Direct Recovery of Deflections of the Vertical Using an Inertial Navigator

An alternative to the standard astrogeodetic and gravimetric methods for estimating vertical deflections is described. This technique, which is particularly well suited to surveys from moving vehicles, utilizes an inertial navigation system, a geodetic position and velocity reference, and an optimal data smoother. An inertial navigation system inherently indicates the astronomic vertical so that vertical deflections cause errors in indicated geodetic position and velocity. This error is measured using an external geodetic position reference (such as LORAN) and a velocity reference. These measurements are then processed by a smoother to recover the vertical deflections. The particular smoother used is the so-called Kalman smoother which treats all of the error sources including vertical deflections as random processes. Both analytic studies are performed and real data from midocean areas are processed. These studies show that if a high-quality inertial system is used in conjunction with a geodetic position reference of accuracy 0.1 nmi rms, vertical deflections of magnitude 10-30 rms can be estimated to within 5-8 rms.