Ocean Wave Recording Information

MHL uses a variety of instrumentation to collect ocean wave data along the NSW coast in water depths from 2 to 100 metres. Brief descriptions of the instruments follow.

Waverider Buoy

A spherical buoy 0.7 m or 0.9 m in diameter used to measure wave height and period. The buoy is manufactured by the Dutch company, Datawell. The wave motion sensor is an accelerometer which measures the vertical accelerations of the buoy as it moves with the water surface. The accelerations are integrated twice within the buoy and the displacement signal so obtained is transmitted to a nearby shore station.
Waverider buoy

Directional Waverider Buoy

A spherical buoy 0.7 m or 0.9 m in diameter used to measure wave height, period and direction. The buoy is manufactured by the Dutch company, Datawell. The vertical motion of the buoy is measured by an accelerometer mounted in the base of the buoy as it follows the water surface. The horizontal acceleration in two planes is measured by two accelerometers and an on-board compass to provide wave direction information. The Directional Waverider buoy also measures sea surface temperature.
Directional Waverider buoy

Electromagnetic Wave and Tide Monitoring System (EWS)

A linear electromagnetic gauge fixed to a wharf or pile fabricated by MHL to record wave height and period information shallow water locations. The EWS is a co-axial transmission line having a 50 mm diameter perforated copper staff as its outer conductor that is the tuning element of an electronic oscillator. This staff, with the oscillator (electronic head) fixed to its top end, becomes the measuring staff. When immersed in water a sharp change in the electrical impedance of the staff occurs at the water surface. The period of the oscillation is linearly proportional to the length of the un-immersed part of the staff and hence the water surface level can be continuously measured. Water level variations measured by the EWS can also be processed to provide tide level data.
EWS Operation and Specifications

Electromagentic Current Meter

A device which measures current and water pressure variations. If deployed in shallow water, current and pressure data can be converted to wave height, period and direction. Between 1979 to 1989 current meters manufactured by the American companies Marsh McBirney and InterOcean were used to collect wave data in shallow water locations.