How can ground-based enhancements improve GPS accuracy to a few centimetres?

To achieve centimeter-level accuracy, GPS systems utilize a technique known as carrier-aided navigation.1

While standard GPS relies on navigation pulses, this method instead uses the carrier waves that convey those pulses to Earth. Because the length of a carrier wave is more than 1,000 times shorter than the standard navigation pulses, the receiver can process a significantly higher number of waves per second. By measuring these much shorter waves, the system can dramatically reduce positioning errors to less than 1 cm (0.4 inch).1

This approach is often used in conjunction with differential GPS, which employs a stationary base station at a known location to calculate and broadcast real-time corrections to roving receivers, effectively eliminating common statistical errors caused by atmospheric distortions or timing discrepancies.1