OBSEA, a permanent underwater cabled seabed observatory located in front of the
Catalan’s coast near Barcelona, at 20 m depth is used as a test site for
different experiments related with marine sensors.
The first EGIM prototype was tested in the OBSEA infrastructure for four months.
Here you can find the data obtained.
From CTD and Oxygen meter
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 range.
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.