function y = ocean_spec_background_removal (wl,x_l,x_s,N)


figure;
% plot(wl,x_l);
% xlabel ('wavelength [nm]');
% ylabel ('Equivalent counts');
% title ('Long length transmission');
% hold on;
% 
% legend('click the start of the first band');
% [start_1, temp] = ginput(1);
% legend('click the end of the first band');
% [end_1, temp] = ginput(1);
% hold off
% legend('click the start of the second band');
% [start_2, temp] = ginput(1);
% legend('click the end of the second band');
% [end_2, temp] = ginput(1);
% close;

start_1 = 185;
end_1 = 210;
start_2 = 240;
end_2 = 260;

index_1 = max(find(round(wl-start_1)==0));
index_2 = min(find(round(wl-end_1)==0));
index_3 = max(find(round(wl-start_2)==0));
index_4 = min(find(round(wl-end_2)==0));

wl_for_fitting = [wl(index_1:index_2);wl(index_3:index_4)];
x_l_for_fitting = [x_l(index_1:index_2);x_l(index_3:index_4)];
x_s_for_fitting = [x_s(index_1:index_2);x_s(index_3:index_4)];

p_l = polyfit(wl_for_fitting,x_l_for_fitting,N);
p_s = polyfit(wl_for_fitting,x_s_for_fitting,N);

figure;
wl_new = wl(index_1:index_4);
x_l_new = x_l(index_1:index_4);
x_s_new = x_s(index_1:index_4);

plot(wl_new,x_l_new,':', wl_new,x_s_new,':');
xlabel ('wavelength [nm]');
ylabel ('Equivalent counts');
hold on;

background_l = polyval(p_l,wl_new);
background_s = polyval(p_s,wl_new);

x_l_new = x_l_new - background_l;
x_s_new = x_s_new - background_s;

plot(wl_new,x_l_new, wl_new,x_s_new);

y = [wl_new,x_l_new,x_s_new];
end