WACSIS-Wave Crest Sensor Intercomparison Study at the Meetpost Noordwijk measurement platform

Offshore structure design needs a knowledge of ocean wave heights. Most of the uncertainty in air-gap calculations comes from our poor knowledge of the distribution of crest heights. Different wave sensors appear to give different results. In October 1997, the Metocean Committee of the E&P Forum decided to start the first phase of a Joint Industry Project (JIP) named `WACSIS´ (Wave Crest Sensor Intercomparison Study). This phase is dealing with continuous and time synchronised data acquisition of various wave crest sensors during the 1997/1998 storm season at the Dutch Meetpost Noordwijk (MPN) measurement platform. Wave crest sensors involved are Baylor Wave Staff, THORN Wave Height Sensor (an upgrade of the EMI Laser), MAREX SO5 Wave Radar, SAAB Radar, Vlissingen Step Gauge and Marine 300 Step Gauge. A Directional Waverider Buoy, a SMART 800 GPS Buoy and a WAVEC Directional Buoy were deployed for obtaining directional wave information. For current and pressure information, an S4ADW Current Meter was deployed at 10 metres below mean sea level. The wave crest measurements are supported by digitised video frames twice a second. The authors studied problems with regard to the instruments´ response due to implicit filtering, influences of spray and positioning at the platform´s structure can be traced back. The whole data acquisition project for the 1997/1998 storm season effectively started mid December 1997 and ended mid May 1998. Following phases of this project may include a thorough data analysis and another measurement campaign including wave kinematics measurements