This satellite transmits the correction signal to the AFS Universal or AFS Satellite Receivers. The receivers combine the GPS and correction signals, pinpointing the actual location within one to two meters. The biggest benefit of Satellite DGPS is the wide area of satellite coverage. This is especially useful in the resale of the unit, for you can sell to someone in an area where there is no tower - based coverage. Also, the satellite system is not susceptible to local electric disturbances such as lightening storms.
Satellite systems have more backups in case any one satellite experiences trouble.
How the Coast Guard Differential Works Coast Guard DGPS works along the same general principles as satellite DPGS, using the actual position of satellite base stations to determine the GPS error. However, the Coast Guard Tower system has three major differences. First, the correctional signal is transmitted directly from the local tower. The United States Coast Guard has an established network of tower-based DGPS systems along inland and coastal waterways throughout the United States. Typically, the transmission operates in a frequency range similar to the AM radio band in ranges of up to 200 miles.