Positioning Accuracy and Signal Interference

A standalone civilian GPS receiver today typically achieves horizontal accuracy of around 5 meters under open-sky conditions, an improvement attributable both to the 2000 discontinuation of Selective Availability and to decades of receiver and satellite signal modernization, though real-world accuracy varies with satellite geometry, a factor quantified as Dilution of Precision (DOP): when visible satellites are spread widely across the sky, positional solutions are more reliable than when they cluster close together, a condition described by a higher, worse DOP value. Two atmospheric layers introduce systematic ranging errors: the ionosphere, a layer of charged particles roughly 50 to 1,000 kilometers above the Earth, delays and bends GPS signals in a frequency-dependent way that dual-frequency receivers can largely cancel out by comparing signals on L1 and L2 or L5, while the troposphere introduces a smaller, frequency-independent delay that models can estimate from local temperature, pressure, and humidity.