Method for selecting wave height threshold

A method for selecting wave height threshold comprising the following steps of:

• S1:
• acquiring, based on a target location, original wave height samples,
• determining the number of the samples Ntot a maximum wave height uM in the samples and a minimum wave height u1 in the samples, and
• calculating, within a candidate threshold interval determined by the maximum wave height uM and the minimum wave height u1, and at a step size, that is a threshold step size, a normalized candidate threshold to obtain a wave height threshold interval;
• each of the threshold in the wave height threshold is called a candidate threshold uj, j is an integer greater than 0;
• S2:
• determining a return period sequence i for a design wave height to determine a specified return period;
• S3:
• for each candidate threshold, by using all original sample data in the original wave height sample greater than the candidate threshold, based on the specified return period and according to a generalized Pareto distribution formula, calculating a design wave height corresponding to each candidate threshold uj within the wave height threshold interval to obtain a design wave height value Hsi,j;
• S4:
• calculating a difference ΔHsi,j=Hsi,j−Hsi,j−1 between design wave height values corresponding to adjacent candidate thresholds, which is called a wave height difference for short;
• and
• S5:
• if ΔHsi,j≤0 and three successive wave height differences following ΔHsi,j includes negative but not all negative or are all 0, considering a candidate threshold uj corresponding to ΔHsi,j as a lower boundary of a stable threshold interval;
• and, if six successive wave height differences following ΔHsi,j+m are all greater than or equal to 0, considering a candidate threshold uj+m corresponding to ΔHsi,j+m as a higher boundary of the stable threshold interval, wherein a threshold interval [uj, uj+m] is the stable threshold interval, and a candidate threshold within the stable threshold interval is selected as a reasonable threshold for design wave height estimation.