Hello
I-Simpa with SPPS is a particle ray-tracing software, based on geometrical and energetic hypothesis. This is not a resolution of wave equation.
It can model sound reflection according to geometrical reflections (specular and diffuse reflection). But you can not model scattering for example.
I'm not sur that it is adapted for ultrasonic (and outdoor?) ultrasonic wave simulation.
Best.
J. Picaut