Sea Technology

OCT 2013

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Sea & Sun Marine Tech Finnish Coast Guard surface rescue swimmer preparing the foat for helicopter recovery. (Photo Credit: Petra Roiha, FMI) deep, with a level bottom. The goal of this test was to establish the amount of overshooting the foat does before it settles to its designated dive depth. Since the diving algorithm of the foat is designed for the oceans, it is generally too slow for shallow sea areas where the bottom is relatively close to chosen dive depths. For the test dive, the foat was equipped with an external micrologger manufactured by Star-Oddi (Gardabaer, Iceland) with a high sampling rate (15-second interval) for measuring the depth of the foat. Thus, the dive profle of the foat could be reconstructed after the foat was recovered. The test showed that the amount of overshooting is not a problem for the foat operations as long as the initial density feld of the water mass is known, at least to some extent. Based on these test results it was decided to deploy one foat for a longer mission in 2012. The other foat was to be used for frmware development. Long-Term Deployment In May 2012, after a fnal, short 24-hour test from RV Aranda, the foat was deployed for a longer mission. The specifc sea area chosen for the mission was the Bothnian Sea, which is the southern part of the Gulf of Bothnia. The optimistic goal was to keep it in water until September, but there was a concern that it would drift to shore much earlier. However, it turned out that the foat exceeded all the expectations, operating fawlessly until December, when it was recovered by a Finnish Coast Guard search and rescue helicopter. Even though the foat was completely free of biofouling, it was decided to ship it to the manufacturer for service. For example, the piston position mechanism will be checked for any mechanical issues. This check is necessary because the foat performed many more cycles during its mission than foats normally encounter during their use in oceanic environments. CTD recalibration is needed as well to fnd out the sensor drift during the mission. Data and Results During its mission, the foat transmitted more than 200 daily vertical CTD profles to FMI. By combining individual CTD profles, a time series can be created. This allows researchers to view seasonal changes in the water mass; for example, the evolution of the surface mixed layer can easily be followed. All the data were made available to the public in the international Argo database. By analyzing the drift of the foat, the current speed and direction at the drift depth can be studied. During the summertime, the currents were weak, but in the fall, with stronger winds and mixed water mass, the currents increased considerably. The longest daily distance the foat drifted was more than 20 kilometers. The drift trajectory followed quite closely the isobaths in the slope area of the deep basin. Thus, there seemed to be little water exchange between the open sea and the coastal region, at least in the deeper layers. In the middle of the basin, the drift path was more variable. Modifcation of the Diving Algorithm Some foat frmware development has also taken place during the project. Since the diving control algorithm of the Argo foat was developed for deep oceans, it is generally too slow for the shallow Baltic Sea. Therefore, a joint development project with Aalto University was carried out with the aim of modifying the APEX foat frmware and thus enabling it to settle to the target dive depth quicker. The algowww.sea-technology.com HDCS11 HIGH DEFINITION 2D LIVESTREAMING CAMERA: • Up to 6000 m depth • Records locally in FullHD • Livestreaming via Ethernet interface • Selectable video streaming resolution and bandwidth for live video streaming • Remote controlled COMING SOON 3D CAMERA: Additionally features: • Records locally 3D FullHD (2x1080p) • 3D livestreaming via ethernet interface • Free selectable output resolution and bandwidth Perfect in combination with our telemetry system Sea & Sun Marine Tech is member of Sea & Sun Technology Sea & Sun Technology GmbH Arndtstrasse 9–13 24610 Trappenkamp / Germany email@sea-sun-tech.com www.sea-sun-tech.com October 2013 / st 43

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