function [sigema1]=sigema1L(q,u,f0)
  g=9.8;
  c=3*10^8;
  k0=2*pi*f0/c;
  kc=g/u^2;
  sita1L=0;
  S=(0.0081/k0^4)*exp(-0.74*(kc^2/k0^2));
  g2=(3/(4*pi))*(cos(sita1L/2-q/2))^4;
  a=64*pi*k0^4;
  sigema1=a*S*g2;