S_TIDE计算流速的旋转谱（rotation spectrum function）

流速旋转谱的定义：

旋转谱计算方法（参考管守德博士毕业论文）

S_TIDE v1.23 update2 版本提供了s_rotation_spectra.m函数来计算旋转谱，s_demo.m提供了旋转谱的计算实例程序：

load tidalcurrents.mat

[Stv,Htv,Gtv,coef,xoutv,ju,Stint,Htint,Gtint,aa,bb,namev]=s_tide_m8(v,1,1,{'M2';'S2';'K1';'O1';'N2';'Q1';'P1';'K2'},8,1,'spline','robustfit',20.5,[2010,08,23,01,00,00],'corrected');

[Stu,Htu,Gtu,coef,xoutu,ju,Stint,Htint,Gtint,aa,bb,nameu]=s_tide_m8(u,1,1,{'M2';'S2';'K1';'O1';'N2';'Q1';'P1';'K2'},8,1,'spline','robustfit',20.5,[2010,08,23,01,00,00],'corrected');

% 20.5 is the latitude of the observation,[2010,08,23,01,00,00] is the start time of observation, users only need to change these two inputs when perform their own harmonic analysis.

% v and u are observed tidal currents at y and x axis

 %demonstration of s_rotation_spectra.m

 % this example was first added in S_TIDE v1.23 update2    2022/01/05

[px,py,pcw,pccw,freq,rdn] = s_rotation_spectra(xoutu,xoutv,1/3600);

plot(24*3600*freq,log10(pcw),'r')

hold on

plot(24*3600*freq,log10(pccw),'k')

xlim([1.8 2.2]);xlabel('cycles per day(cpd)')

ylabel('PSD(m^{2}/s^{2}/Hz)')

line([24*0.080511 24*0.080511],[-5 5],'Linestyle','--');

text(1.94,-4,'M2');legend('clockwise','counterclockwise')

可以看到在M2频率上顺时针能量显著大于逆时针，所以M2潮流是顺时针旋转的

[maxc,minc,maxt,mint,maxp,minp,rr]=s_estimate_tidal_ellipse(Htu(1,1),Gtu(1,1),Htv(1,1),Gtv(1,1),'M2') 

使用s_estimate_tidal_ellipse函数估算M2潮流椭圆旋转率为负，同样表明M2潮流是顺时针旋转