Sonar echo analysis

Pulse mode sonar operation is analyzed under the assumption that the scattering object Gamma lies in the far fields of both the transmitter and the receiver. It is shown that, in this approximation, the sonar signal is a plane wave sx times Theta(0)-t near Gamma, where Theta(0) is a unit vector directed from the transmitter toward Gamma and similarity the echo is a plane wave ex times Theta (0)-t near the receiver, where Theta is a unit vector directed from Gamma toward the receiver.