Determining Ground Vehicle Direction of Travel from a Magnetic Anomaly Time Series

Author(s):

Timothy M. Pritchett

Abstract:

Estimates of two parameters related to the movement of a ground vehicle may be obtained from a time series of the magnetic anomaly resulting from the vehicle, recorded by a single three-axis magnetometer: 1) the ratio v/d_CPA of the vehicle speed v to the distance d_CPA of closest approach of the vehicle to the magnetometer; and 2) direction of vehicle travel (azimuth angle a) modulo 180°. Using data from only a single magnetometer, one cannot determine in which of two diametrically opposed directions the vehicle is traveling; that is, azimuths of a and a + π are indistinguishable. This ambiguity is easily removed using data from a second sensor, either a nearby magnetometer or an acoustic sensor, possibly collocated with the first magnetometer. When d_CPA is at least several vehicle lengths, the determination of v/d_CPA is extremely reliable and can be used to independently verify estimates of speed or closest approach distance obtained from acoustic sensor data. This lower bound on d_CPA establishes a window over which parameter estimates can be successfully extracted from time series data. For a low size, weight, and power magnetometer with limited sensitivity, this window may be inconveniently narrow.