Altitude accuracy while tracking pedestrians using a boot-mounted IMU

This paper characterizes altitude errors based solely on the integration of a boot-mounted inertial measurement unit (IMU) and co-located digital magnetic compass. The system is self-contained, small, and inexpensive and requires only passive sensors (no infrastructure to set up) mounted to the heel of the operator´s boot. During each footstep, there is a natural rest period that is detected and used to perform a zero-velocity update (ZUPT) to significantly constrain the position, velocity, roll and pitch errors through the use of an extended Kalman filter (EKF). This paper describes the fundamental issues that impact accurate altitude estimation based solely on the use of an IMU/compass sensor. Experimental altitude errors are shown for walks based on a simplified IMU error model to show the sensitivity of altitude errors to inadequate dynamic range of the accelerometers and gyros and inadequate detection of ZUPT periods. Experimental altitude errors are shown for multiple users both ascending and descending several floors of a building while walking a common route for 15 minutes, including an acceptance test conducted in June 2008 to track first responders and a test in the stairwell of a seventeen story apartment building. Altitude errors are also shown for an operator climbing a ladder.