GEOG 862
GPS and GNSS for Geospatial Professionals

A Different Strategy

One-Way Ranging: GPS Satellite to GPS Receiver, length rho
One-Way Ranging
Source: GPS for Land Surveyors
Two-Way Ranging: EDM to Retroprism and Retroprism to EDM, length rho
Two-Way Ranging
Source: GPS for Land Surveyors

Unlike an EDM measurement, the wavelengths of GPS carriers cannot be periodically changed to resolve the cycle ambiguity problem. GPS needs a different strategy. The satellites broadcast only three carriers, L1, L2 and L5.  They have constant wavelengths and only propagate from the satellites to the receivers, one direction. Still, the carrier phase measurements remain an important observable in GPS ranging.