  Offroad vehicle movement has to contend with uneven and uncertain terrain
which present challenges to path planning and motion control for both manned
and unmanned ground vehicles. Knowledge of terrain properties can allow a
vehicle to adapt its control and motion planning algorithms. Terrain
properties, however, can change on time scales of days or even hours,
necessitating their online estimation. The kinematics and, in particular the
oscillations experienced by an offroad vehicle carry a signature of the terrain
properties. These terrain properties can thus be estimated from proprioceptive
sensing of the vehicle dynamics with an appropriate model and estimation
algorithm. In this paper, we show that knowledge of the vertical dynamics of a
vehicle due to its suspension can enable faster and more accurate estimation of
terrain parameters. The paper considers a five degree of freedom model that
combines the well known half-car and bicycle models. We show through simulation
that the sinkage exponent, a parameter that can significantly influence the
wheel forces from the terrain and thus greatly impact the vehicle trajectory,
can be estimated from measurements of the vehicle's linear acceleration and
rotational velocity, which can be readily obtained from an onboard IMU. We show
that modelling the vertical vehicle dynamics can lead to significant
improvement in both the estimation of terrain parameters and the prediction of
the vehicle trajectory.
