A New Integrated Radio Navigation System Describes New Lo-Cost, High-Accuracy Integrated Radio Navigation System

Abstract

ABSTRACT To provide the accuracy which is necessary for detailed geophysical surveys, radio positioning systems are the only means available today. Numerous radio navigation systems exist with the capability of providing accurate results. However, all radio systems have their own unique problems. Very high accuracy systems are limited to ranges of 50 miles and the moderately accurate systems are subject to skywave interference. When skywave interference does occur the system must be recalibrated which means delays in survey times. To eliminate costly down in a geophysical vessel for recalibration purposes, the NANO-NAV Radio Navigation System was developed. This system has the capability of re-establishing lane count or in essence to recalibrate itself without returning to a known calibration point, thus is able to increase production time. A description of this system as a stand alone device is presented. However, in order to assure the most reliable navigation possible, the NANO-NAV system is incorporated into an integrated navigation system. The system is configured around a software program that optimally combines navigation information from a variety of radio sensors. The combinations of sensors discussed in this paper include the NANO-NAV System, Loran-C and a satellite receiver. The integrated character of this system allows continual automatic adjustment of each sensor. The software allows stand alone operation of each sensor as well as the combination of all sensors or any combination of sensors. The system is further mechanized to provide continuous steerage information on a CRT for better control of the marine vessel in following a predetermined course. Several systems involving this information of sensors have been in operation. Results for the NANO-NAV system and Loran-C system and for the combined operation will be presented. INTRODUCTION To achieve positioning accuracies necessary for detailed geophysical surveys, radio positioning systems are the only means available today. Numerous radio navigation systems exist today, however all have their own unique problems. High frequency systems can achieve 3-5 meter accuracy but are limited to line of sight ranges. Low frequency provides the extended coverage but are degraded in accuracy not sufficient for detailed seismic work. Medium frequency systems are the best compromise for the necessary accuracy at intermediate ranges. As offshore exploration efforts move to deeper ocean regions from shore, the medium frequency radio navigation systems reach their limitation in maintaining their ability to position marine vessels. This is due primarily to skywave phenomenon which causes these systems to lose their calibration or often referred to as loss of lane count. NAV-CON has addressed this problem directly and established a system which allows the user longer working days at longer ranges. This was accomplished by development of an improved medium range system and introducing a redundant system capable of always providing checks to the primary system. Results and observations from the system while operating in the Gulf of Mexico are presented. This paper briefly describes the new medium range system along with a detailed description of the integrated radio navigation system.