Where to start? High-precision satellite surveying is a far different beast from the more commonly used methods of satellite navigation and positioning. High-precision involves the use of carrier phase measurements (cumulative RF cycles and instantaneous phase angle) combined with an accurate estimate of the integer number of carrier cycles (ambiguity) transpiring between satellite transmission and initial observing station reception (lock). Inseparable from this is the necessity to eliminate or accurately model the noise sources that impact satellite transmissions as they travel from satellite to receiver.
Historically, we categorize two general methods of high precision surveying. In one case, the noise sources or their biases are modeled and applied to correct a station's position estimate. This is the basis for many real-time kinematic (RTK) processes, in which one station at a known position will calculate a set of corrections for its calculated position, then broadcast those corrections to other proximate stations which will apply them to their calculated positions. This is one of many methods for correcting a station's autonomous position estimate. Wide-area networks have been used to generate regional models for space and atmospheric biases applied to the user segment through satellite and terrestrial communications networks. Most recently this has been applied to push the limits of precision on precise (single) point positioning.
In the second case, raw measurement data are collected from two or more stations and processed simultaneously using differential equations to eliminate or estimate systematic noise. This is known as differential positioning and has seen successful implementations as double and triple difference processing. For the most part, Orion has applied this method for deformation monitoring. Although our roots are in the application of dual frequency (L1/L2) GPS for monitoring both long-baseline crustal deformation (10s of kms) and the high-frequency dynamics of long-period structures, we have made extensive use of possibly the simplest form of high-precision GPS as our primary market offering: L1-Static GPS. Reflecting this, our effort to inform and educate the market focuses on the use and benefits of this technique.