Pseudorange

A pseudorange is the raw distance measurement from a GNSS satellite to a receiver, computed as the signal travel time multiplied by the speed of light. It is called "pseudo" rather than true range because it includes systematic errors: the receiver's clock offset from GPS time (since consumer receivers don't carry atomic clocks), ionospheric and tropospheric signal delays, satellite clock and orbit errors, and multipath reflections. A minimum of four pseudorange measurements (from four satellites) are needed to solve for three position coordinates plus the receiver clock offset. Dual-frequency receivers (L1+L5) can measure and remove ionospheric delay, significantly improving accuracy.