DGNSS RTCM SC-104

RTCM SC-104 is the message format used to broadcast differential GNSS corrections, set by Special Committee 104 of the Radio Technical Commission for Maritime Services. The standard defines a set of message types built from 30-bit words. For marine DGPS the key ones are Type 1, carrying the pseudo-range correction (PRC) and range-rate correction (RRC) for every satellite in view, and Type 9, which packs the same corrections in groups of three for faster update. Each correction carries a User Differential Range Error, an Issue Of Data tag, and a modified Z-count time stamp. IALA radiobeacons and many port DGNSS services transmit in this format on the MF band.