A bat-like sonar system for obstacle localization

An active wide-beam sonar system that mimics the sensor configuration of echolocating bats is described for applications in sensor-based robotics. Obstacles in a two-dimensional (2-D) environment are detected and localized using time-of-flight (TOF) measurements of their echoes. The standard threshold detector produces a biased TOF estimate. An unbiased TOF estimate is derived by a parametric fit to the echo waveform, motivated by experimental observations of actual sonar signals. This novel method forms a tradeoff between the complexity of the optimum estimator and the biased threshold detector. Using the TOF information from both methods, the range and azimuth of an obstacle are estimated. Localization is most accurate if the obstacle is located along the system line-of-sight and improves with decreasing range. Standard deviations of the range and azimuth estimators are compared to the Cramer-Rao lower bounds. The parabolic fit method has large variance but zero bias at large deviations from the line-of-sight. The system operation is generalized from isolated obstacles to extended obstacles