Abstract:
The range and velocity of a moving object were measured unambiguously by a computational model of echo location. Based on the echo-location sounds utilized by some species of FM bats, a linear-period-modulated (LPM) signal was adopted in this model. The LPM signal was designed to yield a phase rotation of (pi) rad for velocity of 0.5 m/s, and its frequency was hyperbolically swept down from 60 to 40 kHz within a 1.4-ms duration time. Experiments were performed in air by changing the velocity of a plastic disk of about 20 mm in diameter. When a passage of the disk was detected by a photosensor installed at a distance of 1 m from transducers, the LMP signal was emitted as a location sound. Echoes were processed by a bank of constant-Q filters, and the range and velocity were estimated according to the temporal phase distribution of phase-sensitive elements connected to the output of each filter. Regardless of the relatively small time--bandwidth product of the LPM signal, results of these estimations show that the estimation accuracy was better than 0.1 m/s in velocity and about 0.5 mm in range. On the contrary, a conventional sonar system with an up-chirp signal did not yield reliable results because of its ambiguous property in simultaneous parameter estimation.