On the modelling of swell spectra

Physics-Based Forward Modeling of Ocean Surface Swell Effects on SMAP L1-C NRCS Observations

“…1D swell spectra S s (k) have been modeled in past studies as a narrow-band Gaussian spectrum, but recent studies have shown a JONSWAP spectrum to be a more accurate substitute [36,54]. In [54], the authors use the mean values for JONSWAP peak shape parameters γ, σ a , and σ b identified for wind-driven spectra in [35] (3.3, 0.07, and 0.09, respectively) to show that the resulting JONSWAP model spectral shape and significant wave height reasonably predicts observed swell spectra with periods T p ∈ [10,15] s. Parameter values for γ, σ a , and σ b for other swell period values, however, is not clear in the existing literature. Narrower swell spectra are expected to be associated with larger γ (the "peak enhancement" factor) and smaller σ a and σ b values (which describe the width of the spectral peak).…”

“…Narrower swell spectra are expected to be associated with larger γ (the "peak enhancement" factor) and smaller σ a and σ b values (which describe the width of the spectral peak). Although the high-frequency decay for wind-driven spectra is proportional to f −5 [35] where f is the wave frequency, and [54] uses this rate for swell spectra, the appropriate exponent to use for more general swell spectra is also uncertain.…”

“…where X is an empirically determined factor identified to be 0.8 and 0.75 in [57,58], respectively, with the latter showing minimum marginal impact if varied in the vicinity of 0.75; this study uses X = 0.69. First, a set of class I, 1D swell-only NDBC buoy spectra with their peaks normalized to unity were compiled (see [54] for class definitions). The resulting normalized swell spectra were then binned based on their peak frequency (50 possible locations based on the NDBC frequency axis), and spectra within each bin were averaged to obtain a set of averaged, normalized swell spectra.…”

A wavelet-based test for swell stationarity

“…It is therefore of interest to understand the spectral characteristics of the low-frequency band or swell component of the wave spectrum as well its temporal behaviour, particularly over durations of the order of the offloading operations, some 12-24 h, over which time the sea state characteristics, such as the significant wave height, may change. Lucas and Guedes Soares [29] focus on the description of the swell spectrum, while in this paper the focus is on the temporal variability of these spectral characteristics over durations of the order of a sea state.…”

Safe offloading from floating LNG platforms

“…The importance of the combined seas situation led to particular attention being paid to the swell characteristics, both to its stationarity [10], and to its spectral modelling [11].…”