Goodbye Differential GPS: Introducing the New Generation of Precision Positioning for Cable Surveys, Installation & Maintenance
satellites – irrespective of distance from land. The correction stream is broadcast to the user community through two independent networks; NET-1 and NET-2. Each network comprises of three high-power satellites to cover the Earth while facilitating the use of very small integrated GPS / L-Band antenna designs. C-Nav’s international Satellite Based Augmentation System SBAS, delivers real-time dynamic positioning accuracy (x, y and z) at the decimetric level. It includes many layers of security, quality control, resilience and assured access to provide a unique and robust solution to the cable industry’s need for self-regulating (autonomous) independent horizontal and vertical positioning solutions.
By Edwin Danson For those of us who can remember route surveying with Loran C and SatNav, the introduction of GPS and Differential GPS was a dream come true. Gone were the vagaries and uncertainties; in came reliable accuracy and precision transforming vessel positioning from an art form to a science. Since those heady days, DGPS has become a by-word for navigation – the norm, not the exception. Accuracy improvements accompanied by cost reductions were all very welcomed by the industry. But technology moves on and the days of the DGPS are passing, replaced by Globally Corrected GNSS (GcGPS) thanks to advances in Precise Point Positioning.
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The accuracy and precision of traditional DGPS depended on estimating the errors observed by a network of reference stations. As the network’s spatial configuration opened and the distances
from reference stations grew, so the accuracy became compromised. This was particularly evident in mid-ocean, far from the nearest stations. DGPS essentially treated the symptoms and not the causes of the errors. To address that deficiency, C&C Technologies, Inc introduced its C-Nav GcGPS system. Unlike DGPS, C-Nav corrects for the source of the errors: the uncertainties in the GPS satellites’ clock and orbital parameters, satellite antenna alignment phase errors, and the modelable errors associated with dynamic tides and atmospherics. C-Nav’s software, with its pedigree in NASA’s Jet Propulsion Laboratory’s Real-Time GIPSY (RTG) suite, is an advanced proprietary RTG development for realizing the dynamic version of Precise Point Positioning. C-Nav delivers a single set of globally valid corrections for all GPS
The C-Nav ground segment comprises of a dense network of tracking stations around the world. Typically, up to seven stations track simultaneously the same GPS satellite. The C-Nav tracking stations are equipped with dual frequency receivers operating through a common IGS-style choke ring antenna; these stations are further augmented with tracking stations of the NASA/JPL network. The system is controlled through two independent, geographically separated, Processing Centers. Each centre receives the full complement of tracking station data with a latency of less than two seconds. With hot primary and secondary production layers at each Processing Centre, four sets of orbit and clock correction values are generated. The six geostationary high-power Inmarsat communication satellites provide global L-Band distribution between about 75° north and south