Detection of a Drifting Acoustic Transponder by an AUV

In this work, we examine the effects that an unexpectedly drifting acoustic transponder, such as a transponder that has become unmoored, can have in a navigation system that assumes that the transponder position is stationary. If the transponder is drifting sufficiently fast, the acoustic range measurements acquired from the transponder will be sufficiently different from the range measurements expected by the navigation system that the range measurements can be rejected, in which case the drifting transponder has no effect on the navigation system. If, on the other hand, the transponder is drifting slowly, the navigation system will not reject the measurements and they will be used to correct the navigation estimate. As a result, the navigation estimate will slowly drift. We seek to determine the slowest possible speed that a transponder can move for which range measurements from the transponder can be rejected and therefore have no effect on the navigation system. An innovation test is proposed for the detection of transponder drift. Experimental results using the Virginia Tech 690 AUV are presented to demonstrate the effects of a drifting transponder on a real system.