Testing a Multi-Reference GPS Station Network for OTF Positioning in Brazil

摘要

Differential GPS has the capability to provide cm-levelrnpositioning accuracy, as long as the carrier phasernambiguities are resolved on-the-fly (OTF) to integerrnvalues. Existing methods are based on the use of a singlernfixed reference station located in the vicinity of the rover.rnThe maximum distance allowed between the referencernstation and user is generally limited to within 50 km duernto effects from the atmosphere and orbit. The number ofrnreference stations can be increased to extend therncoverage. However, the installation and maintenance ofrnsuch stations and their data transmission links isrnoperationally complex and expensive. The optimal use ofrnexisting stations is therefore of utmost importance tornmaximize cost effectiveness. A novel and unique methodrndeveloped at the University of Calgary uses all availablernreference stations to generate regional code and carrierrnphase corrections, which can be transmitted to the user inrnorder to resolve integer ambiguities OTF over the region.rnOne of the major advantages of this method is to increasernthe coverage within which successful OTF ambiguityrnresolution is possible. The Brazilian Network forrnContinuous Monitoring of GPS (RBMC) is an activerngeodetic reference network functioning in Brazil sincern1997. As the distances between the established stationsrnare too long for carrier-phase positioning, a 5-dayrndensification campaign was carried out in August 1999rncovering a 700x700-kilometer region. The generated datarnwas used to test the feasibility of the multi-referencernstation approach in a region strongly affected by thernionosphere, under the equatorial anomaly. During therncampaign, a solar eclipse occurred. Despite the fact thatrnthe zone of totality was mainly seen over Europe andrnAsia, this event added an interesting feature to therncollected data. Results and analysis using the regionalrncode and carrier phase corrections are presented andrncompared to the single reference receiver case torndemonstrate the improvement achieved by this methodrnunder the conditions pointed out.