Passive depth tracking of underwater maneuvering targets

As a parallel extension to the adaptive range tracking of underwater targets described by Moose and Dailey [1], this paper discusses the problem of tracking the depth of a maneuvering target using passive time-delay measurements. The target is free to maneuver in velocity and make random depth changes at times unknown to the observer. In modeling target motion, use is made of the linearized polar coordinate model developed and reported in [2] and [3]. The addition of a nonlinear system block to the tracking system leads to a partial decoupling of both depth and polar range estimators which greatly reduces the computational burden and significantly reduces any tendency toward tracking divergence. A modified method to obtain closed-form expressions for the measurement error statistics is presented which replaces conventional extensive off-line simulation procedures. Finally, test results are shown which validate the elimination of all extended Kalman filters in the measurement processing. This makes the passive tracking system very "robust" with respect to convergence characteristics in the presence of adverse target maneuvers.