A self-contained electronic system that makes use of Doppler's principle of frequency shift of waves emanating from a moving source. In this system, a pulsed or continuous wave is sent diagonally downward fore and aft, forward and backward, and the frequencies are compared in order to obtain the true ground speed. The heading is obtained from a special magnetic compass and is maintained by a directional gyro used as an integrating device. The distance thus determined has a precision better than one part in a thousand, which is sufficient for most geophysical surveys.