Magellan MobileMapper Beacon User Manual - Page 31

This could result in a similar error as spatial decorrelation in Coast Guard beacon, however, this is likely to be less significant. More significant is that the ionospheric map is downloaded to users only every 5 minutes. Recent past has shown that the ionosphere, during peak solar activity, can change more quickly than this update rate, causing a significant source of error. This is a very rare condition. Solar activity can be monitored by consulting various Web sites, such as www.spaceweather.com Radiobeacon DGPS Radiobeacons conforming to the standards of the International Association of Lighthouse Authorities broadcast a limited selection of RTCM SC-104 messages, including message types 1, 2, 3, 5, 6, 7, 9, and 16. - A DGPS beacon will broadcast either Type 1 or Type 9 messages, both of which contain similar information. These two messages contain pseudorange corrections and range rate corrections to each GPS satellite. - The Type 2 message contains delta differential corrections that are used when the remote receiver is using a different satellite navigation message than used by the base station. - The Type 3 message contains the position of the beacon's reference station, often accurate to within centimeters with respect to the WGS-84 reference datum. - The Type 5 message contains GPS constellation health information used for improving tracking performance of a GPS receiver - The Type 6 message contains null information, and is broadcast so that a beacon receiver demodulating the data from the broadcast does not lose lock when the beacon station has no new data to transmit. 27