How is it possible for returned echoes to vary in strength?

Returned echoes can vary in strength due to several factors, including the distance between the source and the reflecting surface, the angle of reflection, and the material properties of the surface. For instance, closer objects will produce stronger echoes due to less attenuation of the sound or signal. Additionally, surfaces that are rough or absorbent may scatter or absorb some of the energy, resulting in weaker echoes. Environmental conditions, such as humidity and temperature, can also influence echo strength.