Naldmann et al. 
The six CTD sensors used in this experiment were mounted 
in 9 m (+/- 1.5m tide) water depth in a metal lander frame 
(Figure 1). The sensors were mounted such that the sensor heads 
with the measuring cells were in the same height of 92 cm (+/- 
5 cm) above the seafloor, perpendicular to the main current 
direction and offset at a horizontal distance of 15 cm to each 
other. This setup ensured that, except for micro turbulences 
below decimeter scale, all sensors were exposed to the same 
water body without disturbing each other. 
The experimental procedure was designed as follows. Prior 
co the deployment, all sensors were registered in the AWI Sensor 
Registry (Registry, 2019) and calibrated in the calibration 
laboratory at Leibniz Institute for Baltic Sea Research, 
Warnemuende (IOW) (see Supplementary Material under 
Appendix 2) to ensure a consistency in the calibration process. 
On June 19, 2020, all six CTD were returned to Helgoland 
Centre for Scientific Diving. Five out of the six CTD’s were 
deployed on July 22, 2020 11:00 hours in the experimental field, 
connected to the node system and the internal data logging 
mode was started. From this day on, the data from all sensors 
were downloaded every workday between 10:00 and 13:00 hours, 
10.3389/fmars.2022.1002153 
if necessary, converted to ASCII data and transferred to the 
AWI-O,A Near-Realtime Database (NRT) (Koppe et al., 2015) 
{o ensure open-access within the group. All measured data and 
additional auxiliary sensor data from the MarGate test field were 
automatically displayed in a real-time dashboard at AWI O2A 
(Dashboard, 2020) so that the sensor and the environmental 
situation could be monitored in near real time throughout the 
experiment. Using the O,A REST API data has been transferred 
’nto the PANGAEA ingest format and prepared for long-term 
archiving and publication at PANGAEA from which the data 
can be accessed (PANGAEA, Database 2020). To gain as much 
information as possible on sensor behavior due to different 
handling like in situ cleaning and the calibration and cleaning 
procedure, the different sensors were individually treated (details 
in Supplementary Material Table A2). This information will be 
also used in a further publication on the evaluation of salinity 
measurements. Sensor 3 and sensor 4 were deployed over the 
entire experiment without any in situ Cleaning or maintenance, 
sensor 1 was regularly cleaned under water with a soft tissue, 
sensor 2 was recovered for lab calibration in the very beginning 
of the experiment, sensor 5 was recovered for lab calibration 
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FIGURE 1 
'n situ images (upper panels A and B) and CAD drawing (lower panel C) with dimensions of the experimental setup of the deployed sensors. 
Jpper left panel: Sensors immediately after deployment, Upper right panel: Sensors three month after deployment with one sensor (second 
"om the riaht side) freshlv lab-calibrated and maintained. For details see text 
Zrontiers in Marine Science 
ırontliersin.org