Kaoru Ichikawa (RIAM, Kyushu University, Japan)

Wave frequency has been empirically estimated from altimetry sigma_0 and SWH data by comparing with buoy wave observations. Under low-wind conditions, however, this relationship cannot be used since sigma_0, which is proportional to the inverse of the mean square slope (MSS), is more sensitive to waves with shorter wavelength (or higher frequency) that the large buoys cannot detect. In this study, the MSS for such high-frequency waves missed in buoy observations is estimated from the wind speed. The compensated MSS for the buoy observations by these estimations agrees well with the altimetry MSS. In turn, the estimated MSS for the high-frequency waves are removed from the altimetry MSS data to correctly estimate the wave frequency for longer-frequency waves such as swells.