Oceanographic and Geophysical Surveys

The Ocean Floor Mapping System Using Sea Beam
Sea Floor Seismic Reflection Soundings (Generation of a Local Velocity Model)
Seismic Monitoring (The Generation of a Regional Velocity Model)
Seismic Activity and Monitoring within the Kos - Yali - Nisyros - Tilos Volcanic Field
Gravity and magnetic surveys within the Kos - Yali - Nisyros - Tilos volcanic field
The GPS network

The Ocean Floor Mapping System Using Sea Beam

Detailed investigations of the regional bathymetry (Fig. 5) and of the sub-seafloor structures serve as the basis for the understanding of the neotectonics and of the Quaternary to historical volcanic activity. They include the spatial distribution of all eruption centres, the sea floor topography, and all structural and tectonic features.

Fig. 5 Three-dimensional perspective diagram of the new bathymetry and morphology of the Kos-Yali-Nisyros-Tilos volcanic field with Nisyros volcanic island featured in the centre, viewed from south. 50 m contour lines are indicated. Data derived from a combination of surveys by SeaBeam 1180 and 2120. National Centre for Marine Research NCMR, Hellenikon)
(Click on image to enlarge).

The "ocean floor mapping system" (Figs. 5, 6, and 7) consists principally of two essential units: the deep-water unit and the shallow water unit. Four main auxiliary sensors on board and the relevant peripherals for data storage, post-processing and presentation accompany these units.

The deep-water unit is a 20 kHz SeaBeam 2120 hull-mounted system, accompanied with the relevant peripherals for processing and displaying the data. The shallow water unit is a completely independent portable system based on a SeaBeam 1180 high frequency (180 kHz) multibeam system.

Deep water unit - SeaBeam 2120

SeaBeam 2120 is a new swath system that has been specifically designed to accommodate users with survey requirements exceeding 6,000 m water depth, accomplishing a satisfactory resolution (up to 10 x 10 m ) without mounting a very large array (Fig. 5). The first installation of this type with a 1.80 beam width was completed during 2000 on board the AEGAEO.

Fig. 6 Performance of the SeaBeam 1180 system
(Click on image to enlarge).

Shallow water unit - SeaBeam 1180

SeaBeam 1180 (180 kHz) is a portable, compact shallow water multibeam bathymetric survey sonar system integrating transmitter, receiver, interfaces and power stage within a single unit.

The high operating frequency of 180 kHz in conjunction with special small size transducers offers two advantages, high coverage and narrow beam width. SeaBeam 1180 consists of two transducers mounted on a special pole in a V-shaped orientation, one facing to port and the other to starboard (Fig. 6).

The system can function within depths ranging from 1.0 to 600 meters with a wide angular coverage (Fig. 7). The horizontal coverage varies from 8 times water depth down to a depth of 110 m, 3.4 times water depth down to 240 m and 2 times water depth down to 430 m.

Fig. 7 Three-dimensional perspective diagram of the new bathymetry and morphology of Nisyros volcanic island and neighbouring islets, viewed from the south. 50 m contour lines indicated
(Click on image to enlarge).

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