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A new water level measuring system, using laser rangefinder sensor with phase method as laser water level sensor without cooperative target is presented. The laboratory and field experiments have been done to confirm the application field and measuring accuracy of system. The results show that the measuring accuracy could reach to ±1.5 mm in calm water in case that water turbidity value is greater than 300 NTU. Furthermore, the measuring accuracy can reach to ±3mm for the measuring period taking 5 minute in case of the water surface sloshing. The maximum measuring distance of system could reach to 12m.

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The wave crest is an important factor for the design of both fixed and floating marine structures. Wave crest height is a dominant parameter in assessing the likelihood of wave-in-deck impact and resultant severe damage. Many empirical and theoretical distribution functions for wave crest heights have been proposed, but there is a lack of agreement between them. It is of significance to develop a better new nonlinear wave crest height distribution model. The progress in the research of wave crest heights is reviewed in this paper. Based on Stokes' wave theory, an approximate nonlinear wave crest-height distribution formula with simple parameters is derived. Two sets of measured data are presented and compared with various theoretical distributions of wave crests obtained from nonlinear wave models and analysis of the comparison is given in detail. The new crest-height distribution model agrees well with observations. Also, the new theoretical distribution is more accurate than the other methods cited in this paper and has a greater range of applications.