Information GNSS Anomalies

The Geometrics magnetometer softwares check for some uncommon anomalies in GNSS location and timing messages in data collected with the G-864, MagEx, and MagArrow instruments.

These anomalies have occurred in data from a few instruments:

• Extra PPS timing signals – Sometimes the PPS sensor in the instrument receives an extra timing signal that’s out of phase with the normal 1-second interval. These are almost always easily identified and discarded.
• GNSS timing anomalies – Very rarely, the GNSS appears to change its mind about the current time or location.  For example, after recording a time at 06:30:21, the next measurement – received one second later – might show a time of 6:30:15 – 16 seconds earlier.
• GNSS location anomalies – A GNSS timing jump may be accompanied by a location jump.

Geometrics’ software now makes additional checks for these anomalies, corrects them when possible, and reports them if they affect the use or visualization of the data.  Some of the checking is in the instruments, some in MagNav, and some in Survey Manager.

Users will notice these anomalies and the functionality to repair and report them in these ways:

• During import or export, the software identifies an anomaly.  If it’s judged to be worth reporting – most likely because it affects the reported locations of magnetometer readings – then it is logged and the user asked to review the log file.
• The user exports data and notices something unusual, for example a discontinuity in the GNSS times or locations.  The customer should review the software’s log files for additional information.

These anomalies are unusual; the type where the GPS changes its mind about the time or location is exceedingly rare and will never be seen by most customers.  The main effect of the new functionality is that the data validation process will now be more visible to users.