ABSTRACT Increasing operating cost of marine geophysical surveys, coupled with expansion of surveys into deeper water and further from shore have placed new demands for reliability in navigation. Although numerous navigational system are capable of supplying good data in specific operating environments around the world, most become marginal in the more remote deeper water: areas. Such limitations have-been countered through use of hybrid navigational configurations which often are little more than a lashing together of-backup systems. A shortcoming in these-hybrid systems is that various components may be based upon different geodetic earth models, with the consequent introduction of ambiguities and uncertainties into both real time navigation and post plot solutions. To resolve such ambiguities and to provide world-wide operation for all typically encountered conditions, we-have developed a system that will provide optimal real-time position information based upon the navigation satellite datum. The system is configured around a software program that optimally combines digitized data from whichever sensor units are active. Included among the sensor types are all radio navigation aids, a doppler sonar, a satellite receiver, and an inertial platform. The integrated character of the system allows continual automatic adjustment to optimal solutions during activation or de-activation of individual sensors. Furthermore, the system is mechanized to provide continuous steerage information, thus eliminating the need for preplots which are required for most radio navigation aids. The software allows stand-alone operation of each component system in addition to the optimum blending of all available data. Thus, digitally recorded output from the various systems can be evaluated separately during post plot analysis. Several systems involving a variety of sensor configurations have been operational- since September 1974. Comparisons of results for separate sensors and for combined operation will be presented. Most data is from Loran-C, an-inertial platform, doppler sonar; and a satellite receiver. We expect further refinement in positioning once additional radio aids are incorporated. INTRODUCTION Prior to 1969, positioning of a marine geophysical vessel was done, using radio navigation systems only. Since radio navigation systems relied on shore-based stations at known positions, seismic surveying was confined to the coastal areas of the world. Today, although many varieties of radio navigation systems are available still none are able to provide continuous, world wide navigation with the accuracy required for geophysical surveys. In 1969 the introduction of integrated doppler sonar satellite navigation systems liberated geophysical surveying from coastal restrictions. These systems rely on periodic position fixes from the Navy Navigation Satellite System. Depending upon the latitude, an acceptable position fix can be obtained anywhere in the world approximately every hour or two. Until recently most geophysical exploration had been confined to relatively shallow water (less than 100 fathoms) where dead-reckoning between fixes with doppler sonar velocities and gyro compass heading proved adequate.