added source code for gif animation

README.md

@@ -9,6 +9,9 @@ gnssrefl is an open source software package for GNSS interferometric reflectomet
 
 ![](docs/myAnimation.gif)
 
+I made this animation ages ago - so it is in Matlab.  I would be happy to host a link to 
+a version in python.  The main code is [snr_simulation](docs/pages/snr_simulation.m) 
+and the helper function is [setFrame.m](docs/pages/set_Frame.m). 
 
 Documentation:
 

docs/pages/sc_precourse2024.md

@@ -109,8 +109,6 @@ to both of these codes.
 
 You should read [the overview documentation](https://gnssrefl.readthedocs.io/en/latest/pages/understand.html)
 
-And then the [quickLook documentation](https://gnssrefl.readthedocs.io/en/latest/pages/quickLook.html).
-
 ## What is a Reflection Zone 
 
 [Watch this video](https://www.youtube.com/watch?v=sygZMeCHHDg&t=23s)

docs/pages/set_Frame.m

@@ -0,0 +1,31 @@
+function [startX, bigNumber, Xaxis, Yaxis, SNR] = set_Frame(height,E,Am,atten)
+%function [startX, bigNumber, Xaxis, Yaxis, SNR] = set_Frame(height,E,Am,atten)
+% height - vertical distance of antenna phase center to surface
+% E elevation angles in degrees
+% Am amplitude of the multipath
+% atten boolean if you want to attenuate amplitude as elevation angle increases
+%
+% returns some geometric values for the plot and the simulated SNR data in 
+% variable with that name
+
+wavelength = 0.244; %GPS L2 wavelength
+
+% this is how much longer the reflected signal (red) travels than
+% the direct signal (blue)
+path_del = 2*height.*sind(E);
+psihat = 2*pi*path_del/wavelength;   % radians
+
+% simple attentuation
+if atten
+    Am = 5*Am./E;
+end
+
+% this is the definition of SNR data
+SNR = Am.*(cos(psihat) + sin(psihat));
+
+Xaxis = ceil(height/tand(5));
+Yaxis = 0.33*Xaxis;
+% just so the ray comes from outside the plot, which is what i want.
+% made up number
+startX = 30*height; 
+bigNumber = 20*height;

docs/pages/snr_simulation.m

@@ -0,0 +1,79 @@
+clear all
+close all
+clc
+%https://www.mathworks.com/matlabcentral/answers/1694690-how-to-save-figure-frames-as-gif-file
+FS = 12;
+% min and max elevation angles (degrees)
+emin = 5;
+emax = 20;
+% range of angles to use in the simulation
+E = emin:0.05:emax;
+
+% Normalizing to amplitude of 1.   
+Am=1;
+% use simple attenuation parameter.
+% more realistic ones can be generated from the Nievinski simulator,
+% but that has added complexity of surface type.  Here I am only
+% trying to show what is generating the frequency changes (which are 
+% directly related to reflector height.
+attenuator = true;
+
+% Setup to make movie
+fig1=figure(1); % Create figure handle
+set(gcf,'defaultaxesfontsize',FS)
+winsize = get(fig1,'Position'); % Get Window Size
+winsize(1:2) = [0 0];
+incr = 10;
+numframes = floor(length(E)/incr);
+disp(['Number of frames'  num2str(numframes)])
+
+set(fig1,'NextPlot','replacechildren') % Ensure each plot is the same size
+
+gifFile = '/Users/kristine/Downloads/myAnimation.gif';
+exportgraphics(fig1, gifFile);
+
+
+for height = [4, 10]
+    [startX, bigNumber, Xaxis, Yaxis, SNR] = set_Frame(height,E,Am,attenuator);
+  for i=1:numframes
+    index=i*incr;
+    k=1:index;
+    % how away is the reflected signal on the xaxis
+    Xd = height/tand(E(index));
+    % where does the direct signal start from
+    X3 = startX - Xd;
+    subplot(2,1,1)
+    % GPS antenna is black, reflected signal is red, direct signal is blue
+    plot([0 (0 + bigNumber*cosd(E(index)))], ...
+        [height (height + bigNumber*sind(E(index)))], 'b-', 'linewidth',2);hold on;
+      plot(  [startX Xd 0], [X3*tand(E(index)) 0 height], 'r-',... % reflected signal
+        'linewidth',2); hold on;
+      plot([0 0], [0 height], 'k-', 'linewidth',2); hold on;
+      plot(0, height, 'k^','markerfacecolor','k','markersize',10); 
+      hold off;
+
+    xlim([-1 Xaxis]), ylim([0 Yaxis])
+
+    legend('Direct Signal', 'Reflected Signal', 'Antenna','Location','NorthWest')
+     grid on;
+    xlabel('meters'), ylabel('meters')
+    title(['GNSS Reflection Geometry'],'FontWeight','normal');
+
+    subplot(2,1,2)
+
+    plot(E(k), SNR(k),'k-')
+    xlim([emin emax]),   ylim([-2 2])
+    xlabel('Elevation Angle (deg)')
+    title(['H = ' num2str(height) ' meters-Simulated GPS L2 SNR Data'],...
+        'FontWeight','normal')
+    ylabel('Volts/Volts')
+    grid on
+
+
+    exportgraphics(fig1, gifFile, Append=true);
+  end
+end
+return
+
+
+