Feasibility of DOL-VRS Service for Establishing Survey Control Using Post-Processing Method
The Department of Lands Virtual Reference Station (DOL-VRS) reduces several technical limitations of conventional RTK method and increases the productivity in a cost effective manner. This also opens the question how feasible DOL-VRS service may be for establishing survey control. This study investigates the feasibility from two points of view: the observation time and the influence of ionospheric conditions. In addition, the ambiguity fixing rate, rate of position jumps, and root mean squared error are defined as performance indicators. The numerical analyses reveal that the reliable survey control may be obtained when at least 180 epochs of observation at 5-sec interval are considered on good ionospheric conditions (i.e., low TEC). On the other hand, 720 epochs or more are needed when the ionospheric activity increases. In addition, the VRS based solutions compared to an average least square adjustment solution show an offset of about 0.7 cm. Furthermore, the errors in the vertical direction for 720-epoch solutions display a peakÂtoÂpeak variation of 3.9 cm (low TEC) and 10.1 cm (high TEC), respectively. We can conclude that VRS based survey control may be established using DOL-VRS service precisely and accurately at 2- cm level especially in the low TEC scenario. The user is advised to use this approach with caution and take the average of multiple occupations on the same mark, separated in time to allow changes in the constellation geometry and ionospheric conditions. Such practice will enhance the reliability to establish high accuracy survey control.