Environment and Resource Management

Waverider buoys

The Queensland department uses a number of Waverider buoys to measure the heights of waves at sea along the Queensland coast. As a buoy is raised by each passing wave, its vertical acceleration is measured and processed. Two (2) types of buoy - directional and non-directional - send data to a receiver onshore. Directional buoys send wave height and direction data in bursts. Non-directional buoys send wave data continuously.

The receiver is linked to a computer that stores, analyses and summarises the data. Each day a central computer automatically accesses the linked computer, downloads and stores the data. The linked computer can also be accessed at any time to view wave height and direction.

The department staff use this information to monitor the type and variability of wave conditions.

How the data is used

Wave data is collected, stored and analysed by the department to help short-term and long-term investigations of natural coastal processes including accretion and erosion.

When a cyclone is approaching the coast, Environmental Protection Agency officers provide advice to the State Counter Disaster Organisation on the potential impact of waves on coastal communities.

Maritime organisations use wave data to plan port activities and to support navigational information.

Wave recording

The department's wave recording program uses one of two systems to measure wave data:

The Waverider system uses a Waverider buoy to determine the sea surface fluctuations at an offshore location. Directional and non-directional buoys are in operation.

Directional and non-directional Waverider buoys measure vertical acceleration by means of an accelerometer. The accelerometer is mounted on a gravity-stabilised platform that is suspended in a fluid-filled plastic sphere. The sphere is located at the base of the buoy. This data is then processed to give vertical displacement (Wave height). (See Glossary for technical details.)

The directional buoy measures horizontal acceleration using two accelerometers and an onboard compass to give the directional displacement in two horizontal axes. With this information, the north-south and east-west directions are calculated. The water level and directional data are then transmitted to the shore station as a high-frequency radio signal.

Station configuration

The original configuration of wave stations consisted of a WAREP mark II Waverider receiver coupled to an ANMA analogue recorder. This equipment was upgraded to a WAREP mark II Waverider receiver and a DIMA digitiser/recorder. In both systems, the WAREP receiver controlled the timing of data recording and provided a paper chart of the water level signal. Wave data were recorded by the ANMA and DIMA units in 20-minute bursts and digitised at 0.5 second intervals (2.0Hz). The data were recorded on digital cassettes and, along with the paper charts, transferred to the Brisbane office for processing.

From November 1991, the wave recording system was upgraded to a personal computer (PC) based system utilising the Waverider receiver/digitiser. The water level data, digitised at 0.39 second intervals (2.56Hz), is recorded in bursts of 4096 points (approximately 26 minutes) and recorded on the hard disk of the PC.

The software running on the PC controls the timing of data recording and processes the data in 'near real time' to provide a set of standard sea-state parameters and spectra that can be accessed remotely via the public telephone network. Recorded data and analysis results are downloaded daily to a central computer system in Brisbane for checking, further processing and archiving.

Laboratory calibration checks

Waverider buoys used by the Agency are calibrated before deployment and also after recovery. Normally, a buoy is calibrated every 12 months. Calibration is performed at the department's Queensland Government Hydraulics Laboratory using a buoy calibrator to simulate sinusoidal waves with amplitudes of either 2m or 2.8m, depending on whether a 0.7m or 0.9m diameter buoy is involved.

The wheels are electrically controlled and the frequency can be varied from 0.016-0.25Hz. It is usual to check three frequencies during a calibration. During the calibration procedure, the following characteristics of the buoy are also checked:

Available wave data

Latest permanent site wave plots - updated 3 times daily. Plots are generated after each download at 2am, 9am and 3pm.

Last updated: 16 October 2008

Wave Monitoring

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