Estimate of Tidal Constituents in Nearshore Waters Using X-Band Marine Radar Image Sequences

The accurate observation and prediction of tides are important in coastal waters. A new method is proposed to estimate tidal constituents in nearshore waters from X-band marine radar image sequences, based on the modulation of wave height by tide. The relative wave height is retrieved from the first principal component of the X-band marine radar image sequence, and a self-adaption method is used to remove the low-quality data under very low sea state. To eliminate the influence of atmospheric planetary waves, a type I Chebyshev bandpass filter is applied to the time series of the derived wave heights. Relative tidal amplitudes and phases are then obtained through harmonic analysis of the filtered wave heights, and true tidal amplitudes are derived through a linear relation, while true tidal phases are obtained by cross-spectral analysis. The errors of the amplitudes of M2, S2, K1, and O1 tides retrieved from X-band marine radar image sequences are 0.15-1.12, 2.22-3.83, 3.06-4.29, and 4.50-9.47 cm, respectively, as compared with those predicted by a numerical model; the errors of M2 tidal phase are 3.27°-4.59°. It shows that the proposed method is appropriate for long and continuous observations of X-band marine radar.