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GPS-Based Directional Waverider Achieves One Centimetre Precision up to 100-Second Periods Anywhere in the Ocean
In the field of ocean wave measurement the (directional) Waverider buoy, (D)WR, from Datawell has set the standard, with over 4,000 buoys sold. For over four decades, governmental departments for coastal protection, marine constructors, the oil industry, harbour authorities and oceanographic institutions have relied on these buoys for their wave data.
In the latest version, with the DWR-MkIII featuring three years of continuous operation, the successful stabilised platform is still maintained. With this horizontal platform, one high-precision accelerometer suffices to obtain the wave height, so that the principal wave parameter remains unaffected by other sensor errors.
Datawell is introducing a different wave sensor concept: measuring waves using a single global positioning system (GPS) receiver. Although GPS positioning at sea is common practice in navigation and buoy monitoring, GPS wave measurement is still rare. So far, only differential-GPS (DGPS), requiring an additional GPS reference station on shore, is available for wave measurement. However, because of its first-order atmospheric corrections, DGPS wave buoys are restricted to near-shore applications (circa 10 kilometres). Furthermore, DGPS requires large amounts of data transfer, leaving only short range communication means as a practical solution and reducing the buoy operational life. In contrast, the present single-GPS wave buoy features one and a half years of continuous wave measurement, and even operates on the open ocean.
While experiments on land demonstrate one-centimetre-precision up to 100-second periods, this investigation measures the performance of the new DWR-G buoy at sea. In a unique experiment, the DWR-G is tested directly against the standard of its predecessor by merging the new GPS sensor together with the conventional DWR accelerometer and magnetic compass sensors in a single buoy. Also, the occurrence of infra-gravity waves on the Australian east coast nicely illustrates the performance in the long period wave regime.
Existing Measurement Principles
Essentially, wave sensors fall into two different categories: buoys following the wave orbital motion and fixed-position sea-surface elevation sensors. Pressure gauges and acoustic sounders on the seabed or microwave radars mounted on oil platforms are examples of the latter. The former category exploits linear and angular accelerometers or pitch-roll-meters combined with magnetic field sensors, and more recently DGPS.
On the one...