model inversion’ step, and an ‘extrapolation’ in time and location to the point where waves were to be predicted. The process is continuous. Data from each new step is added to the previous dataset, while older data is discarded.

Two validation campaigns The system was verified in two validation campaigns. The first was done from a stationary location at Scheveningen Pier in the Netherlands. These recordings already showed good results for individual wave crests but could not be compared to a theoretical wave model because of complicated behaviour of waves shoaling and breaking in the surf zone.

Open water tests were then done on board Royal Netherlands Navy Zr. Ms. Karel Doorman

off the coast of IJmuiden around a permanently moored wave rider buoy. Tested conditions included zero-, five- and ten-knot speeds in up and downwind directions. Comparisons between the results of the FMCW system, the wave rider buoy, on board down looking radars and stereo photographic data confirmed the ability of both the FMCW and the stereo photographic systems to capture remote wave elevation maps deterministically. The results clearly showed the proper handling of signal to noise ratio and shadowing at longer ranges. The wave inversion and wave propagation models dealt with the data gaps by relying on the clear crests around them.

Operational efficiency Longer range radar observations made it possible to capture waves inside the propagation window and

predict them some distance outside of it. The short-range stereo imagery approach was found to be accurate only inside the observation window. The accuracy of the extrapolated, wave model typically relies on the extent of the observed data in time and space. A long observation period in a short range can provide good statistics and spectra. A wide spatial window is also needed to provide enough information for a wave propagation model.

The new DoIT JIP combines FMCW radar concepts with proven wave sensing techno logy in a prototype system. The objectives are to implement deterministic wave feed forward for offshore operations and short range ride control for small craft. Having the ability to anticipate wave trains will ultimately help make operations more efficient.

report 19

Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28