GROUND EFFECTS ON HELICOPTER NOISE

摘要

The noise received from rotorcraft (and also aircraft) is modified by atmospheric attenuation and reflections from the ground. The interference of direct and reflected waves is simplest for a flat ground, whereas multiple reflections can occur for rough ground or mountainous surroundings. The ground characteristics, like reflection and absorption factors or impedance, also affect received sound. All these effects have to be considered with respect to the path of the rotorcraft (or aircraft).