The TERRASTAR-D service is a precise positioning service designed to deliver decimetre level position accuracy, globally. The service is based around Precise Point Positioning (PPP) - a technique where all GPS system errors are removed or minimised by direct calculation, precise modelling or estimation. PPP consists of a single set of corrections to the GPS and GLONASS satellite orbits and clocks, allowing position accuracy to be maintained regardless of user location. Measurement precision is achieved by using both L1 and L2 carrier phase observations, along with C/A and P-Code measurements.
To carry out this absolute positioning technique, orbit and clock corrections derived from the TERRASTAR owned and controlled worldwide network of reference stations are broadcast for every GPS and GLONASS satellite to allow the removal of satellite-based error components.
The use of dual-frequency GNSS hardware at the user end allows the calculation and removal of local ionospheric errors, while tropospheric delays are estimated within the calculation. Other sources of error, including ocean loading, earth tides and phase windup are also modelled.
To obtain the high-accuracy solution, multipath and GNSS receiver noise errors are minimised through use of carrier phase observables, which are precise to the millimetre level.
TERRASTAR-D provides a truly global, seamless, high-accuracy position, which is robust and effective in all locations, including areas of ionospheric disturbance.