The eLoran system gets its enhanced accuracy in much the same way that enhanced GPS gear squeezes greater accuracy out of the civil GPS signal for tasks such as surveying and mapping—by using differential correction. A stationary receiver at a known fixed location checks the signal arriving from the beacon and measures the difference between its actual distance from the beacon and the distance calculated from the signal (based on the difference between the signal’s timestamp and the time it was actually received).
Source: Radio navigation set to make global return as GPS backup, because cyber
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