Thursday, January 26, 2006

Maritime DGPS: Coastal Beacons

If you read the Using DGPS post you might have noticed the screenshot from GpsTweak highlighting one of the possible sources for correction information for data obtained from GPS satellites: External RTCM Data.

That means WAAS isn't the only way to get better accuracy with your receiver. Remember that WAAS was an effort from the FAA to improve landing of airplanes. When RTCM is mentioned you are talking about ground stations (currently maintained by the U.S. Coast Guard and other agencies) or "beacons" transmitting data most often used by boats.

By selecting an external RTCM Data source you will be connecting a serial port in your GPS receiver (if one is available) to an external beacon receiver. This way you will be able to grab data that follows the RTCM SC-104 standard (proposed by the Radio Technical Commission for Maritime Services).

Or if your receiver is also capable of tuning frequencies in the KHz range used by the beacon transmitter you might be able to select Internal RTCM Data. Thales produces the MobileMapper CE which includes among its accessories a Bluetooth beacon receiver.

But I haven't seen CF cards that implement an internal RTCM receiver combined with the MHz range required for GPS satellite signals. If you know of any, let us know. Check this article by Chuck Husick for a good description of the Maritime DGPS.

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