Information on directional ocean wave spectrum is important not only for the earth environment but also for ocean-ship-engineering field and for their operation. Artificial satellite can detect averaged wave field, but continuous measurement of the specified sea area following to the specified ship movement is difficult. The authors tried to develop the estimating method of directional ocean wave spectra utilizing the conventional marine radar on board. The main information from the PPI (Plane Position Indicator) image of marine radar are the relative energy distribution of the waves propagating each direction and wave number, but the estimation of wave heights are difficult. For the estimation of significant wave height, we developed new method utilizing the numerical simulation other than from S/N(Signal to Noise) ratio method. For improving the robustness of such kind of measurement system we used the estimating method from ship motions simultaneously. The field tests were carried out and the reliability of estimating method of directional ocean waves especially wave heights was confirmed.
Wave information is very important both on the earth environment and the safety ships/floating structures operation and its design. Visual observation has long history, but visual observation of wave length or period and direction are not so reliable comparing to the wave height. At the same time, visual observation is impossible at the night without moon light. The most reliable method will be the measurement by wave buoy, but the moored buoy cannot show the waves along the moving ship. In recent days, numerical wave forecasting technique became more reliable than the past but there are some limitation in its resolution by the mesh size. So, the most reliable and accurate information of encounter wave will be that measured on board of the running ship or floating structure.