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  • Deployed diving buoy, German research vessel “Elisabeth Mann Borgese“ [Image: Michael Naumann, IOW].

BGC-Argo Floats deployed in the Baltic Sea

The ICBM research group Marine Sensorsystems is currently testing four diving buoys for biogeochemical („BGC“) measurements, so-called BGC Argo floats, in the Baltic. The floats were deployed in tight collaboration with the Leibniz Institute for Baltic Sea Research Warnemünde from aboard RV “Elisabeth Mann Borgese“ to the Gotland Deep, about 280 kilometres north of Kaliningrad.

Comparison of novel light sensors and conventional systems
The ICBM research group Marine Sensorsystems is currently testing four diving buoys for biogeochemical („BGC“) measurements, so-called BGC Argo floats, in the Baltic. The floats were deployed in tight collaboration with the Leibniz Institute for Baltic Sea Research Warnemünde from aboard RV “Elisabeth Mann Borgese“ to the Gotland Deep, about 280 kilometres north of Kaliningrad.

The Argo measuring robots automatically dive to preassigned depths, collecting measuring data while rising up to the surface, and eventually radioing their data and positions to the scientific community via satellite. Within the current series of tests each two of the four BGC floats belong to the projects BGC-Argo-Germany-N and DArgo2025, supported by the German Ministry for Education and Research (BMBF) (as we reported earlier: 1), 2)).

The BGC Argo floats are equipped with so-called radiometers, which in simple terms are kind of a light sensory organ of the buoys. Sensors well established to date are the so-called multichannel radiometers which are able to measure several single wavelengths. Dependent on their design, they are capable of distinguishing, in a manner of speaking, three or four colour shades of the spectral band from violet to blue. The researchers selected this range of colours for it enables them to detect, e.g., microalgae or coloured organic compounds in the water.

Two of the recently deployed diving buoys are equipped with novel RAMSES radiometers of the German enterprise TriOS. Other than their multichannel siblings, they are able to measure the light continuously over a particular range. Therefore, they are called hyperspectral radiometers. The scientists expect them to provide much more comprehensive data, which eventually will help to make even data from space more reliable: ocean observing satellites also measure particular colours of light which are reflected by the ocean surface, this way getting data on what is floating in the seas. Comparison of these data to those of the floats will make the satellite data more precise.

„But beforehand, the RAMSES floats have to prove that they are at least as useful as the conventional four-channel floats, or even better“, says Hendrik Bünger, technical staff member of the resarch group Marine Sensorsystems headed by Prof. Dr Oliver Zielinski. Thus, the four floats have been deployed in two pairs, combining each RAMSES float with a four-channel float, the latter being lowered close by in order to be able to compare the data later on.

On a two-days schedule, the diving-robots will now descend once and again to a parking position at a depth of 40 metres, to sink subsequently to 80 metres and then collect data during ascent.

Further favourable side effects of the current investigation: up to now, floats have been scarcely used in the Baltic due to its shallow depth. Together with diving buoys of other nations, there are 14 floats now in action. They will contribute to getting a more complete data set of this marginal sea. Due to its comparatively small area, the floats can be spotted more easily in the Baltic Sea, which will help to develop more sophisticated recovery routines for the high-priced devices. This will make them even more sustainable in use.

 

(Changed: 2021-04-30)