Determining wind velocity and the speed of sound with redundant transponders for a spread spectrum acoustic ranging system

Acoustic spread spectrum signals offer advantages over radio frequencies when implementing a ranging system. Global Positioning System (GPS) receivers become less accurate when shadowed by buildings and obstacles (see Nebot, E.M. and Durrant-Whyte, H., Robotics and Autonomous Systems, vol.26, p.81-97, 1999). Sound waves offer a larger bandwidth which, when used in conjunction with spread spectrum, can create better immunity to multipath interference. A drawback to transmitting acoustic signals in a ranging system is the fact that the speed of sound can vary. Its speed changes in accordance with the temperature, density and speed of the medium in which it travels. When transmitting an acoustic signal through air, the wind affects the propagation velocity. By accounting for a changing speed of sound, a more accurate acoustic ranging system can be achieved. This paper introduces an approach to calculating both the wind velocity and the propagating speed of sound by using redundant transponders.