OBSEA - Expandable Seafloor Observatory - is an underwater laboratory that offers
the possibility to deploy different types of sensors, communication modules, or
scientific experiments. It allows real-time communication with the shore. It is
placed at 20 m depth in the Balearic Sea (Mediterranean), at 2.16 miles of Vilanova
(Spain). It is used as a shallow-water test site. OBSEA is connected with 4 km of
cable to the coast of Vilanova i la Geltru (Barcelona, Spain) and placed at a depth
of 20 meters in a fishing protected area. Besides, a buoy located at 40m from
OBSEA works as a surface platform for measuring oceanographic and environmental
parameters. The communication between the ground station and the buoy is done via
a wireless 3G connection.
Although the values are highly correlated (correlation factor = 0.986), the values of the
Oxygen meter are always higher than those of the CTD. The highest difference appears on
04/15/2017 at 03:42:34, of 0.809 degrees Celsius. We checked that the values of the CTD are
precise. The reason why the values of the oxygen meter have an offset is unknown but it could be
due to calibration problems of the instrument.
The salinity of the Balearic Sea uses to be between 37 and 38 PSU. The values are in the usual
The typical conductivity of sea waters is 5 S/m. In this
case, all values are close to 5, but below, indicating that the EGIM was situated in a zone
with relativity low electrical conductivity.
On March 15, 2017, on the coast of Vilanova, there was a strong storm caused technical problems.
We had to move the EGIM to a shallower zone next to the original position. In the second
location, the depth was 18.65 meters, and there were maximum tides of approx. 13.8 cm.
A CTD uses Conductivity, Temperature and Pressure sensors to calculate Sound Velocity using any
of a number of well known formulae. For many applications of sonar the speed of sound can be
assumed to be an average speed of 1500 meters per second. However, the speed of sound in
seawater can vary from 1440 to 1570 meters per second. Our values are always in the typical
range of the sound speed of seawater.
From Tsunami meter
Once we transform PSIA to depth, we notice that this sensor is always measuring a higher depth
than the CTD. We do not know the reason. Maybe it's because the sensor is not calibrated.
From Oxygen meter
The dissolved oxygen in the water is stable throughout the measurement period (around 301.58
microMoles / liter). It seems that there have been no significant changes in the population of
oxygen sources (plants, algae, etc.), the exchange of oxygen by currents or sea/air exchanges.
Oxygen saturation is always close to 100%, indicating that no significant increases in oxygen
sources (plants, algae, etc.) have been detected in the measuring period and the water/air
transmission has been reasonably balanced.
From Turbidity meter
The turbidity meter contains a mechanism to clean the optical lens from the creation of
biofouling. However, this mechanism was not activated during the trial period. It is suspected
that these data are incorrect.