Why are different elevation masks recommended for multiple DGPS units in operation?

Different elevation masks are recommended for multiple Differential Global Positioning System (DGPS) units in operation to prevent common mode position jumps across position references. Elevation masks are used to exclude signals from satellites that are positioned too low on the horizon, which are often affected by obstacles such as buildings or the atmosphere.

When multiple DGPS units are used simultaneously, they may pick up similar signals from satellites that are just above the elevation mask. If these signals are unreliable or affected by multipath errors, all units could produce erroneous position data that jump in unison, leading to a common mode failure. By setting different elevation masks for each DGPS unit, the chances of all units experiencing the same signal degradation or interference are reduced. This diversified approach ensures that if one unit suffers from poor signal conditions, others may still provide accurate positioning information, thereby maintaining reliability and enhancing overall system integrity.

Adopting distinct elevation masks not only stabilizes positioning data but also mitigates the risks associated with reliance on a single source of information, ensuring that vessel operations remain safe and effective in various maritime environments.