GNSS multipath refers to what phenomenon, and why does it matter for accuracy?

• A. Reflected signals reaching the receiver cause biases in measurements, degrading precision.
• B. Direct line-of-sight signals only.
• C. A software error in the receiver.
• D. A normalization of signals to improve accuracy.

Answer: (A)

Multipath is when GNSS signals reach the receiver after reflecting off surfaces like buildings, water, or the ground, in addition to the direct line-of-sight signal. The reflected path is longer and can have a different phase, so the receiver ends up interpreting a combination of direct and reflected signals as if the signal came from a slightly different location. This creates biases in the measured distances (pseudorange) and can affect carrier-phase measurements as well, leading to position errors and degraded accuracy. The impact is worse in environments with many reflective surfaces or where the direct signal is weak, making multipath a major concern for precise positioning. The other options miss the core idea: multipath is not about signals being only direct, a software error, or a process that normalizes signals to improve accuracy; it’s a physical phenomenon from reflections that biases measurements.