Trimble's Marine Reference Station Modernization

Autonomous GPS was originally to be accurate to possibly 15 meters (primarily in the vertical) for military users but 100 meters for civilians. This dichotomy was possible based on Selective Availability (SA) whereby intentional errors were added to GPS signals. This hastened the development of differential GPS, or DGPS, which would have been developed anyway since DGPS eliminates many common mode error sources such as orbital errors, clock errors, atmospheric errors, and so on. Furthermore, the DGPS techniques that emerged incorporated integrity as GPS alone did not provide a timely means of end-user integrity notifications. DGPS was deployed, nationwide, by the United States Coast Guard (USCG) around the mid 1990’s so as to provide accurate and available navigation with high integrity along the U.S. coasts and major waterways. Other nations followed this model. These early deployments of DGPS used rigid architecture systems which were hardware oriented, thereby setting the stage for difficulties later. After a decade of use and experience a better system was proposed based on a more software oriented system design, upgraded standards, hardware configurability, and networking (TCP/IP vs. RS-232). This paper will discuss recent improvements in DGPS standards and Trimble’s system and software architectures supporting DGPS modernization. The paper will highlight Trimble’s common software framework architecture that is capable of supporting multiple Trimble products (such as, DGPS, Ntrip caster, and coordinate monitoring) as it applies to DGPS systems of today as well as those of the future. The paper will include examples of modern DGPS architecture deployments.