Re ections on modelling a sonar range sensor

With the advent of inexpensive o -the-shelf sonar ranging units sonar has become a common sensor on mobile robotic platforms. Many di erent algorithms have been proposed to obtain environmental layout and other structural information by integrating sonar measurements from multiple positions and/or sensors. Given perfect distance measurements and telemetry, this integration can be fairly simple. Although sonar has become a ubiquitous sensor in mobile robotic systems, surprisingly few results are available data interpretation strategies are often very simple and surprisingly few results are available that accurately model the typical behaviour of the sensor under such conditions. This paper considers some of the potential causes of sonar errors, their e ect on surface or object recovery, and then develops a simulation-based model of sonar range sensing for robot navigation that accounts for multiple re ections of the sonar signal between transmission and reception. This gives more realistic results than previous models. The approach is based on simulation of the re ection and di raction of sonar rays from re ecting surfaces until they are attenuated beyond detectability or return to the receiver. Parameters of the model include frequency, minimum and maximum range, and signal detection threshold (relative to emitted signal strength, after linear gain compensation). Finally, the usefulness of the model to the development of more e ective algorithms for the interpretation of sonar data is discussed.