Historical perspective on estimation techniques for position and gravity survey with inertial systems

A 25-year review of inertial position and gravity surveying indicates that the development of optimal estimation techniques has resulted in significant commercial and military application. For a single transverse, theoretical relative position, accuracies of a few parts per million are being approached, though for regional surveys comprised of a number of intersecting transverses some theoretical issues remain to be resolved. Optimal performance is achieved in suboptimal filtering of various types whose objective is to control the time-variant sources of system noise using the error in system-computed velocity observed at vehicle stops. Empirical smoothing, to control the effect of systematic error in the survey measurements which are only weakly observable by the velocity error filtering, can be based upon simple parametric models, and can obtain essentially optimal performance. (R.R.)