Echoic flow for radar and sonar

Introduced is radar and sonar echoic flow as the counterpart to its better-known cousin, optical flow. Echoic flow can be computed in a number of forms, the simplest being the ratio of range to range rate. This provides a direct measure of the time to collision between a radar/sonar system and a detected object. Its derivative is a measure of collision intensity. Thus, together, these two quantities provide a powerful basis for autonomous navigation and related applications. The origins of echoic flow are explained and it is shown through simulation how it can be used as a basis for radar-based autonomous navigation.