In certain types of offshore operations, particularly minerals exploration, there is a need for a small fully automatic navigation system which presents position data in such a form that it can be used to steer the vessel without need for further computation or reference to specially prepared charts. Such a system with an effective range in excess of 20 miles and an accuracy of 50 feet was built and tested. It gathered position data by digitally counting the travel time of a microwave pulse from the vessel to two beacons at known locations. This time information is transferred to a small computer which uses this time information to compute the position of the vessel with respect to a predetermined rectangular coordinate system. By appropriate choice of the coordinate system, the coordinates can be used directly to provide steering information necessary to keep the vessel on the desired course.
When extending subsurface survey techniques from land to water, the greatest changes in techniques and equipment occur not in the actual gathering of information but in the methods of determining where that information was actually gathered. The transits and chains of land surveys can be used under some conditions, but an electronic navigation system is generally required. These systems have ranged from the complex through the extremely complex and sometimes require more equipment and technical manpower than the rest of the instruments needed for the survey. I have seen a gravity survey where one man with a gravity meter conducted the survey and three men with the navigation system told him where he was.
The navigation system had more than adequate accuracy under good conditions, but it had a number of serious drawbacks in operation. The boat had to be in a known position to start up the system and had to return to a known position to recalibrate if the signal was ever lost for any reason. Atmospheric disturbances from thunderstorms to skywave propagation around sunrise and sunset upset the system and occasionally rendered it totally useless. Data came out in the form of distances to two remote stations at fixed points and the rough position could be determined by looking at specially prepared charts, but the accurate position was computed at a remote location and had a turnaround time as long as a month.
In addition to the technical problems, there were the human factor s in trying to find competent men willing to sit in a trailer house at each of the remote locations day after day so that they could perform those few tasks which were necessary to the operation of the navigation system.
When Geophysical Research Corporation became involved in offshore exploration for minerals, it became apparent that there was a need for a navigation system designed for that type of work. A range of 20 miles and an accuracy of 50 feet would be adequate for most mineral surveys, but the system must not slow down the surveyor complicate it any more than absolutely necessary.
