ABSTRACT

Over the past four years, integrated satellite navigation systems have found increasing use on offshore geophysical survey vessels. A need has arisen for additional knowledge of the accuracy limitations of these systems. This paper addresses this need.

In the literature, it is possible to find information on the accuracy of individual subsystems which make up an integrated satellite navigation system. Also, one can find theoretical predictions of accuracy for integrated systems. However, what is most important to the user is the actual "real world" accuracy obtained from such a system while in use on a geophysical survey. This paper presents results derived from many thousands of miles of navigation data taken from five geophysical survey vessels operating n various water depths in different locales of the world. Each vessel is equipped with an identical integrated satellite navigation system.

For the purpose of continuity, a brief description is given of the integrated satellite system. Also, brief mention is made regarding accuracy of the individual subsystems and the theoretical prediction of accuracy for the entire system.

The post survey computer program, which analyzes the navigation data, is described. This program provides statistical output in both tabular and graphical form, and in a manner the user can understand. Thus, from this output data, the user can judge, with a high degree of probability, the quality of the navigation data obtained with an integrated satellite navigation system.

Several conclusions are reached in this paper. First, from the data presented, a knowledge of "real world" navigation accuracy for an integrated satellite navigation system is now available. Second, the data also presents evidence on reliability of an integrated system and what quality control features must be implemented to insure a high standard of navigation accuracy.

INTRODUCTION

In order to provide the geophysical industry with the best possible navigation data during a seismic survey, navigation systems with a high degree of sophistication have been developed. One such system now in common use is the integrated satellite navigation system. Approximately half of the free world's ocean going geophysical vessels are equipped with such systems.

With the widespread use of the integrated satellite navigation systems has come the frequently asked questions -

  1. In real-time, just how accurate are integrated systems?

  2. What quality control measures are taken to insure the stated real-time accuracy?

  3. How can the real-time accuracy be improved with post survey processing?

  4. How can this accuracy be verified?

With the use of a recently developed post survey computer program, data from actual surveys is presented in this paper to help answer question number (1). In addition, this paper also addresses question number (2) by explaining the quality control techniques used in a particular integrated satellite navigation system. Question number (3) was the subject of a paper presented at the last Offshore Technology Conference (reference 1).

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