The data file SPdata.txt contains 
   line # , x(m), y(m), SW-NE, SE-NW, Z, East, North
where all the SP electric field data (cols 4-8)  are in mV/m

The following Matlab code will reproduce Figure 3, 5, and 7 of the paper 
---------------------------------------------------------------------

data = load ('SPdata.txt');

figure;
scatter(data(:,2), data(:,3), 100, data(:,4), 'o', 'fill')
axis equal
caxis([-0.2 0.3])
axis ([0 1200 0 1100])
xlabel ('Easting (m)')
ylabel ('Northing (m)')
title ('SW-NE component')
colorbar

figure;
scatter(data(:,2), data(:,3), 100, data(:,5), 'o', 'fill')
axis equal
caxis([-0.2 0.3])
axis ([0 1200 0 1100])
xlabel ('Easting (m)')
ylabel ('Northing (m)')
title ('SE-NW component')
colorbar

figure;
scatter(data(:,2), data(:,3), 100, data(:,6), 'o', 'fill')
axis equal
caxis([-0.2 0.3])
axis ([0 1200 0 1100])
xlabel ('Easting (m)')
ylabel ('Northing (m)')
title ('Z component')
colorbar


z = data(:,6);
zerr = 0.025*ze;  % 2.5 percent error floor
[xx, yy, mz, dp, actrms] = OccamMap(2,data(:,2), data(:,3), z, zerr,  0, 1300, 100, 0, 1200, 100, 100); 
colormap('jet')
title('Vertical electric field, mV, RMS 2 with 2.5% error floor')
xlabel ('Easting (m)')
ylabel ('Northing (m)')

d = [data(:,7) ; data(:,8)]; % make a single data vector out of the x and y components
derr = 0.025*d;  % 2.5 percent error floor
[xx, yy, mSP, dp, actrms] = OccamMapSP(6,data(:,2), data(:,3), d, derr,  0, 1300, 100, 0, 1200, 100, 100); 
colormap(flipud(jet))
title('SP, mV, RMS 6 with 2.5% error floor')
xlabel ('Easting (m)')
ylabel ('Northing (m)')
hold on
quiver(data(:,2), data(:,3), data(:,7), data(:,8),'k')