% Finish the following migration code for demonstrating diffraction-stack migration
% ===========================================================================
% You can rename or add any variables as needed 
% ===========================================================================

% create grids of x and z coordinates covering the area  you used in lab 5.
% However, these grids do not have to be identical to those in lab 5. 
% Try some ranges or denser spacings



x = ...   
z = ...  % depth array
%% ==============================================================================
% Task 1) 
% Perform migration by applying function 'scattering_ellipse() to an individual 
% source/receiver point and plot the results. 
% Try the following commands separately.  Make and understand plots:

sec = scattering_ellipse(x,z,500,400,1,2);          % at one point 
figure(1)
plot_Zsection(x,z,sec,'distance(m)','b-')
pause     % pause here to look at the results
figure(2)
sec = scattering_ellipse(x,z,[400 400],[100 400],[2 1],2);  % two reflections at one S/R point
plot_Zsection(x,z,sec,'distance(m)','b-')

pause

% try some other positions of the source/receiver pairs and save plots

%% ===========================================
% Now load your modeled section from lab 5. Let us say it is called 'section'
% you will also need the arrays 'receivers' and 'time' from lab 5 (coordinates of the points 
% and times at which the records ara output) and velocity (denoted velocity1?)

%load model.mat  load model ZOS from lab 5


%% ================================================
%% Task 2)
% Perform migration by applying 'scattering_ellipse()' to one source/receiver record
% from your modeled section:

i= 20;    % number of record you want to use
figure(3)
sec =  scattering_ellipse(x,z,receivers,time,section(:,i),velocity1);
plot_Zsection(x,z,sec,'distance(m)','b-')

pause     % look and the result and describe it. Try some other value of i

%% ================================================
%% Task 3)
% Perform migration by applying 'scattering_ellipse()' to the whole time records
% from the modeled section:
figure(4)
sec = zeros(length(z),length(x));   % this will be your output depth section

for i=1:size(section,2)     % sum migrated records fom all traces
    xs = ones(size(section,1),1)*receivers(i);  % array of identical receiver 
                        % positions for each sample of the trace
    sec = sec + scattering_ellipse(x,z,xs,time,section(:,i),velocity1);
end

plot_Zsection(x,z,sec,'distance(m)','b-')

pause % look and the result. How does it compare to the preceding one from one trace?
      % How does it compare to the original depth section which you picked in lab 5?

% save the migrated section:

save ... sec