recall that harmonically generated echoes are produced by non linear media further as an example an envelope function a n t may be a gaussian waveform the transmitted signal may additionally be modulated as a chirped waveform i e swept frequency modulation a fourier transform of which is still centered around the fundamental with a broader dispersion optionally a digital waveform generator could be used in place of the convolution method shown in fig2 fig3 shows an embodiment of a signal transmitter unit 120 prior to signal delivery to media of interest the signal transmitter unit 120 includes at least a power amplifier 330 a transmit receive switch 340 and a first transducer 350 optionally a signal transmitter unit 120 may further include a delay circuit 310 the delay circuit 310 may be an analog or digital delay also optionally the signal transmitter unit 120 may include a channel gain unit 320 to drive the power amplifier 330 as a function of channel number and time additionally the signal or pulse may be pulse width modulated not shown to conserve power power conservation can become crucial in field applications of the system where battery power may be utilized fig4 a shows one embodiment of a receiver and raw data averager unit 140 a second transducer 410 receives pulsed sets modified by media of interest 130.