  Successful navigation of a rigid-body traveling with six degrees of freedom
(6 DoF) requires accurate estimation of attitude , position, and linear
velocity. The true navigation dynamics are highly nonlinear and are modeled on
the matrix Lie group of SE2(3). This paper presents novel geometric nonlinear
continuous stochastic navigation observers on SE2(3) capturing the true
nonlinearity of the problem. The proposed observers combines IMU and landmark
measurements. It efficiently handles the IMU measurement noise. The proposed
observers are guaranteed to be almost semi-globally uniformly ultimately
bounded in the mean square. Quaternion representation is provided. A real-world
quadrotor measurement dataset is used to validate the effectiveness of the
proposed observers in its discrete form. Keywords: Inertial navigation,
stochastic system, Brownian motion process, stochastic filter algorithm,
stochastic differential equation, Lie group, SE(3), SO(3), pose estimator,
position, attitude, feature measurement, inertial measurement unit, IMU.
