Geoscience Reference
In-Depth Information
satellite
unknown station
reference station
Fig. 5.1. Concept of relative positioning
Static relative positioning
The reference station and the unknown station are static, i.e., no motion
occurs between the two points of the baseline. When highest accuracy is an
issue, then this is the preferred method. Fully depending on the application
and on the length of the baseline, the observation time may amount from
several tens of minutes to many hours. Referring to navigation, where usually
motion is involved, static relative positioning is of minor importance. The
reader is referred to Hofmann-Wellenhof et al. (2001: Sect. 7.1.2) for details.
Kinematic relative positioning
The kinematic method is very productive because the greatest number of
points can be determined in the least time.
The drawback is that after initialization a continuous lock on at least
four satellites must be maintained.
The semikinematic or stop-and-go technique is characterized by alterna-
tively stopping and moving one receiver to determine the positions of fixed
points along the trajectory. The most important feature of this method is the
increase in accuracy when several measurement epochs at the stop locations
are accumulated and averaged. This technique is often referred to simply as
kinematic method. Relative positional accuracies at the centimeter level can
be achieved for baselines up to some 20 km.
The kinematic technique requires the resolution of the phase ambiguities
by initialization which can be performed by static or kinematic techniques.
Currently available commercial software (for dual-frequency receivers) only
requires 1-2 minutes of observation for baselines up to 20 km to resolve the
ambiguities kinematically (“on the fly”).
