Application of inertial navigation systems to geodetic postion and gravity vector survey

Abstract

Inertial navigation systems are mechanized so as to measure the change in geodetic latitude and longitude and geometric height relative to a specified earth's reference spheroid or datum. Since this is the basic task of geodetic survey, conventional inertial navigation systems, which have been used for decades for missile and aircraft navigation, are in essence low-quality survey systems. Navigation errors result, in inertial systems, from the angular orientation error of the accelerometer-sensing axes relative to the reference surface, the scale factor error, and noise that exists in the measurements themselves. One of the principal noise sources contaminating the specific force measurements made by the accelerometers is the anomalous behavior of the gravity vector relative to the reference spheroid assumed that is not accounted for by a gravity model contained in the system computer, Errors induced in the system-computed velocity and position by the gravity disturbance, observed by the use of appropriate reference sensors, serve as one means for determining the anomalous behavior of the gravity vector along a survey vehicle's travel route. Additionally, if the inertial system is brought to rest, the deviation of the gravity vector from the computer gravity model can be directly determined from the accelerometer measurements. Stopping of a survey vehicle carrying an inertial navigation system also allows the error in the system-computed velocity to be observable to high precision. Stopping of the vehicle at points whose geodetic and astronomic positions and gravity value have been determined by independent means provides observations of the error in system-computed geodetic position and the system-estimated anomalous gravity vector. This tutorial paper discusses the manner in which the observations of the error in the systemcomputed velocity and position and the gravity vector are employed in realizing a practical inertial surveying system of high accuracy. System performance, assuming the application of optimal filtering and smoothing techniques is also indicated.