What is GNSS pseudorange and what factors affect it?

• A. Pseudorange refers to the geometric line-of-sight distance to the satellite.
• B. Pseudorange is the measured C/A code range from receiver to satellite including receiver and satellite clock errors; affected by ionospheric/tropospheric delays, multipath, satellite geometry, and receiver noise.
• C. Pseudorange is the Doppler frequency shift.
• D. Pseudorange is affected by atmospheric water vapor only.

Answer: (B)

GNSS pseudorange is the measured range from the receiver to a satellite that includes the receiver’s clock bias and the satellite’s clock bias, so it’s not just the true geometric distance. In other words, it’s the code-based distance you infer from the signal, plus the time errors from both clocks.

Several factors affect this measurement. Ionospheric and tropospheric delays slow the signal on its way to the receiver, making the measured range larger than the true distance. Multipath occurs when the signal bounces off surfaces before reaching the receiver, introducing bias and noise. The geometry of the satellites relative to the receiver influences how accurately the system can solve for position (dilution of precision). Receiver noise adds random error to the measurement. Additionally, clock errors of the satellite and the receiver are inherently part of the pseudorange value, and inaccuracies in the satellite’s orbit (ephemeris) can also impact the measurement.