The comparison between Synthetic Aperture Radar observations and simulation results of WAVEWATCH III with and without adopting spectral partition

This study presents an method of separating wind sea and swell from the development of numerical simulation of swell in the spectral wave model - WAVEWATCH III by adopting spectral partition. The principle of spectral partition used in WW3 is based on a digital image processing watershed algorithm [1] to isolate different peaks, which should be subsequently divided into wind sea and swell by using a wave age criterion such that swell peaks lie without the parabolic boundaries defined by C_p≤(1.5)U₁₀ cosδ, (1) where C_p is the phase speed of the wind sea, U₁₀ is the wind speed at 10m height above sea surface, and δ is the angle between the wind and the wind sea [2]. After carrying out further processing steps in sequence, including mutual swell peaks combination and energy threshold check, the statistics of every swell partitions can be calculated. It is shown that the value of wavelength of the most remarkable swell partitions increases substantially compared with the original model results before using spectral partition and fits SAR data better.