NDGPS FREQUENTLY ASKED QUESTIONS
What is DGPS?
Differential GPS (DGPS) is the regular Global Positioning System (GPS) with an additional correction (differential) signal added. This correction signal improves the accuracy of the GPS and can be broadcast over any authorized communication channel.
How does DGPS work?
The GPS determined position of a reference station is computed and compared to its surveyed geodetic position. The differential information ... some systems use the error in fix position, while others use individual satellite range errors ... is transmitted to user receivers by radio or other means.
Why use DGPS?
DGPS accuracy and integrity are better than GPS.
* Accuracy improvement (2drms): Positions of 10 meters or better are achievable using DGPS (USCG signals) vs. 100 meters or better for GPS (Standard Positioning Service)
* Integrity improvement: Provides an independent check of each GPS satellite's signal, and reports whether it's good or bad.
Where do I get Radiotechnical Commission Maritime Services (RTCM) documents?
The Coast Guard does not provide RTCM documents. You can order them directly from the RTCM website or via mail. All orders must identify specific documents being ordered and number of copies.
How is DGPS used?
DGPS receivers collect navigational signals from all GPS satellites in view, plus differential corrections from a nearby DGPS site. (Many DGPS receivers consist of two units: a GPS receiver, with a data "port" for DGPS corrections, directly connected to a radio receiver.) DGPS receivers display position, velocity, time, etc., as needed for their marine, terrestrial, or aeronautical applications.
What are the Coast Guard's plans for DGPS?
The Coast Guard is developing a DGPS service for public use in harbor entrance and approach (formerly harbor and harbor entrance) areas of the continental United States, the Great Lakes, Puerto Rico, and portions of Alaska and Hawaii. The DGPS signals will be broadcast via USCG marine radiobeacons.
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