The advent of the differential global positioning system (DGPS) on-the-fly (OTF) and post-processing software has meant that physical positions can be determined with an accuracy of less than a decimeter. Post-processing for wave analysis is acceptable because data have to be captured over a 17-minute period before any analysis can take place.

With these aspects in mind, the CSIR performed tests with a GPS carrier-phase receiver mounted on a wave buoy that was swung on a dynamic calibrator. Vertical movement of the buoy, as recorded from GPS was plotted against the actual sinusoidal locus of the buoy. The recorded positions were very accurate and within 2 centimetres of the actual path of the buoy.

The accuracy of the direction in which the the buoy was swinging was excellent. When compared to existing directional wave systems, which are accurate to within 10 degrees of direction, the GPS has a clear advantage.

Provided a reference station can be established within 30 kilometres of the wave buoy, the differential GPS with OTF software proves to be excellent technology for the measurement of ocean waves (including wave directions) and tidal changes.

The Wavemonitor is a rugged, reliable wave measuring buoy developed from experience gained from over 25 years of wave measurement in the notoriously extreme ocean environment off the southern African coast. It has been thoroughly tested and satisfactorily compared to other commercially available wave buoys.

Sea surface displacement with time is derived from the displacement obtained through double-integrating the vertical acceleration of the buoy. The buoy features an inertially stabilised accelerometer transducer which is insensitive to either horizontal or rotational movement. The wave data are transmitted to a Wavelogger shore station by means of HF radio.

• Rugged design capable of withstanding severe spinning, rolling and impacts
• Modular design with easy access to components through the top cover for servicing and replacement
• Inexpensive battery replacement making use of alkaline cells, which reduces servicing costs
• High measurement resolution and accuracy
• Compatible with other high frequency radio telemetry systems
• Low current consumption providing long deployment intervals between battery replacement

• SYSTEM:
• Wave height range: 20m
• Resolution: 9mm
• Frequency response: 0,04 to 5Hz
• Damping factor: 0,707
• Sensitivity to horizontal acceleration: < 2%
• Non-linearity and hysteresis: 1% of span
• MECHANICAL:
• Mass: 95kg
• Dimension: 720mm diameter sphere
• Hull material: Stainless steel 316
• BATTERIES:
• Battery life: > 7 months
• Quantity: 2 Packs per buoy
• Potential: 22V
• Pack configuration: 60 Alkaline "D" cells
• Capacity: 80Ah/buoy

The CSIR makes use of Datawell's Directional Waverider Mark II, Directional Waverider MKIII, Directional Waverider DWR4, as well as the non-directional Waverider SG buoys to measure waves.

Datawell has a history of over 40 years in the oceanographic instrumentation arena, and their wave height measuring buoys have been the world standard during this period. Their buoys are accurate and have well-proven stabilized platform sensors. They have, for example, standard integrated data loggers, flash cards that store up to 2 Gbyte of measured data, standard GPS position monitoring, and a HF link for ranges up to 50 km.

The CSIR makes use of ADCP's manufactured by Teledyne RD Instruments.  The 300 kHz Workhorse Monitor ADCP is used for current measurements, and the 600kHz Workhorse Monitor ADCP is used for both wave and current measurments.