% this function returns intercep time, critical distance 
% and crossover for headwave
% input parameters:
% p- ray parametr is scaler
% h- layer thickness is array
% v1- velocity of the upper layer(overburden layer)  is array
%return values
%t_intercept- refraction intercept time
%xcritical-critical distance 
%t0- normal incidence reflection time
function [t_intercept xcritical  t0]=one_layer(p,h,v1)

    angle=asin(p*v1);
    xcritical=sum(2*h.*tan(angle));
    t_intercept=sum(2*h.*cos(angle)./v1); %refraction intercept time
    t0=sum(2*h./v1);
  
end