Measuring Infra Gravity Waves with an ADCP Wave Gauge
DHI usually deploys Acoustic Doppler Current Profilers (ADCPs) for wave measurements. By measuring orbital velocities in the upper part of the water column, wave parameters may be obtained using the manufacturer’s standard application software.
DHI usually deploys Acoustic Doppler Current Profilers (ADCPs) for wave measurements. By measuring orbital velocities in the upper part of the water column, wave parameters may be obtained using the manufacturer’s standard application software.
This works well in most situations, but if detailed information about very long periodic and very small waves – so called infra-gravity waves - are required, standard manufacturer software is inadequate.
DHI has demonstrated that traditional PUV processing of data collected with an ADCP wave gauge can clearly reveal wave heights and directions of even very small waves (Hs < 0.20 m with a wave periods between 25 seconds and 500 seconds.).
Such waves can be problematic for berthed vessels because their wavelength is of the same order of magnitude as the length of a ship and they may excite resonance in semi-enclosed basins.
During the 2006 monsoon in Oman, DHI collected continuous wave data with two ADCP wave gauges in order to assess origin and direction of the infra-gravity waves. Both gauges were deployed in the coastal region in 15 m of water. Our PUV processing showed infra-gravity waves with a peak period of 133 seconds and a peak direction away from the coast. This could indicate that the infra-gravity waves are generated by sea and swell in the breaking zone along the coast thereby releasing energy back out to sea.
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