Users Advisory - DGPS
Differential GPS Equipment Generated Errors
The Coast Guard Navigation Information Service (NIS) recently received report of
Differential GPS (DGPS) receivers apparently
ignoring the broadcast alarm which signals immediate discontinuation of a
particularsatellite correction. In accordance with the
international and industry standards (RTCM SC104), the United States Coast Guard DGPS
broadcast sets a satellite correction to
the defined "DO NOT USE" value of 10485.76 meters if broadcast integrity checks
indicate there is a problem with the satellites
correction.
Reports indicate some users equipment does not properly recognize this "DO NOT
USE" correction flag and instead erroneously
processes it as a correction. This can result in correction errors as large as 1500
meters, while the receiver is in the DGPS mode.
DGPS users should contact the manufacturer of their equipment immediately to determine if
they require a receiver upgrade.
An error of this magnitude could result in some pretty serious navigation problems during
night and inclement weather operations.