Fast and accurate sonar trackers using double pulse coding

A sonar target tracking system is presented that is capable of accurately tracking targets at measurement rates exceeding 10 Hz. Two sonar trackers, each consisting of a transmitter and two receivers, are independently controlled to track sonar targets from bearing and range measurements. Bearing and range are accurately estimated using matched filters on two closely spaced receivers, with accuracy better than 0.1 degrees in still air conditions. Accuracy degrades with increasing air turbulence and temperature gradients, and bearing errors are shown experimentally to have significant autocorrelation at times of the order of seconds. The transmitter identity is coded using time separation of double pulses, thus allowing the two transmitters to operate simultaneously without spurious crosstalk readings. The ability to reliably reject interference is demonstrated experimentally. A simple computationally lean double pulse validation approach is analysed and experimentally tested with robot speeds up to 1 metre per second where Doppler shifting of the double pulse separation is an important factor.