuoy site, and during a maintenance trip we swap the current buoy with a fresh one.
Typically at sites around the UK, with our productive seas we have to swap the buoys out fairly often due to biofouling: the accumulation of marine plants and animals which stop the sensors working correctly.
The buoys closest to shore are most affected, so much so that when things are really growing we may only get two weeks of good chlorophyll data from the Warp and Liverpool Bay sites.

biofouled wms2
A heavily fouled WMS2 water sampler system.

However on the 22nd of January we swapped over the Dowsing SmartBuoy which had been in since early October 2013.
This has served as our first successful demonstration of some new anti-biofouling tools I’ve been testing over the last 18 months.
The main tool being mechanical brushes which keep the optical surfaces of the sensors clear.
As you can see from the photos below, the brushes work well at keeping the sensors clean. They are also not damaged by the wiping action. This is particularly important for the oxygen sensors which have a thin permeable membrane rather than a hard quartz glass.

Sorry for the slightly blurry image, the boat was moving quite rapidly and I was trying not to hit my face against the toroid.

All the buoys we are deploying on this trip are now fitted with these brushes, together with some strategically placed copper tape to discourage growth in key areas. This should more than double the time each buoy can spend in the water gathering good data.
Good environmental data is vital for monitoring the health of our seas and the SmartBuoy data is used for validating biogeochemical models, truthing satellite imagery and as a comprehensive dataset in it’s own right.

Below is an example of how biofouling can affect marine sensors.
Here we have the optical backscatter measurements from the Dowsing site. The orange lines show you the data from the standard sensor, while the blue, and then the red lines show the true values revealed by the wiper fitted sensors. The numbers are arbitrary relative units so I’ve cropped off the y axis. What is interesting is while the fouling signal seen in the first deployment is obviously wrong and would be removed by an reasonable quality assurance, the second deployment returns to a reasonable level before end of the year. Without the clean sensor it would be difficult to detect this fouling without a high level of understanding for your particular region.

Near real-time data from the SmartBuoys is publicly available and can be found here

Examples of some of the science done with the Cefas SmartBuoy data can be found here and here


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