LEVELING BY GPS RELATIVE POSITIONING WITH CARRIER PHASES

The successful processing of baseline vectors is an essential step tow ard the application of GPS surveying techniques to leveling. When carr ier phase observables are used, the double-difference integer phase am biguity parameters must be correctly resolved. It is described how the phase ambiguities are resolved with ionospheric-free signals using st andard procedures. With the dual-frequency phase data from satellite s urveying ih rapid static mode baseline vectors of up to 26 km can be s olved. A standard deviation in the vertical component of about 2.5 cm can usually be expected for a baseline length of less than 10 km. The accuracy of the height determination by means of GPS relative position ing is then verified. Precise leveling was conducted over the same per iod of time, in two campaigns. Nine vertical control points with known orthometric heights were used to fit a geoid model to a region of 20 km by 10 km. Orthometric heights were checked at other 17 points in th e project area, resulting in a root mean square error of 2.2 cm. This accuracy compares favorably with the general standards specified for s econd-order (class II) leveling.