Spherical Earth Elevation Angle

Determines elevation angle based on spherical Earth.

ELEV = GETELEVATIONANGLE(GR,H1,H2,REFFECTIVE) Determines the elevation
angle of a target based on ground range (GR), altitude of the observer
(H1) and the altitude of the target (H2), and the effective radius of
the Earth (REFFECTIVE). Ground range and rEffective are in meters.
Altitudes are in meter MSL. and elevation is output in degrees with 0
being parrellel to the ground and 90 being straight up.

Example: The difference between spherical and flat Earth
earthRadius = 6371000;
flatEarthRadius = inf;
oalt = 1000; % Obeserver altitude (m MSL)
talt = 1100; % Target altitude (m MSL)
GRs = logspace(3,7,1000); % From 1 km to 1000 km
elevSpherical = getElevationAngle(GR,oalt,talt,earthRadius);
elevFlat = getElevationAngle(GR,oalt,talt,flatEarthRadius);
figure
semilogx(GR/1e3,elevSpherical,GR/1e3,elevFlat)
xlabel('Ground Range (km)')
ylabel('Elevation Angle (deg)')
legend('Spherical Earth','Flat Earth')
title('Elevation Angle')