Algorithm 2. IPF algorithm for 3D emitter location using azimuth and elevation measurements.

1. If at least a single pulse is emitted by the threat source and the first azimuth and elevation measurements, ${\theta }_1$ and ${\phi }_1$, are available, solve Equations (15)–(25) to determine the cuboid search space, where $i=1$;

2. Generate a set of $P$ particles uniformly distributed within the cuboid search space, according to Equations (33)–(35);

3. Compute azimuth and elevation angle predictions, i.e., ${\theta }_1^p$ and ${\phi }_1^p$, for each particle, $s_p$, according to Equations (29) and (30), where $i=1$;

4. Compute the weight, $w_p$, of each particle, $s_p$, according to Equation (31);

5. Obtain the first estimate of the emitter location, ${\widehat{p}}_e$, by Equation (32);

6. If more measurements are available, i.e., $i>1;$

7. Test whether the recent emitter location estimate, ${\widehat{p}}_{e,i-1}$, is within the new cuboid search space determined by Equations (15)–(25);

8. If the test is positive, move the center of the search cuboid to ${\widehat{p}}_{e,i-1}$, and generate a set of $P$ particles uniformly distributed within the cuboid search space, according to Equations (36)–(38);

9. If the test failed in any of the directions, the particles are generated within the cuboid search space in the respective direction according to the corresponding distribution, from Equations (33)–(35);

10. Execute steps 3–5, where $i>1$.