Wave direction analysis from data buoys

Abstract This paper describes a new procedure of directional wave analysis from pitch–roll buoy measurements. The two previous procedures adopted by the National Data Buoy Center (NDBC) [Steele, K. E., Lau, J. C. K. and Hsu, Y.-H. L. (1985) Theory and application of calibration techniques for an NDBC directional wave measurement buoy. IEEE Journal of Oceanic Engineering OE-10(4), 382–396; Steele, K. E., Teng, C.-C. and Wang, D. W. C. (1992) Wave direction measurements using pitch–roll buoys. Ocean Engineering 19(4), 349–375] are relevant to our formulations. In these two studies, an estimate for the total phase shift of the sea surface displacement/slope spectra from the measured buoy heave/pitch and heave/roll spectra was calculated either by a weighted average method or a maximum heave/pitch quad-spectrum method. These two formulations were based on a fundamental assumption of symmetric hull-mooring effect on pitch and roll motions, which will never be true in the oceans. In the present study we essentially incorporate the basic formulations of NDBC, but calculate two estimates for this total phase shift. Examples of directional wave analysis from data measured by a 3 m diameter discus buoy during Typhoon Herb are presented in this paper. This data set was also analyzed by the weighted average method of Steele et al. (1985) which yielded unsatisfactory results of wave directions during severe wave climates.