A spectral description of the wave spectrum is usually required in the design of offshore structures, and a generalised form of the JONSWAP spectrum is often used. The JONSWAP spectrum involves parameters that allow flexibility in the specification of the spectral peak, which is important for the response of both fixed and floating structures, but particularly for the floating structures. The peak of the wave spectrum is also important in nonlinear effects that for example contribute to the probability of a large crest occurring in a sea state time series realisation in a model basin, used to test a design platform.

There has been a number of studies focused on the uncertainties of JONSWAP parameter estimates. We review these to establish an overview of the present understanding of the uncertainties, and we undertake further analyses to investigate the sensitivity of the uncertainties to the method of analysis and the types of data typically available for analysis, including both time series and spectral data.

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