function [s2]=S2(y,sita,m2,k0,u,q)
  k1=y^2;
  g=9.8;
  kc=(g/u^2)/(2*k0);
  k2=sqrt(1+2*k1*cos(sita)+k1^2);
  sita1=pi+asin(k1*sin(sita)/k2);
  if m2==1
      S=(0.0081/k2^4)*exp(-0.74*kc^2/k2^2);
      G=(4/(3*pi))*(cos(sita1/2-q/2))^4;
      s2=S*G; 
  elseif m2==-1
      S=(0.0081/k2^4)*exp(-0.74*kc^2/k2^2);
      G=(4/(3*pi))*(cos((sita1+pi-q)/2))^4;
      s2=S*G; 
  end