Surface ocean waves are commonly de

Surface ocean waves are commonly described by their directional spectrum, which gives the distribution of wave amplitude with frequency and direction. The knowledge of the wave directional spectrum is fundamental for various marine applications (safety at sea, offshore industry, ship design, ship routine, coastal engineering, survey and protection of coastal environment). Furthermore, most of the wave prediction models, which provide forecast of sea state over ocean basins for several days are based on the concept of directional wave spectra. In situ observation systems are developed and used to provide directional wave spectra. These observations can be used to validate or constrain these models. They can also be used as local observations for the various marine applications. Information on surface waves can now also be obtained from remote sensing techniques (mainly radar). The main advantage of this technique is that it provides information on the wave field in regions and over scales, which cannot be covered by in situ instruments. Although remote sensing is very promising, the analysis techniques still need assessment, so that there is a need of coincident in situ measurements.