Vertical accuracy of two differentially corrected global positioning satellite systems.

Farmers and scientists are using topographic maps resulting from data collected by differentially corrected global positioning systems (DGPS) to identify management zones and characterize the influence of conservation practices and landscape position on soil productivity, erosion, and agricultural sustainability. To develop accurate topographic maps, watershed managers must know positional errors associated with the different types of differentially corrected global positioning systems (DGPS). The objective of this study was to determine under field conditions, the vertical errors associated with real time kinematic (RTK) and real time stop-and-go (RTSG) sampling approaches using a single frequency carrier phase DGPS and RTK using CIA code DGPS. Research was conducted with and without selective availability. This experiment showed that elevation information determined by: 1.) a single frequency carrier phase DGPS receiver using RTK and RTSG sampling approaches, measured prior and post selective availability, had consistent results with standard deviations of less than 3.5 cm; 2.) a CIA code DGPS receiver, measured prior and post selective availability, had inconsistent results with relatively large standard deviations (83-100 cm); and 3.) GPS, measured post selective availability, had inconsistent results with relatively large standard deviations (100-200 cm). Results suggest that caution should he used in using elevation information collected from CIA code DGPS or GPS.