Oceanography

Wave buoy

Principle

Implementation and data processing

Application

A wave buoy measures amplitude and possibly direction of waves and swell.
Principle:

  • Buoy on which one accelerometer is installed. More than one accelerometer is requested for directional wave.
  • Vertical acceleration is measured and buoy vertical movements are inferred and recorded.
  • Data are transmitted on line trough a wireless modem to shore for processing.

Mooring of the buoy on a dead weight and mooring line.

Real time data processing trough dedicated software.

This type of equipment although conventional remains very reliable.

Waves amplitudes and tide height measurements.

Real time Utilization :

  • Aid to marine navigation and vessel berthing and mooring.
  • Sea conditions monitoring for worksite supervision.


Exemple of wave buoy utilisation

Context

This autonomous buoy for oceanographic data measurements has been provided for collecting and sharing in real time environmental conditions in marine environment. The pilot of offshore oil production sites performing the vessel mooring to a Single Point Mooring buoy system (SPM) can obtain decision making help in re time for tanker approach.

Book of specifications

Requested measures:

  • Wave parameters: Significant height, wave direction and period.
  • Surface current: Speed and direction.

Conditions:

  • Rela time data.
  • Water depth around 50 meters.
  • Receiving station located at 4 km.
  • Monsson duration of 6 months. Maintenance is not achievable during this cyclonic period.
  • Survival conditions for design: Hs 11.4m, Tp 14.6 sec, Hmax 18.2m, wind speed 13.4 m/s, surface current 2 m/s.

Technical solution

A wave buoy composed of :

  • 3 axis accelerometer.
  • Doppler current meter.
  • GPS system.
  • Radio system – 50 km range.
  • Light signalling device
  • Electronic cabinet with data logger
  • Batteries for 16 month autonomy

The buoy mooring is designed for allowing the buoy to follow the waves.

For avoiding the possibly data lost due to radio transmission, the measures are also recorded locally on the buoy.

The buoy position is sent in order being monitored after the cyclone’s arrival.

Result

Measured data:

  • Speed and direction of surface current.
  • Waves significant height.
  • Period and direction of the peak values of the waves.
  • Waves average period.
  • Height and direction of the waves crest.
  • Spectral decomposition.

The current’s data are received with 10 minutes interval and the wave’s data are received with 30 minutes interval.

Surface current - receiving station