The IONIAN System – the marine survey (2)

In the previous post we learned about the methods and devices used for the different stages of the survey (in-shore, shallow waters, deep waters), here we discuss the functionality of the different devices and we see some examples of the information and measurements they have generated during the survey of the IONIAN route.


Figure 11 is a bathymetric view produced by the Multi-Beam Echo Sounder (MBES) showing a channel that crosses the survey route close to the Greek coast. Variations in sea-floor relief are depicted with color and contour lines called depth contours or isobaths. Figure 12 shows a profile view along the survey route (yellow line in figure 11) where the channel is very pronounced. Figure 13 is a profile view 350m South of the survey route (red line in figure 11) that avoids the channel and reduces the slope: we should rather modify the cable route and cross the channel close to the red line to avoid this type of irregularity and avoid potential suspensions.

Figure 11 – Preveza shallow water MBES view
Figure 12 - Profile view corresponding to the yellow line on Figure 11
Figure 13 - Profile view corresponding to the red line on figure 11

The Sub Bottom Profiler (SBP) provides information on the general geological stratigraphy around the route and is the main source of information for the burial feasibility study in shallow waters. Figure 19 shows typical sediment profiles obtained from the SBP found along the route in the shallow waters near Crotone. Note that the Y axis on these figures represents the distance from the SBP towfish (the sharp peaks on the profile are due to the change of altitude of the towfish, not to actual seabed slopes).

Figure 14 - SBP Sediment profile - Shallow waters near Crotone

The Side Scan Sonar (SSS) sweeps the seafloor from directly under the towfish to either side, typically to a distance of 100 meters. The image generated is continuously recorded, creating a “picture” of the ocean bottom. Figure 15 shows the image with an uncharted wreck of about 60m length that was found near the Greek coast, located at approximately 320m North of the cable route. Other objects are detected by the SSS such as rocks, pipelines, cables.

Figure 15 – SSS image showing a Ship Wreck 320 meters North of IONIAN’s route. Location (left) and detailed image of the wreck (right)

Figure 16 shows a sample of the seabed soil obtained by Gravity coring

Figure 16 - Gravity core samples allow to study the nature of the top layer (3 m) of the seabed