% homework 8
% Due: Thursday, April 1
% Radiation objective:
%    To understand the spectral relationship between cirrus emissivity 
%    Brightness temperature
% Matlab Objective:
%    To use a computer program to explore relationships between two or 
%    more paramters.

% Calls planck_wl function to calculate planck radiance
%       bt_wl     function to calculate brightness temperatures

emi = [0:.1:1];                % Emissivity
Tcloud = 210;                  % Temperature of cloud
Tbase_11 = 287;                % Brightness temperature of radiance 
Tbase_12 = 282;                %              incident at cloud base

% Radiance calculations
irradtop_11 = planck_wl(11,Tbase_11)*(1-emi) + planck_wl(11,Tcloud)*emi;
Bttop_11 = bt_wl(11,irradtop_11);

irradtop_12 = planck_wl(12,Tbase_12)*(1-emi) + planck_wl(12,Tcloud)*emi;
Bttop_12 = bt_wl(12,irradtop_12);

subplot(2,1,1)
   plot(emi,Bttop_11,'-','linewidth',[1.5])
   hold on
   plot(emi,Bttop_12,'--','linewidth',[1.5])
   hold off
   title('Brightness Temperature vs Emissivity of Cirrus Cloud')
   xlabel('Emissivity')
   ylabel('Brightness Temperature (K)')
   [lh,oh] = legend('11 \mum','12 \mum');
   set(oh(:,2),'fontsize',[10],'fontunits','points')
subplot(2,1,2)
   plot(emi,Bttop_11-Bttop_12,'-','linewidth',[1.5])
   title('Brightness Temperature Difference vs Emissivity of Cirrus Cloud')
   xlabel('Emissivity')
   ylabel('BT_{11\mum} - BT_{12\mum} (K)')