Differential correction is necessary to achieve the higher levels of resolution. It is a technique for overcoming GPS position determination errors. In addition to errors related to satellite geometry, there are clock errors, atmospheric errors, and multipath errors, to name a few. There are several systems designed to correct your position.
WAAS—A system provided by the Federal Aviation Administration to do real-time GPS positioning correction. This is not consistently and reliably available for the Gothic area.
OMNIstar satellites—A company that provides real-time GPS corrections. This is available for the Gothic area, but our unit (GeoXT) does not pick up this signal.
Beacon on a Belt—A system provided by the Coast Guard to do real-time GPS correction. Available for the Gothic area, but not financially feasible.
Post-processing—There are various software packages that will post-process GPS data, such as Pathfinder Office, Pathfinder Express, and Geomatics Office. We will be using Pathfinder Office post-processing to differentially correct our data.
RTK-RTK is only an option with the high-end survey unit (Hiper Pro). It allows real-time corrections to be done. It does this by communicating via radio with a local base station that continuously collects data. We will be using RTK for all our Hiper Pro data collections.