This paper describes the infrastructure and concept of two multi-site reference station differential GPS (DGPS) options being offered to land and marine users by Racal Survey. The infrastructure of the Racal SkyFix system is briefly outlined followed by descriptions of Racal's internetting and network capabilities.

The two systems are compared including infrastructure, differential data management, user coverage, datalinks and positioning performance in various parts of the world. The paper describes the design of each of the systems and the tests undertaken to assess their functionality, before going on to compare their performances under a variety of conditions. Emphasis is placed on the technical issues associated with multi-reference station DGPS including error sources, weighting observations and monitoring of the data. The fundamental approach of the systems is shown to achieve high data integrity which is necessary to develop the systems to their next phase.

Having described the two options, examples of various combinations of reference stations are used to illustrate the potential of the system and to show the increased performance over ordinary, single-station DGPS. The conclusions summarize the paper's findings and make recommendations for the future development of the system. The object of the developments so far have been to improve the quality of real-time offshore DGPS positioning. The internetting and network options are providing real-time results to illustrate the benefits and, together with SkyFix, offer significant developments in the ability of DGPS to provide accurate and reliable positioning over vast areas of the world.